cityturn.c

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/***********************************************************************
 Freeciv - Copyright (C) 1996 - A Kjeldberg, L Gregersen, P Unold
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
***********************************************************************/
 
#ifdef HAVE_CONFIG_H
#include <fc_config.h>
#endif
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h> /* exp, sqrt */
 
/* dependencies/lua */
#include "lua.h" /* lua_Integer */
 
/* utility */
#include "fcintl.h"
#include "log.h"
#include "mem.h"
#include "rand.h"
#include "shared.h"
#include "support.h"
 
/* common/aicore */
#include "cm.h"
 
/* common */
#include "achievements.h"
#include "actiontools.h"
#include "borders.h"
#include "calendar.h"
#include "citizens.h"
#include "city.h"
#include "culture.h"
#include "events.h"
#include "disaster.h"
#include "game.h"
#include "government.h"
#include "map.h"
#include "player.h"
#include "research.h"
#include "road.h"
#include "server_settings.h"
#include "specialist.h"
#include "tech.h"
#include "traderoutes.h"
#include "unit.h"
#include "unitlist.h"
 
/* common/scriptcore */
#include "luascript_types.h"
 
/* server */
#include "citizenshand.h"
#include "citytools.h"
#include "cityturn.h"
#include "maphand.h"
#include "notify.h"
#include "plrhand.h"
#include "sanitycheck.h"
#include "spacerace.h"
#include "srv_log.h"
#include "srv_main.h"
#include "techtools.h"
#include "unittools.h"
#include "unithand.h"
 
/* server/advisors */
#include "advbuilding.h"
#include "advdata.h"
#include "autosettlers.h"
 
/* server/scripting */
#include "script_server.h"
 
/* Queue for pending city_refresh() */
static struct city_list *city_refresh_queue = NULL;
 
/* The game is currently considering to remove the listed units because of
 * missing gold upkeep. A unit ends up here if it has gold upkeep that
 * can't be paid. A random unit in the list will be removed until the
 * problem is solved. */
static struct unit_list *uk_rem_gold = NULL;
 
static void check_pollution(struct city *pcity);
static void city_populate(struct city *pcity, struct player *nationality);
 
static bool worklist_change_build_target(struct player *pplayer,
                                         struct city *pcity);
 
static bool city_distribute_surplus_shields(struct player *pplayer,
                                            struct city *pcity);
static bool city_build_building(struct player *pplayer, struct city *pcity);
static bool city_build_unit(struct player *pplayer, struct city *pcity);
static bool city_build_stuff(struct player *pplayer, struct city *pcity);
static struct unit *city_create_unit(struct city *pcity,
                                     const struct unit_type *utype,
                                     struct citizens_reduction *red)
  fc__attribute((nonnull (1, 2)));
static const struct impr_type *building_upgrades_to(struct city *pcity,
                                                    const struct impr_type *pimprove);
static void upgrade_building_prod(struct city *pcity);
static const struct unit_type *unit_upgrades_to(struct city *pcity,
                                                const struct unit_type *id);
static void upgrade_unit_prod(struct city *pcity);
 
/* Helper struct for associating a building to a city. */
struct cityimpr {
  struct city *pcity;
  struct impr_type *pimprove;
};
 
#define SPECLIST_TAG cityimpr
#define SPECLIST_TYPE struct cityimpr
#include "speclist.h"
 
#define cityimpr_list_iterate(cityimprlist, pcityimpr) \
    TYPED_LIST_ITERATE(struct cityimpr, cityimprlist, pcityimpr)
#define cityimpr_list_iterate_end  LIST_ITERATE_END
 
static bool sell_random_building(struct player *pplayer,
                                 struct cityimpr_list *imprs);
static struct unit *sell_random_unit(struct player *pplayer,
                                     struct unit_list *punitlist);
 
static citizens city_reduce_specialists(struct city *pcity, citizens change);
static citizens city_reduce_workers(struct city *pcity, citizens change);
 
static bool city_balance_treasury_buildings(struct city *pcity);
static bool city_balance_treasury_units(struct city *pcity);
static bool player_balance_treasury_units_and_buildings
            (struct player *pplayer);
static bool player_balance_treasury_units(struct player *pplayer);
 
static bool disband_city(struct city *pcity);
 
static void define_orig_production_values(struct city *pcity);
static void update_city_activity(struct city *pcity);
static void nullify_caravan_and_disband_plus(struct city *pcity);
static bool city_illness_check(const struct city * pcity);
 
static float city_migration_score(struct city *pcity);
static bool do_city_migration(struct city *pcity_from,
                              struct city *pcity_to);
static bool check_city_migrations_player(const struct player *pplayer);
 
/**********************************************************************/
bool city_refresh(struct city *pcity)
{
  bool retval;
 
  pcity->server.needs_refresh = FALSE;
 
  retval = city_map_update_radius_sq(pcity);
  city_units_upkeep(pcity); /* update unit upkeep */
  city_refresh_from_main_map(pcity, NULL);
  city_style_refresh(pcity);
 
  if (retval) {
    /* Force a sync of the city after the change. */
    send_city_info(city_owner(pcity), pcity);
  }
 
  return retval;
}
 
/**********************************************************************/
void city_refresh_for_player(struct player *pplayer)
{
  conn_list_do_buffer(pplayer->connections);
  city_list_iterate(pplayer->cities, pcity) {
    if (city_refresh(pcity)) {
      auto_arrange_workers(pcity);
    }
    send_city_info(pplayer, pcity);
  } city_list_iterate_end;
  conn_list_do_unbuffer(pplayer->connections);
}
 
/**********************************************************************/
void city_refresh_queue_add(struct city *pcity)
{
  if (NULL == city_refresh_queue) {
    city_refresh_queue = city_list_new();
  } else if (city_list_find_number(city_refresh_queue, pcity->id)) {
    return;
  }
 
  city_list_prepend(city_refresh_queue, pcity);
  pcity->server.needs_refresh = TRUE;
}
 
/**********************************************************************/
void city_refresh_queue_processing(void)
{
  if (NULL == city_refresh_queue) {
    return;
  }
 
  city_list_iterate(city_refresh_queue, pcity) {
    if (pcity->server.needs_refresh) {
      if (city_refresh(pcity)) {
        auto_arrange_workers(pcity);
      }
      send_city_info(city_owner(pcity), pcity);
    }
  } city_list_iterate_end;
 
  city_list_destroy(city_refresh_queue);
  city_refresh_queue = NULL;
}
 
/**********************************************************************/
void remove_obsolete_buildings_city(struct city *pcity, bool refresh)
{
  struct player *pplayer = city_owner(pcity);
  bool sold = FALSE;
 
  city_built_iterate(pcity, pimprove) {
    if (improvement_obsolete(pplayer, pimprove, pcity)
        && can_city_sell_building(pcity, pimprove)) {
      int sgold;
 
      do_sell_building(pplayer, pcity, pimprove, "obsolete");
      sgold = impr_sell_gold(pimprove);
      notify_player(pplayer, city_tile(pcity), E_IMP_SOLD, ftc_server,
                    PL_("%s is selling %s (obsolete) for %d.",
                        "%s is selling %s (obsolete) for %d.",
                        sgold),
                    city_link(pcity),
                    improvement_name_translation(pimprove),
                    sgold);
      sold = TRUE;
    }
  } city_built_iterate_end;
 
  if (sold && refresh) {
    if (city_refresh(pcity)) {
      auto_arrange_workers(pcity);
    }
    send_city_info(pplayer, pcity);
    send_player_info_c(pplayer, NULL); /* Send updated gold to all */
  }
}
 
/**********************************************************************/
void remove_obsolete_buildings(struct player *pplayer)
{
  city_list_iterate(pplayer->cities, pcity) {
    remove_obsolete_buildings_city(pcity, FALSE);
  } city_list_iterate_end;
}
 
/**********************************************************************/
void apply_cmresult_to_city(struct city *pcity,
                            const struct cm_result *cmr)
{
  struct tile *pcenter = city_tile(pcity);
  const struct civ_map *nmap = &(wld.map);
 
  /* Now apply results */
  city_tile_iterate_skip_free_worked(nmap, city_map_radius_sq_get(pcity), pcenter,
                                     ptile, idx, x, y) {
    struct city *pwork = tile_worked(ptile);
 
    if (cmr->worker_positions[idx]) {
      if (NULL == pwork) {
        city_map_update_worker(pcity, ptile);
      } else {
        fc_assert(pwork == pcity);
      }
    } else {
      if (pwork == pcity) {
        city_map_update_empty(pcity, ptile);
      }
    }
  } city_tile_iterate_skip_free_worked_end;
 
  specialist_type_iterate(sp) {
    pcity->specialists[sp] = cmr->specialists[sp];
  } specialist_type_iterate_end;
}
 
/**********************************************************************/
static void set_default_city_manager(struct cm_parameter *cmp,
                                     struct city *pcity)
{
  int csize = city_size_get(pcity);
  int gsize = city_granary_size(csize);
 
  cmp->require_happy = FALSE;
  cmp->allow_disorder = FALSE;
  cmp->allow_specialists = TRUE;
 
  /* We used to look at pplayer->ai.xxx_priority to determine the values
   * to be used here. However that doesn't work at all because those values
   * are on a different scale. Later the AI may wish to adjust its
   * priorities - this should be done via a separate set of variables. */
  if (csize > 1) {
    if (csize <= game.info.notradesize) {
      cmp->factor[O_FOOD] = 15;
    } else {
      if (gsize == pcity->food_stock) {
        /* We don't need more food if the granary is full. */
        cmp->factor[O_FOOD] = 0;
      } else {
        cmp->factor[O_FOOD] = 10;
      }
    }
  } else {
    /* Growing to size 2 is the highest priority. */
    cmp->factor[O_FOOD] = 20;
  }
 
  cmp->factor[O_SHIELD] = 5;
  cmp->factor[O_TRADE] = 0; /* Trade only provides gold/science. */
  cmp->factor[O_GOLD] = 2;
  cmp->factor[O_LUXURY] = 0; /* Luxury only influences happiness. */
  cmp->factor[O_SCIENCE] = 2;
  cmp->happy_factor = 0;
 
  if (gsize == pcity->food_stock) {
    cmp->minimal_surplus[O_FOOD] = 0;
  } else {
    cmp->minimal_surplus[O_FOOD] = 1;
  }
 
  cmp->minimal_surplus[O_SHIELD] = 1;
  cmp->minimal_surplus[O_TRADE] = 0;
  cmp->minimal_surplus[O_GOLD] = -FC_INFINITY;
  cmp->minimal_surplus[O_LUXURY] = 0;
  cmp->minimal_surplus[O_SCIENCE] = 0;
}
 
/**********************************************************************/
void auto_arrange_workers(struct city *pcity)
{
  struct cm_parameter cmp;
  struct cm_parameter *pcmp;
  struct cm_result *cmr;
  bool broadcast_needed;
 
  /* See comment in freeze_workers(): we can't rearrange while
   * workers are frozen (i.e. multiple updates need to be done). */
  if (pcity->server.workers_frozen > 0) {
    if (pcity->server.needs_arrange == CNA_NOT) {
      pcity->server.needs_arrange = CNA_NORMAL;
    }
    return;
  }
  TIMING_LOG(AIT_CITIZEN_ARRANGE, TIMER_START);
 
  broadcast_needed = (pcity->server.needs_arrange == CNA_BROADCAST_PENDING);
 
  /* Freeze the workers and make sure all the tiles around the city
   * are up to date. Then thaw, but hackishly make sure that thaw
   * doesn't call us recursively, which would waste time. */
  city_freeze_workers(pcity);
  pcity->server.needs_arrange = CNA_NOT;
 
  city_map_update_all(pcity);
 
  pcity->server.needs_arrange = CNA_NOT;
  city_thaw_workers(pcity);
 
  /* Now start actually rearranging. */
  city_refresh(pcity);
 
  sanity_check_city(pcity);
  cm_clear_cache(pcity);
 
  if (pcity->cm_parameter) {
    pcmp = pcity->cm_parameter;
  } else {
    pcmp = &cmp;
    cm_init_parameter(pcmp);
    set_default_city_manager(pcmp, pcity);
  }
 
  /* This must be after city_refresh() so that the result gets created for the right
   * city radius */
  cmr = cm_result_new(pcity);
  cm_query_result(pcity, pcmp, cmr, FALSE);
 
  if (!cmr->found_a_valid) {
    if (pcity->cm_parameter) {
      /* If player-defined parameters fail, cancel and notify player. */
      free(pcity->cm_parameter);
      pcity->cm_parameter = NULL;
 
      notify_player(city_owner(pcity), city_tile(pcity),
                    E_CITY_CMA_RELEASE, ftc_server,
                    _("The citizen governor can't fulfill the requirements "
                     "for %s. Passing back control."),
                    city_link(pcity));
 
      /* Switch to default parameters, and try with them */
      pcmp = &cmp;
      cm_init_parameter(pcmp);
      set_default_city_manager(pcmp, pcity);
      cm_query_result(pcity, pcmp, cmr, FALSE);
    }
 
    if (!cmr->found_a_valid) {
      /* Drop surpluses and try again. */
      output_type_iterate(o) {
        cmp.minimal_surplus[o] = 0;
      } output_type_iterate_end;
      cmp.minimal_surplus[O_GOLD] = -FC_INFINITY;
      cm_query_result(pcity, pcmp, cmr, FALSE);
    }
  }
  if (!cmr->found_a_valid) {
    /* Emergency management. Get _some_ result. This doesn't use
     * cm_init_emergency_parameter() so we can keep the factors from
     * above. */
    output_type_iterate(o) {
      cmp.minimal_surplus[o] = MIN(cmp.minimal_surplus[o],
                                   MIN(pcity->surplus[o], 0));
    } output_type_iterate_end;
    cmp.require_happy = FALSE;
    cmp.allow_disorder = is_ai(city_owner(pcity)) ? FALSE : TRUE;
    cm_query_result(pcity, pcmp, cmr, FALSE);
  }
  if (!cmr->found_a_valid) {
    CITY_LOG(LOG_DEBUG, pcity, "emergency management");
    pcmp = &cmp;
    cm_init_emergency_parameter(pcmp);
    cm_query_result(pcity, pcmp, cmr, TRUE);
  }
  fc_assert_ret(cmr->found_a_valid);
 
  apply_cmresult_to_city(pcity, cmr);
 
  if (pcity->server.debug) {
    /* Print debug output if requested. */
    cm_print_city(pcity);
    cm_print_result(cmr);
  }
 
  if (city_refresh(pcity)) {
    log_error("%s radius changed when already arranged workers.",
              city_name_get(pcity));
    /* Can't do anything - don't want to enter infinite recursive loop
     * by trying to arrange workers more. */
  }
  sanity_check_city(pcity);
 
  if (broadcast_needed) {
    broadcast_city_info(pcity);
  }
 
  cm_result_destroy(cmr);
  TIMING_LOG(AIT_CITIZEN_ARRANGE, TIMER_STOP);
}
 
/**********************************************************************/
static void city_global_turn_notify(struct conn_list *dest)
{
  cities_iterate(pcity) {
    const struct impr_type *pimprove = pcity->production.value.building;
 
    if (VUT_IMPROVEMENT == pcity->production.kind
        && is_great_wonder(pimprove)
        && (1 >= city_production_turns_to_build(pcity, TRUE)
        && can_city_build_improvement_now(pcity, pimprove))) {
      notify_conn(dest, city_tile(pcity),
                  E_WONDER_WILL_BE_BUILT, ftc_server,
                  _("Notice: Wonder %s in %s will be finished next turn."),
                  improvement_name_translation(pimprove), city_link(pcity));
    }
  } cities_iterate_end;
}
 
/**********************************************************************/
static void city_turn_notify(const struct city *pcity,
                             struct conn_list *dest,
                             const struct player *cache_for_player)
{
  const struct impr_type *pimprove = pcity->production.value.building;
  struct packet_chat_msg packet;
  int turns_growth, turns_granary;
 
  if (0 < pcity->surplus[O_FOOD]) {
    turns_growth = (city_granary_size(city_size_get(pcity))
                    - pcity->food_stock - 1) / pcity->surplus[O_FOOD];
 
    if (get_city_bonus(pcity, EFT_GROWTH_FOOD) <= 0
        && 0 < get_current_construction_bonus(pcity, EFT_GROWTH_FOOD,
                                              RPT_CERTAIN)
        && 0 < pcity->surplus[O_SHIELD]) {
      /* From the check above, the surplus must always be positive. */
      turns_granary = (impr_build_shield_cost(pcity, pimprove)
                       - pcity->shield_stock) / pcity->surplus[O_SHIELD];
      /* If growth and granary completion occur simultaneously, granary
       * preserves food.  -AJS. */
      if (5 > turns_growth && 5 > turns_granary
          && turns_growth < turns_granary) {
        package_event(&packet, city_tile(pcity),
                      E_CITY_GRAN_THROTTLE, ftc_server,
                      _("Suggest throttling growth in %s to use %s "
                        "(being built) more effectively."),
                      city_link(pcity),
                      improvement_name_translation(pimprove));
        lsend_packet_chat_msg(dest, &packet);
        if (NULL != cache_for_player) {
          event_cache_add_for_player(&packet, cache_for_player);
        }
      }
    }
 
    if (0 >= turns_growth && !city_celebrating(pcity)
        && city_can_grow_to(pcity, city_size_get(pcity) + 1)) {
      package_event(&packet, city_tile(pcity),
                    E_CITY_MAY_SOON_GROW, ftc_server,
                    _("%s may soon grow to size %i."),
                    city_link(pcity), city_size_get(pcity) + 1);
      lsend_packet_chat_msg(dest, &packet);
      if (NULL != cache_for_player) {
        event_cache_add_for_player(&packet, cache_for_player);
      }
    }
  } else {
    if (0 >= pcity->food_stock + pcity->surplus[O_FOOD]
        && 0 > pcity->surplus[O_FOOD]) {
      package_event(&packet, city_tile(pcity),
                    E_CITY_FAMINE_FEARED, ftc_server,
                    _("Warning: Famine feared in %s."), city_link(pcity));
      lsend_packet_chat_msg(dest, &packet);
      if (NULL != cache_for_player) {
        event_cache_add_for_player(&packet, cache_for_player);
      }
    }
  }
}
 
/**********************************************************************/
void send_city_turn_notifications(struct connection *pconn)
{
  if (NULL != pconn) {
    struct player *pplayer = conn_get_player(pconn);
 
    if (NULL != pplayer) {
      city_list_iterate(pplayer->cities, pcity) {
        city_turn_notify(pcity, pconn->self, NULL);
      } city_list_iterate_end;
    }
    city_global_turn_notify(pconn->self);
  } else {
    players_iterate(pplayer) {
      city_list_iterate(pplayer->cities, pcity) {
        city_turn_notify(pcity, pplayer->connections, pplayer);
      } city_list_iterate_end;
    } players_iterate_end;
    /* NB: notifications to 'game.est_connections' are automatically
     * cached. */
    city_global_turn_notify(game.est_connections);
  }
}
 
/**********************************************************************/
void update_city_activities(struct player *pplayer)
{
  char buf[4 * MAX_LEN_NAME];
  int n, gold;
 
  fc_assert(NULL != pplayer->cities);
 
  n = city_list_size(pplayer->cities);
  gold = pplayer->economic.gold;
  pplayer->server.bulbs_last_turn = 0;
 
  if (n > 0) {
    struct city *cities[n];
    int i = 0, r;
 
    city_list_iterate(pplayer->cities, pcity) {
 
      citizens_convert(pcity);
 
      /* Cancel trade routes that cannot exist any more */
      trade_routes_iterate_safe(pcity, proute) {
        struct city *tcity = game_city_by_number(proute->partner);
 
        if (tcity != NULL) {
          bool cancel = FALSE;
 
          if (proute->dir != RDIR_FROM && goods_has_flag(proute->goods, GF_DEPLETES)
              && !goods_can_be_provided(tcity, proute->goods, NULL)) {
            cancel = TRUE;
          }
          if (!cancel && !can_cities_trade(pcity, tcity)) {
            enum trade_route_type type = cities_trade_route_type(pcity, tcity);
            struct trade_route_settings *settings = trade_route_settings_by_type(type);
 
            if (settings->cancelling == TRI_CANCEL) {
              cancel = TRUE;
            }
          }
 
          if (cancel) {
            struct trade_route *back;
 
            back = remove_trade_route(pcity, proute, TRUE, FALSE);
            free(proute);
            free(back);
          }
        }
      } trade_routes_iterate_safe_end;
 
      /* Add cities to array for later random order handling */
      cities[i++] = pcity;
    } city_list_iterate_end;
 
    /* How gold upkeep is handled depends on the setting
     * 'game.info.gold_upkeep_style':
     * GOLD_UPKEEP_CITY: Each city tries to balance its upkeep individually
     *                   (this is done in update_city_activity()).
     * GOLD_UPKEEP_MIXED: Each city tries to balance its upkeep for
     *                    buildings individually; the upkeep for units is
     *                    paid by the nation.
     * GOLD_UPKEEP_NATION: The nation as a whole balances the treasury. If
     *                     the treasury is not balance units and buildings
     *                     are sold. */
 
    /* Iterate over cities in a random order. */
    while (i > 0) {
      r = fc_rand(i);
      /* update unit upkeep */
      city_units_upkeep(cities[r]);
      update_city_activity(cities[r]);
      cities[r] = cities[--i];
    }
 
    if (pplayer->economic.infra_points < 0) {
      pplayer->economic.infra_points = 0;
    }
 
    if (pplayer->economic.gold < 0) {
      switch (game.info.gold_upkeep_style) {
      case GOLD_UPKEEP_CITY:
        break;
      case GOLD_UPKEEP_MIXED:
        /* Nation pays for units. */
        player_balance_treasury_units(pplayer);
        break;
      case GOLD_UPKEEP_NATION:
        /* Nation pays for units and buildings. */
        player_balance_treasury_units_and_buildings(pplayer);
        break;
      }
    }
 
    /* Should not happen. */
    fc_assert(pplayer->economic.gold >= 0);
  }
 
  /* This test includes the cost of the units because
   * units are paid for in update_city_activity() or
   * player_balance_treasury_units(). */
  if (gold - (gold - pplayer->economic.gold) * 3 < 0) {
    notify_player(pplayer, NULL, E_LOW_ON_FUNDS, ftc_server,
                  _("WARNING, we're LOW on FUNDS %s."),
                  ruler_title_for_player(pplayer, buf, sizeof(buf)));
  }
 
#if 0
  /* Uncomment to unbalance the game, like in civ1 (CLG). */
  if (pplayer->got_tech && pplayer->research->researched > 0) {
    pplayer->research->researched = 0;
  }
#endif
 
  city_refresh_queue_processing();
}
 
/**********************************************************************/
static bool upkeep_kill_unit(struct unit *punit, Output_type_id outp,
                             enum unit_loss_reason wipe_reason,
                             bool wipe_in_the_end)
{
  int punit_id;
 
  if (!action_auto_perf_unit_sel(AAPC_UNIT_UPKEEP, punit,
                                 NULL, get_output_type(outp), NULL)) {
    /* Can't get rid of this unit. It is undisbandable for the current
     * situation. */
    return FALSE;
  }
 
  punit_id = punit->id;
 
  /* Try to perform this unit's can't upkeep actions. */
  action_auto_perf_unit_do(AAPC_UNIT_UPKEEP, punit,
                           NULL, get_output_type(outp), NULL,
                           NULL, NULL, NULL, NULL);
 
  if (wipe_in_the_end && unit_is_alive(punit_id)) {
    /* No forced action was able to kill the unit. Finish the job. */
    wipe_unit(punit, wipe_reason, NULL);
  }
 
  return !unit_is_alive(punit_id);
}
 
/**********************************************************************/
static citizens city_reduce_specialists(struct city *pcity, citizens change)
{
  citizens want = change;
 
  fc_assert_ret_val(0 < change, 0);
 
  specialist_type_iterate(sp) {
    citizens fix = MIN(want, pcity->specialists[sp]);
 
    pcity->specialists[sp] -= fix;
    want -= fix;
  } specialist_type_iterate_end;
 
  return change - want;
}
 
/**********************************************************************/
static citizens city_reduce_workers(struct city *pcity, citizens change)
{
  struct tile *pcenter = city_tile(pcity);
  int want = change;
  const struct civ_map *nmap = &(wld.map);
 
  fc_assert_ret_val(0 < change, 0);
 
  city_tile_iterate_skip_free_worked(nmap, city_map_radius_sq_get(pcity), pcenter,
                                     ptile, _index, _x, _y) {
    if (0 < want && tile_worked(ptile) == pcity) {
      city_map_update_empty(pcity, ptile);
      want--;
    }
  } city_tile_iterate_skip_free_worked_end;
 
  return change - want;
}
 
/**********************************************************************/
bool city_reduce_size(struct city *pcity, citizens pop_loss,
                      struct player *destroyer, const char *reason)
{
  citizens loss_remain;
  int old_radius_sq;
 
  if (pop_loss == 0) {
    return TRUE;
  }
 
  if (city_size_get(pcity) <= pop_loss) {
    int id = pcity->id;
 
    citizens_update(pcity, NULL); /* To avoid warnings during the script */
    /* Won't refresh a doomed city, or should we? */
    script_server_signal_emit("city_destroyed", pcity, pcity->owner,
                              destroyer);
 
    if (city_exist(id)) {
      remove_city(pcity);
    }
    return FALSE;
  }
  old_radius_sq = tile_border_source_radius_sq(pcity->tile);
  city_size_add(pcity, -pop_loss);
  map_update_border(pcity->tile, pcity->owner, old_radius_sq,
                    tile_border_source_radius_sq(pcity->tile));
 
  /* Cap the food stock at the new granary size. */
  if (pcity->food_stock > city_granary_size(city_size_get(pcity))) {
    pcity->food_stock = city_granary_size(city_size_get(pcity));
  }
 
  /* First try to kill off the specialists */
  loss_remain = pop_loss - city_reduce_specialists(pcity, pop_loss);
 
  if (loss_remain > 0) {
    /* Take it out on workers */
#ifndef FREECIV_NDEBUG
    loss_remain -=
#endif /* FREECIV_NDEBUG */
      city_reduce_workers(pcity, loss_remain);
  }
 
  /* Update citizens. */
  citizens_update(pcity, NULL);
 
  /* Update number of people in each feelings category.
   * This also updates the city radius if needed. */
  city_refresh(pcity);
 
  auto_arrange_workers(pcity);
 
  /* Send city data. */
  sync_cities();
 
  fc_assert_ret_val_msg(0 == loss_remain, TRUE,
                        "city_reduce_size() has remaining"
                        "%d of %d for \"%s\"[%d]",
                        loss_remain, pop_loss,
                        city_name_get(pcity), city_size_get(pcity));
 
  /* Update cities that have trade routes with us */
  trade_partners_iterate(pcity, pcity2) {
    if (city_refresh(pcity2)) {
      /* This should never happen, but if it does, make sure not to
       * leave workers outside city radius. */
      auto_arrange_workers(pcity2);
    }
  } trade_partners_iterate_end;
 
  sanity_check_city(pcity);
 
  if (reason != NULL) {
    int id = pcity->id;
 
    script_server_signal_emit("city_size_change", pcity,
                              (lua_Integer)(-pop_loss), reason);
 
    return city_exist(id);
  }
 
  return TRUE;
}
 
/**********************************************************************/
void city_repair_size(struct city *pcity, int change)
{
  if (change > 0) {
    pcity->specialists[DEFAULT_SPECIALIST] += change;
  } else if (change < 0) {
    int need = change + city_reduce_specialists(pcity, -change);
 
    if (0 > need) {
#ifndef FREECIV_NDEBUG
      need +=
#endif /* FREECIV_NDEBUG */
        city_reduce_workers(pcity, -need);
    }
 
    fc_assert_msg(0 == need,
                  "city_repair_size() has remaining %d of %d for \"%s\"[%d]",
                  need, change, city_name_get(pcity), city_size_get(pcity));
  }
}
 
/**********************************************************************/
int city_granary_savings(const struct city *pcity)
{
  int savings = get_city_bonus(pcity, EFT_GROWTH_FOOD);
 
  return CLIP(0, savings, 100);
}
 
/**********************************************************************/
static void city_reset_foodbox(struct city *pcity, int new_size)
{
  fc_assert_ret(pcity != NULL);
 
  pcity->food_stock = (city_granary_size(new_size)
                       * city_granary_savings(pcity)) / 100;
}
 
/**********************************************************************/
static bool city_increase_size(struct city *pcity)
{
  int new_food;
  int savings_pct = city_granary_savings(pcity);
  bool have_square = FALSE;
  bool rapture_grow = city_rapture_grow(pcity); /* Check before size increase! */
  struct tile *pcenter = city_tile(pcity);
  struct player *powner = city_owner(pcity);
  const struct impr_type *pimprove = pcity->production.value.building;
  const struct civ_map *nmap = &(wld.map);
 
  if (!city_can_grow_to(pcity, city_size_get(pcity) + 1)) {
    /* Need improvement */
    if (get_current_construction_bonus(pcity, EFT_SIZE_ADJ, RPT_CERTAIN) > 0
        || get_current_construction_bonus(pcity, EFT_SIZE_UNLIMIT, RPT_CERTAIN) > 0) {
      notify_player(powner, city_tile(pcity), E_CITY_AQ_BUILDING, ftc_server,
                    _("%s needs %s (being built) to grow beyond size %d."),
                    city_link(pcity),
                    improvement_name_translation(pimprove),
                    city_size_get(pcity));
    } else {
      notify_player(powner, city_tile(pcity), E_CITY_AQUEDUCT, ftc_server,
                    _("%s needs an improvement to grow beyond size %d."),
                    city_link(pcity), city_size_get(pcity));
    }
    /* Granary can only hold so much */
    new_food = (city_granary_size(city_size_get(pcity))
                * (100 * 100 - game.server.aqueductloss * (100 - savings_pct))
                / (100 * 100));
    pcity->food_stock = MIN(pcity->food_stock, new_food);
 
    return FALSE;
  }
 
  city_size_add(pcity, 1);
 
  /* Do not empty food stock if city is growing by celebrating */
  if (rapture_grow) {
    new_food = city_granary_size(city_size_get(pcity));
  } else {
    new_food = city_granary_size(city_size_get(pcity)) * savings_pct / 100;
  }
  pcity->food_stock = MIN(pcity->food_stock, new_food);
 
  /* If there is enough food, and the city is big enough,
   * make new citizens into scientists or taxmen -- Massimo */
 
  /* Ignore food if no square can be worked */
  city_tile_iterate_skip_free_worked(nmap, city_map_radius_sq_get(pcity), pcenter,
                                     ptile, _index, _x, _y) {
    if (tile_worked(ptile) != pcity /* Quick test */
     && city_can_work_tile(pcity, ptile)) {
      have_square = TRUE;
    }
  } city_tile_iterate_skip_free_worked_end;
 
  if ((pcity->surplus[O_FOOD] >= 2 || !have_square)
      && is_city_option_set(pcity, CITYO_SCIENCE_SPECIALISTS)) {
    pcity->specialists[best_specialist(O_SCIENCE, pcity)]++;
  } else if ((pcity->surplus[O_FOOD] >= 2 || !have_square)
             && is_city_option_set(pcity, CITYO_GOLD_SPECIALISTS)) {
    pcity->specialists[best_specialist(O_GOLD, pcity)]++;
  } else {
    pcity->specialists[DEFAULT_SPECIALIST]++; /* or else city is !sane */
  }
 
  /* Deprecated signal. Connect your lua functions to "city_size_change" that's
   * emitted from calling functions which know the 'reason' of the increase. */
  script_server_signal_emit("city_growth", pcity,
                            (lua_Integer)city_size_get(pcity));
 
  return TRUE;
}
 
/**********************************************************************/
static void city_refresh_after_city_size_increase(struct city *pcity,
                                                  struct player *nationality)
{
  struct player *powner = city_owner(pcity);
 
  /* Update citizens. */
  citizens_update(pcity, nationality);
 
  /* Refresh the city data; this also checks the squared city radius. */
  city_refresh(pcity);
 
  auto_arrange_workers(pcity);
 
  /* Update cities that have trade routes with us */
  trade_partners_iterate(pcity, pcity2) {
    if (city_refresh(pcity2)) {
      /* This should never happen, but if it does, make sure not to
       * leave workers outside city radius. */
      auto_arrange_workers(pcity2);
    }
  } trade_partners_iterate_end;
 
  notify_player(powner, city_tile(pcity), E_CITY_GROWTH, ftc_server,
                _("%s grows to size %d."),
                city_link(pcity), city_size_get(pcity));
 
  sanity_check_city(pcity);
 
  sync_cities();
}
 
/**********************************************************************/
bool city_change_size(struct city *pcity, citizens size,
                      struct player *nationality, const char *reason)
{
  int change = size - city_size_get(pcity);
 
  if (change > 0) {
    int old_size = city_size_get(pcity);
    int real_change;
    int current_size = city_size_get(pcity);
    int id = pcity->id;
 
    /* Increase city size until size reached, or increase fails */
    while (size > current_size && city_increase_size(pcity)) {
      /* TODO: This is currently needed only because there's
       *       deprecated script signal "city_growth" emitted.
       *       Check the need after signal has been dropped completely. */
      if (!city_exist(id)) {
        return FALSE;
      }
 
      current_size++;
    }
 
    city_refresh_after_city_size_increase(pcity, nationality);
 
    real_change = current_size - old_size;
 
    if (real_change != 0 && reason != NULL) {
      script_server_signal_emit("city_size_change", pcity,
                                (lua_Integer)real_change, reason);
 
      if (!city_exist(id)) {
        return FALSE;
      }
    }
  } else if (change < 0) {
    /* We assume that city_change_size() is never called because
     * of enemy actions. If that changes, enemy must be passed
     * to city_reduce_size() */
    return city_reduce_size(pcity, -change, NULL, reason);
  }
 
  map_claim_border(pcity->tile, pcity->owner, -1);
 
  return TRUE;
}
 
/**********************************************************************/
static void city_populate(struct city *pcity, struct player *nationality)
{
  int saved_id = pcity->id;
  int granary_size = city_granary_size(city_size_get(pcity));
 
  pcity->food_stock += pcity->surplus[O_FOOD];
  if (pcity->food_stock >= granary_size || city_rapture_grow(pcity)) {
    if (city_had_recent_plague(pcity)) {
      notify_player(city_owner(pcity), city_tile(pcity),
                    E_CITY_PLAGUE, ftc_server,
                    _("A recent plague outbreak prevents growth in %s."),
                    city_link(pcity));
      /* Lose excess food */
      pcity->food_stock = MIN(pcity->food_stock, granary_size);
    } else {
      bool success;
 
      success = city_increase_size(pcity);
      map_claim_border(pcity->tile, pcity->owner, -1);
 
      if (success) {
        city_refresh_after_city_size_increase(pcity, nationality);
        script_server_signal_emit("city_size_change", pcity,
                                  (lua_Integer)1, "growth");
      }
    }
  } else if (pcity->food_stock < 0) {
    /* FIXME: should this depend on units with ability to build
     * cities or on units that require food in upkeep?
     * I'll assume citybuilders (units that 'contain' 1 pop) -- sjolie
     * The above may make more logical sense, but in game terms
     * you want to disband a unit that is draining your food
     * reserves.  Hence, I'll assume food upkeep > 0 units. -- jjm
     */
    unit_list_iterate_safe(pcity->units_supported, punit) {
      if (punit->upkeep[O_FOOD] > 0) {
        const char *punit_link = unit_tile_link(punit);
 
        if (upkeep_kill_unit(punit, O_FOOD, ULR_STARVED,
                             game.info.muuk_food_wipe)) {
          notify_player(city_owner(pcity), city_tile(pcity),
                        E_UNIT_LOST_MISC, ftc_server,
                        _("Famine feared in %s, %s lost!"),
                        city_link(pcity), punit_link);
        }
 
        if (city_exist(saved_id)) {
          city_reset_foodbox(pcity, city_size_get(pcity));
        }
 
        return;
      }
    } unit_list_iterate_safe_end;
    if (city_size_get(pcity) > 1) {
      notify_player(city_owner(pcity), city_tile(pcity),
                    E_CITY_FAMINE, ftc_server,
                    _("Famine causes population loss in %s."),
                    city_link(pcity));
    } else {
      notify_player(city_owner(pcity), city_tile(pcity),
                    E_CITY_FAMINE, ftc_server,
                    _("Famine destroys %s entirely."),
                    city_link(pcity));
    }
    city_reset_foodbox(pcity, city_size_get(pcity) - 1);
    city_reduce_size(pcity, 1, NULL, "famine");
  }
}
 
/**********************************************************************/
static bool worklist_item_postpone_req_vec(struct universal *target,
                                           struct city *pcity,
                                           struct player *pplayer,
                                           int saved_id)
{
  const void *ptarget;
  const char *tgt_name;
  const struct requirement_vector *build_reqs;
  const char *signal_name;
  const struct req_context city_ctxt = {
    .player = pplayer,
    .city = pcity,
    .tile = city_tile(pcity)
    /* FIXME: Setting .unittype is currently redundant
     * but can_city_build_unit_direct() does it */
  };
  bool purge = FALSE;
  bool known = FALSE;
 
  switch (target->kind) {
  case VUT_UTYPE:
    ptarget = target->value.utype;
    build_reqs = &target->value.utype->build_reqs;
    tgt_name = utype_name_translation(ptarget);
    signal_name = "unit_cant_be_built";
    break;
  case VUT_IMPROVEMENT:
    ptarget = target->value.building;
    build_reqs = &target->value.building->reqs;
    tgt_name = city_improvement_name_translation(pcity, ptarget);
    signal_name = "building_cant_be_built";
    break;
  default:
    fc_assert_ret_val((target->kind == VUT_IMPROVEMENT
                       || target->kind == VUT_UTYPE), FALSE);
    return FALSE;
    break;
  }
 
  requirement_vector_iterate(build_reqs, preq) {
    if (!is_req_active(&city_ctxt, NULL, preq, RPT_POSSIBLE)) {
      known = TRUE;
      switch (preq->source.kind) {
      case VUT_ADVANCE:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "tech %s not yet available. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        advance_name_translation
                            (preq->source.value.advance));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_tech");
        } else {
          /* While techs can be unlearned, this isn't useful feedback */
          purge = TRUE;
        }
        break;
      case VUT_TECHFLAG:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "no tech with flag \"%s\" yet available. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        tech_flag_id_name(preq->source.value.techflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_techflag");
        } else {
          /* While techs can be unlearned, this isn't useful feedback */
          purge = TRUE;
        }
        break;
      case VUT_IMPROVEMENT:
        if (preq->range == REQ_RANGE_LOCAL) {
          /* Building itself is never going to change */
          purge = TRUE;
        } else {
          if (preq->present) {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          _("%s can't build %s from the worklist; "
                            "need to have %s first. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          city_improvement_name_translation(pcity,
                            preq->source.value.building));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "need_building");
          } else {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          _("%s can't build %s from the worklist; "
                            "need to not have %s. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          city_improvement_name_translation(pcity,
                            preq->source.value.building));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "have_building");
          }
        }
        break;
      case VUT_IMPR_GENUS:
        if (preq->range == REQ_RANGE_LOCAL) {
          /* Building's own genus is never going to change */
          purge = TRUE;
        } else {
          if (preq->present) {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          _("%s can't build %s from the worklist; "
                            "need to have %s first. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          impr_genus_id_translated_name(
                            preq->source.value.impr_genus));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "need_building_genus");
          } else {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          _("%s can't build %s from the worklist; "
                            "need to not have %s. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          impr_genus_id_translated_name(
                            preq->source.value.impr_genus));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "have_building_genus");
          }
        }
        break;
      case VUT_GOVERNMENT:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "it needs %s government. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        government_name_translation(preq->source.value.govern));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_government");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "it cannot have %s government. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        government_name_translation(preq->source.value.govern));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_government");
        }
        break;
      case VUT_ACHIEVEMENT:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "it needs \"%s\" achievement. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        achievement_name_translation(preq->source.value.achievement));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_achievement");
        } else {
          /* Can't unachieve things. */
          purge = TRUE;
        }
        break;
      case VUT_EXTRA:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?extra:%s can't build %s from the worklist; "
                           "%s is required. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        extra_name_translation(preq->source.value.extra));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_extra");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?extra:%s can't build %s from the worklist; "
                           "%s is prohibited. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        extra_name_translation(preq->source.value.extra));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_extra");
        }
        break;
      case VUT_GOOD:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?extra:%s can't build %s from the worklist; "
                           "%s is required. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        goods_name_translation(preq->source.value.good));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_good");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?extra:%s can't build %s from the worklist; "
                           "%s is prohibited. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        goods_name_translation(preq->source.value.good));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_good");
        }
        break;
      case VUT_TERRAIN:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?terrain:%s can't build %s from the worklist; "
                           "%s terrain is required. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        terrain_name_translation(preq->source.value.terrain));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_terrain");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        Q_("?terrain:%s can't build %s from the worklist; "
                           "%s terrain is prohibited. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        terrain_name_translation(preq->source.value.terrain));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_terrain");
        }
        break;
      case VUT_NATION:
        if (preq->range < REQ_RANGE_TRADE_ROUTE
            || preq->range == REQ_RANGE_PLAYER) {
          /* At higher ranges, new players with their nations may arrive */
          purge = TRUE;
        } else {
          if (preq->present) {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          /* TRANS: "%s nation" is adjective */
                          Q_("?nation:%s can't build %s from the worklist; "
                             "%s nation is required. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          nation_adjective_translation(preq->source.value.nation));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "need_nation");
          } else {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          Q_("?nation:%s can't build %s from the worklist; "
                             "%s nation is prohibited. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          nation_adjective_translation(preq->source.value.nation));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "have_nation");
          }
        }
        break;
      case VUT_NATIONGROUP:
        if (preq->range < REQ_RANGE_TRADE_ROUTE
            || preq->range == REQ_RANGE_PLAYER) {
          /* At higher ranges, new players with their nations may arrive */
          purge = TRUE;
        } else {
          if (preq->present) {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          /* TRANS: "%s nation" is adjective */
                          Q_("?ngroup:%s can't build %s from the worklist; "
                             "%s nation is required. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          nation_group_name_translation(preq->source.value.nationgroup));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "need_nationgroup");
          } else {
            notify_player(pplayer, city_tile(pcity),
                          E_CITY_CANTBUILD, ftc_server,
                          Q_("?ngroup:%s can't build %s from the worklist; "
                             "%s nation is prohibited. Postponing..."),
                          city_link(pcity),
                          tgt_name,
                          nation_group_name_translation(preq->source.value.nationgroup));
            script_server_signal_emit(signal_name, ptarget,
                                      pcity, "have_nationgroup");
          }
        }
        break;
      case VUT_STYLE:
        /* FIXME: City styles sometimes change over time, but it isn't
         * entirely under player control. Probably better to purge
         * with useful explanation. */
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "only %s style cities may build this. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        style_name_translation(preq->source.value.style));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_style");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "%s style cities may not build this. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        style_name_translation(preq->source.value.style));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_style");
        }
        break;
      case VUT_NATIONALITY:
        /* FIXME: Changing citizen nationality is hard: purging might be
         * more useful in this case. */
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: Latter %s is citizen nationality */
                        _("%s can't build %s from the worklist; "
                          "only city with %s may build this. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        nation_plural_translation(preq->source.value.nationality));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_nationality");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: Latter %s is citizen nationality */
                        _("%s can't build %s from the worklist; "
                          "only city without %s may build this. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        nation_plural_translation(preq->source.value.nationality));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_nationality");
        }
        break;
      case VUT_DIPLREL:
      case VUT_DIPLREL_TILE: /* The tile owner is the city owner */
      case VUT_DIPLREL_TILE_O: /* The tile owner is the city owner */
        if (preq->present) {
          const char *reason;
 
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: '%s' is a wide range of relationships;
                         * e.g., 'Peace', 'Never met', 'Foreign',
                         * 'Hosts embassy', 'Provided Casus Belli' */
                        _("%s can't build %s from the worklist; "
                          "the relationship '%s' is required."
                          "  Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        diplrel_name_translation(
                          preq->source.value.diplrel));
 
          if (preq->source.kind == VUT_DIPLREL_TILE) {
            reason = "need_diplrel_tile";
          } else if (preq->source.kind == VUT_DIPLREL_TILE_O) {
            reason = "need_diplrel_tile_o";
          } else {
            fc_assert(preq->source.kind == VUT_DIPLREL);
            reason = "need_diplrel";
          }
 
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, reason);
        } else {
          const char *reason;
 
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "the relationship '%s' is prohibited."
                          "  Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        diplrel_name_translation(
                          preq->source.value.diplrel));
 
          if (preq->source.kind == VUT_DIPLREL_TILE) {
            reason = "have_diplrel_tile";
          } else if (preq->source.kind == VUT_DIPLREL_TILE_O) {
            reason = "have_diplrel_tile_o";
          } else {
            fc_assert(preq->source.kind == VUT_DIPLREL);
            reason = "have_diplrel";
          }
 
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, reason);
        }
        break;
      case VUT_DIPLREL_UNITANY:
      case VUT_DIPLREL_UNITANY_O:
        if (preq->present) {
          const char *reason;
 
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: '%s' is a wide range of relationships;
                         * e.g., 'Peace', 'Never met', 'Foreign',
                         * 'Hosts embassy', 'Provided Casus Belli' */
                        _("%s can't build %s from the worklist; "
                          "unit with the relationship '%s' is required."
                          "  Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        diplrel_name_translation(
                          preq->source.value.diplrel));
 
          if (preq->source.kind == VUT_DIPLREL_UNITANY) {
            reason = "need_diplrel_unitany";
          } else {
            fc_assert(preq->source.kind == VUT_DIPLREL_UNITANY_O);
            reason = "need_diplrel_unitany_o";
          }
 
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, reason);
        } else {
          const char *reason;
 
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "unit with the relationship '%s' is prohibited."
                          "  Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        diplrel_name_translation(
                          preq->source.value.diplrel));
 
          if (preq->source.kind == VUT_DIPLREL_UNITANY) {
            reason = "have_diplrel_unitany";
          } else {
            fc_assert(preq->source.kind == VUT_DIPLREL_UNITANY_O);
            reason = "have_diplrel_unitany_o";
          }
 
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, reason);
        }
        break;
      case VUT_MINSIZE:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "city must be of size %d or larger. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.minsize);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minsize");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "city must be of size %d or smaller."
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        (preq->source.value.minsize - 1));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minsize");
        }
        break;
      case VUT_MINCULTURE:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "city must have culture of %d. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.minculture);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minculture");
        } else {
          /* What has been written may not be unwritten. */
          purge = TRUE;
        }
        break;
      case VUT_MINFOREIGNPCT:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "city must have %d%% foreign population. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.minforeignpct);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minforeignpct");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "city must have %d%% native population. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        100 - preq->source.value.minforeignpct);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minforeignpct");
        }
        break;
      case VUT_MINTECHS:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "%d techs must be known. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.min_techs);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_mintechs");
        } else {
          purge = TRUE;
        }
        break;
      case VUT_MAXTILEUNITS:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        PL_("%s can't build %s from the worklist; "
                            "more than %d unit on tile."
                            "  Postponing...",
                            "%s can't build %s from the worklist; "
                            "more than %d units on tile."
                            "  Postponing...",
                            preq->source.value.max_tile_units),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.max_tile_units);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_tileunits");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        PL_("%s can't build %s from the worklist; "
                            "fewer than %d unit on tile."
                            "  Postponing...",
                            "%s can't build %s from the worklist; "
                            "fewer than %d units on tile."
                            "  Postponing...",
                            preq->source.value.max_tile_units + 1),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.max_tile_units + 1);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_tileunits");
        }
        break;
      case VUT_AI_LEVEL:
        /* Can't change AI level. */
        purge = TRUE;
        break;
      case VUT_TERRAINCLASS:
        /* Change of terrain class is expected to be very unlikely. Purge!
         * TODO: Analyze ruleset to see how unlikely terrain class change actually is. */
        purge = TRUE;
        break;
      case VUT_TERRFLAG:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "terrain with \"%s\" flag is required. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        terrain_flag_id_name(preq->source.value.terrainflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_terrainflag");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "terrain with \"%s\" flag is prohibited. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        terrain_flag_id_name(preq->source.value.terrainflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_terrainflag");
        }
        break;
      case VUT_ROADFLAG:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "road with \"%s\" flag is required. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        road_flag_id_name(preq->source.value.roadflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_roadflag");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "road with \"%s\" flag is prohibited. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        road_flag_id_name(preq->source.value.roadflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_roadflag");
        }
        break;
      case VUT_EXTRAFLAG:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "extra with \"%s\" flag is required. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        extra_flag_id_translated_name(preq->source.value.extraflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_extraflag");
        } else {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "extra with \"%s\" flag is prohibited. "
                          "Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        extra_flag_id_translated_name(preq->source.value.extraflag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_extraflag");
        }
        break;
      case VUT_UTYPE:
      case VUT_UTFLAG:
      case VUT_UCLASS:
      case VUT_UCFLAG:
      case VUT_MINVETERAN:
      case VUT_UNITSTATE:
      case VUT_ACTIVITY:
      case VUT_MINMOVES:
      case VUT_MINHP:
      case VUT_ACTION:
      case VUT_OTYPE:
      case VUT_SPECIALIST:
      case VUT_TERRAINALTER: /* XXX could do this in principle */
      case VUT_CITYTILE:
        /* Will only happen with a bogus ruleset. */
        log_error("worklist_change_build_target() has bogus preq");
        break;
      case VUT_CITYSTATUS:
        if (preq->source.value.citystatus == CITYS_OWNED_BY_ORIGINAL) {
          if (preq->range == REQ_RANGE_CITY) {
            /* Can't change at this range */
            purge = TRUE;
          } else {
            if (preq->present) {
              notify_player(pplayer, city_tile(pcity),
                            E_CITY_CANTBUILD, ftc_server,
                            /* TRANS: last %s is a CityStatus ("OwnedByOriginal") */
                            _("%s can't build %s from the worklist; "
                              "only available when city in range %s \"%s\". "
                              "Postponing..."),
                            city_link(pcity),
                            tgt_name, req_range_name(preq->range),
                            citystatus_type_name(preq->source.value.citystatus));
              script_server_signal_emit(signal_name, ptarget,
                                        pcity, "need_citystatus");
            } else {
              notify_player(pplayer, city_tile(pcity),
                            E_CITY_CANTBUILD, ftc_server,
                            /* TRANS: last %s is a CityStatus ("OwnedByOriginal") */
                             _("%s can't build %s from the worklist; "
                               "not available when city in range %s is \"%s\". "
                               "Postponing..."),
                             city_link(pcity),
                             tgt_name, req_range_name(preq->range),
                             citystatus_type_name(preq->source.value.citystatus));
              script_server_signal_emit(signal_name, ptarget,
                                        pcity, "have_citystatus");
            }
          }
        } else {
          /* Other status types will only happen with a bogus ruleset. */
          log_error("worklist_change_build_target() has bogus citystatus preq");
        }
        break;
      case VUT_MINYEAR:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: last %s is a date */
                        _("%s can't build %s from the worklist; "
                          "only available from %s. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        textyear(preq->source.value.minyear));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_minyear");
        } else {
          /* Can't go back in time. */
          purge = TRUE;
        }
        break;
      case VUT_MINCALFRAG:
        /* Unlike VUT_MINYEAR, a requirement in either direction is
         * likely to be fulfilled sooner or later. */
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: last %s is a calendar fragment from
                         * the ruleset; may be a bare number */
                        _("%s can't build %s from the worklist; "
                          "only available from %s. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        textcalfrag(preq->source.value.mincalfrag));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_mincalfrag");
        } else {
          fc_assert_action(preq->source.value.mincalfrag > 0, break);
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: last %s is a calendar fragment from
                         * the ruleset; may be a bare number */
                        _("%s can't build %s from the worklist; "
                          "not available after %s. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        textcalfrag(preq->source.value.mincalfrag - 1));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "have_mincalfrag");
        }
        break;
      case VUT_TOPO:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        /* TRANS: third %s is topology flag name
                         * ("WrapX", "ISO", etc) */
                        _("%s can't build %s from the worklist; "
                          "only available in worlds with %s map."),
                        city_link(pcity),
                        tgt_name,
                        _(topo_flag_name(preq->source.value.topo_property)));
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_topo");
        }
        purge = TRUE;
        break;
      case VUT_SERVERSETTING:
        notify_player(pplayer, city_tile(pcity),
                      E_CITY_CANTBUILD, ftc_server,
                      /* TRANS: %s is a server setting, its value and
                       * if it is required to be present or absent.
                       * The string's format is specified in
                       * ssetv_human_readable().
                       * Example: "killstack is enabled". */
                      _("%s can't build %s from the worklist; "
                        "only available when the server setting "
                        "%s."),
                      city_link(pcity),
                      tgt_name,
                      ssetv_human_readable(preq->source.value.ssetval,
                                           preq->present));
        script_server_signal_emit(signal_name, ptarget,
                                  pcity, "need_setting");
        /* Don't assume that the server setting will be changed. */
        purge = TRUE;
        break;
      case VUT_AGE:
        if (preq->present) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "only available once %d turns old. Postponing..."),
                        city_link(pcity),
                        tgt_name,
                        preq->source.value.age);
          script_server_signal_emit(signal_name, ptarget,
                                    pcity, "need_age");
        } else {
          /* Can't go back in time. */
          purge = TRUE;
        }
        break;
      case VUT_NONE:
      case VUT_COUNT:
        fc_assert_ret_val_msg(FALSE, TRUE,
                              "worklist_change_build_target() "
                              "called with invalid preq");
      break;
      /* No default handling here, as we want compiler warning
       * if new requirement type is added to enum and it's not handled
       * here. */
      };
      break;
    }
 
    /* Almost all cases emit signal in the end, so city check needed. */
    if (!city_exist(saved_id)) {
      /* Some script has removed city */
      return TRUE;
    }
 
  } requirement_vector_iterate_end;
 
  if (!known) {
    /* FIXME: make can_city_build_improvement_now() return a reason enum,
     *        so we can notify user with it.
     *        Likely the building already exist. */
    purge = TRUE;
  }
 
  return purge;
}
 
/**********************************************************************/
static bool worklist_change_build_target(struct player *pplayer,
                                         struct city *pcity)
{
  struct universal target;
  bool success = FALSE;
  int i;
  int saved_id = pcity->id;
  bool city_checked = TRUE; /* This is used to avoid spurious city_exist() calls */
  struct worklist *pwl = &pcity->worklist;
 
  if (worklist_is_empty(pwl)) {
    /* Nothing in the worklist; bail now. */
    return FALSE;
  }
 
  i = 0;
  while (!success && i < worklist_length(pwl)) {
 
    if (!city_checked) {
      if (!city_exist(saved_id)) {
        /* Some script has removed useless city that cannot build
         * what it is told to! */
        return FALSE;
      }
      city_checked = TRUE;
    }
 
    if (worklist_peek_ith(pwl, &target, i)) {
      success = can_city_build_now(pcity, &target);
    } else {
      success = FALSE;
    }
    i++;
 
    if (success) {
      break; /* while */
    }
 
    switch (target.kind) {
    case VUT_UTYPE:
    {
      const struct unit_type *ptarget = target.value.utype;
      const struct unit_type *pupdate = unit_upgrades_to(pcity, ptarget);
      bool purge;
 
      /* Maybe we can just upgrade the target to what the city /can/ build. */
      if (U_NOT_OBSOLETED == pupdate) {
        /* Nope, we're stuck.  Skip this item from the worklist. */
        if (ptarget->require_advance != NULL
            && TECH_KNOWN != research_invention_state
                          (research_get(pplayer),
                           advance_number(ptarget->require_advance))) {
          notify_player(pplayer, city_tile(pcity),
                        E_CITY_CANTBUILD, ftc_server,
                        _("%s can't build %s from the worklist; "
                          "tech %s not yet available. Postponing..."),
                        city_link(pcity), utype_name_translation(ptarget),
                        advance_name_translation(ptarget->require_advance));
          script_server_signal_emit("unit_cant_be_built", ptarget, pcity,
                                    "need_tech");
        } else {
          /* Unknown or requirement from vector. */
          purge = worklist_item_postpone_req_vec(&target, pcity, pplayer,
                                                 saved_id);
        }
        city_checked = FALSE;
        break;
      } else {
        purge = !can_city_build_unit_later(pcity, pupdate);
      }
      if (purge) {
        /* If the city can never build this unit or its descendants,
         * drop it. */
        notify_player(pplayer, city_tile(pcity),
                      E_CITY_CANTBUILD, ftc_server,
                      _("%s can't build %s from the worklist. Purging..."),
                      city_link(pcity),
                         /* Yes, warn about the targets that's actually
                            in the worklist, not its obsolete-closure
                            pupdate. */
                         utype_name_translation(ptarget));
        script_server_signal_emit("unit_cant_be_built", ptarget, pcity,
                                  "never");
        if (city_exist(saved_id)) {
          city_checked = TRUE;
          /* Purge this worklist item. */
          i--;
          worklist_remove(pwl, i);
        } else {
          city_checked = FALSE;
        }
      } else {
        /* Yep, we can go after pupdate instead.  Joy! */
        notify_player(pplayer, city_tile(pcity), E_WORKLIST, ftc_server,
                      _("Production of %s is upgraded to %s in %s."),
                      utype_name_translation(ptarget), 
                      utype_name_translation(pupdate),
                      city_link(pcity));
        target.value.utype = pupdate;
      }
      break;
    }
    case VUT_IMPROVEMENT:
    {
      const struct impr_type *ptarget = target.value.building;
      const struct impr_type *pupdate = building_upgrades_to(pcity, ptarget);
      bool purge;
 
      /* If the city can never build this improvement, drop it. */
      success = can_city_build_improvement_later(pcity, pupdate);
      purge = !success;
 
      /* Maybe this improvement has been obsoleted by something that
         we can build. */
      if (purge) {
        /* Nope, no use.  *sigh*  */
 
        /* Can it be postponed? */
        if (can_city_build_improvement_later(pcity, ptarget)) {
          purge = worklist_item_postpone_req_vec(&target, pcity, pplayer,
                                                 saved_id);
 
          /* Almost all cases emit signal in the end, so city check needed. */
          if (!city_exist(saved_id)) {
            /* Some script has removed city */
            return FALSE;
          }
          city_checked = TRUE;
        }
      } else if (success) {
        /* Hey, we can upgrade the improvement! */
        notify_player(pplayer, city_tile(pcity), E_WORKLIST, ftc_server,
                      _("Production of %s is upgraded to %s in %s."),
                      city_improvement_name_translation(pcity, ptarget), 
                      city_improvement_name_translation(pcity, pupdate),
                      city_link(pcity));
        target.value.building = pupdate;
      }
 
      if (purge) {
        /* Never in a million years. */
        notify_player(pplayer, city_tile(pcity),
                      E_CITY_CANTBUILD, ftc_server,
                      _("%s can't build %s from the worklist. Purging..."),
                      city_link(pcity),
                      city_improvement_name_translation(pcity, ptarget));
        script_server_signal_emit("building_cant_be_built", ptarget, pcity,
                                  "never");
        if (city_exist(saved_id)) {
          city_checked = TRUE;
          /* Purge this worklist item. */
          i--;
          worklist_remove(pwl, i);
        } else {
          city_checked = FALSE;
        }
      }
      break;
    }
    default:
      /* skip useless target */
      log_error("worklist_change_build_target() has unrecognized "
                "target kind (%d)", target.kind);
      break;
    };
  } /* while */
 
  if (success) {
    /* All okay.  Switch targets. */
    change_build_target(pplayer, pcity, &target, E_WORKLIST);
 
    /* i is the index immediately _after_ the item we're changing to.
       Remove the (i-1)th item from the worklist. */
    worklist_remove(pwl, i - 1);
  }
 
  if (worklist_is_empty(pwl)) {
    /* There *was* something in the worklist, but it's empty now.  Bug the
       player about it. */
    notify_player(pplayer, city_tile(pcity), E_WORKLIST, ftc_server,
                  /* TRANS: The <city> worklist .... */
                  _("The %s worklist is now empty."),
                  city_link(pcity));
  }
 
  return success;
}
 
/**********************************************************************/
void choose_build_target(struct player *pplayer, struct city *pcity)
{
  /* Pick the next thing off the worklist. */
  if (worklist_change_build_target(pplayer, pcity)) {
    return;
  }
 
  /* Try building the same thing again.  Repeat building doesn't require a
   * call to change_build_target, so just return. */
  switch (pcity->production.kind) {
  case VUT_UTYPE:
    /* We can build a unit again unless it's unique or we have lost the tech. */
    if (!utype_has_flag(pcity->production.value.utype, UTYF_UNIQUE)
        && can_city_build_unit_now(pcity, pcity->production.value.utype)) {
      log_base(LOG_BUILD_TARGET, "%s repeats building %s", city_name_get(pcity),
               utype_rule_name(pcity->production.value.utype));
      return;
    }
    break;
  case VUT_IMPROVEMENT:
    if (can_city_build_improvement_now(pcity, pcity->production.value.building)) {
      /* We can build space and coinage again, and possibly others. */
      log_base(LOG_BUILD_TARGET, "%s repeats building %s", city_name_get(pcity),
               improvement_rule_name(pcity->production.value.building));
      return;
    }
    break;
  default:
    /* fallthru */
    break;
  };
 
  /* Find *something* to do! */
  log_debug("Trying advisor_choose_build.");
  advisor_choose_build(pplayer, pcity);
  log_debug("Advisor_choose_build didn't kill us.");
}
 
/**********************************************************************/
static const struct impr_type *building_upgrades_to(struct city *pcity,
                                                    const struct impr_type *pimprove)
{
  const struct impr_type *check = pimprove;
  const struct impr_type *best_upgrade = NULL;
 
  if (!can_city_build_improvement_direct(pcity, check)) {
    return NULL;
  }
  while (valid_improvement(check = improvement_replacement(check))) {
    if (can_city_build_improvement_direct(pcity, check)) {
      best_upgrade = check;
    }
  }
 
  return best_upgrade;
}
 
/**********************************************************************/
static void upgrade_building_prod(struct city *pcity)
{
  const struct impr_type *producing = pcity->production.value.building;
  const struct impr_type *upgrading = building_upgrades_to(pcity, producing);
 
  if (upgrading && can_city_build_improvement_now(pcity, upgrading)) {
    notify_player(city_owner(pcity), city_tile(pcity),
                  E_UNIT_UPGRADED, ftc_server,
                  _("Production of %s is upgraded to %s in %s."),
                  improvement_name_translation(producing),
                  improvement_name_translation(upgrading),
                  city_link(pcity));
    pcity->production.kind = VUT_IMPROVEMENT;
    pcity->production.value.building = upgrading;
  }
}
 
/**********************************************************************/
static const struct unit_type *unit_upgrades_to(struct city *pcity,
                                                const struct unit_type *punittype)
{
  const struct unit_type *check = punittype;
  const struct unit_type *best_upgrade = U_NOT_OBSOLETED;
 
  if (!can_city_build_unit_direct(pcity, punittype)) {
    return U_NOT_OBSOLETED;
  }
  while ((check = check->obsoleted_by) != U_NOT_OBSOLETED) {
    if (can_city_build_unit_direct(pcity, check)) {
      best_upgrade = check;
    }
  }
 
  return best_upgrade;
}
 
/**********************************************************************/
static void upgrade_unit_prod(struct city *pcity)
{
  const struct unit_type *producing = pcity->production.value.utype;
  const struct unit_type *upgrading = unit_upgrades_to(pcity, producing);
 
  if (upgrading && can_city_build_unit_direct(pcity, upgrading)) {
    notify_player(city_owner(pcity), city_tile(pcity),
                  E_UNIT_UPGRADED, ftc_server,
                  _("Production of %s is upgraded to %s in %s."),
                  utype_name_translation(producing),
                  utype_name_translation(upgrading), 
                  city_link(pcity));
    pcity->production.value.utype = upgrading;
  }
}
 
/**********************************************************************/
static bool city_distribute_surplus_shields(struct player *pplayer,
                                            struct city *pcity)
{
  int size_reduction = 0;
  struct unit *sacrifizer;
 
  if (pcity->surplus[O_SHIELD] < 0) {
    unit_list_iterate_safe(pcity->units_supported, punit) {
      if (utype_upkeep_cost(unit_type_get(punit), pplayer, O_SHIELD) > 0
          && pcity->surplus[O_SHIELD] < 0) {
        const char *punit_link = unit_link(punit);
 
        /* TODO: Should the unit try to help cities on adjacent tiles? That
         * would be a rules change. (This action is performed by the game
         * it self) */
        if (upkeep_kill_unit(punit, O_SHIELD, ULR_UPKEEP,
                             game.info.muuk_shield_wipe)) {
          notify_player(pplayer, city_tile(pcity),
                        E_UNIT_LOST_MISC, ftc_server,
                        _("%s can't upkeep %s, unit disbanded."),
                        city_link(pcity), punit_link);
        }
 
        /* pcity->surplus[O_SHIELD] is automatically updated. */
      }
    } unit_list_iterate_safe_end;
  }
 
  if (pcity->surplus[O_SHIELD] < 0) {
    /* Special case: MissingXProtected. This nasty unit won't go so easily.
     * It'd rather make the citizens pay in blood for their failure to upkeep
     * it! If we make it here all normal units are already disbanded, so only
     * undisbandable ones remain. */
    unit_list_iterate_safe(pcity->units_supported, punit) {
      int upkeep = utype_upkeep_cost(unit_type_get(punit), pplayer, O_SHIELD);
 
      if (upkeep > 0 && pcity->surplus[O_SHIELD] < 0) {
 
        size_reduction++;
        sacrifizer = punit;
 
        /* No upkeep for the unit this turn. */
        pcity->surplus[O_SHIELD] += upkeep;
      }
    } unit_list_iterate_safe_end;
  }
 
  /* Now we confirm changes made last turn. */
  pcity->shield_stock += pcity->surplus[O_SHIELD];
  pcity->before_change_shields = pcity->shield_stock;
  pcity->last_turns_shield_surplus = pcity->surplus[O_SHIELD];
 
  /* Previous turn values stored, and they are consistent with
   * other previous turn data.
   * Now reduce city size, likely messing all the values. */
  if (size_reduction > 0) {
    if (size_reduction == 1) {
      notify_player(pplayer, city_tile(pcity),
                    E_UNIT_LOST_MISC, ftc_server,
                    _("Citizens in %s perish for their failure to "
                      "upkeep %s!"),
                    city_link(pcity), unit_link(sacrifizer));
    } else {
      notify_player(pplayer, city_tile(pcity),
                    E_UNIT_LOST_MISC, ftc_server,
                    _("Citizens in %s perish for their failure to "
                      "upkeep units!"),
                    city_link(pcity));
    }
 
    if (!city_reduce_size(pcity, size_reduction, NULL, "upkeep_failure")) {
      return FALSE;
    }
  }
 
  return TRUE;
}
 
/**********************************************************************/
static bool city_build_building(struct player *pplayer, struct city *pcity)
{
  bool space_part;
  int mod;
  const struct impr_type *pimprove;
  int saved_id = pcity->id;
 
  if (city_production_has_flag(pcity, IF_GOLD)) {
    fc_assert(pcity->before_change_shields >= 0);
 
    /* pcity->before_change_shields already contains the surplus from
     * this turn. */
    pplayer->economic.gold += pcity->before_change_shields;
    pcity->before_change_shields = 0;
    pcity->shield_stock = 0;
    choose_build_target(pplayer, pcity);
 
    return TRUE;
  }
 
  upgrade_building_prod(pcity);
 
  /* The final (after upgrade) build target */
  pimprove = pcity->production.value.building;
 
  if (!can_city_build_improvement_now(pcity, pimprove)) {
    notify_player(pplayer, city_tile(pcity), E_CITY_CANTBUILD, ftc_server,
                  _("%s is building %s, which is no longer available."),
                  city_link(pcity),
                  city_improvement_name_translation(pcity, pimprove));
    script_server_signal_emit("building_cant_be_built", pimprove, pcity,
                              "unavailable");
    return TRUE;
  }
  if (pcity->shield_stock >= impr_build_shield_cost(pcity, pimprove)) {
    int cost;
 
    if (is_small_wonder(pimprove)) {
      city_list_iterate(pplayer->cities, wcity) {
        if (city_has_building(wcity, pimprove)) {
          city_remove_improvement(wcity, pimprove);
          break;
        }
      } city_list_iterate_end;
    }
 
    space_part = TRUE;
    if (get_current_construction_bonus(pcity, EFT_SS_STRUCTURAL,
                                       RPT_CERTAIN) > 0) {
      pplayer->spaceship.structurals++;
    } else if (get_current_construction_bonus(pcity, EFT_SS_COMPONENT,
                                              RPT_CERTAIN) > 0) {
      pplayer->spaceship.components++;
    } else if (get_current_construction_bonus(pcity, EFT_SS_MODULE,
                                              RPT_CERTAIN) > 0) {
      pplayer->spaceship.modules++;
    } else {
      space_part = FALSE;
      city_add_improvement(pcity, pimprove);
    }
    cost = impr_build_shield_cost(pcity, pimprove);
    pcity->before_change_shields -= cost;
    pcity->shield_stock -= cost;
    pcity->turn_last_built = game.info.turn;
    /* to eliminate micromanagement */
    if (is_great_wonder(pimprove)) {
      notify_player(NULL, city_tile(pcity), E_WONDER_BUILD, ftc_server,
                    _("The %s have finished building %s in %s."),
                    nation_plural_for_player(pplayer),
                    city_improvement_name_translation(pcity, pimprove),
                    city_link(pcity));
    }
 
    notify_player(pplayer, city_tile(pcity), E_IMP_BUILD, ftc_server,
                  _("%s has finished building %s."),
                  city_link(pcity), improvement_name_translation(pimprove));
    script_server_signal_emit("building_built", pimprove, pcity);
 
    if (!city_exist(saved_id)) {
      /* Script removed city */
      return FALSE;
    }
 
    /* Call this function since some buildings may change the
     * the vision range of a city */
    city_refresh_vision(pcity);
 
    if ((mod = get_current_construction_bonus(pcity, EFT_GIVE_IMM_TECH,
                                              RPT_CERTAIN))) {
      struct research *presearch = research_get(pplayer);
      char research_name[MAX_LEN_NAME * 2];
      int i;
      const char *provider = improvement_name_translation(pimprove);
 
      notify_research(presearch, NULL, E_TECH_GAIN, ftc_server,
                      PL_("%s boosts research; you gain %d immediate "
                          "advance.",
                          "%s boosts research; you gain %d immediate "
                          "advances.",
                          mod), provider, mod);
 
      research_pretty_name(presearch, research_name, sizeof(research_name));
      for (i = 0; i < mod; i++) {
        Tech_type_id tech = pick_free_tech(presearch);
        const char *adv_name = research_advance_name_translation(presearch, tech);
 
        give_immediate_free_tech(presearch, tech);
        notify_research(presearch, NULL, E_TECH_GAIN, ftc_server,
                        /* TRANS: Tech from building (Darwin's Voyage) */
                        Q_("?frombldg:Acquired %s from %s."), adv_name,
                        provider);
 
        notify_research_embassies(presearch, NULL, E_TECH_EMBASSY, ftc_server,
                                  /* TRANS: Tech from building (Darwin's
                                   * Voyage) */
                                  Q_("?frombldg:The %s have acquired %s "
                                     "from %s."),
                                  research_name, adv_name, provider);
      }
    }
    if (space_part && pplayer->spaceship.state == SSHIP_NONE) {
      notify_player(NULL, city_tile(pcity), E_SPACESHIP, ftc_server,
                    _("The %s have started building a spaceship!"),
                    nation_plural_for_player(pplayer));
      pplayer->spaceship.state = SSHIP_STARTED;
    }
    if (space_part) {
      /* space ship part build */
      send_spaceship_info(pplayer, NULL);
    } else {
      /* Update city data. */
      if (city_refresh(pcity)) {
        auto_arrange_workers(pcity);
      }
    }
 
    /* Move to the next thing in the worklist */
    choose_build_target(pplayer, pcity);
  }
 
  return TRUE;
}
 
/**********************************************************************/
static struct unit *city_create_unit(struct city *pcity,
                                     const struct unit_type *utype,
                                     struct citizens_reduction *red)
{
  struct player *pplayer = city_owner(pcity);
  struct unit *punit;
  int saved_unit_id;
  int pop_cost = utype_pop_value(utype, pcity);
 
  punit = unit_virtual_prepare(pplayer, pcity->tile, utype,
                               city_production_unit_veteran_level(pcity, utype),
                               pcity->id, -1, -1);
  pplayer->score.units_built++;
  if (pop_cost > 0 && pcity->nationality) {
    /* We don't reduce city size in-place to keep it correct and
     * existing at all while we call the following callback */
    citizens_unit_nationality(pcity, pop_cost, red);
  } else if (red) {
    red->change = 0;
  }
  (void) place_unit(punit, pplayer, pcity, NULL, FALSE);
  saved_unit_id = punit->id;
 
  /* If city has a rally point set, give the unit a move order. */
  if (pcity->rally_point.length) {
    punit->has_orders = TRUE;
    punit->orders.length = pcity->rally_point.length;
    punit->orders.vigilant = pcity->rally_point.vigilant;
    punit->orders.list = fc_malloc(pcity->rally_point.length
                                   * sizeof(struct unit_order));
    memcpy(punit->orders.list, pcity->rally_point.orders,
           pcity->rally_point.length * sizeof(struct unit_order));
  }
 
  /* This might destroy pcity and/or punit: */
  script_server_signal_emit("unit_built", punit, pcity);
 
  if (unit_is_alive(saved_unit_id)) {
    return punit;
  } else {
    return NULL;
  }
}
 
/**********************************************************************/
static bool city_build_unit(struct player *pplayer, struct city *pcity)
{
  const struct unit_type *utype;
  struct worklist *pwl = &pcity->worklist;
  int unit_shield_cost, num_units, i;
  int saved_city_id = pcity->id;
 
  fc_assert_ret_val(pcity->production.kind == VUT_UTYPE, FALSE);
 
  /* If the city has already bought a unit which is now obsolete, don't try
   * to upgrade the production. The new unit might require more shields, which
   * would be bad if it was bought to urgently defend a city. (Equally it
   * might be the same cost or cheaper, but tough; you hurried the unit so
   * you miss out on technological advances.) */
  if (city_can_change_build(pcity)) {
    upgrade_unit_prod(pcity);
  }
 
  utype = pcity->production.value.utype;
  unit_shield_cost = utype_build_shield_cost(pcity, NULL, utype);
 
  /* We must make a special case for barbarians here, because they are
     so dumb. Really. They don't know the prerequisite techs for units
     they build!! - Per */
  if (!can_city_build_unit_direct(pcity, utype)
      && !is_barbarian(pplayer)) {
    notify_player(pplayer, city_tile(pcity), E_CITY_CANTBUILD, ftc_server,
                  _("%s is building %s, which is no longer available."),
                  city_link(pcity), utype_name_translation(utype));
 
    /* Log before signal emitting, so pointers are certainly valid */
    log_verbose("%s %s tried to build %s, which is not available.",
                nation_rule_name(nation_of_city(pcity)),
                city_name_get(pcity), utype_rule_name(utype));
    script_server_signal_emit("unit_cant_be_built", utype, pcity,
                              "unavailable");
    return city_exist(saved_city_id);
  }
 
  if (pcity->shield_stock >= unit_shield_cost) {
    int pop_cost = utype_pop_value(utype, pcity);
    struct unit *punit;
 
    /* Should we disband the city? -- Massimo */
    if (city_size_get(pcity) == pop_cost
        && is_city_option_set(pcity, CITYO_DISBAND)) {
      return !disband_city(pcity);
    }
 
    if (city_size_get(pcity) <= pop_cost) {
      notify_player(pplayer, city_tile(pcity), E_CITY_CANTBUILD, ftc_server,
                    /* TRANS: city ... utype ... size ... pop_cost */
                    _("%s can't build %s yet. "
                      "(city size: %d, unit population cost: %d)"),
                    city_link(pcity), utype_name_translation(utype),
                    city_size_get(pcity), pop_cost);
      script_server_signal_emit("unit_cant_be_built", utype, pcity,
                                "pop_cost");
      return city_exist(saved_city_id);
    }
 
    fc_assert(pop_cost == 0 || city_size_get(pcity) >= pop_cost);
 
    /* don't update turn_last_built if we returned above */
    pcity->turn_last_built = game.info.turn;
 
    /* check if we can build more than one unit (effect City_Build_Slots) */
    (void) city_production_build_units(pcity, FALSE, &num_units);
 
    /* We should be able to build at least one (by checks above) */
    fc_assert(num_units >= 1);
 
    for (i = 0; i < num_units; i++) {
      struct citizens_reduction natred[MAX_CITY_NATIONALITIES + 1];
 
      punit = city_create_unit(pcity, utype, natred);
 
      /* Check if the city still exists (script might have removed it).
       * If not, we assume any effects / announcements done below were
       * already replaced by the script if necessary. */
      if (!city_exist(saved_city_id)) {
        break;
      }
 
      if (punit) {
        notify_player(pplayer, city_tile(pcity), E_UNIT_BUILT, ftc_server,
                      /* TRANS: <city> is finished building <unit/building>. */
                      _("%s is finished building %s."),
                      city_link(pcity), utype_name_translation(utype));
      }
 
      /* After we created the unit remove the citizen. This will also
       * rearrange the worker to take into account the extra resources
       * (food) needed. */
      if (pop_cost > 0) {
        /* This won't disband city due to pop_cost, but script might
         * still destroy city. */
        citizens_reduction_apply(pcity, natred);
        /* If the city has changed its nationalities during
         * "unit_built" signal, we take some other citizens instead */
        if (!city_reduce_size(pcity, pop_cost, NULL, "unit_built")) {
          break;
        }
      }
 
      /* to eliminate micromanagement, we only subtract the unit's cost */
      /* signals could change the prod stock! */
      if ((pcity->before_change_shields -= unit_shield_cost) < 0) {
        pcity->before_change_shields = 0;
      }
      if ((pcity->shield_stock -= unit_shield_cost) < 0) {
        log_normal("City %s (%s) has built %s but has no %d shields "
                   "for it, nullifying shield stock", city_name_get(pcity),
                   player_name(pplayer), utype_rule_name(utype),
                   unit_shield_cost);
        pcity->shield_stock = 0;
      }
 
      if (pop_cost > 0) {
        /* Additional message if the unit has population cost. */
        notify_player(pplayer, city_tile(pcity), E_UNIT_BUILT_POP_COST,
                      ftc_server,
                      /* TRANS: "<unit> cost... <city> shrinks..."
                       * Plural in "%d population", not "size %d". */
                      PL_("%s cost %d population. %s shrinks to size %d.",
                          "%s cost %d population. %s shrinks to size %d.",
                          pop_cost),
                      utype_name_translation(utype), pop_cost,
                      city_link(pcity), city_size_get(pcity));
      }
 
      if (i != 0 && worklist_length(pwl) > 0) {
        /* remove the build unit from the worklist; it has to be one less
         * than units build to preserve the next build target from the
         * worklist */
        worklist_remove(pwl, 0);
      }
    } /* for */
 
    if (city_exist(saved_city_id)) {
      if (pcity->rally_point.length && !pcity->rally_point.persistent) {
        city_rally_point_clear(pcity);
      }
 
      /* Done building this unit; time to move on to the next. */
      choose_build_target(pplayer, pcity);
    }
  } /* if */
 
  return city_exist(saved_city_id);
}
 
/**********************************************************************/
static bool city_build_stuff(struct player *pplayer, struct city *pcity)
{
  if (!city_distribute_surplus_shields(pplayer, pcity)) {
    return FALSE;
  }
 
  nullify_caravan_and_disband_plus(pcity);
  define_orig_production_values(pcity);
 
  switch (pcity->production.kind) {
  case VUT_IMPROVEMENT:
    return city_build_building(pplayer, pcity);
  case VUT_UTYPE:
    return city_build_unit(pplayer, pcity);
  default:
    /* must never happen! */
    fc_assert(FALSE);
    break;
  };
  return FALSE;
}
 
/**********************************************************************/
static bool sell_random_building(struct player *pplayer,
                                 struct cityimpr_list *imprs)
{
  struct cityimpr *pcityimpr;
  int r;
 
  fc_assert_ret_val(pplayer != NULL, FALSE);
 
  if (!imprs || cityimpr_list_size(imprs) == 0) {
    return FALSE;
  }
 
  r = fc_rand(cityimpr_list_size(imprs));
  pcityimpr = cityimpr_list_get(imprs, r);
 
  notify_player(pplayer, city_tile(pcityimpr->pcity), E_IMP_AUCTIONED,
                ftc_server,
                _("Can't afford to maintain %s in %s, building sold!"),
                improvement_name_translation(pcityimpr->pimprove),
                city_link(pcityimpr->pcity));
  log_debug("%s: sold building (%s)", player_name(pplayer),
            improvement_name_translation(pcityimpr->pimprove));
 
  do_sell_building(pplayer, pcityimpr->pcity, pcityimpr->pimprove, "cant_maintain");
 
  cityimpr_list_remove(imprs, pcityimpr);
 
  /* Get back the gold upkeep that was already paid this turn. */
  pplayer->economic.gold += city_improvement_upkeep(pcityimpr->pcity,
                                                    pcityimpr->pimprove);
 
  city_refresh_queue_add(pcityimpr->pcity);
 
  FC_FREE(pcityimpr);
 
  return TRUE;
}
 
/**********************************************************************/
static void uk_rem_gold_callback(struct unit *punit)
{
  int gold_upkeep;
 
  /* Remove the unit from uk_rem_gold. */
  unit_list_remove(uk_rem_gold, punit);
 
  gold_upkeep = punit->server.upkeep_paid[O_GOLD];
 
  /* All units in uk_rem_gold should have gold upkeep! */
  fc_assert_ret_msg(gold_upkeep > 0, "%s has %d gold upkeep",
                    unit_rule_name(punit), gold_upkeep);
 
  /* Get the upkeep gold back. */
  unit_owner(punit)->economic.gold += gold_upkeep;
}
 
/**********************************************************************/
static void uk_rem_gold_append(struct unit *punit)
{
  /* Make the unit aware that it is on the uk_rem_gold list. */
  unit_set_removal_callback(punit, uk_rem_gold_callback);
 
  /* Add the unit to the list. */
  unit_list_append(uk_rem_gold, punit);
}
 
/**********************************************************************/
static void unit_list_referred_destroy(struct unit_list *punitlist)
{
  unit_list_iterate(punitlist, punit) {
    /* Clear the unit's knowledge of the list. */
    unit_unset_removal_callback(punit);
  } unit_list_iterate_end;
 
  /* Destroy the list it self. */
  unit_list_destroy(punitlist);
}
 
/**********************************************************************/
static struct unit *sell_random_unit(struct player *pplayer,
                                     struct unit_list *punitlist)
{
  struct unit *punit;
  int r;
  struct unit_list *cargo;
 
  fc_assert_ret_val(pplayer != NULL, NULL);
 
  if (!punitlist || unit_list_size(punitlist) == 0) {
    return NULL;
  }
 
  r = fc_rand(unit_list_size(punitlist));
  punit = unit_list_get(punitlist, r);
 
  cargo = unit_list_new();
 
  /* Check if unit is transporting other units from punitlist,
   * and sell one of those (recursively) instead.
   * Note that in case of recursive transports we have to iterate
   * also through those middle transports that themselves are not in
   * punitlist. */
  unit_cargo_iterate(punit, pcargo) {
    /* Optimization, do not iterate over punitlist
     * if we are sure that pcargo is not in it. */
    if (pcargo->server.upkeep_paid[O_GOLD] > 0) {
      unit_list_iterate(punitlist, p2) {
        if (pcargo == p2) {
          unit_list_append(cargo, pcargo);
        }
      } unit_list_iterate_end;
    }
  } unit_cargo_iterate_end;
 
  if (unit_list_size(cargo) > 0) {
    /* Recursively sell. Note that cargo list has both
     * leaf units and middle transports in case of
     * recursive transports. */
    struct unit *ret = sell_random_unit(pplayer, cargo);
 
    unit_list_destroy(cargo);
 
    unit_list_remove(punitlist, ret);
 
    return ret;
  }
 
  unit_list_destroy(cargo);
 
  {
    const char *punit_link = unit_tile_link(punit);
#ifdef FREECIV_DEBUG
    const char *punit_logname = unit_rule_name(punit);
#endif /* FREECIV_DEBUG */
    struct tile *utile = unit_tile(punit);
 
    if (upkeep_kill_unit(punit, O_GOLD, ULR_SOLD,
                         game.info.muuk_gold_wipe)) {
      unit_list_remove(punitlist, punit);
 
      /* The gold was paid back when the unit removal made
       * uk_rem_gold_callback() run as the unit's removal call back. */
 
      notify_player(pplayer, utile, E_UNIT_LOST_MISC, ftc_server,
                    _("Not enough gold. %s disbanded."),
                    punit_link);
      log_debug("%s: unit sold (%s)", player_name(pplayer),
                punit_logname);
    } else {
      /* Not able to get rid of punit */
      return NULL;
    }
  }
 
  unit_list_remove(punitlist, punit);
 
  return punit;
}
 
/**********************************************************************/
static bool player_balance_treasury_units_and_buildings
            (struct player *pplayer)
{
  struct cityimpr_list *pimprlist;
  bool sell_unit = TRUE;
 
  if (!pplayer) {
    return FALSE;
  }
 
  pimprlist = cityimpr_list_new();
  uk_rem_gold = unit_list_new();
 
  city_list_iterate(pplayer->cities, pcity) {
    city_built_iterate(pcity, pimprove) {
      if (can_city_sell_building(pcity, pimprove)) {
        struct cityimpr *ci = fc_malloc(sizeof(*ci));
 
        ci->pcity = pcity;
        ci->pimprove = pimprove;
        cityimpr_list_append(pimprlist, ci);
      }
    } city_built_iterate_end;
 
    unit_list_iterate(pcity->units_supported, punit) {
      if (punit->server.upkeep_paid[O_GOLD] > 0) {
        uk_rem_gold_append(punit);
      }
    } unit_list_iterate_end;
  } city_list_iterate_end;
 
  while (pplayer->economic.gold < 0
         && (cityimpr_list_size(pimprlist) > 0
             || unit_list_size(uk_rem_gold) > 0)) {
    if ((!sell_unit && cityimpr_list_size(pimprlist) > 0)
        || unit_list_size(uk_rem_gold) == 0) {
      sell_random_building(pplayer, pimprlist);
    } else {
      sell_random_unit(pplayer, uk_rem_gold);
    }
    sell_unit = !sell_unit;
  }
 
  /* Free remaining entries from list */
  cityimpr_list_iterate(pimprlist, pimpr) {
    FC_FREE(pimpr);
  } cityimpr_list_iterate_end;
 
  if (pplayer->economic.gold < 0) {
    /* If we get here it means the player has
     * negative gold. This should never happen. */
    fc_assert_msg(FALSE, "Player %s (nb %d) cannot have negative gold!",
                  player_name(pplayer), player_number(pplayer));
  }
 
  cityimpr_list_destroy(pimprlist);
  unit_list_referred_destroy(uk_rem_gold);
 
  return pplayer->economic.gold >= 0;
}
 
/**********************************************************************/
static bool player_balance_treasury_units(struct player *pplayer)
{
  if (!pplayer) {
    return FALSE;
  }
 
  uk_rem_gold = unit_list_new();
 
  city_list_iterate(pplayer->cities, pcity) {
    unit_list_iterate(pcity->units_supported, punit) {
      if (punit->server.upkeep_paid[O_GOLD] > 0) {
        uk_rem_gold_append(punit);
      }
    } unit_list_iterate_end;
  } city_list_iterate_end;
 
  while (pplayer->economic.gold < 0
         && sell_random_unit(pplayer, uk_rem_gold)) {
    /* all done in sell_random_unit() */
  }
 
  if (pplayer->economic.gold < 0) {
    /* If we get here it means the player has
     * negative gold. This should never happen. */
    fc_assert_msg(FALSE, "Player %s (nb %d) cannot have negative gold!",
                  player_name(pplayer), player_number(pplayer));
  }
 
  unit_list_referred_destroy(uk_rem_gold);
 
  return pplayer->economic.gold >= 0;
}
 
/**********************************************************************/
static bool city_balance_treasury_buildings(struct city *pcity)
{
  struct player *pplayer;
  struct cityimpr_list *pimprlist;
 
  if (!pcity) {
    return TRUE;
  }
 
  pplayer = city_owner(pcity);
  pimprlist = cityimpr_list_new();
 
  /* Create a vector of all buildings that can be sold. */
  city_built_iterate(pcity, pimprove) {
    if (can_city_sell_building(pcity, pimprove)) {
      struct cityimpr *ci = fc_malloc(sizeof(*ci));
 
      ci->pcity = pcity;
      ci->pimprove = pimprove;
      cityimpr_list_append(pimprlist, ci);
    }
  } city_built_iterate_end;
 
  /* Try to sell some buildings. */
  while (pplayer->economic.gold < 0
         && sell_random_building(pplayer, pimprlist)) {
    /* all done in sell_random_building */
  }
 
  /* Free remaining entries from list */
  cityimpr_list_iterate(pimprlist, pimpr) {
    FC_FREE(pimpr);
  } cityimpr_list_iterate_end;
 
  cityimpr_list_destroy(pimprlist);
 
  return pplayer->economic.gold >= 0;
}
 
/**********************************************************************/
static bool city_balance_treasury_units(struct city *pcity)
{
  struct player *pplayer;
 
  if (!pcity) {
    return TRUE;
  }
 
  pplayer = city_owner(pcity);
  uk_rem_gold = unit_list_new();
 
  /* Create a vector of all supported units with gold upkeep. */
  unit_list_iterate(pcity->units_supported, punit) {
    if (punit->server.upkeep_paid[O_GOLD] > 0) {
      uk_rem_gold_append(punit);
    }
  } unit_list_iterate_end;
 
  /* Still not enough gold, so try "selling" some units. */
  while (pplayer->economic.gold < 0
         && sell_random_unit(pplayer, uk_rem_gold)) {
    /* all done in sell_random_unit() */
  }
 
  /* If we get here the player has negative gold, but hopefully
   * another city will be able to pay the deficit, so continue. */
 
  unit_list_referred_destroy(uk_rem_gold);
 
  return pplayer->economic.gold >= 0;
}
 
/**********************************************************************/
static bool place_pollution(struct city *pcity, enum extra_cause cause)
{
  struct tile *ptile;
  struct tile *pcenter = city_tile(pcity);
  int city_radius_sq = city_map_radius_sq_get(pcity);
  int k = 100;
  const struct civ_map *nmap = &(wld.map);
 
  while (k > 0) {
    /* Place pollution on a random city tile */
    int cx, cy;
    int tile_id = fc_rand(city_map_tiles(city_radius_sq));
    struct extra_type *pextra;
 
    city_tile_index_to_xy(&cx, &cy, tile_id, city_radius_sq);
 
    /* Check for a real map position */
    if (!(ptile = city_map_to_tile(nmap, pcenter, city_radius_sq, cx, cy))) {
      continue;
    }
 
    pextra = rand_extra_for_tile(ptile, cause, FALSE);
 
    if (pextra != NULL && !tile_has_extra(ptile, pextra)) {
      tile_add_extra(ptile, pextra);
      update_tile_knowledge(ptile);
 
      return TRUE;
    }
    k--;
  }
  log_debug("pollution not placed: city: %s", city_name_get(pcity));
 
  return FALSE;
}
 
/**********************************************************************/
static void check_pollution(struct city *pcity)
{
  if (fc_rand(100) < pcity->pollution) {
    if (place_pollution(pcity, EC_POLLUTION)) {
      notify_player(city_owner(pcity), city_tile(pcity), E_POLLUTION, ftc_server,
                    _("Pollution near %s."), city_link(pcity));
    }
  }
}
 
/**********************************************************************/
int city_incite_cost(struct player *pplayer, struct city *pcity)
{
  int dist, size;
  double cost; /* Intermediate values can get very large */
 
  /* Gold factor */
  cost = city_owner(pcity)->economic.gold + game.server.base_incite_cost;
 
  unit_list_iterate(pcity->tile->units, punit) {
    cost += (unit_build_shield_cost(pcity, punit)
             * game.server.incite_unit_factor);
  } unit_list_iterate_end;
 
  /* Buildings */
  city_built_iterate(pcity, pimprove) {
    cost += impr_build_shield_cost(pcity, pimprove)
            * game.server.incite_improvement_factor;
  } city_built_iterate_end;
 
  /* Stability bonuses */
  if (!city_unhappy(pcity)) {
    cost *= 2;
  }
  if (city_celebrating(pcity)) {
    cost *= 2;
  }
 
  /* Buy back is cheap, conquered cities are also cheap */
  if (!game.info.citizen_nationality) {
    if (city_owner(pcity) != pcity->original) {
      if (pplayer == pcity->original) {
        cost /= 2;            /* Buy back: 50% price reduction */
      } else {
        cost = cost * 2 / 3;  /* Buy conquered: 33% price reduction */
      }
    }
  }
 
  /* Distance from capital */
  /* Max penalty. Applied if there is no capital, or it's even further away. */
  dist = 32;
  city_list_iterate(city_owner(pcity)->cities, capital) {
    if (is_capital(capital)) {
      int tmp = map_distance(capital->tile, pcity->tile);
 
      if (tmp < dist) {
        dist = tmp;
      }
    }
  } city_list_iterate_end;
 
  size = MAX(1, city_size_get(pcity)
                + pcity->feel[CITIZEN_HAPPY][FEELING_FINAL]
                - pcity->feel[CITIZEN_UNHAPPY][FEELING_FINAL]
                - pcity->feel[CITIZEN_ANGRY][FEELING_FINAL] * 3);
  cost *= size;
  cost *= game.server.incite_total_factor;
  cost = cost / (dist + 3);
 
  if (game.info.citizen_nationality) {
    int cost_per_citizen = cost / pcity->size;
    int natives = citizens_nation_get(pcity, city_owner(pcity)->slot);
    int tgt_cit = citizens_nation_get(pcity, pplayer->slot);
    int third_party = pcity->size - natives - tgt_cit;
 
    cost = cost_per_citizen * (natives + 0.7 * third_party + 0.5 * tgt_cit); 
  }
 
  cost += (cost * get_city_bonus(pcity, EFT_INCITE_COST_PCT)) / 100;
  cost /= 100;
 
  if (cost >= INCITE_IMPOSSIBLE_COST) {
    return INCITE_IMPOSSIBLE_COST;
  } else {
    return cost;
  }
}
 
/**********************************************************************/
static void define_orig_production_values(struct city *pcity)
{
  /* Remember what this city is building last turn, so that on the next turn
   * the player can switch production to something else and then change it
   * back without penalty.  This has to be updated _before_ production for
   * this turn is calculated, so that the penalty will apply if the player
   * changes production away from what has just been completed.  This makes
   * sense if you consider what this value means: all the shields in the
   * city have been dedicated toward the project that was chosen last turn,
   * so the player shouldn't be penalized if the governor has to pick
   * something different.  See city_change_production_penalty(). */
  pcity->changed_from = pcity->production;
 
  log_debug("In %s, building %s.  Beg of Turn shields = %d",
            city_name_get(pcity), universal_rule_name(&pcity->changed_from),
            pcity->before_change_shields);
}
 
/**********************************************************************/
static void nullify_caravan_and_disband_plus(struct city *pcity)
{
  pcity->disbanded_shields=0;
  pcity->caravan_shields=0;
}
 
/**********************************************************************/
void nullify_prechange_production(struct city *pcity)
{
  nullify_caravan_and_disband_plus(pcity);
  pcity->before_change_shields=0;
}
 
/**********************************************************************/
static void update_city_activity(struct city *pcity)
{
  struct player *pplayer;
  struct government *gov;
  bool is_happy;
  bool is_celebrating;
 
  if (!pcity) {
    return;
  }
 
  pplayer = city_owner(pcity);
  gov = government_of_city(pcity);
  is_happy = city_happy(pcity);
  is_celebrating = city_celebrating(pcity);
 
  if (city_refresh(pcity)) {
    auto_arrange_workers(pcity);
  }
 
  /* Reporting of celebrations rewritten, copying the treatment of disorder below,
     with the added rapture rounds count.  991219 -- Jing */
  if (city_build_stuff(pplayer, pcity)) {
    int saved_id;
    int revolution_turns;
 
    pcity->history += city_history_gain(pcity);
 
    /* History can decrease, but never go below zero */
    pcity->history = MAX(pcity->history, 0);
 
    /* Keep old behaviour when building new improvement could keep
       city celebrating */
    if (!is_happy) {
      is_happy = city_happy(pcity);
    }
 
    if (city_celebrating(pcity) || is_celebrating) {
      pcity->rapture++;
      if (pcity->rapture == 1) {
        notify_player(pplayer, city_tile(pcity), E_CITY_LOVE, ftc_server,
                      _("Celebrations in your honor in %s."),
                      city_link(pcity));
      }
    } else {
      if (pcity->rapture != 0) {
        notify_player(pplayer, city_tile(pcity), E_CITY_NORMAL, ftc_server,
                      _("Celebrations canceled in %s."),
                      city_link(pcity));
      }
      pcity->rapture = 0;
    }
    pcity->was_happy = is_happy;
 
    /* Handle the illness. */
    if (game.info.illness_on) {
      /* Recalculate city illness; illness due to trade has to be saved
       * within the city struct, as the client does not have all
       * the data to calculate it */
      pcity->server.illness
        = city_illness_calc(pcity, NULL, NULL, &(pcity->illness_trade), NULL);
 
      if (city_illness_check(pcity)) {
        if (!city_illness_strike(pcity)) {
          /* Illness destroyed the city */
          return;
        }
      }
    }
 
    /* City population updated here, after the rapture stuff above. --Jing */
    saved_id = pcity->id;
    city_populate(pcity, pplayer);
    if (NULL == player_city_by_number(pplayer, saved_id)) {
      return;
    }
 
    pcity->did_sell = FALSE;
    pcity->did_buy = FALSE;
    pcity->airlift = city_airlift_max(pcity);
    update_bulbs(pplayer, pcity->prod[O_SCIENCE], FALSE);
 
    pplayer->economic.infra_points += get_city_bonus(pcity, EFT_INFRA_POINTS);
 
    /* Update the treasury. */
    pplayer->economic.gold += pcity->surplus[O_GOLD];
 
    /* FIXME: Nation level upkeep should be paid after ALL cities
     *        have been processed, not after each individual city. */
    if (game.info.gold_upkeep_style != GOLD_UPKEEP_CITY) {
      /* Unit upkeep was not included in city balance ->
       * not reduced from the city surplus. */
      pplayer->economic.gold -= city_total_unit_gold_upkeep(pcity);
 
      if (game.info.gold_upkeep_style == GOLD_UPKEEP_NATION) {
        /* Building upkeep was not included in city balance ->
         * not reduced from the city surplus. */
        pplayer->economic.gold -= city_total_impr_gold_upkeep(pcity);
      }
    }
 
    /* Remember how much gold upkeep each unit was paid. */
    unit_list_iterate(pcity->units_supported, punit) {
      punit->server.upkeep_paid[O_GOLD] = punit->upkeep[O_GOLD];
    } unit_list_iterate_end;
 
    if (pplayer->economic.gold < 0) {
      /* Not enough gold - we have to sell some buildings, and if that
       * is not enough, disband units with gold upkeep, taking into
       * account the setting of 'game.info.gold_upkeep_style':
       * GOLD_UPKEEP_CITY: Cities pay for buildings and units.
       * GOLD_UPKEEP_MIXED: Cities pay only for buildings; the nation pays
       *                    for units.
       * GOLD_UPKEEP_NATION: The nation pays for buildings and units. */
      switch (game.info.gold_upkeep_style) {
      case GOLD_UPKEEP_CITY:
      case GOLD_UPKEEP_MIXED:
        if (!city_balance_treasury_buildings(pcity)
            && game.info.gold_upkeep_style == GOLD_UPKEEP_CITY) {
          city_balance_treasury_units(pcity);
        }
        break;
      case GOLD_UPKEEP_NATION:
        break;
      }
    }
 
    revolution_turns = get_city_bonus(pcity, EFT_REVOLUTION_UNHAPPINESS);
    if (city_unhappy(pcity)) {
      const char *revomsg;
 
      pcity->anarchy++;
      if (pcity->anarchy == revolution_turns) {
        /* Revolution next turn if not dealt with */
        /* TRANS: preserve leading space; this string will be appended to
         * another sentence */
        revomsg = _(" Unrest threatens to spread beyond the city.");
      } else {
        revomsg = "";
      }
      if (pcity->anarchy == 1) {
        notify_player(pplayer, city_tile(pcity), E_CITY_DISORDER, ftc_server,
                      /* TRANS: second %s is an optional extra sentence */
                      _("Civil disorder in %s.%s"),
                      city_link(pcity), revomsg);
      } else {
        notify_player(pplayer, city_tile(pcity), E_CITY_DISORDER, ftc_server,
                      /* TRANS: second %s is an optional extra sentence */
                      _("CIVIL DISORDER CONTINUES in %s.%s"),
                      city_link(pcity), revomsg);
      }
    } else {
      if (pcity->anarchy != 0) {
        notify_player(pplayer, city_tile(pcity), E_CITY_NORMAL, ftc_server,
                      _("Order restored in %s."),
                      city_link(pcity));
      }
      pcity->anarchy = 0;
    }
    check_pollution(pcity);
 
    send_city_info(NULL, pcity);
 
    if (revolution_turns > 0 && pcity->anarchy > revolution_turns) {
      notify_player(pplayer, city_tile(pcity), E_ANARCHY, ftc_server,
                    /* TRANS: %s - government form, e.g., Democracy */
                    _("The people have overthrown your %s, "
                      "your country is in turmoil."),
                    government_name_translation(gov));
      handle_player_change_government(pplayer, government_number(gov));
    }
    if (city_refresh(pcity)) {
      auto_arrange_workers(pcity);
    }
    sanity_check_city(pcity);
  }
}
 
/**********************************************************************/
static bool city_illness_check(const struct city * pcity)
{
  if (fc_rand(1000) < pcity->server.illness) {
    return TRUE;
  }
 
  return FALSE;
}
 
/**********************************************************************/
static bool disband_city(struct city *pcity)
{
  struct player *pplayer = city_owner(pcity);
  struct tile *ptile = pcity->tile;
  struct city *rcity=NULL;
  const struct unit_type *utype = pcity->production.value.utype;
  struct unit *punit;
  int saved_id = pcity->id;
 
  /* find closest city other than pcity */
  rcity = find_closest_city(ptile, pcity, pplayer, FALSE, FALSE, FALSE, TRUE,
                            FALSE, NULL);
 
  if (!rcity) {
    /* What should we do when we try to disband our only city? */
    notify_player(pplayer, ptile, E_CITY_CANTBUILD, ftc_server,
                  _("%s can't build %s yet, "
                    "as we can't disband our only city."),
                  city_link(pcity), utype_name_translation(utype));
    script_server_signal_emit("unit_cant_be_built", utype, pcity,
                              "pop_cost");
    if (!city_exist(saved_id)) {
      /* Script decided to remove even the last city */
      return TRUE;
    } else {
      return FALSE;
    }
  }
 
  punit = city_create_unit(pcity, utype, NULL);
 
  /* "unit_built" script handler may have destroyed city. If so, we
   * assume something sensible happened to its units, and that the
   * script took care of announcing unit creation if required. */
  if (city_exist(saved_id)) {
    /* Shift all the units supported by pcity (including the new unit)
     * to rcity.  transfer_city_units does not make sure no units are
     * left floating without a transport, but since all units are
     * transferred this is not a problem. */
    transfer_city_units(pplayer, pplayer, pcity->units_supported, rcity, 
                        pcity, -1, TRUE);
 
    if (punit) {
      notify_player(pplayer, ptile, E_UNIT_BUILT, ftc_server,
                    /* TRANS: "<city> is disbanded into Settler." */
                    _("%s is disbanded into %s."), 
                    city_tile_link(pcity), utype_name_translation(utype));
    }
 
    script_server_signal_emit("city_destroyed", pcity, pcity->owner, NULL);
 
    if (!city_exist(saved_id)) {
      /* Already removed during the script */
      return TRUE;
    }
    remove_city(pcity);
 
    /* Since we've removed the city, we don't need to worry about
     * charging for production, disabling rally points, etc. */
  }
 
  return TRUE;
}
 
/**********************************************************************/
static float city_migration_score(struct city *pcity)
{
  float score = 0.0;
  int build_shield_cost = 0;
  bool has_wonder = FALSE;
 
  if (!pcity) {
    return score;
  }
 
  if (pcity->server.mgr_score_calc_turn == game.info.turn) {
    /* up-to-date migration score */
    return pcity->server.migration_score;
  }
 
  /* feeling of the citizens */
  score = (city_size_get(pcity)
           + 1.00 * pcity->feel[CITIZEN_HAPPY][FEELING_FINAL]
           + 0.00 * pcity->feel[CITIZEN_CONTENT][FEELING_FINAL]
           - 0.25 * pcity->feel[CITIZEN_UNHAPPY][FEELING_FINAL]
           - 0.50 * pcity->feel[CITIZEN_ANGRY][FEELING_FINAL]);
 
  /* calculate shield build cost for all buildings */
  city_built_iterate(pcity, pimprove) {
    build_shield_cost += impr_build_shield_cost(pcity, pimprove);
    if (is_wonder(pimprove)) {
      /* this city has a wonder */
      has_wonder = TRUE;
    }
  } city_built_iterate_end;
 
  /* take shield costs of all buidings into account; normalized by 1000 */
  score *= (1 + (1 - exp(- (float) MAX(0, build_shield_cost) / 1000)) / 5);
  /* take trade into account; normalized by 100 */
  score *= (1 + (1 - exp(- (float) MAX(0, pcity->surplus[O_TRADE]) / 100))
                / 5);
  /* take luxury into account; normalized by 100 */
  score *= (1 + (1 - exp(- (float) MAX(0, pcity->surplus[O_LUXURY]) / 100))
                / 5);
  /* take science into account; normalized by 100 */
  score *= (1 + (1 - exp(- (float) MAX(0, pcity->surplus[O_SCIENCE]) / 100))
                / 5);
 
  score += city_culture(pcity) * game.info.culture_migration_pml / 1000;
 
  /* Take food into account; the food surplus is clipped to values between
   * -10..20 and normalize by 10. Thus, the factor is between 0.9 and 1.2. */
  score *= (1 + (float) CLIP(-10, pcity->surplus[O_FOOD], 20) / 10 );
 
  /* Reduce the score due to city illness (plague). The illness is given in
   * tenth of percent (0..1000) and normalized by 25. Thus, this factor is
   * between 0.6 (ill city) and 1.0 (health city). */
  score *= (100 - (float)city_illness_calc(pcity, NULL, NULL, NULL, NULL)
                  / 25);
 
  if (has_wonder) {
    /* people like wonders */
    score *= 1.25;
  }
 
  if (is_capital(pcity)) {
    /* the capital is a magnet for the citizens */
    score *= 1.25;
  }
 
  /* take into account effects */
  score *= (1.0 + get_city_bonus(pcity, EFT_MIGRATION_PCT) / 100.0);
 
  log_debug("[M] %s score: %.3f", city_name_get(pcity), score);
 
  /* set migration score for the city */
  pcity->server.migration_score = score;
  /* set the turn, when the score was calculated */
  pcity->server.mgr_score_calc_turn = game.info.turn;
 
  return score;
}
 
/**********************************************************************/
static bool do_city_migration(struct city *pcity_from,
                              struct city *pcity_to)
{
  struct player *pplayer_from, *pplayer_to, *pplayer_citizen;
  struct tile *ptile_from, *ptile_to;
  char name_from[MAX_LEN_LINK], name_to[MAX_LEN_LINK];
  const char *nation_from, *nation_to;
  struct city *rcity = NULL;
  int to_id = pcity_to->id;
  const struct civ_map *nmap = &(wld.map);
 
  if (!pcity_from || !pcity_to) {
    return FALSE;
  }
 
  pplayer_from = city_owner(pcity_from);
  pplayer_citizen = pplayer_from;
  pplayer_to = city_owner(pcity_to);
  /* We copy that, because city_link always returns the same pointer. */
  sz_strlcpy(name_from, city_link(pcity_from));
  sz_strlcpy(name_to, city_link(pcity_to));
  nation_from = nation_adjective_for_player(pplayer_from);
  nation_to = nation_adjective_for_player(pplayer_to);
  ptile_from = city_tile(pcity_from);
  ptile_to = city_tile(pcity_to);
 
  /* Check food supply in the receiver city */
  if (game.server.mgr_foodneeded) {
    bool migration = FALSE;
 
    if (pcity_to->surplus[O_FOOD] >= game.info.food_cost) {
      migration = TRUE;
    } else {
      /* Check if there is a free tile for the new citizen which, when worked,
       * leads to zero or positive food surplus for the enlarged city */
      int max_food_tile = -1;  /* no free tile */
 
      city_tile_iterate(nmap, city_map_radius_sq_get(pcity_to),
                        city_tile(pcity_to), ptile) {
        if (city_can_work_tile(pcity_to, ptile)
            && tile_worked(ptile) != pcity_to) {
          /* Safest assumption is that city won't be celebrating once an
           * additional citizen is added */
          max_food_tile = MAX(max_food_tile,
                              city_tile_output(pcity_to, ptile, FALSE, O_FOOD));
        }
      } city_tile_iterate_end;
      if (max_food_tile >= 0
          && pcity_to->surplus[O_FOOD] + max_food_tile >= game.info.food_cost) {
        migration = TRUE;
      }
    }
 
    if (!migration) {
      /* insufficiency food in receiver city; no additional citizens */
      if (pplayer_from == pplayer_to) {
        /* migration between one nation */
        notify_player(pplayer_to, ptile_to, E_CITY_TRANSFER, ftc_server,
                      /* TRANS: From <city1> to <city2>. */
                      _("Migrants from %s can't go to %s because there is "
                        "not enough food available!"),
                      name_from, name_to);
      } else {
        /* migration between different nations */
        notify_player(pplayer_from, ptile_to, E_CITY_TRANSFER, ftc_server,
                      /* TRANS: From <city1> to <city2> (<city2 nation adjective>). */
                      _("Migrants from %s can't go to %s (%s) because there "
                        "is not enough food available!"),
                      name_from, name_to, nation_to);
        notify_player(pplayer_to, ptile_to, E_CITY_TRANSFER, ftc_server,
                      /* TRANS: From <city1> (<city1 nation adjective>) to <city2>. */
                      _("Migrants from %s (%s) can't go to %s because there "
                        "is not enough food available!"),
                      name_from, nation_from, name_to);
      }
 
      return FALSE;
    }
  }
 
  if (!city_can_grow_to(pcity_to, city_size_get(pcity_to) + 1)) {
    /* receiver city can't grow  */
    if (pplayer_from == pplayer_to) {
      /* migration between one nation */
      notify_player(pplayer_to, ptile_to, E_CITY_TRANSFER, ftc_server,
                    /* TRANS: From <city1> to <city2>. */
                    _("Migrants from %s can't go to %s because it needs "
                      "an improvement to grow!"),
                    name_from, name_to);
    } else {
      /* migration between different nations */
      notify_player(pplayer_from, ptile_to, E_CITY_TRANSFER, ftc_server,
                    /* TRANS: From <city1> to <city2> of <city2 nation adjective>. */
                    _("Migrants from %s can't go to %s (%s) because it "
                      "needs an improvement to grow!"),
                    name_from, name_to, nation_to);
      notify_player(pplayer_to, ptile_to, E_CITY_TRANSFER, ftc_server,
                    /* TRANS: From <city1> (<city1 nation adjective>) to <city2>. */
                    _("Migrants from %s (%s) can't go to %s because it "
                      "needs an improvement to grow!"),
                    name_from, nation_from, name_to);
    }
 
    return FALSE;
  }
 
  /* reduce size of giver */
  if (city_size_get(pcity_from) == 1) {
 
    if (game.info.citizen_nationality) {
      /* Preserve nationality of city's only citizen */
      pplayer_citizen = player_slot_get_player(citizens_random(pcity_from));
    }
 
    /* do not destroy wonders */
    city_built_iterate(pcity_from, pimprove) {
      if (is_wonder(pimprove)) {
        return FALSE;
      }
    } city_built_iterate_end;
 
    /* find closest city other of the same player than pcity_from */
    rcity = find_closest_city(ptile_from, pcity_from, pplayer_from, FALSE,
                              FALSE, FALSE, TRUE, FALSE, NULL);
 
    if (rcity) {
      int id = pcity_from->id;
 
      /* transfer all units to the closest city */
      transfer_city_units(pplayer_from, pplayer_from,
                          pcity_from->units_supported, rcity, pcity_from,
                          -1, TRUE);
      sz_strlcpy(name_from, city_tile_link(pcity_from));
 
      script_server_signal_emit("city_size_change", pcity_from,
                                (lua_Integer)(-1), "migration_from");
 
      if (city_exist(id)) {
        script_server_signal_emit("city_destroyed", pcity_from,
                                  pcity_from->owner, NULL);
 
        if (city_exist(id)) {
          remove_city(pcity_from);
        }
      }
 
      notify_player(pplayer_from, ptile_from, E_CITY_LOST, ftc_server,
                    _("%s was disbanded by its citizens."),
                    name_from);
    } else {
      /* it's the only city of the nation */
      return FALSE;
    }
  } else {
    /* the migrants take half of the food box with them (this prevents
     * migration -> grow -> migration -> ... cycles) */
    pcity_from->food_stock /= 2;
 
    if (game.info.citizen_nationality) {
      /* Those citizens that are from the target nation are most
       * ones migrating. */
      if (citizens_nation_get(pcity_from, pplayer_to->slot) > 0) {
        pplayer_citizen = pplayer_to;
      } else if (!citizens_nation_get(pcity_from, pplayer_citizen->slot)) {
        /* No native citizens at all in the city, choose random foreigner */
        struct player_slot *cit_slot = citizens_random(pcity_from);
 
        pplayer_citizen = player_slot_get_player(cit_slot);
      }
      /* This should be followed by city_reduce_size(). */
      citizens_nation_add(pcity_from, pplayer_citizen->slot, -1);
    }
    city_reduce_size(pcity_from, 1, pplayer_from, "migration_from");
    city_refresh_vision(pcity_from);
    if (city_refresh(pcity_from)) {
      auto_arrange_workers(pcity_from);
    }
  }
 
  /* This should be _before_ the size of the city is increased. Thus, the
   * order of the messages is correct (1: migration; 2: increased size). */
  if (pplayer_from == pplayer_to) {
    /* migration between one nation */
    notify_player(pplayer_from, ptile_to, E_CITY_TRANSFER, ftc_server,
                  /* TRANS: From <city1> to <city2>. */
                  _("Migrants from %s moved to %s in search of a better "
                    "life."), name_from, name_to);
  } else {
    /* migration between different nations */
    notify_player(pplayer_from, ptile_to, E_CITY_TRANSFER, ftc_server,
                  /* TRANS: From <city1> to <city2> (<city2 nation adjective>). */
                  _("Migrants from %s moved to %s (%s) in search of a "
                    "better life."),
                  name_from, name_to, nation_to);
    notify_player(pplayer_to, ptile_to, E_CITY_TRANSFER, ftc_server,
                  /* TRANS: From <city1> (<city1 nation adjective>) to <city2>. */
                  _("Migrants from %s (%s) moved to %s in search of a "
                    "better life."),
                  name_from, nation_from, name_to);
  }
 
  /* Increase size of receiver city */
  if (city_exist(to_id)) {
    bool incr_success = city_increase_size(pcity_to);
 
    if (city_exist(to_id)) {
      city_refresh_after_city_size_increase(pcity_to, pplayer_citizen);
      city_refresh_vision(pcity_to);
      if (city_refresh(pcity_to)) {
        auto_arrange_workers(pcity_to);
      }
      if (incr_success) {
        script_server_signal_emit("city_size_change", pcity_to,
                                  (lua_Integer)1, "migration_to");
      }
    }
  }
 
  log_debug("[M] T%d migration successful (%s -> %s)",
            game.info.turn, name_from, name_to);
 
  return TRUE;
}
 
/**********************************************************************/
bool check_city_migrations(void)
{
  bool internat = FALSE;
 
  if (!game.server.migration) {
    return FALSE;
  }
 
  if (game.server.mgr_turninterval <= 0
      || (game.server.mgr_worldchance <= 0
          && game.server.mgr_nationchance <= 0)) {
    return FALSE;
  }
 
  /* check for migration */
  players_iterate(pplayer) {
    if (!pplayer->cities) {
      continue;
    }
 
    if (check_city_migrations_player(pplayer)) {
      internat = TRUE;
    }
  } players_iterate_end;
 
  return internat;
}
 
/**********************************************************************/
bool city_empty_food_stock(struct city *pcity) {
  struct player *pplayer = city_owner(pcity);
  struct tile *ptile = city_tile(pcity);
 
  fc_assert_ret_val(pcity != NULL, FALSE);
 
  if (pcity->food_stock > 0) {
    pcity->food_stock = 0;
 
    notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                  /* TRANS: %s is a city name */
                  _("All stored food destroyed in %s."), city_link(pcity));
 
    return TRUE;
  }
 
  return FALSE;
}
 
/**********************************************************************/
static void apply_disaster(struct city *pcity, struct disaster_type *pdis)
{
  struct player *pplayer = city_owner(pcity);
  struct tile *ptile = city_tile(pcity);
  bool had_internal_effect = FALSE;
 
  log_debug("%s at %s", disaster_rule_name(pdis), city_name_get(pcity));
 
  notify_player(pplayer, ptile, E_DISASTER,
                ftc_server,
                /* TRANS: Disasters such as Earthquake */
                _("%s was hit by %s."), city_name_get(pcity),
                disaster_name_translation(pdis));
 
  if (disaster_has_effect(pdis, DE_POLLUTION)) {
    if (place_pollution(pcity, EC_POLLUTION)) {
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    _("Pollution near %s."), city_link(pcity));
      had_internal_effect = TRUE;
    }
  }
 
  if (disaster_has_effect(pdis, DE_FALLOUT)) {
    if (place_pollution(pcity, EC_FALLOUT)) {
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    _("Fallout near %s."), city_link(pcity));
      had_internal_effect = TRUE;
    }
  }
 
  if (disaster_has_effect(pdis, DE_REDUCE_DESTROY)
      || (disaster_has_effect(pdis, DE_REDUCE_POP)
          && pcity->size > 1)) {
    if (!city_reduce_size(pcity, 1, NULL, "disaster")) {
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    /* TRANS: "Industrial Accident destroys Bogota entirely." */
                    _("%s destroys %s entirely."),
                    disaster_name_translation(pdis), city_link(pcity));
      pcity = NULL;
    } else {
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    /* TRANS: "Nuclear Accident ... Montreal." */
                    _("%s causes population loss in %s."),
                    disaster_name_translation(pdis), city_link(pcity));
    }
 
    had_internal_effect = TRUE;
  }
 
  if (pcity && disaster_has_effect(pdis, DE_DESTROY_BUILDING)) {
    int total = 0;
    struct impr_type *imprs[B_LAST];
 
    city_built_iterate(pcity, pimprove) {
      if (is_improvement(pimprove)
          && !improvement_has_flag(pimprove, IF_DISASTER_PROOF)) {
        imprs[total++] = pimprove;
      }
    } city_built_iterate_end;
 
    if (total > 0) {
      int num = fc_rand(total);
 
      building_lost(pcity, imprs[num], "disaster", NULL);
 
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    /* TRANS: second %s is the name of a city improvement */
                    _("%s destroys %s in %s."),
                    disaster_name_translation(pdis),
                    improvement_name_translation(imprs[num]),
                    city_link(pcity));
 
      had_internal_effect = TRUE;
    }
  }
 
  if (pcity && disaster_has_effect(pdis, DE_EMPTY_FOODSTOCK)) {
    if (city_empty_food_stock(pcity)) {
      had_internal_effect = TRUE;
    }
  }
 
  if (pcity && disaster_has_effect(pdis, DE_EMPTY_PRODSTOCK)) {
    if (pcity->shield_stock > 0) {
      char prod[256];
 
      pcity->shield_stock = 0;
      nullify_prechange_production(pcity); /* Make it impossible to recover */
 
      universal_name_translation(&pcity->production, prod, sizeof(prod));
      notify_player(pplayer, ptile, E_DISASTER, ftc_server,
                    /* TRANS: "Production of Colossus in Rhodes destroyed." */
                    _("Production of %s in %s destroyed."),
                    prod, city_link(pcity));
 
      had_internal_effect = TRUE;
    }
  }
 
  script_server_signal_emit("disaster_occurred", pdis, pcity,
                            had_internal_effect);
  script_server_signal_emit("disaster", pdis, pcity);
}
 
/**********************************************************************/
void check_disasters(void)
{
  if (game.info.disasters == 0) {
    /* Shortcut out as no disaster is possible. */
    return;
  }
 
  players_iterate(pplayer) {
    /* Safe city iterator needed as disaster may destroy city */
    city_list_iterate_safe(pplayer->cities, pcity) {
      int id = pcity->id;
 
      disaster_type_iterate(pdis) {
        if (city_exist(id)) {
          /* City survived earlier disasters. */
          int probability = game.info.disasters * pdis->frequency;
          int result = fc_rand(DISASTER_BASE_RARITY);
 
          if (result < probability)  {
            if (can_disaster_happen(pdis, pcity)) {
              apply_disaster(pcity, pdis);
            }
          }
        }
      } disaster_type_iterate_end;
    } city_list_iterate_safe_end;
  } players_iterate_end;
}
 
/**********************************************************************/
static bool check_city_migrations_player(const struct player *pplayer)
{
  char city_link_text[MAX_LEN_LINK];
  float best_city_player_score, best_city_world_score;
  struct city *best_city_player, *best_city_world, *acity;
  float score_from, score_tmp, weight;
  int dist, mgr_dist;
  bool internat = FALSE;
 
  /* check for each city
   * city_list_iterate_safe_end must be used because we could
   * remove one city from the list */
  city_list_iterate_safe(pplayer->cities, pcity) {
    /* no migration out of the capital */
    if (is_capital(pcity)) {
      continue;
    }
 
    /* check only each (game.server.mgr_turninterval) turn
     * (counted from the funding turn) and do not migrate
     * the same turn a city is founded */
    if (game.info.turn == pcity->turn_founded
        || ((game.info.turn - pcity->turn_founded)
            % game.server.mgr_turninterval) != 0) {
      continue;
    }
 
    best_city_player_score = 0.0;
    best_city_world_score = 0.0;
    best_city_player = NULL;
    best_city_world = NULL;
 
    /* score of the actual city
     * taking into account a persistence factor of 3 */
    score_from = city_migration_score(pcity) * 3;
 
    log_debug("[M] T%d check city: %s score: %6.3f (%s)",
              game.info.turn, city_name_get(pcity), score_from,
              player_name(pplayer));
 
    /* consider all cities within the maximal possible distance
     * (= CITY_MAP_MAX_RADIUS + GAME_MAX_MGR_DISTANCE) */
    iterate_outward(&(wld.map), city_tile(pcity),
                    CITY_MAP_MAX_RADIUS + GAME_MAX_MGR_DISTANCE, ptile) {
      acity = tile_city(ptile);
 
      if (!acity || acity == pcity) {
        /* no city or the city in the center */
        continue;
      }
 
      /* Calculate the migration distance. The value of
       * game.server.mgr_distance is added to the current city radius. If the
       * distance between both cities is lower or equal than this value,
       * migration is possible. */
      mgr_dist = (int)sqrt((double)MAX(city_map_radius_sq_get(acity),0))
                 + game.server.mgr_distance;
 
      /* distance between the two cities */
      dist = real_map_distance(city_tile(pcity), city_tile(acity));
 
      if (dist > mgr_dist) {
        /* to far away */
        continue;
      }
 
      /* score of the second city, weighted by the distance */
      weight = ((float) (mgr_dist + 1 - dist) / (float) (mgr_dist + 1));
      score_tmp = city_migration_score(acity) * weight;
 
      log_debug("[M] T%d - compare city: %s (%s) dist: %d mgr_dist: %d "
                "score: %6.3f", game.info.turn, city_name_get(acity),
                player_name(city_owner(acity)), dist, mgr_dist, score_tmp);
 
      if (game.server.mgr_nationchance > 0 && city_owner(acity) == pplayer) {
        /* migration between cities of the same owner */
        if (score_tmp > score_from && score_tmp > best_city_player_score) {
          /* select the best! */
          best_city_player_score = score_tmp;
          best_city_player = acity;
 
          log_debug("[M] T%d - best city (player): %s (%s) score: "
                    "%6.3f (> %6.3f)", game.info.turn,
                    city_name_get(best_city_player), player_name(pplayer),
                    best_city_player_score, score_from);
        }
      } else if (game.server.mgr_worldchance > 0
                 && city_owner(acity) != pplayer) {
        /* migration between cities of different owners */
        if (game.info.citizen_nationality) {
          /* Modify the score if citizens could migrate to a city of their
           * original nation. */
          if (citizens_nation_get(pcity, city_owner(acity)->slot) > 0) {
            score_tmp *= 2;
          }
        }
 
        if (score_tmp > score_from && score_tmp > best_city_world_score) {
          /* select the best! */
          best_city_world_score = score_tmp;
          best_city_world = acity;
 
          log_debug("[M] T%d - best city (world): %s (%s) score: "
                    "%6.3f (> %6.3f)", game.info.turn,
                    city_name_get(best_city_world),
                    player_name(city_owner(best_city_world)),
                    best_city_world_score, score_from);
        }
      }
    } iterate_outward_end;
 
    if (best_city_player != NULL) {
      /* First, do the migration within one nation */
      if (fc_rand(100) >= game.server.mgr_nationchance) {
        /* No migration */
        /* N.B.: city_link always returns the same pointer. */
        sz_strlcpy(city_link_text, city_link(pcity));
        notify_player(pplayer, city_tile(pcity), E_CITY_TRANSFER, ftc_server,
                      _("Citizens of %s are thinking about migrating to %s "
                        "for a better life."),
                      city_link_text, city_link(best_city_player));
      } else {
        do_city_migration(pcity, best_city_player);
      }
 
      /* Stop here */
      continue;
    }
 
    if (best_city_world != NULL) {
      /* Second, do the migration between all nations */
      if (fc_rand(100) >= game.server.mgr_worldchance) {
        const char *nname;
 
        nname = nation_adjective_for_player(city_owner(best_city_world));
        /* No migration */
        /* N.B.: city_link always returns the same pointer. */
        sz_strlcpy(city_link_text, city_link(pcity));
        notify_player(pplayer, city_tile(pcity), E_CITY_TRANSFER, ftc_server,
                      /* TRANS: <city1> to <city2> (<city2 nation adjective>). */
                      _("Citizens of %s are thinking about migrating to %s "
                        "(%s) for a better life."),
                      city_link_text, city_link(best_city_world), nname);
      } else {
        do_city_migration(pcity, best_city_world);
        internat = TRUE;
      }
 
      /* Stop here */
      continue;
    }
  } city_list_iterate_safe_end;
 
  return internat;
}
 
/**********************************************************************/
void city_style_refresh(struct city *pcity)
{
  pcity->style = city_style(pcity);
}
 
/**********************************************************************/
void city_tc_effect_refresh(struct player *pplayer)
{
  const struct civ_map *nmap = &(wld.map);
 
  city_list_iterate(pplayer->cities, pcity) {
    bool changed = FALSE;
 
    city_tile_iterate_skip_free_worked(nmap, city_map_radius_sq_get(pcity),
                                       city_tile(pcity), ptile, idx, x, y) {
      if (ptile->worked == pcity
          && get_city_tile_output_bonus(pcity, ptile, NULL, EFT_TILE_WORKABLE) <= 0) {
        city_map_update_empty(pcity, ptile);
        pcity->specialists[DEFAULT_SPECIALIST]++;
        changed = TRUE;
      }
    } city_tile_iterate_skip_free_worked_end;
 
    if (changed) {
      auto_arrange_workers(pcity);
      send_city_info(NULL, pcity);
    }
  } city_list_iterate_end;
}