daimilitary.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 <string.h>
 
/* utility */
#include "log.h"
 
/* common */
#include "combat.h"
#include "game.h"
#include "government.h"
#include "map.h"
#include "movement.h"
#include "research.h"
#include "specialist.h"
#include "unitlist.h"
 
/* common/aicore */
#include "pf_tools.h"
 
/* server */
#include "citytools.h"
#include "cityturn.h"
#include "srv_log.h"
#include "srv_main.h"
 
/* server/advisors */
#include "advbuilding.h"
#include "advchoice.h"
#include "advdata.h"
#include "advgoto.h"
#include "advtools.h"
#include "autosettlers.h"
#include "infracache.h" /* adv_city */
 
/* ai */
#include "aitraits.h"
#include "difficulty.h"
#include "handicaps.h"
 
/* ai/default */
#include "aiair.h"
#include "aidata.h"
#include "aidiplomat.h"
#include "aiferry.h"
#include "aihand.h"
#include "aihunt.h"
#include "ailog.h"
#include "aiparatrooper.h"
#include "aiplayer.h"
#include "aitech.h"
#include "aitools.h"
#include "aiunit.h"
#include "daicity.h"
#include "daieffects.h"
 
#include "daimilitary.h"
 
/* Size 1 city gets destroyed when conquered. It's still a good thing
 * stop enemy from having it. */
#define CITY_CONQUEST_WORTH(_city_, _data_) \
  (_data_->worth * 0.9 + (city_size_get(_city_) - 0.5) * 10)
 
static unsigned int assess_danger(struct ai_type *ait, struct city *pcity,
                                  const struct civ_map *dmap,
                                  player_unit_list_getter ul_cb);
 
static adv_want dai_unit_attack_desirability(struct ai_type *ait,
                                             const struct unit_type *punittype);
static adv_want dai_unit_defense_desirability(struct ai_type *ait,
                                              const struct unit_type *punittype);
 
/**********************************************************************/
struct unit_type *dai_choose_defender_versus(struct city *pcity,
                                             struct unit *attacker)
{
  struct unit_type *bestunit = NULL;
  double best = 0;
  int best_cost = FC_INFINITY;
  struct player *pplayer = city_owner(pcity);
  struct civ_map *nmap = &(wld.map);
 
  simple_ai_unit_type_iterate(punittype) {
    if (can_city_build_unit_now(pcity, punittype)) {
      int fpatt, fpdef, defense, attack;
      double want, loss, cost = utype_build_shield_cost(pcity, NULL, punittype);
      struct unit *defender;
      int veteran = get_unittype_bonus(city_owner(pcity), pcity->tile,
                                       punittype, NULL,
                                       EFT_VETERAN_BUILD);
 
      defender = unit_virtual_create(pplayer, pcity, punittype, veteran);
      defense = get_total_defense_power(attacker, defender);
      attack = get_total_attack_power(attacker, defender);
      get_modified_firepower(nmap, attacker, defender, &fpatt, &fpdef);
 
      /* Greg's algorithm. loss is the average number of health lost by
       * defender. If loss > attacker's hp then we should win the fight,
       * which is always a good thing, since we avoid shield loss. */
      loss = (double) defense * punittype->hp * fpdef / (attack * fpatt);
      want = (loss + MAX(0, loss - attacker->hp)) / cost;
 
#ifdef NEVER
      CITY_LOG(LOG_DEBUG, pcity, "desire for %s against %s(%d,%d) is %.2f",
               unit_name_orig(punittype),
               unit_name_orig(unit_type_get(attacker)), 
               TILE_XY(attacker->tile), want);
#endif /* NEVER */
 
      if (want > best || (ADV_WANTS_EQ(want, best)
                          && cost <= best_cost)) {
        best = want;
        bestunit = punittype;
        best_cost = cost;
      }
      unit_virtual_destroy(defender);
    }
  } simple_ai_unit_type_iterate_end;
 
  return bestunit;
}
 
/**********************************************************************/
static struct unit_type *dai_choose_attacker(struct ai_type *ait,
                                             struct city *pcity,
                                             enum terrain_class tc,
                                             bool allow_gold_upkeep)
{
  struct unit_type *bestid = NULL;
  adv_want best = -1;
  adv_want cur;
  struct player *pplayer = city_owner(pcity);
 
  simple_ai_unit_type_iterate(putype) {
    if (!allow_gold_upkeep && utype_upkeep_cost(putype, pplayer, O_GOLD) > 0) {
      continue;
    }
 
    cur = dai_unit_attack_desirability(ait, putype);
    if ((tc == TC_LAND && utype_class(putype)->adv.land_move != MOVE_NONE)
        || (tc == TC_OCEAN
            && utype_class(putype)->adv.sea_move != MOVE_NONE)) {
      if (can_city_build_unit_now(pcity, putype)
          && (cur > best
              || (ADV_WANTS_EQ(cur, best)
                  && utype_build_shield_cost(pcity, NULL, putype)
                    <= utype_build_shield_cost(pcity, NULL, bestid)))) {
        best = cur;
        bestid = putype;
      }
    }
  } simple_ai_unit_type_iterate_end;
 
  return bestid;
}
 
/**********************************************************************/
static struct unit_type *dai_choose_bodyguard(struct ai_type *ait,
                                              struct city *pcity,
                                              enum terrain_class tc,
                                              enum unit_role_id role,
                                              bool allow_gold_upkeep)
{
  struct unit_type *bestid = NULL;
  adv_want best = 0;
  struct player *pplayer = city_owner(pcity);
 
  simple_ai_unit_type_iterate(putype) {
    /* Only consider units of given role, or any if invalid given */
    if (unit_role_id_is_valid(role)) {
      if (!utype_has_role(putype, role)) {
        continue;
      }
    }
 
    if (!allow_gold_upkeep && utype_upkeep_cost(putype, pplayer, O_GOLD) > 0) {
      continue;
    }
 
    /* Only consider units of same move type */
    if ((tc == TC_LAND && utype_class(putype)->adv.land_move == MOVE_NONE)
        || (tc == TC_OCEAN
            && utype_class(putype)->adv.sea_move == MOVE_NONE)) {
      continue;
    }
 
    /* Now find best */
    if (can_city_build_unit_now(pcity, putype)) {
      const adv_want desire = dai_unit_defense_desirability(ait, putype);
 
      if (desire > best
          || (ADV_WANTS_EQ(desire, best) && utype_build_shield_cost(pcity, NULL, putype) <=
              utype_build_shield_cost(pcity, NULL, bestid))) {
        best = desire;
        bestid = putype;
      }
    }
  } simple_ai_unit_type_iterate_end;
 
  return bestid;
}
 
/**********************************************************************/
static int base_assess_defense_unit(struct city *pcity, struct unit *punit,
                                    bool igwall, bool quadratic,
                                    int wall_value)
{
  int defense;
  int fp;
 
  if (!is_military_unit(punit)) {
    return 0;
  }
 
  defense = get_fortified_defense_power(NULL, punit) * punit->hp;
  fp = unit_type_get(punit)->firepower;
  if (unit_has_type_flag(punit, UTYF_BADCITYDEFENDER)) {
    /* Attacker firepower doubled, defender firepower set to
     * game.info.low_firepower_pearl_harbour at max. */
    defense *= MIN(fp, game.info.low_firepower_pearl_harbour);
    defense /= 2;
  } else {
    defense *= fp;
  }
 
  defense /= POWER_DIVIDER;
 
  if (quadratic) {
    defense *= defense;
  }
 
  if (pcity != NULL && !igwall && city_got_defense_effect(pcity, NULL)) {
    /* FIXME: We checked if city got defense effect against *some*
     * unit type. Sea unit danger might cause us to build defenses
     * against air units... */
 
    /* TODO: What about wall_value < 10? Do we really want walls to
     *       result in decrease in the returned value? */
    defense *= wall_value;
    defense /= 10;
  }
 
  return defense;
}
 
/**********************************************************************/
int assess_defense_quadratic(struct ai_type *ait, struct city *pcity)
{
  int defense = 0, walls = 0;
  /* This can be an arg if needed, but we don't need to change it now. */
  const bool igwall = FALSE;
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
  /* wallvalue = 10, walls = 10,
   * wallvalue = 40, walls = 20,
   * wallvalue = 90, walls = 30 */
 
  while (walls * walls < city_data->wallvalue * 10) {
    walls++;
  }
 
  unit_list_iterate(pcity->tile->units, punit) {
    defense += base_assess_defense_unit(pcity, punit, igwall, FALSE,
                                        walls);
  } unit_list_iterate_end;
 
  if (defense > 1<<12) {
    CITY_LOG(LOG_VERBOSE, pcity, "Overflow danger in assess_defense_quadratic:"
             " %d", defense);
    if (defense > 1<<15) {
      defense = 1<<15; /* more defense than we know what to do with! */
    }
  }
 
  return defense * defense;
}
 
/**********************************************************************/
int assess_defense_unit(struct ai_type *ait, struct city *pcity,
                        struct unit *punit, bool igwall)
{
  return base_assess_defense_unit(pcity, punit, igwall, TRUE,
                                  def_ai_city_data(pcity, ait)->wallvalue);
}
 
/**********************************************************************/
static int assess_defense_backend(struct ai_type *ait, struct city *pcity,
                                  bool igwall)
{
  /* Estimate of our total city defensive might */
  int defense = 0;
 
  unit_list_iterate(pcity->tile->units, punit) {
    defense += assess_defense_unit(ait, pcity, punit, igwall);
  } unit_list_iterate_end;
 
  return defense;
}
 
/**********************************************************************/
int assess_defense(struct ai_type *ait, struct city *pcity)
{
  return assess_defense_backend(ait, pcity, FALSE);
}
 
/**********************************************************************/
static int assess_defense_igwall(struct ai_type *ait, struct city *pcity)
{
  return assess_defense_backend(ait, pcity, TRUE);
}
 
/**********************************************************************/
static enum fc_tristate
tactical_req_cb(const struct req_context *context,
                const struct player *other_player,
                const struct requirement *req,
                void *data, int n_data)
{
  switch (req->source.kind) {
  case VUT_IMPROVEMENT:
    {
      const struct impr_type *b = req->source.value.building;
 
      /* FIXME: in actor_reqs, may allow attack _from_ a city with... */
      if (req->survives || NULL == context->city || is_great_wonder(b)
          || !city_has_building(context->city, b) || b->sabotage <= 0) {
        return tri_req_active(context, other_player, req);
      }
      /* Else may be sabotaged */
    }
    fc__fallthrough;
  case VUT_UNITSTATE:
  case VUT_ACTIVITY:
  case VUT_MINSIZE:
  case VUT_MAXTILEUNITS:
  case VUT_MINHP:
  case VUT_MINMOVES:
    /* Can be changed back or forth quickly */
    return TRI_MAYBE;
  case VUT_MINVETERAN:
    /* Can be changed forth but not back */
    return is_req_preventing(context, other_player, req, RPT_POSSIBLE)
           > REQUCH_CTRL ? TRI_NO : TRI_MAYBE;
  case VUT_MINFOREIGNPCT:
  case VUT_NATIONALITY:
    /* Can be changed back but hardly forth (foreign citizens reduced first) */
    switch (tri_req_active(context, other_player, req)) {
    case TRI_NO:
      return req->present ? TRI_NO : TRI_MAYBE;
    case TRI_YES:
      return req->present ? TRI_MAYBE : TRI_YES;
    default:
      return TRI_MAYBE;
    }
  case VUT_DIPLREL:
  case VUT_DIPLREL_TILE:
  case VUT_DIPLREL_TILE_O:
  case VUT_DIPLREL_UNITANY:
  case VUT_DIPLREL_UNITANY_O:
    /* If the attack happens, there is a diplrel that allows it */
    return TRI_YES;
  case VUT_AGE:
  case VUT_MINCALFRAG:
  case VUT_MINYEAR:
    /* If it is not near, won't change */
    return tri_req_active_turns(n_data, 5 /* WAG */,
                                context, other_player, req);
  case VUT_UTYPE:
  case VUT_UTFLAG:
  case VUT_UCLASS:
  case VUT_UCFLAG:
    /* FIXME: support converting siege machines (needs hard reqs checked) */
  case VUT_CITYSTATUS:
  case VUT_ACTION:
  case VUT_OTYPE:
  case VUT_SPECIALIST:
  case VUT_EXTRAFLAG:
  case VUT_AI_LEVEL:
  case VUT_CITYTILE:
  case VUT_STYLE:
  case VUT_TOPO:
  case VUT_SERVERSETTING:
  case VUT_NATION:
  case VUT_NATIONGROUP:
  case VUT_ADVANCE:
  case VUT_TECHFLAG:
  case VUT_GOVERNMENT:
  case VUT_ACHIEVEMENT:
  case VUT_IMPR_GENUS:
  case VUT_MINCULTURE:
  case VUT_MINTECHS:
  case VUT_ROADFLAG:
  case VUT_TERRAIN:
  case VUT_EXTRA:
  case VUT_GOOD:
  case VUT_TERRAINCLASS:
  case VUT_TERRFLAG:
  case VUT_TERRAINALTER:
  case VUT_NONE:
    return tri_req_active(context, other_player, req);
  case VUT_COUNT:
    /* Not implemented. */
    break;
  }
  fc_assert(FALSE);
 
  return TRI_NO;
}
 
/**********************************************************************/
static bool
action_may_happen_unit_on_city(const action_id wanted_action,
                               const struct unit *actor,
                               const struct city *pcity,
                               int turns)
{
  const struct player *target_player = city_owner(pcity),
      *actor_player = unit_owner(actor);
  const struct unit_type *utype = unit_type_get(actor);
  const struct req_context target_ctx = {
      .player = target_player,
      .city = pcity,
      .tile = city_tile(pcity)
  }, actor_ctx = {
      .player = actor_player,
      .unit = actor,
      .unittype = utype
  };
 
  if (!utype_can_do_action(utype, wanted_action)) {
    return FALSE;
  }
  action_enabler_list_iterate(action_enablers_for_action(wanted_action),
                              enabler) {
    /* We assume that we could build or move units into the city
     * that are not present there yet */
    if (TRI_NO != tri_reqs_cb_active(&actor_ctx, target_player,
                                     &enabler->actor_reqs, NULL,
                                     tactical_req_cb, NULL, turns)
        &&
        TRI_NO != tri_reqs_cb_active(&target_ctx, actor_player,
                                     &enabler->target_reqs, NULL,
                                     tactical_req_cb, NULL, turns)) {
      return TRUE;
    }
  } action_enabler_list_iterate_end;
 
  return FALSE;
}
 
/**********************************************************************/
static unsigned int assess_danger_unit(const struct city *pcity,
                                       struct pf_reverse_map *pcity_map,
                                       const struct unit *punit,
                                       int *move_time)
{
  struct pf_position pos;
  const struct unit_type *punittype = unit_type_get(punit);
  const struct tile *ptile = city_tile(pcity);
  const struct player *uowner = unit_owner(punit);
  const struct unit *ferry;
  unsigned int danger;
  int amod = -99, dmod;
  struct civ_map *nmap = &(wld.map);
  bool attack_danger = FALSE;
 
  *move_time = PF_IMPOSSIBLE_MC;
 
  if ((utype_can_do_action_result(punittype, ACTRES_PARADROP)
       || utype_can_do_action_result(punittype, ACTRES_PARADROP_CONQUER))
      && 0 < punittype->paratroopers_range) {
    *move_time = (real_map_distance(ptile, unit_tile(punit))
                  / punittype->paratroopers_range);
  }
 
  if (pf_reverse_map_unit_position(pcity_map, punit, &pos)
      && (PF_IMPOSSIBLE_MC == *move_time
          || *move_time > pos.turn)) {
    *move_time = pos.turn;
  }
 
  if (unit_transported(punit)
      && (ferry = unit_transport_get(punit))
      && pf_reverse_map_unit_position(pcity_map, ferry, &pos)) {
    if ((PF_IMPOSSIBLE_MC == *move_time
         || *move_time > pos.turn)) {
      *move_time = pos.turn;
      if (!can_attack_from_non_native(punittype)) {
        (*move_time)++;
      }
    }
  }
 
  if (PF_IMPOSSIBLE_MC == *move_time) {
    return 0;
  }
  if (!is_native_tile(punittype, ptile)
      && !can_attack_non_native(punittype)) {
    return 0;
  }
  if (!is_native_near_tile(nmap, unit_class_get(punit), ptile)) {
    return 0;
  }
 
  /* Find the worst attack action to expect */
  action_by_result_iterate(paction, ACTRES_ATTACK) {
    /* Is it possible that punit will do action id to the city? */
 
    if (action_may_happen_unit_on_city(paction->id, punit, pcity, *move_time)) {
      int b;
 
      attack_danger = TRUE;
 
      b = get_unittype_bonus(uowner, ptile, punittype, paction, EFT_ATTACK_BONUS);
      if (b > amod) {
        amod = b;
      }
    }
  } action_by_result_iterate_end;
 
  /* FIXME: it's a dummy support for anti-bombard defense just to do something against
   * approaching bombarders. Some better logic is needed, see OSDN#41778 */
  if (!attack_danger) {
    action_by_result_iterate(paction, ACTRES_BOMBARD) {
      if (action_may_happen_unit_on_city(paction->id, punit, pcity, *move_time)) {
        int b;
 
        attack_danger = TRUE;
 
        b = get_unittype_bonus(uowner, ptile, punittype, paction, EFT_ATTACK_BONUS);
        if (b > amod) {
          amod = b;
        }
      }
    } action_by_result_iterate_end;
    /* Here something should be done cuz the modifier affects
     * more than one unit but not their full hp, but is not done yet...*/
  }
  if (!attack_danger) {
    /* If the unit is dangerous, it's not about its combat strength */
    return 0;
  }
 
  danger = adv_unit_att_rating(punit);
  dmod = 100 + get_unittype_bonus(city_owner(pcity), ptile,
                                  punittype, NULL, EFT_DEFEND_BONUS);
  return danger * (amod + 100) / MAX(dmod, 1);
}
 
/**********************************************************************/
void dai_assess_danger_player(struct ai_type *ait, struct player *pplayer,
                              const struct civ_map *dmap)
{
  /* Do nothing if game is not running */
  if (S_S_RUNNING == server_state()) {
    city_list_iterate(pplayer->cities, pcity) {
      (void) assess_danger(ait, pcity, dmap, NULL);
    } city_list_iterate_end;
  }
}
 
/**********************************************************************/
static void dai_reevaluate_building(struct city *pcity, adv_want *value, 
                                    unsigned int urgency, unsigned int danger, 
                                    int defense)
{
  if (*value == 0 || danger <= 0) {
    return;
  }
 
  *value = MAX(*value, 100 + urgency); /* default */
 
  if (urgency > 0 && danger > defense * 2) {
    *value += 100;
  } else if (defense != 0 && danger > defense) {
    *value = MAX(danger * 100 / defense, *value);
  }
}
 
/**********************************************************************/
static unsigned int assess_danger(struct ai_type *ait, struct city *pcity,
                                  const struct civ_map *dmap,
                                  player_unit_list_getter ul_cb)
{
  struct player *pplayer = city_owner(pcity);
  struct tile *ptile = city_tile(pcity);
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
  /* How much such danger there is that building would help against. */
  unsigned int danger_reduced[B_LAST];
  int i;
  int defender;
  unsigned int urgency = 0;
  int defense;
  int total_danger = 0;
 
  /* TODO: Presumably most, or even all, of these arrays
   *       could be of size game.control.num_unit_types instead
   *       of full U_LAST */
  int defense_bonuses_pct[U_LAST];
  bool defender_type_handled[U_LAST];
  int best_non_scramble[U_LAST];
  bool sth_does_not_scramble = FALSE;
  int city_def_against[U_LAST];
  int assess_turns;
  bool omnimap;
 
  TIMING_LOG(AIT_DANGER, TIMER_START);
 
  /* Initialize data. */
  memset(&danger_reduced, 0, sizeof(danger_reduced));
  if (has_handicap(pplayer, H_DANGER)) {
    /* Always thinks that city is in grave danger */
    city_data->grave_danger = 1;
  } else {
    city_data->grave_danger = 0;
  }
  city_data->diplomat_threat = FALSE;
  city_data->has_diplomat = FALSE;
 
  unit_type_iterate(utype) {
    int idx = utype_index(utype);
 
    defense_bonuses_pct[idx] = 0;
    defender_type_handled[idx] = FALSE;
    best_non_scramble[idx] = -1;
    /* FIXME: cache it somewhere? */
    city_def_against[idx]
      = 100 + get_unittype_bonus(pplayer, ptile, utype, NULL,
                                 EFT_DEFEND_BONUS);
    city_def_against[idx] = MAX(city_def_against[idx], 1);
  } unit_type_iterate_end;
 
  /* What flag-specific bonuses do our units have. */
  /* We value them less than general defense increment */
  unit_list_iterate(ptile->units, punit) {
    const struct unit_type *def = unit_type_get(punit);
 
    if (unit_has_type_flag(punit, UTYF_DIPLOMAT)) {
      city_data->has_diplomat = TRUE;
    }
    if (!defender_type_handled[utype_index(def)]) {
      /* This is first defender of this type. Check defender type
       * specific bonuses. */
 
      /* Skip defenders that have no bonuses at all. Acceptable
       * side-effect is that we can't consider negative bonuses at
       * all ("No bonuses" should be better than "negative bonus") */
      if (def->cache.max_defense_mp_bonus_pct > 0) {
        unit_type_iterate(utype) {
          int idx = utype_index(utype);
          int coeff = def->cache.scramble_coeff[idx];
          int bonus;
 
          /* FIXME: consider EFT_FORTIFY_DEFENSE_BONUS */
          if (coeff) {
            bonus = coeff / city_def_against[idx] - 100;
          } else {
            bonus = def->cache.defense_mp_bonuses_pct[idx];
          }
 
          if (bonus > defense_bonuses_pct[idx]) {
            if (!coeff) {
              best_non_scramble[idx] = bonus;
            }
            defense_bonuses_pct[idx] = bonus;
          } else if (!coeff) {
            best_non_scramble[idx] = MAX(best_non_scramble[idx], bonus);
          }
        } unit_type_iterate_end;
      } else {
        /* Just remember that such a unit exists and hope its bonuses are just 0 */
        sth_does_not_scramble = TRUE;
      }
 
      defender_type_handled[utype_index(def)] = TRUE;
    }
  } unit_list_iterate_end;
  if (sth_does_not_scramble || unit_list_size(ptile->units) <= 0) {
    /* Scrambling units tend to be expensive. If we have a barenaked city, we'll
     * need at least a cheap unit. If we have only scramblers,
     * maybe it's OK. */
    unit_type_iterate(scrambler_type) {
      Unit_type_id id = utype_index(scrambler_type);
 
      best_non_scramble[id] = MAX(best_non_scramble[id], 0);
    } unit_type_iterate_end;
  }
 
  if (player_is_cpuhog(pplayer)) {
    assess_turns = 6;
  } else {
    assess_turns = has_handicap(pplayer, H_ASSESS_DANGER_LIMITED) ? 2 : 3;
  }
 
  omnimap = !has_handicap(pplayer, H_MAP);
 
  /* Check. */
  players_iterate(aplayer) {
    struct pf_reverse_map *pcity_map;
    struct unit_list *units;
 
    if (!adv_is_player_dangerous(pplayer, aplayer)) {
      continue;
    }
    /* Note that we still consider the units of players we are not (yet)
     * at war with. */
 
    pcity_map = pf_reverse_map_new_for_city(pcity, aplayer, assess_turns,
                                            omnimap, dmap);
 
    if (ul_cb != NULL) {
      units = ul_cb(aplayer);
    } else {
      units = aplayer->units;
    }
    unit_list_iterate(units, punit) {
      int move_time;
      unsigned int vulnerability;
      int defbonus_pct;
      const struct unit_type *utype = unit_type_get(punit);
      struct unit_type_ai *utai = utype_ai_data(utype, ait);
 
#ifdef FREECIV_WEB
      /* freeciv-web ignores danger that is far in distance,
       * no matter how quickly it would reach us; even if
       * that's *immediately* over a road type that allows
       * unlimited movement. */
      int unit_distance = real_map_distance(ptile, unit_tile(punit));
 
      if (unit_distance > ASSESS_DANGER_MAX_DISTANCE
          || (has_handicap(pplayer, H_ASSESS_DANGER_LIMITED)
              && unit_distance > AI_HANDICAP_DISTANCE_LIMIT)) {
        /* Too far away. */
        continue;
      }
#endif /* FREECIV_WEB */
 
      if (!utai->carries_occupiers
          && !utype_acts_hostile(utype)) {
        /* Harmless unit. */
        continue;
      }
 
      /* Defender unspecific vulnerability and potential move time */
      vulnerability = assess_danger_unit(pcity, pcity_map,
                                         punit, &move_time);
 
      if (PF_IMPOSSIBLE_MC == move_time) {
        continue;
      }
 
      if (unit_can_take_over(punit) || utai->carries_occupiers) {
        /* Even if there is no attack strength,
         * we need ANY protector for the city */
        vulnerability = MAX(vulnerability, 1);
        if (3 >= move_time) {
          urgency++;
          if (1 >= move_time) {
            city_data->grave_danger++;
          }
        }
      }
 
      defbonus_pct = defense_bonuses_pct[utype_index(utype)];
      if (defbonus_pct > 100) {
        defbonus_pct = (defbonus_pct + 100) / 2;
      }
      /* Reduce vulnerability for specific bonuses we do have */
      vulnerability = vulnerability * 100 / (defbonus_pct + 100);
      /* Pass the order for a new defender type against it
       * to the scientific advisor, urgency considered */
      (void) dai_wants_defender_against(ait, pplayer, pcity, utype,
                                        vulnerability / MAX(move_time, 1));
 
      if (utype_acts_hostile(unit_type_get(punit)) && 2 >= move_time) {
        city_data->diplomat_threat = TRUE;
      }
 
      vulnerability *= vulnerability; /* positive feedback */
      if (1 < move_time) {
        vulnerability /= move_time;
      }
 
      if (unit_can_do_action(punit, ACTION_NUKE)
          || unit_can_do_action(punit, ACTION_NUKE_CITY)
          || unit_can_do_action(punit, ACTION_NUKE_UNITS)) {
        defender = dai_find_source_building(pcity, EFT_NUKE_PROOF, utype);
        if (defender != B_LAST) {
          danger_reduced[defender] += vulnerability / MAX(move_time, 1);
        }
      } else if (best_non_scramble[utype_index(utype)] >= 0) {
        /* To consider building a defensive building,
         * build first a defender that gets any profit of it */
        defender = dai_find_source_building(pcity, EFT_DEFEND_BONUS, utype);
        if (defender != B_LAST) {
          int danred = vulnerability / MAX(move_time, 1);
          /* Maybe we can build an improvement
           * that gets normal defender over scrambling one?
           * Effectively a sqrt-scale because we don't test how high
           * the effect is. */
          if (best_non_scramble[utype_index(utype)]
              < defense_bonuses_pct[utype_index(utype)]) {
            danred = danred * (100 + best_non_scramble[utype_index(utype)])
                     / (100 + defense_bonuses_pct[utype_index(utype)]);
          }
          danger_reduced[defender] += danred;
        }
      }
 
      total_danger += vulnerability;
    } unit_list_iterate_end;
 
    pf_reverse_map_destroy(pcity_map);
 
  } players_iterate_end;
 
  if (total_danger) {
    /* If any hostile player has any dangerous unit that can in any time
     * reach the city, we consider building walls here, if none yet.
     * FIXME: this value assumes that walls give x3 defense. */
    city_data->wallvalue = 90;
  } else {
    /* No danger.
     * This is half of the wallvalue of what danger 1 would produce. */
    city_data->wallvalue = 5;
  }
 
  if (0 < city_data->grave_danger) {
    /* really, REALLY urgent to defend */
    urgency += 10 * city_data->grave_danger;
  }
 
  /* HACK: This needs changing if multiple improvements provide
   * this effect. */
  /* FIXME: Accept only buildings helping unit classes we actually use.
   *        Now we consider any land mover helper suitable. */
  /* Sum of squared defense ratings */
  defense = assess_defense_igwall(ait, pcity);
 
  for (i = 0; i < B_LAST; i++) {
    if (0 < danger_reduced[i]) {
      dai_reevaluate_building(pcity, &pcity->server.adv->building_want[i],
                              urgency, danger_reduced[i], defense);
    }
  }
 
  if (has_handicap(pplayer, H_DANGER) && 0 == total_danger) {
    /* Has to have some danger
     * Otherwise grave_danger will be ignored. */
    city_data->danger = 1;
  } else {
    city_data->danger = total_danger;
  }
  city_data->urgency = urgency;
 
  TIMING_LOG(AIT_DANGER, TIMER_STOP);
 
  return urgency;
}
 
/**********************************************************************/
static adv_want dai_unit_defense_desirability(struct ai_type *ait,
                                              const struct unit_type *punittype)
{
  adv_want desire = punittype->hp;
  int attack = punittype->attack_strength;
  int defense = punittype->defense_strength;
  int maxbonus_pct = 0;
  int fp = punittype->firepower;
 
  /* Sea and helicopters often have their firepower set to low firepower when
   * defending. We can't have such units as defenders. */
  if (utype_has_flag(punittype, UTYF_BADCITYDEFENDER)) {
    fp = MIN(fp, game.info.low_firepower_pearl_harbour);
  }
  if (((struct unit_type_ai *)utype_ai_data(punittype, ait))->low_firepower) {
    fp = MIN(fp, game.info.low_firepower_combat_bonus);
  }
  desire *= fp;
  desire *= defense;
  desire += punittype->move_rate / SINGLE_MOVE;
  desire += attack;
 
  maxbonus_pct = punittype->cache.max_defense_mp_bonus_pct;
  if (maxbonus_pct > 100) {
    maxbonus_pct = (maxbonus_pct + 100) / 2;
  }
  desire += desire * maxbonus_pct / 100;
  if (utype_has_flag(punittype, UTYF_GAMELOSS)) {
    desire /= 10; /* But might actually be worth it */
  }
 
  return desire;
}
 
/**********************************************************************/
static adv_want dai_unit_attack_desirability(struct ai_type *ait,
                                             const struct unit_type *punittype)
{
  adv_want desire = punittype->hp;
  int attack = punittype->attack_strength;
  int defense = punittype->defense_strength;
 
  desire *= punittype->move_rate;
  desire *= punittype->firepower;
  desire *= attack;
  desire += defense;
  if (utype_has_flag(punittype, UTYF_IGTER)) {
    desire += desire / 2;
  }
  if (utype_has_flag(punittype, UTYF_GAMELOSS)) {
    desire /= 10; /* But might actually be worth it */
  }
  if (utype_has_flag(punittype, UTYF_CITYBUSTER)) {
    desire += desire / 2;
  }
  if (can_attack_from_non_native(punittype)) {
    desire += desire / 4;
  }
  if (punittype->adv.igwall) {
    desire += desire / 4;
  }
 
  return desire;
}
 
/**********************************************************************/
bool dai_process_defender_want(struct ai_type *ait, struct player *pplayer,
                               struct city *pcity, unsigned int danger,
                               struct adv_choice *choice, adv_want extra_want)
{
  const struct research *presearch = research_get(pplayer);
  /* FIXME: We check if the city has *some* defensive structure,
   * but not whether the city has a defensive structure against
   * any specific attacker. The actual danger may not be mitigated
   * by the defense selected... */
  bool walls = city_got_defense_effect(pcity, NULL);
  /* Technologies we would like to have. */
  adv_want tech_desire[U_LAST];
  /* Our favourite unit. */
  adv_want best = -1;
  struct unit_type *best_unit_type = NULL;
  int best_unit_cost = 1;
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
  struct ai_plr *plr_data = def_ai_player_data(pplayer, ait);
  adv_want total_want = danger + extra_want;
 
  memset(tech_desire, 0, sizeof(tech_desire));
 
  simple_ai_unit_type_iterate(punittype) {
    adv_want desire; /* How much we want the unit? */
 
    /* Only consider proper defenders - otherwise waste CPU and
     * bump tech want needlessly. */
    if (!utype_has_role(punittype, L_DEFEND_GOOD)
        && !utype_has_role(punittype, L_DEFEND_OK)) {
      continue;
    }
 
    desire = dai_unit_defense_desirability(ait, punittype);
 
    if (!utype_has_role(punittype, L_DEFEND_GOOD)) {
      desire /= 2; /* Not good, just ok */
    }
 
    if (utype_has_flag(punittype, UTYF_FIELDUNIT)) {
      /* Causes unhappiness even when in defense, so not a good
       * idea for a defender, unless it is _really_ good.
       * Downright counter productive, if we want unit just for
       * maintaining peace. */
      if (danger == 0) {
        desire = -50;
      } else {
        desire /= 2;
      }
    }
 
    if (desire > 0) {
      desire /= POWER_DIVIDER / 2; /* Good enough, no rounding errors. */
      desire *= desire;
 
      if (can_city_build_unit_now(pcity, punittype)) {
        /* We can build the unit now... */
 
        int build_cost = utype_build_shield_cost(pcity, NULL, punittype);
        int limit_cost = pcity->shield_stock + 40;
 
        if (walls && !utype_has_flag(punittype, UTYF_BADCITYDEFENDER)) {
          desire *= city_data->wallvalue;
          /* TODO: More use of POWER_FACTOR ! */
          desire /= POWER_FACTOR;
        }
 
        if ((best_unit_cost > limit_cost
             && build_cost < best_unit_cost)
            || ((desire > best
                 || (ADV_WANTS_EQ(desire, best)
                     && build_cost <= best_unit_cost))
                && (best_unit_type == NULL
                    /* In case all units are more expensive than limit_cost */
                    || limit_cost <= pcity->shield_stock + 40))) {
          best = desire;
          best_unit_type = punittype;
          best_unit_cost = build_cost;
        }
      } else if (can_city_build_unit_later(pcity, punittype)) {
        /* We first need to develop the tech required by the unit... */
 
        /* Cost (shield equivalent) of gaining these techs. */
        /* FIXME? Katvrr advises that this should be weighted more heavily in
         * big danger. */
        int tech_cost = research_goal_bulbs_required(presearch,
                            advance_number(punittype->require_advance)) / 4
                            / city_list_size(pplayer->cities);
 
        /* Contrary to the above, we don't care if walls are actually built
         * - we're looking into the future now. */
        if (!utype_has_flag(punittype, UTYF_BADCITYDEFENDER)) {
          desire *= city_data->wallvalue;
          desire /= POWER_FACTOR;
        }
 
        /* Yes, there's some similarity with kill_desire(). */
        /* TODO: Explain what shield cost has to do with tech want. */
        tech_desire[utype_index(punittype)] =
          (desire * total_want
           / (utype_build_shield_cost(pcity, NULL, punittype) + tech_cost));
      }
    }
  } simple_ai_unit_type_iterate_end;
 
  if (best == -1) {
    CITY_LOG(LOG_DEBUG, pcity, "Ooops - we cannot build any defender!");
  }
 
  if (best_unit_type != NULL) {
    if (!walls && !utype_has_flag(best_unit_type, UTYF_BADCITYDEFENDER)) {
      best *= city_data->wallvalue;
      best /= POWER_FACTOR;
    }
  } else {
    best_unit_cost = 100; /* Building impossible is considered costly.
                           * This should increase want for tech providing
                           * first defender type. */
  }
 
  if (best <= 0) {
    best = 1; /* Avoid division by zero below. */
  }
 
  /* Update tech_want for appropriate techs for units we want to build. */
  simple_ai_unit_type_iterate(punittype) {
    if (tech_desire[utype_index(punittype)] > 0) {
      /* TODO: Document or fix the algorithm below. I have no idea why
       * it is written this way, and the results seem strange to me. - Per */
      adv_want desire = tech_desire[utype_index(punittype)] * best_unit_cost / best;
 
      plr_data->tech_want[advance_index(punittype->require_advance)]
        += desire;
      TECH_LOG(ait, LOG_DEBUG, pplayer, punittype->require_advance,
               "+ " ADV_WANT_PRINTF " for %s to defend %s",
               desire,
               utype_rule_name(punittype),
               city_name_get(pcity));
    }
  } simple_ai_unit_type_iterate_end;
 
  if (!best_unit_type) {
    return FALSE;
  }
 
  choice->value.utype = best_unit_type;
  choice->want = danger; /* FIXME: Not 'total_want' because of the way callers
                          * are constructed. They may overwrite this value,
                          * and then the value will NOT contain 'extra_want'.
                          * Later we may add 'extra_want', and don't want it
                          * already included in case this was NOT overwritten. */
  choice->type = CT_DEFENDER;
 
  return TRUE;
}
 
/**********************************************************************/
static void process_attacker_want(struct ai_type *ait,
                                  struct city *pcity,
                                  adv_want value,
                                  const struct unit_type *victim_unit_type,
                                  struct player *victim_player,
                                  int veteran, struct tile *ptile,
                                  struct adv_choice *best_choice,
                                  struct pf_map *ferry_map,
                                  struct unit *boat,
                                  const struct unit_type *boattype)
{
  struct player *pplayer = city_owner(pcity);
  const struct research *presearch = research_get(pplayer);
  /* The enemy city.  acity == NULL means stray enemy unit */
  struct city *acity = tile_city(ptile);
  struct pf_parameter parameter;
  struct pf_map *pfm;
  struct pf_position pos;
  const struct unit_type *orig_utype = best_choice->value.utype;
  int victim_count = 1;
  int needferry = 0;
  bool unhap = dai_assess_military_unhappiness(pcity);
  struct ai_plr *plr_data = def_ai_player_data(pplayer, ait);
  const struct civ_map *nmap = &(wld.map);
 
  /* Has to be initialized to make gcc happy */
  struct ai_city *acity_data = NULL;
 
  if (acity != NULL) {
    acity_data = def_ai_city_data(acity, ait);
  }
 
  if (utype_class(orig_utype)->adv.sea_move == MOVE_NONE
      && !boat && boattype) {
    /* Cost of ferry */
    needferry = utype_build_shield_cost(pcity, NULL, boattype);
  }
 
  if (!is_stack_vulnerable(ptile)) {
    /* If it is a city, a fortress or an air base,
     * we may have to whack it many times */
    victim_count += unit_list_size(ptile->units);
  }
 
  simple_ai_unit_type_iterate(punittype) {
    Tech_type_id tech_req = advance_number(punittype->require_advance);
    int tech_dist = research_goal_unknown_techs(presearch, tech_req);
 
    if (dai_can_unit_type_follow_unit_type(punittype, orig_utype, ait)
        && is_native_near_tile(&(wld.map), utype_class(punittype), ptile)
        && (U_NOT_OBSOLETED == punittype->obsoleted_by
            || !can_city_build_unit_direct(pcity, punittype->obsoleted_by))
        && punittype->attack_strength > 0 /* or we'll get SIGFPE */) {
      /* Values to be computed */
      adv_want desire;
      adv_want want;
      int move_time;
      int vuln;
      int veteran_level
        = get_target_bonus_effects(NULL,
                                   &(const struct req_context) {
                                     .player = pplayer,
                                     .city = pcity,
                                     .tile = city_tile(pcity),
                                     .unittype = punittype,
                                   },
                                   NULL,
                                   EFT_VETERAN_BUILD);
      /* Cost (shield equivalent) of gaining these techs. */
      /* FIXME? Katvrr advises that this should be weighted more heavily in big
       * danger. */
      int tech_cost = research_goal_bulbs_required(presearch, tech_req) / 4
                      / city_list_size(pplayer->cities);
      int bcost_balanced = build_cost_balanced(punittype);
      /* See description of kill_desire() for info about this variables. */
      int bcost = utype_build_shield_cost(pcity, NULL, punittype);
      int attack = adv_unittype_att_rating(punittype, veteran_level,
                                           SINGLE_MOVE,
                                           punittype->hp);
 
      /* Take into account reinforcements strength */
      if (acity) {
        attack += acity_data->attack;
      }
 
      if (attack == 0) {
       /* Yes, it can happen that a military unit has attack = 1,
        * for example militia with HP = 1 (in civ1 ruleset). */
        continue;
      }
 
      attack *= attack;
 
      pft_fill_utype_parameter(&parameter, nmap, punittype, city_tile(pcity),
                               pplayer);
      parameter.omniscience = !has_handicap(pplayer, H_MAP);
      pfm = pf_map_new(&parameter);
 
      /* Set the move_time appropriately. */
      move_time = -1;
      if (NULL != ferry_map) {
        struct tile *dest_tile;
 
        if (find_beachhead(pplayer, ferry_map, ptile, punittype,
                           &dest_tile, NULL)
            && pf_map_position(ferry_map, dest_tile, &pos)) {
          move_time = pos.turn;
          dest_tile = pf_map_parameter(ferry_map)->start_tile;
          pf_map_tiles_iterate(pfm, atile, FALSE) {
            if (atile == dest_tile) {
              pf_map_iter_position(pfm, &pos);
              move_time += pos.turn;
              break;
            } else if (atile == ptile) {
              /* Reaching directly seems better. */
              pf_map_iter_position(pfm, &pos);
              move_time = pos.turn;
              break;
            }
          } pf_map_tiles_iterate_end;
        }
      }
 
      if (-1 == move_time) {
        if (pf_map_position(pfm, ptile, &pos)) {
          move_time = pos.turn;
        } else {
          pf_map_destroy(pfm);
          continue;
        }
      }
      pf_map_destroy(pfm);
 
      /* Estimate strength of the enemy. */
 
      if (victim_unit_type) {
        vuln = unittype_def_rating_squared(punittype, victim_unit_type,
                                           victim_player,
                                           ptile, FALSE, veteran);
      } else {
        vuln = 0;
      }
 
      /* Not bothering to s/!vuln/!pdef/ here for the time being. -- Syela
       * (this is noted elsewhere as terrible bug making warships yoyoing) 
       * as the warships will go to enemy cities hoping that the enemy builds 
       * something for them to kill. */
      if (vuln == 0
          && (utype_class(punittype)->adv.land_move == MOVE_NONE
              || 0 < utype_fuel(punittype))) {
        desire = 0;
 
      } else {
        if (acity
            && utype_can_take_over(punittype)
            && acity_data->invasion.attack > 0
            && acity_data->invasion.occupy == 0) {
          int owner_size = city_list_size(city_owner(acity)->cities);
          float finishing_factor = 1;
 
          if (owner_size <= FINISH_HIM_CITY_COUNT) {
            finishing_factor = (2 - (float)owner_size / FINISH_HIM_CITY_COUNT);
          }
          desire = CITY_CONQUEST_WORTH(acity, acity_data) * 10 * finishing_factor;
        } else {
          desire = 0;
        }
 
        if (!acity) {
          desire = kill_desire(value, attack, bcost, vuln, victim_count);
        } else {
          adv_want kd;
          int city_attack = acity_data->attack * acity_data->attack;
 
          /* See aiunit.c:find_something_to_kill() for comments. */
          kd = kill_desire(value, attack,
                           (bcost + acity_data->bcost), vuln,
                           victim_count);
 
          if (value * city_attack > acity_data->bcost * vuln) {
            kd -= kill_desire(value, city_attack,
                              acity_data->bcost, vuln,
                              victim_count);
          }
 
          desire = MAX(desire, kd);
        }
      }
 
      desire -= tech_cost * SHIELD_WEIGHTING;
      /* We can be possibly making some people of our homecity unhappy - then
       * we don't want to travel too far away to our victims. */
      /* TODO: Unify the 'unhap' dependency to some common function. */
      desire -= move_time * (unhap ? SHIELD_WEIGHTING + 2 * TRADE_WEIGHTING
                             : SHIELD_WEIGHTING);
 
      want = military_amortize(pplayer, pcity, desire, MAX(1, move_time),
                               bcost_balanced + needferry);
 
      if (want > 0) {
        if (tech_dist > 0) {
          /* This is a future unit, tell the scientist how much we need it */
          plr_data->tech_want[advance_index(punittype->require_advance)]
            += want;
          TECH_LOG(ait, LOG_DEBUG, pplayer, punittype->require_advance,
                   "+ " ADV_WANT_PRINTF " for %s vs %s(%d,%d)",
                   want,
                   utype_rule_name(punittype),
                   (acity ? city_name_get(acity) : utype_rule_name(victim_unit_type)),
                   TILE_XY(ptile));
        } else if (want > best_choice->want) {
          const struct impr_type *impr_req;
 
          if (can_city_build_unit_now(pcity, punittype)) {
            /* This is a real unit and we really want it */
 
            CITY_LOG(LOG_DEBUG, pcity, "overriding %s(" ADV_WANT_PRINTF
                     ") with %s(" ADV_WANT_PRINTF ")"
                     " [attack=%d,value=" ADV_WANT_PRINTF
                     ",move_time=%d,vuln=%d,bcost=%d]",
                     utype_rule_name(best_choice->value.utype),
                     best_choice->want,
                     utype_rule_name(punittype),
                     want,
                     attack, value, move_time, vuln, bcost);
 
            best_choice->value.utype = punittype;
            best_choice->want = want;
            best_choice->type = CT_ATTACKER;
          } else if (!((impr_req = utype_needs_improvement(punittype,
                                                           pcity)))) {
            CITY_LOG(LOG_DEBUG, pcity, "cannot build unit %s",
                     utype_rule_name(punittype));
          } else if (can_city_build_improvement_now(pcity, impr_req)) {
            /* Building this unit requires a specific type of improvement.
             * So we build this improvement instead.  This may not be the
             * best behavior. */
            CITY_LOG(LOG_DEBUG, pcity, "building %s to build unit %s",
                     improvement_rule_name(impr_req),
                     utype_rule_name(punittype));
            best_choice->value.building = impr_req;
            best_choice->want = want;
            best_choice->type = CT_BUILDING;
          } else {
            /* This should never happen? */
            CITY_LOG(LOG_DEBUG, pcity, "cannot build %s or unit %s",
                     improvement_rule_name(impr_req),
                     utype_rule_name(punittype));
          }
        }
      }
    }
  } simple_ai_unit_type_iterate_end;
}
 
/**********************************************************************/
static struct adv_choice *kill_something_with(struct ai_type *ait,
                                              struct player *pplayer,
                                              struct city *pcity, struct unit *myunit,
                                              struct adv_choice *choice)
{
  /* Our attack rating (with reinforcements) */
  int attack;
  /* Benefit from fighting the target */
  adv_want benefit;
  /* Defender of the target city/tile */
  struct unit *pdef; 
  const struct unit_type *def_type;
  struct player *def_owner;
  int def_vet; /* Is the defender veteran? */
  /* Target coordinates */
  struct tile *ptile;
  /* Our transport */
  struct unit *ferryboat;
  /* Our target */
  struct city *acity;
  /* Type of the boat (real or a future one) */
  const struct unit_type *boattype;
  struct pf_map *ferry_map = NULL;
  int move_time;
  struct adv_choice *best_choice;
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
  struct ai_city *acity_data;
  struct civ_map *nmap = &(wld.map);
 
  best_choice = adv_new_choice();
  best_choice->value.utype = unit_type_get(myunit);
  best_choice->type = CT_ATTACKER;
  adv_choice_set_use(best_choice, "attacker");
 
  fc_assert_ret_val(is_military_unit(myunit) && !utype_fuel(unit_type_get(myunit)), choice);
 
  if (city_data->danger != 0 && assess_defense(ait, pcity) == 0) {
    /* Defense comes first! */
    goto cleanup;
  }
 
  best_choice->want = find_something_to_kill(ait, pplayer, myunit, &ptile, NULL,
                                             &ferry_map, &ferryboat,
                                             &boattype, &move_time);
  if (NULL == ptile
      || ptile == unit_tile(myunit)
      || !can_unit_attack_tile(myunit, NULL, ptile)) {
    goto cleanup;
  }
 
  acity = tile_city(ptile);
 
  if (myunit->id != 0) {
    log_error("%s(): non-virtual unit!", __FUNCTION__);
    goto cleanup;
  }
 
  attack = adv_unit_att_rating(myunit);
  if (acity) {
    acity_data = def_ai_city_data(acity, ait);
    attack += acity_data->attack;
  }
  attack *= attack;
 
  if (NULL != acity) {
    /* Rating of enemy defender */
    int vulnerability;
 
    if (!POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, city_owner(acity))) {
      /* Not a valid target */
      goto cleanup;
    }
 
    def_type = dai_choose_defender_versus(acity, myunit);
    def_owner = city_owner(acity);
    if (1 < move_time && def_type) {
      def_vet = city_production_unit_veteran_level(acity, def_type);
      vulnerability = unittype_def_rating_squared(unit_type_get(myunit), def_type,
                                                  city_owner(acity), ptile,
                                                  FALSE, def_vet);
      benefit = utype_build_shield_cost_base(def_type);
    } else {
      vulnerability = 0;
      benefit = 0;
      def_vet = 0;
    }
 
    pdef = get_defender(nmap, myunit, ptile);
    if (pdef) {
      int m = unittype_def_rating_squared(unit_type_get(myunit), unit_type_get(pdef),
                                          city_owner(acity), ptile, FALSE,
                                          pdef->veteran);
      if (vulnerability < m) {
        benefit = unit_build_shield_cost_base(pdef);
        def_vet = pdef->veteran;
        def_type = unit_type_get(pdef);
        def_owner = unit_owner(pdef);
      }
    }
    if (unit_can_take_over(myunit) || acity_data->invasion.occupy > 0) {
      /* Bonus for getting the city */
      int owner_size = city_list_size(city_owner(acity)->cities);
      float finishing_factor = 1;
 
      if (owner_size <= FINISH_HIM_CITY_COUNT) {
        finishing_factor = (2 - (float)owner_size / FINISH_HIM_CITY_COUNT);
      }
      benefit += CITY_CONQUEST_WORTH(acity, acity_data) * finishing_factor / 3;
    }
 
    /* end dealing with cities */
  } else {
 
    if (NULL != ferry_map) {
      pf_map_destroy(ferry_map);
      ferry_map = NULL;
    }
 
    pdef = get_defender(nmap, myunit, ptile);
    if (!pdef) {
      /* Nobody to attack! */
      goto cleanup;
    }
 
    benefit = unit_build_shield_cost_base(pdef);
 
    def_type = unit_type_get(pdef);
    def_vet = pdef->veteran;
    def_owner = unit_owner(pdef);
    /* end dealing with units */
  }
 
  if (NULL == ferry_map) {
    process_attacker_want(ait, pcity, benefit, def_type, def_owner,
                          def_vet, ptile,
                          best_choice, NULL, NULL, NULL);
  } else { 
    /* Attract a boat to our city or retain the one that's already here */
    fc_assert_ret_val(unit_class_get(myunit)->adv.sea_move != MOVE_FULL, choice);
    best_choice->need_boat = TRUE;
    process_attacker_want(ait, pcity, benefit, def_type, def_owner,
                          def_vet, ptile,
                          best_choice, ferry_map, ferryboat, boattype);
  }
 
  if (best_choice->want > choice->want) {
    /* We want attacker more than what we have selected before */
    adv_free_choice(choice);
    choice = best_choice;
    CITY_LOG(LOG_DEBUG, pcity, "kill_something_with()"
             " %s has chosen attacker, %s, want=" ADV_WANT_PRINTF,
             city_name_get(pcity),
             utype_rule_name(best_choice->value.utype),
             best_choice->want);
 
    if (NULL != ferry_map && !ferryboat) { /* need a new ferry */
      /* We might need a new boat even if there are boats free,
       * if they are blockaded or in inland seas*/
      fc_assert_ret_val(unit_class_get(myunit)->adv.sea_move != MOVE_FULL, choice);
      if (dai_choose_role_unit(ait, pplayer, pcity, choice, CT_ATTACKER,
                               L_FERRYBOAT, choice->want, TRUE)
          && dai_is_ferry_type(choice->value.utype, ait)) {
#ifdef FREECIV_DEBUG
        struct ai_plr *ai = dai_plr_data_get(ait, pplayer, NULL);
 
        log_debug("kill_something_with() %s has chosen attacker ferry, "
                  "%s, want=" ADV_WANT_PRINTF ", %d of %d free",
                  city_name_get(pcity),
                  utype_rule_name(choice->value.utype),
                  choice->want,
                  ai->stats.available_boats, ai->stats.boats);
#endif /* FREECIV_DEBUG */
 
        adv_choice_set_use(choice, "attacker ferry");
      } /* else can not build ferries yet */
    }
  }
 
cleanup:
  if (best_choice != choice) {
    /* It was not taken to use.
     * This hackery needed since 'goto cleanup:' might skip
     * sensible points to do adv_free_choice(). */
    adv_free_choice(best_choice);
  }
  if (NULL != ferry_map) {
    pf_map_destroy(ferry_map);
  }
 
  return choice;
}
 
/**********************************************************************/
static void dai_unit_consider_bodyguard(struct ai_type *ait,
                                        struct city *pcity,
                                        struct unit_type *punittype,
                                        struct adv_choice *choice)
{
  if (choice->want < DAI_WANT_MILITARY_EMERGENCY) {
    struct player *pplayer = city_owner(pcity);
    struct unit *aunit = NULL;
    struct city *acity = NULL;
    struct unit *virtualunit
      = unit_virtual_create(pplayer, pcity, punittype,
                            city_production_unit_veteran_level(pcity,
                                                               punittype));
    const adv_want want = look_for_charge(ait, pplayer, virtualunit,
                                          &aunit, &acity);
 
    if (want > choice->want) {
      choice->want = want;
      choice->value.utype = punittype;
      choice->type = CT_DEFENDER;
      adv_choice_set_use(choice, "bodyguard");
    }
 
    unit_virtual_destroy(virtualunit);
  }
}
 
/**********************************************************************/
static void adjust_ai_unit_choice(struct city *pcity, 
                                  struct adv_choice *choice)
{
  Impr_type_id id;
 
  /* Sanity */
  if (!is_unit_choice_type(choice->type)
      || utype_has_flag(choice->value.utype, UTYF_CIVILIAN)
      || city_production_unit_veteran_level(pcity, choice->value.utype)) {
    return;
  }
 
  /*  N.B.: have to check that we haven't already built the building --mck */
  if ((id = dai_find_source_building(pcity, EFT_VETERAN_BUILD,
                                     choice->value.utype)) != B_LAST
       && !city_has_building(pcity, improvement_by_number(id))) {
    choice->value.building = improvement_by_number(id);
    choice->want = choice->want * (0.5 + (ai_trait_get_value(TRAIT_BUILDER,
                                                             city_owner(pcity))
                                          / TRAIT_DEFAULT_VALUE / 2));
    choice->type = CT_BUILDING;
    adv_choice_set_use(choice, "veterancy building");
  }
}
 
/**********************************************************************/
struct adv_choice *military_advisor_choose_build(struct ai_type *ait,
                                                 struct player *pplayer,
                                                 struct city *pcity,
                                                 const struct civ_map *mamap,
                                                 player_unit_list_getter ul_cb)
{
  struct adv_data *ai = adv_data_get(pplayer, NULL);
  struct unit_type *punittype;
  unsigned int our_def, urgency;
  struct tile *ptile = pcity->tile;
  struct unit *virtualunit;
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
  adv_want martial_value = 0;
  bool martial_need = FALSE;
  struct adv_choice *choice = adv_new_choice();
  bool allow_gold_upkeep;
 
  urgency = assess_danger(ait, pcity, mamap, ul_cb);
  /* Changing to quadratic to stop AI from building piles 
   * of small units -- Syela */
  /* It has to be AFTER assess_danger thanks to wallvalue. */
  our_def = assess_defense_quadratic(ait, pcity); 
 
  dai_choose_diplomat_defensive(ait, pplayer, pcity, choice, our_def);
 
  if (pcity->feel[CITIZEN_UNHAPPY][FEELING_NATIONALITY]
      + pcity->feel[CITIZEN_ANGRY][FEELING_NATIONALITY] > 0) {
    martial_need = TRUE;
  }
 
  if (!martial_need) {
    specialist_type_iterate(sp) {
      if (pcity->specialists[sp] > 0
          && get_specialist_output(pcity, sp, O_LUXURY) > 0) {
        martial_need = TRUE;
        break;
      }
    } specialist_type_iterate_end;
  }
 
  if (martial_need
      && unit_list_size(pcity->tile->units) < get_city_bonus(pcity, EFT_MARTIAL_LAW_MAX)) {
    martial_value = dai_content_effect_value(pplayer, pcity,
                                             get_city_bonus(pcity, EFT_MARTIAL_LAW_EACH),
                                             1, FEELING_FINAL);
  }
 
  /* Otherwise no need to defend yet */
  if (city_data->danger != 0 || martial_value > 0) {
    struct impr_type *pimprove;
    int num_defenders = unit_list_size(ptile->units);
    int wall_id, danger;
    bool build_walls = TRUE;
    bool def_unit_selected = FALSE;
    int qdanger = city_data->danger * city_data->danger;
 
    if (qdanger <= 0) {
      /* We only need these defenders because of Martial Law value */
      danger = 0;
      build_walls = FALSE; /* Walls don't provide Martial Law */
    } else {
      /* First determine the danger. It is measured in percents of our
       * defensive strength, capped at 200 + urgency */
      if (qdanger >= our_def) {
        if (urgency == 0) {
          /* Don't waste money */
          danger = 100;
        } else if (our_def == 0) {
          danger = 200 + urgency;
        } else {
          danger = MIN(200, 100 * qdanger / our_def) + urgency;
        }
      } else {
        danger = 100 * qdanger / our_def;
      }
 
      if (pcity->surplus[O_SHIELD] <= 0 && our_def != 0) {
        /* Won't be able to support anything */
        danger = 0;
      }
    }
 
    CITY_LOG(LOG_DEBUG, pcity, "m_a_c_d urgency=%d danger=%d num_def=%d "
             "our_def=%d", urgency, danger, num_defenders, our_def);
 
    if (our_def == 0 && danger > 0) {
      /* Build defensive unit first! Walls will help nothing if there's
       * nobody behind them. */
      if (dai_process_defender_want(ait, pplayer, pcity, danger, choice,
                                    martial_value)) {
        choice->want = DAI_WANT_BELOW_MIL_EMERGENCY + danger;
        adv_choice_set_use(choice, "first defender");
        build_walls = FALSE;
        def_unit_selected = TRUE;
 
        CITY_LOG(LOG_DEBUG, pcity, "m_a_c_d wants first defender with " ADV_WANT_PRINTF,
                 choice->want);
      }
    }
    if (build_walls) {
      /* FIXME: 1. Does not consider what kind of future danger is likely, so
       * may build SAM batteries when enemy has only land units. */
      /* We will build walls if we can and want and (have "enough" defenders or
       * can just buy the walls straight away) */
 
      /* HACK: This needs changing if multiple improvements provide
       * this effect. */
      wall_id = dai_find_source_building(pcity, EFT_DEFEND_BONUS, NULL);
      pimprove = improvement_by_number(wall_id);
 
      if (wall_id != B_LAST
          && pcity->server.adv->building_want[wall_id] != 0 && our_def != 0
          && can_city_build_improvement_now(pcity, pimprove)
          && (danger < 101 || num_defenders > 1
              || (city_data->grave_danger == 0
                  && pplayer->economic.gold
                     > impr_buy_gold_cost(pcity, pimprove, pcity->shield_stock)))
          && ai_fuzzy(pplayer, TRUE)) {
        if (pcity->server.adv->building_want[wall_id] > 0) {
          /* NB: great wall is under domestic */
          choice->value.building = pimprove;
          /* building_want is hacked by assess_danger */
          choice->want = pcity->server.adv->building_want[wall_id];
          choice->want = choice->want * (0.5 + (ai_trait_get_value(TRAIT_BUILDER, pplayer)
                                                / TRAIT_DEFAULT_VALUE / 2));
          if (urgency == 0 && choice->want > DAI_WANT_BELOW_MIL_EMERGENCY) {
            choice->want = DAI_WANT_BELOW_MIL_EMERGENCY;
          }
          choice->type = CT_BUILDING;
          adv_choice_set_use(choice, "defense building");
          CITY_LOG(LOG_DEBUG, pcity,
                   "m_a_c_d wants defense building with " ADV_WANT_PRINTF,
                   choice->want);
        } else {
          build_walls = FALSE;
        }
      } else {
        build_walls = FALSE;
      }
    }
 
    /* If our choice isn't defender unit already, consider one */
    if (!def_unit_selected) {
      if ((danger > 0 && num_defenders <= urgency) || martial_value > 0) {
        struct adv_choice uchoice;
 
        adv_init_choice(&uchoice);
 
        /* Consider building defensive units */
        if (dai_process_defender_want(ait, pplayer, pcity, danger, &uchoice,
                                      martial_value)) {
          /* Potential defender found */
          if (urgency == 0
              && uchoice.value.utype->defense_strength == 1) {
            /* FIXME: check other reqs (unit class?) */
            if (get_city_bonus(pcity, EFT_HP_REGEN) > 0) {
              /* Unlikely */
              uchoice.want = MIN(49, danger);
            } else {
              uchoice.want = MIN(25, danger);
            }
          } else {
            uchoice.want = danger;
          }
 
          uchoice.want += martial_value;
          if (danger > 0) {
            adv_choice_set_use(&uchoice, "defender");
          } else {
            adv_choice_set_use(&uchoice, "police");
          }
 
          if (!build_walls || uchoice.want > choice->want) {
            adv_choice_copy(choice, &uchoice);
          }
          adv_deinit_choice(&uchoice);
 
          CITY_LOG(LOG_DEBUG, pcity, "m_a_c_d wants %s with desire " ADV_WANT_PRINTF,
                   utype_rule_name(choice->value.utype),
                   choice->want);
        } else {
          CITY_LOG(LOG_DEBUG, pcity, "m_a_c_d cannot select defender");
        }
      } else {
        CITY_LOG(LOG_DEBUG, pcity, "m_a_c_d does not want defenders");
      }
    }
  } /* ok, don't need to defend */
 
  if (pcity->surplus[O_SHIELD] <= 0 
      || pcity->feel[CITIZEN_UNHAPPY][FEELING_FINAL] > pcity->feel[CITIZEN_UNHAPPY][FEELING_EFFECT]
      || pcity->id == ai->wonder_city) {
    /* Things we consider below are not life-saving so we don't want to 
     * build them if our populace doesn't feel like it */
    return choice;
  }
 
  if (pplayer->economic.tax <= 50 || city_total_unit_gold_upkeep(pcity) <= 0) {
    /* Always allow one unit with real gold upkeep (after EFT_UNIT_UPKEEP_FREE_PER_CITY)
     * Allow more if economics is so strong that we have not increased taxes. */
    allow_gold_upkeep = TRUE;
  } else {
    allow_gold_upkeep = FALSE;
  }
 
  /* Consider making a land bodyguard */
  punittype = dai_choose_bodyguard(ait, pcity, TC_LAND, L_DEFEND_GOOD,
                                   allow_gold_upkeep);
  if (punittype) {
    dai_unit_consider_bodyguard(ait, pcity, punittype, choice);
  }
 
  /* If we are in severe danger, don't consider attackers. This is probably
     too general. In many cases we will want to buy attackers to counterattack.
     -- Per */
  if (choice->want - martial_value >= DAI_WANT_MILITARY_EMERGENCY
      && city_data->grave_danger > 0) {
    CITY_LOG(LOGLEVEL_BUILD, pcity,
             "severe danger (want " ADV_WANT_PRINTF "), force defender",
             choice->want);
    return choice;
  }
 
  /* Consider making an offensive diplomat */
  dai_choose_diplomat_offensive(ait, pplayer, pcity, choice);
 
  /* Consider making a sea bodyguard */
  punittype = dai_choose_bodyguard(ait, pcity, TC_OCEAN, L_DEFEND_GOOD,
                                   allow_gold_upkeep);
  if (punittype) {
    dai_unit_consider_bodyguard(ait, pcity, punittype, choice);
  }
 
  /* Consider making an airplane */
  (void) dai_choose_attacker_air(ait, pplayer, pcity, choice, allow_gold_upkeep);
 
  /* Consider making a paratrooper */
  dai_choose_paratrooper(ait, pplayer, pcity, choice, allow_gold_upkeep);
 
  /* Check if we want a sailing attacker. Have to put sailing first
     before we mung the seamap */
  punittype = dai_choose_attacker(ait, pcity, TC_OCEAN, allow_gold_upkeep);
  if (punittype) {
    virtualunit = unit_virtual_create(
      pplayer, pcity, punittype,
      city_production_unit_veteran_level(pcity, punittype));
    choice = kill_something_with(ait, pplayer, pcity, virtualunit, choice);
    unit_virtual_destroy(virtualunit);
  }
 
  /* Consider a land attacker or a ferried land attacker
   * (in which case, we might want a ferry before an attacker)
   */
  punittype = dai_choose_attacker(ait, pcity, TC_LAND, allow_gold_upkeep);
  if (punittype) {
    virtualunit = unit_virtual_create(pplayer, pcity, punittype, 1);
    choice = kill_something_with(ait, pplayer, pcity, virtualunit, choice);
    unit_virtual_destroy(virtualunit);
  }
 
  /* Consider a hunter */
  dai_hunter_choice(ait, pplayer, pcity, choice, allow_gold_upkeep);
 
  /* Consider veteran level enhancing buildings before non-urgent units */
  adjust_ai_unit_choice(pcity, choice);
 
  if (choice->want <= 0) {
    CITY_LOG(LOGLEVEL_BUILD, pcity, "military advisor has no advice");
  } else {
    CITY_LOG(LOGLEVEL_BUILD, pcity,
             "military advisor choice: %s (want " ADV_WANT_PRINTF ")",
             adv_choice_rule_name(choice),
             choice->want);
  }
 
  return choice;
}