aitools.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
 
/* utility */
#include "bitvector.h"
#include "log.h"
#include "mem.h"
#include "shared.h"
 
/* common */
#include "city.h"
#include "combat.h"
#include "game.h"
#include "government.h"
#include "map.h"
#include "movement.h"
#include "packets.h"
#include "player.h"
#include "unit.h"
#include "unitlist.h"
 
/* common/aicore */
#include "citymap.h"
#include "pf_tools.h"
 
/* server */
#include "barbarian.h"
#include "citytools.h"
#include "cityturn.h"
#include "maphand.h"
#include "plrhand.h"
#include "score.h"
#include "srv_log.h"
#include "unithand.h"
#include "unittools.h"
 
/* server/advisors */
#include "advdata.h"
#include "advgoto.h"
#include "advtools.h"
#include "autosettlers.h"
#include "infracache.h" /* adv_city */
 
/* ai */
#include "handicaps.h"
 
/* ai/default */
#include "aidata.h"
#include "aiferry.h"
#include "aiguard.h"
#include "ailog.h"
#include "aiplayer.h"
#include "aitech.h"
#include "aiunit.h"
#include "daimilitary.h"
 
#include "aitools.h"
 
/**********************************************************************/
const char *dai_unit_task_rule_name(const enum ai_unit_task task)
{
  switch (task) {
   case AIUNIT_NONE:
     return "None";
   case AIUNIT_AUTO_SETTLER:
     return "Auto settler";
   case AIUNIT_BUILD_CITY:
     return "Build city";
   case AIUNIT_DEFEND_HOME:
     return "Defend home";
   case AIUNIT_ATTACK:
     return "Attack";
   case AIUNIT_ESCORT:
     return "Escort";
   case AIUNIT_EXPLORE:
     return "Explore";
   case AIUNIT_RECOVER:
     return "Recover";
   case AIUNIT_HUNTER:
     return "Hunter";
   case AIUNIT_TRADE:
     return "Trade";
   case AIUNIT_WONDER:
     return "Wonder";
  }
 
  /* No default, ensure all types handled somehow */
  log_error("Unsupported ai_unit_task %d.", task);
 
  return NULL;
}
 
/**********************************************************************/
adv_want military_amortize(struct player *pplayer, struct city *pcity,
                           adv_want value, int delay, int build_cost)
{
  struct adv_data *ai = adv_data_get(pplayer, NULL);
  int city_output = (pcity ? pcity->surplus[O_SHIELD] : 1);
  int output = MAX(city_output, ai->stats.average_production);
  int build_time = build_cost / MAX(output, 1);
 
  if (value <= 0) {
    return 0;
  }
 
  return amortize(value, delay + build_time);
}
 
/**********************************************************************/
void dai_consider_plr_dangerous(struct ai_type *ait, struct player *plr1,
                                struct player *plr2,
                                enum override_bool *result)
{
  struct ai_dip_intel *adip;
 
  adip = dai_diplomacy_get(ait, plr1, plr2);
 
  if (adip->countdown >= 0) {
    /* Don't trust our war target */
    *result = OVERRIDE_TRUE;
  }
}
 
/**********************************************************************/
static bool dai_gothere_bodyguard(struct ai_type *ait,
                                  struct unit *punit, struct tile *dest_tile)
{
  struct player *pplayer = unit_owner(punit);
  unsigned int danger = 0;
  struct city *dcity;
  struct unit *guard = aiguard_guard_of(ait, punit);
  const struct veteran_level *vlevel;
  bool bg_needed = FALSE;
  const struct unit_type *ptype;
 
  if (is_barbarian(unit_owner(punit))) {
    /* Barbarians must have more courage (ie less brains) */
    aiguard_clear_guard(ait, punit);
    return FALSE;
  }
 
  /* Estimate enemy attack power. */
  unit_list_iterate(dest_tile->units, aunit) {
    if (POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, unit_owner(aunit))) {
      danger += adv_unit_att_rating(aunit);
    }
  } unit_list_iterate_end;
  dcity = tile_city(dest_tile);
  if (dcity && POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, city_owner(dcity))) {
    /* Assume enemy will build another defender, add it's attack strength */
    struct unit_type *d_type = dai_choose_defender_versus(dcity, punit);
 
    if (d_type) {
      /* Enemy really can build something */
      danger +=
        adv_unittype_att_rating(
          d_type, city_production_unit_veteran_level(dcity, d_type),
          SINGLE_MOVE, d_type->hp);
    }
  }
  danger *= POWER_DIVIDER;
 
  /* If we are fast, there is less danger.
   * FIXME: that assumes that most units have move_rate == SINGLE_MOVE;
   * not true for all rulesets */
  ptype = unit_type_get(punit);
  danger /= (ptype->move_rate / SINGLE_MOVE);
  if (unit_has_type_flag(punit, UTYF_IGTER)) {
    danger /= 1.5;
  }
 
  vlevel = utype_veteran_level(ptype, punit->veteran);
  fc_assert_ret_val(vlevel != NULL, FALSE);
 
  /* We look for the bodyguard where we stand. */
  if (guard == NULL || unit_tile(guard) != unit_tile(punit)) {
    int my_def = (punit->hp * ptype->defense_strength
                  * POWER_FACTOR * vlevel->power_fact / 100);
 
    if (danger >= my_def) {
      UNIT_LOG(LOGLEVEL_BODYGUARD, punit, 
               "want bodyguard @(%d, %d) danger=%d, my_def=%d", 
               TILE_XY(dest_tile), danger, my_def);
      aiguard_request_guard(ait, punit);
      bg_needed = TRUE;
    } else {
      aiguard_clear_guard(ait, punit);
      bg_needed = FALSE;
    }
  } else if (guard != NULL) {
    bg_needed = TRUE;
  }
 
  /* What if we have a bodyguard, but don't need one? */
 
  return bg_needed;
}
 
#define LOGLEVEL_GOTHERE LOG_DEBUG
/**********************************************************************/
bool dai_gothere(struct ai_type *ait, struct player *pplayer,
                 struct unit *punit, struct tile *dest_tile)
{
  CHECK_UNIT(punit);
  bool bg_needed;
 
  if (same_pos(dest_tile, unit_tile(punit)) || punit->moves_left <= 0) {
    /* Nowhere to go */
    return TRUE;
  }
 
  /* See if we need a bodyguard at our destination */
  /* FIXME: If bodyguard is _really_ necessary, don't go anywhere */
  bg_needed = dai_gothere_bodyguard(ait, punit, dest_tile);
 
  if (unit_transported(punit)
      || !goto_is_sane(punit, dest_tile)) {
    /* Must go by boat, call an aiferryboat function */
    if (!aiferry_gobyboat(ait, pplayer, punit, dest_tile,
                          bg_needed)) {
      return FALSE;
    }
  }
 
  /* Go where we should be going if we can, and are at our destination 
   * if we are on a ferry */
  if (goto_is_sane(punit, dest_tile) && punit->moves_left > 0) {
    punit->goto_tile = dest_tile;
    UNIT_LOG(LOGLEVEL_GOTHERE, punit, "Walking to (%d,%d)", TILE_XY(dest_tile));
    if (!dai_unit_goto(ait, punit, dest_tile)) {
      /* died */
      return FALSE;
    }
    /* liable to bump into someone that will kill us.  Should avoid? */
  } else {
    UNIT_LOG(LOGLEVEL_GOTHERE, punit, "Not moving");
    return FALSE;
  }
 
  if (def_ai_unit_data(punit, ait)->ferryboat > 0
      && !unit_transported(punit)) {
    /* We probably just landed, release our boat */
    aiferry_clear_boat(ait, punit);
  }
  
  /* Dead unit shouldn't reach this point */
  CHECK_UNIT(punit);
 
  return (same_pos(unit_tile(punit), dest_tile)
          || is_tiles_adjacent(unit_tile(punit), dest_tile));
}
 
/**********************************************************************/
struct tile *immediate_destination(struct unit *punit,
                                   struct tile *dest_tile)
{
  const struct civ_map *nmap = &(wld.map);
 
  if (!same_pos(unit_tile(punit), dest_tile)
      && utype_fuel(unit_type_get(punit))) {
    struct pf_parameter parameter;
    struct pf_map *pfm;
    struct pf_path *path;
    size_t i;
    struct player *pplayer = unit_owner(punit);
 
    pft_fill_unit_parameter(&parameter, nmap, punit);
    parameter.omniscience = !has_handicap(pplayer, H_MAP);
    pfm = pf_map_new(&parameter);
    path = pf_map_path(pfm, punit->goto_tile);
 
    if (path) {
      for (i = 1; i < path->length; i++) {
        if (path->positions[i].tile == path->positions[i - 1].tile) {
          /* The path-finding code advices us to wait there to refuel. */
          struct tile *ptile = path->positions[i].tile;
 
          pf_path_destroy(path);
          pf_map_destroy(pfm);
          return ptile;
        }
      }
      pf_path_destroy(path);
      pf_map_destroy(pfm);
      /* Seems it's the immediate destination */
      return punit->goto_tile;
    }
 
    pf_map_destroy(pfm);
    log_verbose("Did not find an air-route for "
                "%s %s[%d] (%d,%d)->(%d,%d)",
                nation_rule_name(nation_of_unit(punit)),
                unit_rule_name(punit),
                punit->id,
                TILE_XY(unit_tile(punit)),
                TILE_XY(dest_tile));
    /* Prevent take off */
    return unit_tile(punit);
  }
 
  /* else does not need way-points */
  return dest_tile;
}
 
/**********************************************************************/
void dai_log_path(struct unit *punit,
                  struct pf_path *path, struct pf_parameter *parameter)
{
  const struct pf_position *last = pf_path_last_position(path);
  const unsigned cc = PF_TURN_FACTOR * last->total_MC
    + parameter->move_rate * last->total_EC;
  const unsigned tc = cc / (PF_TURN_FACTOR * parameter->move_rate);
 
  UNIT_LOG(LOG_DEBUG, punit, "path L=%d T=%d(%u) MC=%u EC=%u CC=%u",
           path->length - 1, last->turn, tc,
           last->total_MC, last->total_EC, cc);
}
 
/**********************************************************************/
bool dai_unit_goto_constrained(struct ai_type *ait, struct unit *punit,
                               struct tile *ptile,
                               struct pf_parameter *parameter)
{
  bool alive = TRUE;
  struct pf_map *pfm;
  struct pf_path *path;
 
  UNIT_LOG(LOG_DEBUG, punit, "constrained goto to %d,%d", TILE_XY(ptile));
 
  if (same_pos(unit_tile(punit), ptile)) {
    /* Was not an error in previous versions but now is dubious... */
    UNIT_LOG(LOG_DEBUG, punit, "constrained goto: already there!");
    send_unit_info(NULL, punit);
 
    return TRUE;
  } else if (!goto_is_sane(punit, ptile)) {/* FIXME: why do we check it? */
    UNIT_LOG(LOG_DEBUG, punit, "constrained goto: 'insane' goto!");
    punit->activity = ACTIVITY_IDLE;
    send_unit_info(NULL, punit);
 
    return TRUE;
  } else if (punit->moves_left == 0) {
    UNIT_LOG(LOG_DEBUG, punit, "constrained goto: no moves left!");
    send_unit_info(NULL, punit);
 
    return TRUE;
  }
 
  pfm = pf_map_new(parameter);
  path = pf_map_path(pfm, ptile);
 
  if (path) {
    dai_log_path(punit, path, parameter);
    UNIT_LOG(LOG_DEBUG, punit, "constrained goto: following path.");
    alive = adv_follow_path(punit, path, ptile);
  } else {
    UNIT_LOG(LOG_DEBUG, punit, "no path to destination");
  }
 
  pf_path_destroy(path);
  pf_map_destroy(pfm);
 
  return alive;
}
 
/**********************************************************************/
bool goto_is_sane(struct unit *punit, struct tile *ptile)
{
  bool can_get_there = FALSE;
  const struct civ_map *nmap = &(wld.map);
 
  if (same_pos(unit_tile(punit), ptile)) {
    can_get_there = TRUE;
  } else {
    struct pf_parameter parameter;
    struct pf_map *pfm;
 
    pft_fill_unit_attack_param(&parameter, nmap, punit);
    pfm = pf_map_new(&parameter);
 
    if (pf_map_move_cost(pfm, ptile) != PF_IMPOSSIBLE_MC) {
      can_get_there = TRUE;
    }
    pf_map_destroy(pfm);
  }
  return can_get_there;
}
 
/*
 * The length of time, in turns, which is long enough to be optimistic
 * that enemy units will have moved from their current position.
 * WAG
 */
#define LONG_TIME 4
/**********************************************************************/
void dai_fill_unit_param(struct ai_type *ait, struct pf_parameter *parameter,
                         struct adv_risk_cost *risk_cost,
                         struct unit *punit, struct tile *ptile)
{
  const bool long_path = LONG_TIME < (map_distance(unit_tile(punit),
                                                   unit_tile(punit))
                                      * SINGLE_MOVE
                                      / unit_type_get(punit)->move_rate);
  const bool barbarian = is_barbarian(unit_owner(punit));
  bool is_ferry;
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
  struct player *pplayer = unit_owner(punit);
  const struct civ_map *nmap = &(wld.map);
 
  /* This function is now always omniscient and should not be used
   * for human players any more. */
  fc_assert(is_ai(pplayer));
 
  /* If a unit is hunting, don't expect it to be a ferry. */
  is_ferry = (unit_data->task != AIUNIT_HUNTER
              && dai_is_ferry(punit, ait));
 
  if (is_ferry) {
    /* The destination may be a coastal land tile,
     * in which case the ferry should stop on an adjacent tile. */
    pft_fill_unit_overlap_param(parameter, nmap, punit);
  } else if (!utype_fuel(unit_type_get(punit))
             && utype_can_do_action_result(unit_type_get(punit),
                                           ACTRES_ATTACK)
             && (unit_data->task == AIUNIT_DEFEND_HOME
                 || unit_data->task == AIUNIT_ATTACK
                 || unit_data->task ==  AIUNIT_ESCORT
                 || unit_data->task == AIUNIT_HUNTER)) {
    /* Use attack movement for defenders and escorts so they can
     * make defensive attacks */
    pft_fill_unit_attack_param(parameter, nmap, punit);
  } else {
    pft_fill_unit_parameter(parameter, nmap, punit);
  }
  parameter->omniscience = !has_handicap(pplayer, H_MAP);
 
  /* Should we use the risk avoidance code?
   * The risk avoidance code uses omniscience, so do not use for
   * human-player units under temporary AI control.
   * Barbarians bravely/stupidly ignore risks
   */
  if (!uclass_has_flag(unit_class_get(punit), UCF_UNREACHABLE)
      && !barbarian) {
    adv_avoid_risks(parameter, risk_cost, punit, NORMAL_STACKING_FEARFULNESS);
  }
 
  /* Should we absolutely forbid ending a turn on a dangerous tile?
   * Do not annoy human players by killing their units for them.
   * For AI units be optimistic; allows attacks across dangerous terrain,
   * and polar settlements.
   * TODO: This is compatible with old code,
   * but probably ought to be more cautious for non military units
   */
  if (!is_ferry && !utype_fuel(unit_type_get(punit))) {
    parameter->get_moves_left_req = NULL;
  }
 
  if (long_path) {
    /* Move as far along the path to the destination as we can;
     * that is, ignore the presence of enemy units when computing the
     * path.
     * Hopefully, ai_avoid_risks will have produced a path that avoids enemy
     * ZoCs. Ignoring ZoCs allows us to move closer to a destination
     * for which there is not yet a clear path.
     * That is good if the destination is several turns away,
     * so we can reasonably expect blocking enemy units to move or
     * be destroyed. But it can be bad if the destination is one turn away
     * or our destination is far but there are enemy units near us and on the
     * shortest path to the destination.
     */
    parameter->get_zoc = NULL;
  }
 
  if (unit_has_type_flag(punit, UTYF_SETTLERS)) {
    parameter->get_TB = no_fights;
  } else if (long_path && unit_is_cityfounder(punit)) {
    /* Default tile behaviour;
     * move as far along the path to the destination as we can;
     * that is, ignore the presence of enemy units when computing the
     * path.
     */
  } else if (unit_is_cityfounder(punit)) {
    /* Short path */
    parameter->get_TB = no_fights;
  } else if (unit_has_type_role(punit, L_BARBARIAN_LEADER)) {
    /* Avoid capture */
    parameter->get_TB = no_fights;
  } else if (is_ferry) {
    /* Ferries are not warships */
    parameter->get_TB = no_fights;
  } else if (is_losing_hp(punit)) {
    /* Losing hitpoints over time (helicopter in default rules) */
    /* Default tile behaviour */
  } else if (utype_may_act_at_all(unit_type_get(punit))) {
    switch (unit_data->task) {
    case AIUNIT_AUTO_SETTLER:
    case AIUNIT_BUILD_CITY:
      /* Strange, but not impossible */
      parameter->get_TB = no_fights;
      break;
    case AIUNIT_DEFEND_HOME:
    case AIUNIT_ATTACK: /* Includes spy actions */
    case AIUNIT_ESCORT:
    case AIUNIT_HUNTER:
    case AIUNIT_TRADE:
    case AIUNIT_WONDER:
      parameter->get_TB = no_intermediate_fights;
      break;
    case AIUNIT_EXPLORE:
    case AIUNIT_RECOVER:
      parameter->get_TB = no_fights;
      break;
    case AIUNIT_NONE:
      /* Default tile behaviour */
      break;
    }
  } else {
    /* Probably an explorer */
    parameter->get_TB = no_fights;
  }
 
  if (is_ferry) {
    /* Show the destination in the client when watching an AI: */
    punit->goto_tile = ptile;
  }
}
 
/**********************************************************************/
bool dai_unit_goto(struct ai_type *ait, struct unit *punit, struct tile *ptile)
{
  struct pf_parameter parameter;
  struct adv_risk_cost risk_cost;
 
  UNIT_LOG(LOG_DEBUG, punit, "dai_unit_goto to %d,%d", TILE_XY(ptile));
  dai_fill_unit_param(ait, &parameter, &risk_cost, punit, ptile);
 
  return dai_unit_goto_constrained(ait, punit, ptile, &parameter);
}
 
/**********************************************************************/
void dai_unit_new_adv_task(struct ai_type *ait, struct unit *punit,
                           enum adv_unit_task task, struct tile *ptile)
{
  /* Keep ai_unit_task in sync with adv task */
  switch (task) {
   case AUT_AUTO_SETTLER:
     dai_unit_new_task(ait, punit, AIUNIT_AUTO_SETTLER, ptile);
     break;
   case AUT_BUILD_CITY:
     dai_unit_new_task(ait, punit, AIUNIT_BUILD_CITY, ptile);
     break;
   case AUT_NONE:
     dai_unit_new_task(ait, punit, AIUNIT_NONE, ptile);
     break;
  }
}
 
/**********************************************************************/
void dai_unit_new_task(struct ai_type *ait, struct unit *punit,
                       enum ai_unit_task task, struct tile *ptile)
{
  struct unit *bodyguard = aiguard_guard_of(ait, punit);
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  /* If the unit is under (human) orders we shouldn't control it.
   * Allow removal of old role with AIUNIT_NONE. */
  fc_assert_ret(!unit_has_orders(punit) || task == AIUNIT_NONE);
 
  UNIT_LOG(LOG_DEBUG, punit, "changing task from %s to %s",
           dai_unit_task_rule_name(unit_data->task),
           dai_unit_task_rule_name(task));
 
  /* Free our ferry.  Most likely it has been done already. */
  if (task == AIUNIT_NONE || task == AIUNIT_DEFEND_HOME) {
    aiferry_clear_boat(ait, punit);
  }
 
  if (punit->activity == ACTIVITY_GOTO) {
    /* It would indicate we're going somewhere otherwise */
    unit_activity_handling(punit, ACTIVITY_IDLE);
  }
 
  if (unit_data->task == AIUNIT_BUILD_CITY) {
    if (punit->goto_tile) {
      citymap_free_city_spot(punit->goto_tile, punit->id);
    } else {
      /* Print error message instead of crashing in citymap_free_city_spot()
       * This probably means that some city spot reservation has not been
       * properly cleared; bad for the AI, as it will leave that area
       * uninhabited. */
      log_error("%s was on city founding mission without target tile.",
                unit_rule_name(punit));
    }
  }
 
  if (unit_data->task == AIUNIT_HUNTER) {
    /* Clear victim's hunted bit - we're no longer chasing. */
    struct unit *target = game_unit_by_number(unit_data->target);
 
    if (target) {
      BV_CLR(def_ai_unit_data(target, ait)->hunted,
             player_index(unit_owner(punit)));
      UNIT_LOG(LOGLEVEL_HUNT, target, "no longer hunted (new task %d, old %d)",
               task, unit_data->task);
    }
  }
 
  aiguard_clear_charge(ait, punit);
  /* Record the city to defend; our goto may be to transport. */
  if (task == AIUNIT_DEFEND_HOME && ptile && tile_city(ptile)) {
    aiguard_assign_guard_city(ait, tile_city(ptile), punit);
  }
 
  unit_data->task = task;
 
  /* Verify and set the goto destination.  Eventually this can be a lot more
   * stringent, but for now we don't want to break things too badly. */
  punit->goto_tile = ptile; /* May be NULL. */
 
  if (unit_data->task == AIUNIT_NONE && bodyguard) {
    dai_unit_new_task(ait, bodyguard, AIUNIT_NONE, NULL);
  }
 
  /* Reserve city spot, _unless_ we want to add ourselves to a city. */
  if (unit_data->task == AIUNIT_BUILD_CITY && !tile_city(ptile)) {
    citymap_reserve_city_spot(ptile, punit->id);
  }
  if (unit_data->task == AIUNIT_HUNTER) {
    /* Set victim's hunted bit - the hunt is on! */
    struct unit *target = game_unit_by_number(unit_data->target);
 
    fc_assert_ret(target != NULL);
    BV_SET(def_ai_unit_data(target, ait)->hunted, player_index(unit_owner(punit)));
    UNIT_LOG(LOGLEVEL_HUNT, target, "is being hunted");
 
    /* Grab missiles lying around and bring them along */
    unit_list_iterate(unit_tile(punit)->units, missile) {
      if (unit_owner(missile) == unit_owner(punit)
          && def_ai_unit_data(missile, ait)->task != AIUNIT_ESCORT
          && !unit_transported(missile)
          && unit_owner(missile) == unit_owner(punit)
          && utype_can_do_action(unit_type_get(missile),
                                 ACTION_SUICIDE_ATTACK)
          && can_unit_load(missile, punit)) {
        UNIT_LOG(LOGLEVEL_HUNT, missile, "loaded on hunter");
        dai_unit_new_task(ait, missile, AIUNIT_ESCORT, unit_tile(target));
        unit_transport_load_send(missile, punit);
      }
    } unit_list_iterate_end;
  }
 
  /* Map ai tasks to advisor tasks. For most ai tasks there is
     no advisor, so AUT_NONE is set. */
  switch (unit_data->task) {
   case AIUNIT_AUTO_SETTLER:
     punit->server.adv->task = AUT_AUTO_SETTLER;
     break;
   case AIUNIT_BUILD_CITY:
     punit->server.adv->task = AUT_BUILD_CITY;
     break;
   default:
     punit->server.adv->task = AUT_NONE;
     break;
  }
}
 
/**********************************************************************/
bool dai_unit_make_homecity(struct unit *punit, struct city *pcity)
{
  CHECK_UNIT(punit);
  fc_assert_ret_val(unit_owner(punit) == city_owner(pcity), TRUE);
 
  if (punit->homecity == 0 && !unit_has_type_role(punit, L_EXPLORER)) {
    /* This unit doesn't pay any upkeep while it doesn't have a homecity,
     * so it would be stupid to give it one. There can also be good reasons
     * why it doesn't have a homecity. */
    /* However, until we can do something more useful with them, we
       will assign explorers to a city so that they can be disbanded for 
       the greater good -- Per */
    return FALSE;
  }
  if (pcity->surplus[O_SHIELD] >= unit_type_get(punit)->upkeep[O_SHIELD]
      && pcity->surplus[O_FOOD] >= unit_type_get(punit)->upkeep[O_FOOD]) {
    unit_do_action(unit_owner(punit), punit->id, pcity->id,
                   0, "", ACTION_HOME_CITY);
    return TRUE;
  }
  return FALSE;
}
 
/**********************************************************************/
static void dai_unit_bodyguard_move(struct ai_type *ait,
                                    struct unit *bodyguard, struct tile *ptile)
{
  fc_assert_ret(bodyguard != NULL);
  fc_assert_ret(unit_owner(bodyguard) != NULL);
 
#ifndef FREECIV_NDEBUG
  struct unit *punit =
#endif
    aiguard_charge_unit(ait, bodyguard);
 
  fc_assert_ret(punit != NULL);
 
  CHECK_GUARD(ait, bodyguard);
  CHECK_CHARGE_UNIT(ait, punit);
 
  if (!is_tiles_adjacent(ptile, unit_tile(bodyguard))) {
    return;
  }
 
  if (bodyguard->moves_left <= 0) {
    /* should generally should not happen */
    BODYGUARD_LOG(ait, LOG_DEBUG, bodyguard, "was left behind by charge");
    return;
  }
 
  unit_activity_handling(bodyguard, ACTIVITY_IDLE);
  (void) dai_unit_move(ait, bodyguard, ptile);
}
 
/**********************************************************************/
bool dai_unit_attack(struct ai_type *ait, struct unit *punit, struct tile *ptile)
{
  struct unit *ptrans;
  struct unit *bodyguard = aiguard_guard_of(ait, punit);
  int sanity = punit->id;
  bool alive;
  struct city *tcity;
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
  fc_assert_ret_val(is_ai(unit_owner(punit)), TRUE);
  fc_assert_ret_val(is_tiles_adjacent(unit_tile(punit), ptile), TRUE);
 
  unit_activity_handling(punit, ACTIVITY_IDLE);
  /* FIXME: try the next action if the unit tried to do an illegal action.
   * That would allow the AI to stop using the omniscient
   * is_action_enabled_unit_on_*() functions. */
  if (is_action_enabled_unit_on_units(nmap, ACTION_CAPTURE_UNITS,
                                      punit, ptile)) {
    /* Choose capture. */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_CAPTURE_UNITS);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_BOMBARD,
                                             punit, ptile)) {
    /* Choose "Bombard". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_BOMBARD);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_BOMBARD2,
                                             punit, ptile)) {
    /* Choose "Bombard 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_BOMBARD2);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_BOMBARD3,
                                             punit, ptile)) {
    /* Choose "Bombard 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_BOMBARD3);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_NUKE_UNITS,
                                             punit, ptile)) {
    /* Choose "Nuke Units". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_NUKE_UNITS);
  } else if (action_id_get_target_kind(ACTION_NUKE) == ATK_TILE
             && is_action_enabled_unit_on_tile(nmap, ACTION_NUKE,
                                               punit, ptile, NULL)) {
    /* Choose "Explode Nuclear". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_NUKE);
  } else if (action_id_get_target_kind(ACTION_NUKE) == ATK_CITY
             && (tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_NUKE,
                                               punit, tcity)) {
    /* Choose "Explode Nuclear". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_NUKE);
  } else if (action_id_get_target_kind(ACTION_NUKE_CITY) == ATK_TILE
             && is_action_enabled_unit_on_tile(nmap, ACTION_NUKE_CITY,
                                               punit, ptile, NULL)) {
    /* Choose "Nuke City". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_NUKE_CITY);
  } else if (action_id_get_target_kind(ACTION_NUKE_CITY) == ATK_CITY
             && (tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_NUKE_CITY,
                                               punit, tcity)) {
    /* Choose "Nuke City". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_NUKE_CITY);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_ATTACK,
                                             punit, ptile)) {
    /* Choose regular attack. */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_ATTACK);
  } else if (is_action_enabled_unit_on_units(nmap, ACTION_SUICIDE_ATTACK,
                                             punit, ptile)) {
    /* Choose suicide attack (explode missile). */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_SUICIDE_ATTACK);
  } else if ((tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_CONQUER_CITY,
                                               punit, tcity)) {
    /* Choose "Conquer City". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_CONQUER_CITY);
  } else if ((tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_CONQUER_CITY2,
                                               punit, tcity)) {
    /* Choose "Conquer City 2". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_CONQUER_CITY2);
  } else if ((tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_CONQUER_CITY3,
                                               punit, tcity)) {
    /* Choose "Conquer City 3". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_CONQUER_CITY3);
  } else if ((tcity = tile_city(ptile))
             && is_action_enabled_unit_on_city(nmap, ACTION_CONQUER_CITY4,
                                               punit, tcity)) {
    /* Choose "Conquer City 4". */
    unit_do_action(unit_owner(punit), punit->id, tcity->id,
                   0, "", ACTION_CONQUER_CITY4);
  } else if (!can_unit_survive_at_tile(nmap, punit, ptile)
             && ((ptrans = transporter_for_unit_at(punit, ptile)))
             && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK,
                                               punit, ptrans)) {
    /* "Transport Embark". */
    unit_do_action(unit_owner(punit), punit->id, ptrans->id,
                   0, "", ACTION_TRANSPORT_EMBARK);
  } else if (!can_unit_survive_at_tile(nmap, punit, ptile)
             && ((ptrans = transporter_for_unit_at(punit, ptile)))
             && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK2,
                                               punit, ptrans)) {
    /* "Transport Embark 2". */
    unit_do_action(unit_owner(punit), punit->id, ptrans->id,
                   0, "", ACTION_TRANSPORT_EMBARK2);
  } else if (!can_unit_survive_at_tile(nmap, punit, ptile)
             && ((ptrans = transporter_for_unit_at(punit, ptile)))
             && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK3,
                                               punit, ptrans)) {
    /* "Transport Embark 3". */
    unit_do_action(unit_owner(punit), punit->id, ptrans->id,
                   0, "", ACTION_TRANSPORT_EMBARK3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK1,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_TRANSPORT_DISEMBARK1);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK2,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_TRANSPORT_DISEMBARK2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK3,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_TRANSPORT_DISEMBARK3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK4,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 4". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_TRANSPORT_DISEMBARK4);
  } else if (tile_has_claimable_base(ptile, unit_type_get(punit))
             && is_action_enabled_unit_on_extras(nmap, ACTION_CONQUER_EXTRAS,
                                                 punit, ptile, NULL)) {
    /* Choose "Conquer Extras". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_CONQUER_EXTRAS);
  } else if (tile_has_claimable_base(ptile, unit_type_get(punit))
             && is_action_enabled_unit_on_extras(nmap, ACTION_CONQUER_EXTRAS2,
                                                 punit, ptile, NULL)) {
    /* Choose "Conquer Extras 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_CONQUER_EXTRAS2);
  } else if (tile_has_claimable_base(ptile, unit_type_get(punit))
             && is_action_enabled_unit_on_extras(nmap, ACTION_CONQUER_EXTRAS3,
                                                 punit, ptile, NULL)) {
    /* Choose "Conquer Extras 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_CONQUER_EXTRAS3);
  } else if (tile_has_claimable_base(ptile, unit_type_get(punit))
             && is_action_enabled_unit_on_extras(nmap, ACTION_CONQUER_EXTRAS4,
                                                 punit, ptile, NULL)) {
    /* Choose "Conquer Extras 4". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_CONQUER_EXTRAS4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER,
                                            punit, ptile, NULL)) {
    /* Choose "Enter Hut". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_ENTER);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER2,
                                            punit, ptile, NULL)) {
    /* Choose "Enter Hut 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_ENTER2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER3,
                                            punit, ptile, NULL)) {
    /* Choose "Enter Hut 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_ENTER3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER4,
                                            punit, ptile, NULL)) {
    /* Choose "Enter Hut 4". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_ENTER4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN,
                                            punit, ptile, NULL)) {
    /* Choose "Frighten Hut". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_FRIGHTEN);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN2,
                                            punit, ptile, NULL)) {
    /* Choose "Frighten Hut 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_FRIGHTEN2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN3,
                                            punit, ptile, NULL)) {
    /* Choose "Frighten Hut 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_FRIGHTEN3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN4,
                                            punit, ptile, NULL)) {
    /* Choose "Frighten Hut 4". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_HUT_FRIGHTEN4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_UNIT_MOVE,
                                            punit, ptile, NULL)) {
    /* Choose "Unit Move". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_UNIT_MOVE);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_UNIT_MOVE2,
                                            punit, ptile, NULL)) {
    /* Choose "Unit Move 2". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_UNIT_MOVE2);
  } else {
    /* Choose "Unit Move 3". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", ACTION_UNIT_MOVE3);
  }
  alive = (game_unit_by_number(sanity) != NULL);
 
  if (alive && same_pos(ptile, unit_tile(punit))
      && bodyguard != NULL  && def_ai_unit_data(bodyguard, ait)->charge == punit->id) {
    dai_unit_bodyguard_move(ait, bodyguard, ptile);
    /* Clumsy bodyguard might trigger an auto-attack */
    alive = (game_unit_by_number(sanity) != NULL);
  }
 
  return alive;
}
 
/**********************************************************************/
void dai_unit_move_or_attack(struct ai_type *ait, struct unit *punit,
                             struct tile *ptile, struct pf_path *path, int step)
{
  if (step == path->length - 1) {
    (void) dai_unit_attack(ait, punit, ptile);
  } else {
    (void) dai_unit_move(ait, punit, ptile);
  }
}
 
/**********************************************************************/
bool dai_unit_move(struct ai_type *ait, struct unit *punit, struct tile *ptile)
{
  struct action *paction;
  struct unit *bodyguard;
  struct unit *ptrans = NULL;
  int sanity = punit->id;
  struct player *pplayer = unit_owner(punit);
  const bool is_plr_ai = is_ai(pplayer);
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
  fc_assert_ret_val_msg(is_tiles_adjacent(unit_tile(punit), ptile), FALSE,
                        "Tiles not adjacent: Unit = %d, "
                        "from = (%d, %d]) to = (%d, %d).",
                        punit->id, TILE_XY(unit_tile(punit)),
                        TILE_XY(ptile));
 
  /* if enemy, stop and give a chance for the ai attack function
   * to handle this case */
  if (is_enemy_unit_tile(ptile, pplayer)
      || is_enemy_city_tile(ptile, pplayer)) {
    UNIT_LOG(LOG_DEBUG, punit, "movement halted due to enemy presence");
    return FALSE;
  }
 
  /* barbarians shouldn't enter huts */
  /* FIXME: use unit_can_displace_hut(punit, ptile) better */
  if (is_barbarian(pplayer) && hut_on_tile(ptile)) {
    return FALSE;
  }
 
  /* don't leave bodyguard behind */
  if (is_plr_ai
      && (bodyguard = aiguard_guard_of(ait, punit))
      && same_pos(unit_tile(punit), unit_tile(bodyguard))
      && bodyguard->moves_left == 0) {
    UNIT_LOG(LOGLEVEL_BODYGUARD, punit, "does not want to leave "
             "its bodyguard");
    return FALSE;
  }
 
  /* Select move kind. */
  if (!can_unit_survive_at_tile(nmap, punit, ptile)
      && ((ptrans = transporter_for_unit_at(punit, ptile)))
      && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK,
                                        punit, ptrans)) {
    /* "Transport Embark". */
    paction = action_by_number(ACTION_TRANSPORT_EMBARK);
  } else if (!can_unit_survive_at_tile(nmap, punit, ptile)
             && ptrans != NULL
             && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK2,
                                               punit, ptrans)) {
    /* "Transport Embark 2". */
    paction = action_by_number(ACTION_TRANSPORT_EMBARK2);
  } else if (!can_unit_survive_at_tile(nmap, punit, ptile)
             && ptrans != NULL
             && is_action_enabled_unit_on_unit(nmap, ACTION_TRANSPORT_EMBARK3,
                                               punit, ptrans)) {
    /* "Transport Embark 3". */
    paction = action_by_number(ACTION_TRANSPORT_EMBARK3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK1,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark". */
    paction = action_by_number(ACTION_TRANSPORT_DISEMBARK1);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK2,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 2". */
    paction = action_by_number(ACTION_TRANSPORT_DISEMBARK2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK3,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 3". */
    paction = action_by_number(ACTION_TRANSPORT_DISEMBARK3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_TRANSPORT_DISEMBARK4,
                                            punit, ptile, NULL)) {
    /* "Transport Disembark 4". */
    paction = action_by_number(ACTION_TRANSPORT_DISEMBARK4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER,
                                            punit, ptile, NULL)) {
    /* "Enter Hut". */
    paction = action_by_number(ACTION_HUT_ENTER);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER2,
                                            punit, ptile, NULL)) {
    /* "Enter Hut 2". */
    paction = action_by_number(ACTION_HUT_ENTER2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER3,
                                            punit, ptile, NULL)) {
    /* "Enter Hut 3". */
    paction = action_by_number(ACTION_HUT_ENTER3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_ENTER4,
                                            punit, ptile, NULL)) {
    /* "Enter Hut 4". */
    paction = action_by_number(ACTION_HUT_ENTER4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN,
                                            punit, ptile, NULL)) {
    /* "Frighten Hut". */
    paction = action_by_number(ACTION_HUT_FRIGHTEN);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN2,
                                            punit, ptile, NULL)) {
    /* "Frighten Hut 2". */
    paction = action_by_number(ACTION_HUT_FRIGHTEN2);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN3,
                                            punit, ptile, NULL)) {
    /* "Frighten Hut 3". */
    paction = action_by_number(ACTION_HUT_FRIGHTEN3);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_HUT_FRIGHTEN4,
                                            punit, ptile, NULL)) {
    /* "Frighten Hut 4". */
    paction = action_by_number(ACTION_HUT_FRIGHTEN4);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_UNIT_MOVE,
                                            punit, ptile, NULL)) {
    /* "Unit Move". */
    paction = action_by_number(ACTION_UNIT_MOVE);
  } else if (is_action_enabled_unit_on_tile(nmap, ACTION_UNIT_MOVE2,
                                            punit, ptile, NULL)) {
    /* "Unit Move 2". */
    paction = action_by_number(ACTION_UNIT_MOVE2);
  } else {
    /* "Unit Move 3". */
    paction = action_by_number(ACTION_UNIT_MOVE3);
  }
 
  /* Try not to end move next to an enemy if we can avoid it by waiting */
  if (action_has_result(paction, ACTRES_UNIT_MOVE)
      || action_has_result(paction, ACTRES_TRANSPORT_DISEMBARK)) {
    /* The unit will have to move it self rather than being moved. */
    int mcost = map_move_cost_unit(nmap, punit, ptile);
 
    if (paction) {
      struct tile *from_tile;
 
      /* Ugly hack to understand the OnNativeTile unit state requirements
       * used in the Action_Success_Actor_Move_Cost effect. */
      fc_assert(utype_is_moved_to_tgt_by_action(paction,
                                                unit_type_get(punit)));
      from_tile = unit_tile(punit);
      punit->tile = ptile;
 
      mcost += unit_pays_mp_for_action(paction, punit);
 
      punit->tile = from_tile;
    }
 
    if (punit->moves_left <= mcost
        && unit_move_rate(punit) > mcost
        && adv_danger_at(punit, ptile)
        && !adv_danger_at(punit, unit_tile(punit))) {
      UNIT_LOG(LOG_DEBUG, punit,
               "ending move early to stay out of trouble");
      return FALSE;
    }
  }
 
  /* go */
  unit_activity_handling(punit, ACTIVITY_IDLE);
  /* Move */
  if (paction && ptrans
      && action_has_result(paction, ACTRES_TRANSPORT_EMBARK)) {
      /* "Transport Embark". */
      unit_do_action(unit_owner(punit), punit->id, ptrans->id,
                     0, "", action_number(paction));
    } else if (paction
               && (action_has_result(paction,
                                     ACTRES_TRANSPORT_DISEMBARK)
                   || action_has_result(paction, ACTRES_UNIT_MOVE)
                   || action_has_result(paction,
                                        ACTRES_HUT_ENTER)
                   || action_has_result(paction,
                                        ACTRES_HUT_FRIGHTEN))) {
    /* "Transport Disembark", "Transport Disembark 2", "Enter Hut",
     * "Frighten Hut" or "Unit Move". */
    unit_do_action(unit_owner(punit), punit->id, tile_index(ptile),
                   0, "", action_number(paction));
  }
 
  /* handle the results */
  if (game_unit_by_number(sanity) && same_pos(ptile, unit_tile(punit))) {
    bodyguard = aiguard_guard_of(ait, punit);
 
    if (is_plr_ai && bodyguard != NULL
        && def_ai_unit_data(bodyguard, ait)->charge == punit->id) {
      dai_unit_bodyguard_move(ait, bodyguard, ptile);
    }
    return TRUE;
  }
  return FALSE;
}
 
/**********************************************************************/
int stack_cost(struct unit *pattacker, struct unit *pdefender)
{
  struct tile *ptile = unit_tile(pdefender);
  int victim_cost = 0;
 
  if (is_stack_vulnerable(ptile)) {
    /* lotsa people die */
    unit_list_iterate(ptile->units, aunit) {
      if (unit_attack_unit_at_tile_result(pattacker, NULL, aunit, ptile)
          == ATT_OK) {
        victim_cost += unit_build_shield_cost_base(aunit);
      }
    } unit_list_iterate_end;
  } else if (unit_attack_unit_at_tile_result(pattacker, NULL,
                                             pdefender, ptile)
             == ATT_OK) {
    /* Only one unit dies if attack is successful */
    victim_cost = unit_build_shield_cost_base(pdefender);
  }
 
  return victim_cost;
}
 
/**********************************************************************/
void dai_government_change(struct player *pplayer, struct government *gov)
{
  if (gov == government_of_player(pplayer)) {
    return;
  }
 
  handle_player_change_government(pplayer, government_number(gov));
 
  city_list_iterate(pplayer->cities, pcity) {
    auto_arrange_workers(pcity); /* update cities */
  } city_list_iterate_end;
}
 
/**********************************************************************/
int dai_gold_reserve(struct player *pplayer)
{
  int i = total_player_citizens(pplayer) * 2;
 
  return MAX(pplayer->ai_common.maxbuycost, i);
}
 
/**********************************************************************/
void adjust_choice(int pct, struct adv_choice *choice)
{
  choice->want = (choice->want * pct) / 100;
}
 
/**********************************************************************/
bool dai_choose_role_unit(struct ai_type *ait, struct player *pplayer,
                          struct city *pcity, struct adv_choice *choice,
                          enum choice_type type, int role, int want,
                          bool need_boat)
{
  struct unit_type *iunit = dai_wants_role_unit(ait, pplayer, pcity, role, want);
 
  if (iunit != NULL) {
    choice->type = type;
    choice->value.utype = iunit;
    choice->want = want;
 
    choice->need_boat = need_boat;
 
    return TRUE;
  }
 
  return FALSE;
}
 
/**********************************************************************/
void dai_build_adv_override(struct ai_type *ait, struct city *pcity,
                            struct adv_choice *choice)
{
  const struct impr_type *chosen;
  adv_want want;
 
  if (choice->type == CT_NONE) {
    want = 0;
    chosen = NULL;
  } else {
    want = choice->want;
    chosen = choice->value.building;
  }
 
  improvement_iterate(pimprove) {
    /* Advisor code did not consider wonders, let's do it here */
    if (is_wonder(pimprove)) {
      int id = improvement_index(pimprove);
 
      if (pcity->server.adv->building_want[id] > want
          && can_city_build_improvement_now(pcity, pimprove)) {
        want = pcity->server.adv->building_want[id];
        chosen = pimprove;
      }
    }
  } improvement_iterate_end;
 
  choice->want = want;
  choice->value.building = chosen;
 
  if (chosen) {
    choice->type = CT_BUILDING; /* In case advisor had not chosen anything */
 
    CITY_LOG(LOG_DEBUG, pcity, "AI wants to build %s with want "
             ADV_WANT_PRINTF,
             improvement_rule_name(chosen), want);
  }
}
 
/**********************************************************************/
bool dai_assess_military_unhappiness(const struct civ_map *nmap,
                                     struct city *pcity)
{
  int free_unhappy = get_city_bonus(pcity, EFT_MAKE_CONTENT_MIL);
  int unhap = 0;
 
  /* bail out now if happy_cost is 0 */
  if (get_player_bonus(city_owner(pcity), EFT_UNHAPPY_FACTOR) == 0) {
    return FALSE;
  }
 
  unit_list_iterate(pcity->units_supported, punit) {
    int happy_cost = city_unit_unhappiness(nmap, punit, &free_unhappy);
 
    if (happy_cost > 0) {
      unhap += happy_cost;
    }
  } unit_list_iterate_end;
 
  if (unhap < 0) {
    unhap = 0;
  }
  return (unhap > 0);
}