aiunit.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 <math.h>
 
/* utility */
#include "bitvector.h"
#include "log.h"
#include "mem.h"
#include "rand.h"
#include "registry.h"
#include "shared.h"
#include "timing.h"
 
/* common */
#include "city.h"
#include "combat.h"
#include "game.h"
#include "government.h"
#include "map.h"
#include "movement.h"
#include "packets.h"
#include "specialist.h"
#include "traderoutes.h"
#include "unit.h"
#include "unitlist.h"
 
/* common/aicore */
#include "caravan.h"
#include "pf_tools.h"
 
/* server */
#include "barbarian.h"
#include "citytools.h"
#include "cityturn.h"
#include "diplomats.h"
#include "maphand.h"
#include "srv_log.h"
#include "unithand.h"
#include "unittools.h"
 
/* server/advisors */
#include "advbuilding.h"
#include "advgoto.h"
#include "advtools.h"
#include "autoexplorer.h"
#include "autosettlers.h"
 
/* ai */
#include "difficulty.h"
#include "handicaps.h"
 
/* ai/default */
#include "aiair.h"
#include "aidata.h"
#include "aidiplomat.h"
#include "aiferry.h"
#include "aiguard.h"
#include "aihand.h"
#include "aihunt.h"
#include "ailog.h"
#include "aiparatrooper.h"
#include "aiplayer.h"
#include "aitools.h"
#include "daicity.h"
#include "daieffects.h"
#include "daimilitary.h"
 
#include "aiunit.h"
 
 
#define LOGLEVEL_RECOVERY LOG_DEBUG
#define LOG_CARAVAN       LOG_DEBUG
#define LOG_CARAVAN2      LOG_DEBUG
#define LOG_CARAVAN3      LOG_DEBUG
 
static bool dai_find_boat_for_unit(struct ai_type *ait, struct unit *punit);
static bool dai_caravan_can_trade_cities_diff_cont(struct player *pplayer, 
                                                   struct unit *punit);
static void dai_manage_caravan(struct ai_type *ait, struct player *pplayer,
                               struct unit *punit);
static void dai_manage_barbarian_leader(struct ai_type *ait,
                                        struct player *pplayer,
                                        struct unit *leader);
 
static void dai_military_findjob(struct ai_type *ait,
                                 struct player *pplayer, struct unit *punit);
static void dai_military_defend(struct ai_type *ait, struct player *pplayer,
                                struct unit *punit);
static void dai_military_attack(struct ai_type *ait, struct player *pplayer,
                                struct unit *punit);
 
static bool unit_role_defender(const struct unit_type *punittype);
static int unit_def_rating_squared(const struct unit *punit,
                                   const struct unit *pdef);
 
/*
 * Cached values. Updated by update_simple_ai_types.
 *
 * This a hack to enable emulation of old loops previously hardwired
 * as 
 *    for (i = U_WARRIORS; i <= U_BATTLESHIP; i++)
 *
 * (Could probably just adjust the loops themselves fairly simply,
 * but this is safer for regression testing.)
 *
 * Not dealing with planes yet.
 *
 * Terminated by NULL.
 */
struct unit_type *simple_ai_types[U_LAST];
 
/**********************************************************************/
static struct city *find_neediest_airlift_city(struct ai_type *ait,
                                               const struct player *pplayer)
{
  struct city *neediest_city = NULL;
  int most_danger = 0;
  int most_urgent = 0;
 
  city_list_iterate(pplayer->cities, pcity) {
    struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
    if (pcity->airlift) {
      if (city_data->urgency > most_urgent) {
        most_urgent = city_data->urgency;
        neediest_city = pcity;
      } else if (0 == most_urgent /* urgency trumps danger */
                 && city_data->danger > most_danger) {
        most_danger = city_data->danger;
        neediest_city = pcity;
      }
    }
  } city_list_iterate_end;
 
  return neediest_city;
}
 
/**********************************************************************/
static void dai_airlift(struct ai_type *ait, struct player *pplayer)
{
  struct city *most_needed;
  int comparison;
  struct unit *transported;
 
  do {
    most_needed = find_neediest_airlift_city(ait, pplayer);
    comparison = 0;
    transported = NULL;
 
    if (!most_needed) {
      return;
    }
 
    unit_list_iterate(pplayer->units, punit) {
      struct tile *ptile = (unit_tile(punit));
      struct city *pcity = tile_city(ptile);
 
      if (pcity) {
        struct ai_city *city_data = def_ai_city_data(pcity, ait);
        struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
        const struct unit_type *ptype = unit_type_get(punit);
 
        if (city_data->urgency == 0
            && city_data->danger - DEFENSE_POWER(ptype) < comparison
            && unit_can_airlift_to(punit, most_needed)
            && DEFENSE_POWER(ptype) > 2
            && (unit_data->task == AIUNIT_NONE
                || unit_data->task == AIUNIT_DEFEND_HOME)
            && IS_ATTACKER(ptype)) {
          comparison = city_data->danger;
          transported = punit;
        }
      }
    } unit_list_iterate_end;
    if (!transported) {
      return;
    }
    UNIT_LOG(LOG_DEBUG, transported, "airlifted to defend %s",
             city_name_get(most_needed));
    unit_do_action(pplayer, transported->id, most_needed->id,
                   0, "", ACTION_AIRLIFT);
  } while (TRUE);
}
 
/**********************************************************************/
static bool has_defense(struct city *pcity)
{
  struct tile *ptile = city_tile(pcity);
 
  unit_list_iterate(ptile->units, punit) {
    if (is_military_unit(punit) && base_get_defense_power(punit) != 0
        && punit->hp != 0) {
      struct unit_class *pclass = unit_class_get(punit);
 
      if (pclass->non_native_def_pct > 0
          || is_native_tile_to_class(pclass, ptile)) {
        return TRUE;
      }
    }
  }
  unit_list_iterate_end;
 
  return FALSE;
}
 
/**********************************************************************/
int build_cost_balanced(const struct unit_type *punittype)
{
  return 2 * utype_build_shield_cost_base(punittype) * punittype->attack_strength /
      (punittype->attack_strength + punittype->defense_strength);
}
 
/**********************************************************************/
static int unit_att_rating_now(const struct unit *punit)
{
  return adv_unittype_att_rating(unit_type_get(punit), punit->veteran,
                                 punit->moves_left, punit->hp);
}
 
/**********************************************************************/
static int unit_att_rating_squared(const struct unit *punit)
{
  int v = adv_unit_att_rating(punit);
 
  return v * v;
}
 
/**********************************************************************/
static int unit_def_rating(const struct unit *attacker,
                           const struct unit *defender)
{
  const struct unit_type *def_type = unit_type_get(defender);
 
  return (get_total_defense_power(attacker, defender)
          * (attacker->id != 0 ? defender->hp : def_type->hp)
          * def_type->firepower / POWER_DIVIDER);
}
 
/**********************************************************************/
static int unit_def_rating_squared(const struct unit *attacker,
                                   const struct unit *defender)
{
  int v = unit_def_rating(attacker, defender);
 
  return v * v;
}
 
/**********************************************************************/
int unittype_def_rating_squared(const struct unit_type *att_type,
                                const struct unit_type *def_type,
                                struct player *def_player,
                                struct tile *ptile, bool fortified,
                                int veteran)
{
  struct civ_map *nmap = &(wld.map);
  int v = get_virtual_defense_power(nmap, att_type, def_type, def_player,
                                    ptile, fortified, veteran)
    * def_type->hp * def_type->firepower / POWER_DIVIDER;
 
  return v * v;
}
 
/**********************************************************************/
adv_want kill_desire(adv_want benefit, int attack, int loss, int vuln,
                     int victim_count)
{
  adv_want desire;
 
  /*                       attractiveness     danger */
  desire = (benefit * attack - loss * vuln) * victim_count
    * SHIELD_WEIGHTING / (attack + vuln * victim_count);
 
  return desire;
}
 
/**********************************************************************/
static int avg_benefit(int benefit, int loss, double chance)
{
  return (int)(((benefit + loss) * chance - loss) * SHIELD_WEIGHTING);
}
 
/**********************************************************************/
static void reinforcements_cost_and_value(struct unit *punit,
                                          struct tile *ptile0,
                                          int *value, int *cost)
{
  *cost = 0;
  *value = 0;
  square_iterate(&(wld.map), ptile0, 1, ptile) {
    unit_list_iterate(ptile->units, aunit) {
      if (aunit != punit
          && pplayers_allied(unit_owner(punit), unit_owner(aunit))) {
        int val = adv_unit_att_rating(aunit);
 
        if (val != 0) {
          *value += val;
          *cost += unit_build_shield_cost_base(aunit);
        }
      }
    } unit_list_iterate_end;
  } square_iterate_end;
}
 
/**********************************************************************/
static bool is_my_turn(struct unit *punit, struct unit *pdef)
{
  int val = unit_att_rating_now(punit);
  int cur, d;
  const struct unit_type *def_type = unit_type_get(pdef);
  struct tile *def_tile = unit_tile(pdef);
  struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
 
  square_iterate(nmap, def_tile, 1, ptile) {
    unit_list_iterate(ptile->units, aunit) {
      if (aunit == punit || unit_owner(aunit) != unit_owner(punit)) {
        continue;
      }
      if ((unit_attack_units_at_tile_result(aunit, NULL, def_tile)
           != ATT_OK)
          || (unit_attack_unit_at_tile_result(aunit, NULL,
                                              pdef, def_tile)
              != ATT_OK)) {
        continue;
      }
      d = get_virtual_defense_power(nmap, unit_type_get(aunit), def_type,
                                    unit_owner(pdef), def_tile,
                                    FALSE, 0);
      if (d == 0) {
        return TRUE;            /* Thanks, Markus -- Syela */
      }
      cur = unit_att_rating_now(aunit) *
        get_virtual_defense_power(nmap, unit_type_get(punit), def_type,
                                  unit_owner(pdef), def_tile,
                                  FALSE, 0) / d;
      if (cur > val && ai_fuzzy(unit_owner(punit), TRUE)) {
        return FALSE;
      }
    } unit_list_iterate_end;
  } square_iterate_end;
 
  return TRUE;
}
 
/**********************************************************************/
static int dai_rampage_want(struct unit *punit, struct tile *ptile)
{
  struct player *pplayer = unit_owner(punit);
  struct unit *pdef;
  struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
 
  if (can_unit_attack_tile(punit, NULL, ptile)
      && (pdef = get_defender(nmap, punit, ptile))) {
    /* See description of kill_desire() about these variables. */
    int attack = unit_att_rating_now(punit);
    int benefit = stack_cost(punit, pdef);
    int loss = unit_build_shield_cost_base(punit);
 
    attack *= attack;
 
    /* If the victim is in the city/fortress, we correct the benefit
     * with our health because there could be reprisal attacks.  We
     * shouldn't send already injured units to useless suicide.
     * Note that we do not specially encourage attacks against
     * cities: rampage is a hit-n-run operation. */
    if (!is_stack_vulnerable(ptile) 
        && unit_list_size(ptile->units) > 1) {
      benefit = (benefit * punit->hp) / unit_type_get(punit)->hp;
    }
 
    /* If we have non-zero attack rating... */
    if (attack > 0 && is_my_turn(punit, pdef)) {
      double chance = unit_win_chance(nmap, punit, pdef);
      int desire = avg_benefit(benefit, loss, chance);
 
      /* No need to amortize, our operation takes one turn. */
      UNIT_LOG(LOG_DEBUG, punit, "Rampage: Desire %d to kill %s(%d,%d)",
               desire,
               unit_rule_name(pdef),
               TILE_XY(unit_tile(pdef)));
 
      return MAX(0, desire);
    }
  } else if (0 == unit_list_size(ptile->units)) {
    /* No defender. */
    struct city *pcity = tile_city(ptile);
 
    /* ...and free foreign city waiting for us. Who would resist! */
    if (NULL != pcity
        && pplayers_at_war(pplayer, city_owner(pcity))
        && unit_can_take_over(punit)) {
      return -RAMPAGE_FREE_CITY_OR_BETTER;
    }
 
    /* ...or tiny pleasant hut here! */
    /* FIXME: unhardcode and variate the desire to enter a hut. */
    if (unit_can_enter_hut(punit, ptile) && !is_barbarian(pplayer)
        && is_native_tile(unit_type_get(punit), ptile)) {
      return -RAMPAGE_HUT_OR_BETTER;
    }
  }
 
  return 0;
}
 
/**********************************************************************/
static struct pf_path *find_rampage_target(struct unit *punit,
                                           int thresh_adj, int thresh_move)
{
  struct pf_map *tgt_map;
  struct pf_path *path = NULL;
  struct pf_parameter parameter;
  /* Coordinates of the best target (initialize to silence compiler) */
  struct tile *ptile = unit_tile(punit);
  /* Want of the best target */
  int max_want = 0;
  struct player *pplayer = unit_owner(punit);
  const struct civ_map *nmap = &(wld.map);
 
  pft_fill_unit_attack_param(&parameter, nmap, punit);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  /* When trying to find rampage targets we ignore risks such as
   * enemy units because we are looking for trouble!
   * Hence no call ai_avoid_risks()
   */
 
  tgt_map = pf_map_new(&parameter);
  pf_map_move_costs_iterate(tgt_map, iter_tile, move_cost, FALSE) {
    int want;
    bool move_needed;
    int thresh;
 
    if (move_cost > punit->moves_left) {
      /* This is too far */
      break;
    }
 
    if (has_handicap(pplayer, H_TARGETS) 
        && !map_is_known_and_seen(iter_tile, pplayer, V_MAIN)) {
      /* The target is under fog of war */
      continue;
    }
    
    want = dai_rampage_want(punit, iter_tile);
 
    /* Negative want means move needed even though the tiles are adjacent */
    move_needed = (!is_tiles_adjacent(unit_tile(punit), iter_tile)
                   || want < 0);
    /* Select the relevant threshold */
    thresh = (move_needed ? thresh_move : thresh_adj);
    want = (want < 0 ? -want : want);
 
    if (want > max_want && want > thresh) {
      /* The new want exceeds both the previous maximum 
       * and the relevant threshold, so it's worth recording */
      max_want = want;
      ptile = iter_tile;
    }
  } pf_map_move_costs_iterate_end;
 
  if (max_want > 0) {
    /* We found something */
    path = pf_map_path(tgt_map, ptile);
    fc_assert(path != NULL);
  }
 
  pf_map_destroy(tgt_map);
  
  return path;
}
 
/**********************************************************************/
bool dai_military_rampage(struct unit *punit, int thresh_adj, 
                          int thresh_move)
{
  int count = punit->moves_left + 1; /* break any infinite loops */
  struct pf_path *path = NULL;
 
  TIMING_LOG(AIT_RAMPAGE, TIMER_START);  
  CHECK_UNIT(punit);
 
  fc_assert_ret_val(thresh_adj <= thresh_move, TRUE);
  /* This teaches the AI about the dangers inherent in occupychance. */
  thresh_adj += ((thresh_move - thresh_adj) * game.server.occupychance / 100);
 
  while (count-- > 0 && punit->moves_left > 0
         && (path = find_rampage_target(punit, thresh_adj, thresh_move))) {
    if (!adv_unit_execute_path(punit, path)) {
      /* Died */
      count = -1;
    }
    pf_path_destroy(path);
    path = NULL;
  }
 
  fc_assert(NULL == path);
 
  TIMING_LOG(AIT_RAMPAGE, TIMER_STOP);
  return (count >= 0);
}
 
/**********************************************************************/
static void dai_military_bodyguard(struct ai_type *ait, struct player *pplayer,
                                   struct unit *punit)
{
  struct unit *aunit = aiguard_charge_unit(ait, punit);
  struct city *acity = aiguard_charge_city(ait, punit);
  struct tile *ptile;
 
  CHECK_UNIT(punit);
  CHECK_GUARD(ait, punit);
 
  if (aunit && unit_owner(aunit) == unit_owner(punit)) {
    /* protect a unit */
    if (aunit->goto_tile != NULL) {
      /* Our charge is going somewhere: maybe we should meet them there */
      /* FIXME: This probably isn't the best algorithm for this. */
      int me2them = real_map_distance(unit_tile(punit), unit_tile(aunit));
      int me2goal = real_map_distance(unit_tile(punit), aunit->goto_tile);
      int them2goal = real_map_distance(unit_tile(aunit), aunit->goto_tile);
 
      if (me2goal < me2them
          || (me2goal/unit_move_rate(punit) < them2goal/unit_move_rate(aunit)
              && me2goal/unit_move_rate(punit) < me2them/unit_move_rate(punit)
              && unit_move_rate(punit) > unit_move_rate(aunit))) {
        ptile = aunit->goto_tile;
      } else {
        ptile = unit_tile(aunit);
      }
    } else {
      ptile = unit_tile(aunit);
    }
  } else if (acity && city_owner(acity) == unit_owner(punit)) {
    /* protect a city */
    ptile = acity->tile;
  } else {
    /* should be impossible */
    BODYGUARD_LOG(ait, LOG_DEBUG, punit, "we lost our charge");
    dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
    return;
  }
 
  if (same_pos(unit_tile(punit), ptile)) {
    BODYGUARD_LOG(ait, LOG_DEBUG, punit, "at RV");
  } else {
    if (goto_is_sane(punit, ptile)) {
      BODYGUARD_LOG(ait, LOG_DEBUG, punit, "meeting charge");
      if (!dai_gothere(ait, pplayer, punit, ptile)) {
        /* We died */
        return;
      }
    } else {
      BODYGUARD_LOG(ait, LOG_DEBUG, punit, "can not meet charge");
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
    }
  }
  /* We might have stopped because of an enemy nearby.
   * Perhaps we can kill it.*/
  if (dai_military_rampage(punit, BODYGUARD_RAMPAGE_THRESHOLD,
                           RAMPAGE_FREE_CITY_OR_BETTER)
      && same_pos(unit_tile(punit), ptile)) {
    def_ai_unit_data(punit, ait)->done = TRUE; /* Stay with charge */
  }
}
 
/**********************************************************************/
static bool unit_role_defender(const struct unit_type *punittype)
{
  return (utype_has_role(punittype, L_DEFEND_GOOD));
}
 
/**********************************************************************/
adv_want look_for_charge(struct ai_type *ait, struct player *pplayer,
                         struct unit *punit,
                         struct unit **aunit, struct city **acity)
{
  struct pf_parameter parameter;
  struct pf_map *pfm;
  struct city *pcity;
  struct ai_city *data, *best_data = NULL;
  const int toughness = adv_unit_def_rating_basic_squared(punit);
  int def, best_def = -1;
  /* Arbitrary: 3 turns. */
  const int max_move_cost = 3 * unit_move_rate(punit);
  const struct civ_map *nmap = &(wld.map);
 
  *aunit = NULL;
  *acity = NULL;
 
  if (0 == toughness) {
    /* useless */
    return 0;
  }
 
  pft_fill_unit_parameter(&parameter, nmap, punit);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  pfm = pf_map_new(&parameter);
 
  pf_map_move_costs_iterate(pfm, ptile, move_cost, TRUE) {
    if (move_cost > max_move_cost) {
      /* Consider too far. */
      break;
    }
 
    pcity = tile_city(ptile);
 
    /* Consider unit bodyguard. */
    unit_list_iterate(ptile->units, buddy) {
      const struct unit_type *ptype = unit_type_get(punit);
      const struct unit_type *buddy_type = unit_type_get(buddy);
 
      /* TODO: allied unit bodyguard? */
      if (!dai_can_unit_type_follow_unit_type(ptype, buddy_type, ait)
          || unit_owner(buddy) != pplayer
          || !aiguard_wanted(ait, buddy)
          || unit_move_rate(buddy) > unit_move_rate(punit)
          || DEFENSE_POWER(buddy_type) >= DEFENSE_POWER(ptype)
          || (utype_can_do_action_result(buddy_type, ACTRES_ATTACK)
              && 0 == get_transporter_capacity(buddy)
              && ATTACK_POWER(buddy_type) <= ATTACK_POWER(ptype))) {
 
        continue;
      }
 
      def = (toughness - adv_unit_def_rating_basic_squared(buddy));
      if (0 >= def) {
        continue;
      }
 
      if (0 == get_transporter_capacity(buddy)) {
        /* Reduce want based on move cost. We can't do this for
         * transports since they move around all the time, leading
         * to hillarious flip-flops. */
        def >>= move_cost / (2 * unit_move_rate(punit));
      }
      if (def > best_def) {
        *aunit = buddy;
        *acity = NULL;
        best_def = def;
      }
    } unit_list_iterate_end;
 
    /* City bodyguard. TODO: allied city bodyguard? */
    if (ai_fuzzy(pplayer, TRUE)
        && NULL != pcity
        && city_owner(pcity) == pplayer
        && (data = def_ai_city_data(pcity, ait))
        && 0 < data->urgency) {
      if (NULL != best_data
          && (0 < best_data->grave_danger
              || best_data->urgency > data->urgency
              || ((best_data->danger > data->danger
                   || AIUNIT_DEFEND_HOME == def_ai_unit_data(punit, ait)->task)
                  && 0 == data->grave_danger))) {
        /* Chances are we'll be between cities when we are needed the most!
         * Resuming pf_map_move_costs_iterate()... */
        continue;
      }
      def = (data->danger - assess_defense_quadratic(ait, pcity));
      if (def <= 0) {
        continue;
      }
      /* Reduce want based on move cost. */
      def >>= move_cost / (2 * unit_move_rate(punit));
      if (def > best_def && ai_fuzzy(pplayer, TRUE)) {
       *acity = pcity;
       *aunit = NULL;
       best_def = def;
       best_data = data;
     }
    }
  } pf_map_move_costs_iterate_end;
 
  pf_map_destroy(pfm);
 
  UNIT_LOG(LOGLEVEL_BODYGUARD, punit, "%s(), best_def=%d, type=%s (%d, %d)",
           __FUNCTION__, best_def * 100 / toughness,
           (NULL != *acity ? city_name_get(*acity)
            : (NULL != *aunit ? unit_rule_name(*aunit) : "")),
           (NULL != *acity ? index_to_map_pos_x(tile_index(city_tile(*acity)))
            : (NULL != *aunit ?
               index_to_map_pos_x(tile_index(unit_tile(*aunit))) : -1)),
           (NULL != *acity ? index_to_map_pos_y(tile_index(city_tile(*acity)))
            : (NULL != *aunit ?
               index_to_map_pos_y(tile_index(unit_tile(*aunit))) : -1)));
 
  return ((best_def * 100) / toughness);
}
 
/**********************************************************************/
bool dai_can_unit_type_follow_unit_type(const struct unit_type *follower,
                                        const struct unit_type *followee,
                                        struct ai_type *ait)
{
  struct unit_type_ai *utai = utype_ai_data(follower, ait);
 
  unit_type_list_iterate(utai->potential_charges, pcharge) {
    if (pcharge == followee) {
      return TRUE;
    }
  } unit_type_list_iterate_end;
 
  return FALSE;
}
 
/**********************************************************************/
static void dai_military_findjob(struct ai_type *ait,
                                 struct player *pplayer, struct unit *punit)
{
  const struct unit_type *punittype = unit_type_get(punit);
  struct unit_ai *unit_data;
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
 
  /* Keep barbarians aggressive and primitive */
  if (is_barbarian(pplayer)) {
    if (can_unit_do_activity(nmap, punit, ACTIVITY_PILLAGE)
        && is_land_barbarian(pplayer)) {
      /* Land barbarians pillage */
      unit_activity_handling(punit, ACTIVITY_PILLAGE);
    }
    dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
 
    return;
  }
 
  unit_data = def_ai_unit_data(punit, ait);
 
  /* If I am a bodyguard, check whether I can do my job. */
  if (unit_data->task == AIUNIT_ESCORT
      || unit_data->task == AIUNIT_DEFEND_HOME) {
    aiguard_update_charge(ait, punit);
  }
 
  if (aiguard_has_charge(ait, punit)
      && unit_data->task == AIUNIT_ESCORT) {
    struct unit *aunit = aiguard_charge_unit(ait, punit);
    struct city *acity = aiguard_charge_city(ait, punit);
    struct ai_city *city_data = NULL;
 
    if (acity != NULL) {
      city_data = def_ai_city_data(acity, ait);
    }
 
    /* Check if the city we are on our way to rescue is still in danger,
     * or the unit we should protect is still alive... */
    if ((aunit && (aiguard_has_guard(ait, aunit) || aiguard_wanted(ait, aunit))
         && adv_unit_def_rating_basic(punit) > adv_unit_def_rating_basic(aunit)) 
        || (acity && city_owner(acity) == unit_owner(punit)
            && city_data->urgency != 0 
            && city_data->danger > assess_defense_quadratic(ait, acity))) {
      return; /* Yep! */
    } else {
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL); /* Nope! */
    }
  }
 
  /* Is the unit badly damaged? */
  if ((unit_data->task == AIUNIT_RECOVER
       && punit->hp < punittype->hp)
      || punit->hp < punittype->hp * 0.25) { /* WAG */
    UNIT_LOG(LOGLEVEL_RECOVERY, punit, "set to hp recovery");
    dai_unit_new_task(ait, punit, AIUNIT_RECOVER, NULL);
    return;
  }
 
  TIMING_LOG(AIT_BODYGUARD, TIMER_START);
  if (unit_role_defender(unit_type_get(punit))) {
    /* This is a defending unit that doesn't need to stay put.
     * It needs to defend something, but not necessarily where it's at.
     * Therefore, it will consider becoming a bodyguard. -- Syela */
    struct city *acity;
    struct unit *aunit;
 
    look_for_charge(ait, pplayer, punit, &aunit, &acity);
    if (acity) {
      dai_unit_new_task(ait, punit, AIUNIT_ESCORT, acity->tile);
      aiguard_assign_guard_city(ait, acity, punit);
      BODYGUARD_LOG(ait, LOG_DEBUG, punit, "going to defend city");
    } else if (aunit) {
      dai_unit_new_task(ait, punit, AIUNIT_ESCORT, unit_tile(aunit));
      aiguard_assign_guard_unit(ait, aunit, punit);
      BODYGUARD_LOG(ait, LOG_DEBUG, punit, "going to defend unit");
    }
  }
  TIMING_LOG(AIT_BODYGUARD, TIMER_STOP);
}
 
/**********************************************************************/
static void dai_military_defend(struct ai_type *ait, struct player *pplayer,
                                struct unit *punit)
{
  struct city *pcity = aiguard_charge_city(ait, punit);
 
  CHECK_UNIT(punit);
 
  if (!pcity || city_owner(pcity) != pplayer) {
    pcity = tile_city(unit_tile(punit));
    /* Do not stay defending an allied city forever */
    aiguard_clear_charge(ait, punit);
  }
 
  if (!pcity) {
    /* Try to find a place to rest. Sitting duck out in the wilderness
     * is generally a bad idea, since we protect no cities that way, and
     * it looks silly. */
    pcity = find_closest_city(unit_tile(punit), NULL, pplayer,
                              FALSE, FALSE, FALSE, TRUE, FALSE,
                              unit_class_get(punit));
  }
 
  if (!pcity) {
    pcity = game_city_by_number(punit->homecity);
  }
 
  if (dai_military_rampage(punit, BODYGUARD_RAMPAGE_THRESHOLD * 5,
                           RAMPAGE_FREE_CITY_OR_BETTER)) {
    /* ... we survived */
    if (pcity) {
      UNIT_LOG(LOG_DEBUG, punit, "go to defend %s", city_name_get(pcity));
      if (same_pos(unit_tile(punit), pcity->tile)) {
        UNIT_LOG(LOG_DEBUG, punit, "go defend successful");
        def_ai_unit_data(punit, ait)->done = TRUE;
      } else {
        (void) dai_gothere(ait, pplayer, punit, pcity->tile);
      }
    } else {
      UNIT_LOG(LOG_VERBOSE, punit, "defending nothing...?");
    }
  }
}
 
/**********************************************************************/
static void single_invader(struct ai_city *city_data,
                           const struct unit_type *utype,
                           int which)
{
  int attacks;
 
  if (utype_action_takes_all_mp(utype,
                                action_by_number(ACTION_ATTACK))) {
    attacks = 1;
  } else {
    attacks = utype->move_rate;
  }
  city_data->invasion.attack += attacks;
  if (which == INVASION_OCCUPY) {
    city_data->invasion.occupy++;
  }
}
 
/**********************************************************************/
static void invasion_funct(struct ai_type *ait, struct unit *punit,
                           bool dest, int radius, int which)
{
  struct tile *ptile;
  struct player *pplayer = unit_owner(punit);
 
  CHECK_UNIT(punit);
 
  if (dest) {
    ptile = punit->goto_tile;
  } else {
    ptile = unit_tile(punit);
  }
 
  square_iterate(&(wld.map), ptile, radius, tile1) {
    struct city *pcity = tile_city(tile1);
 
    if (pcity
        && POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, city_owner(pcity))
        && (dest || !has_defense(pcity))) {
      struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
      /* Unit itself */
      single_invader(city_data, unit_type_get(punit), which);
 
      /* Cargo */
      unit_cargo_iterate(punit, cargo) {
        const struct unit_type *utype = unit_type_get(cargo);
 
        if (IS_ATTACKER(utype)) {
          single_invader(city_data, utype,
                         unit_can_take_over(cargo)
                         ? INVASION_OCCUPY : INVASION_ATTACK);
        }
      } unit_cargo_iterate_end;
    }
  } square_iterate_end;
}
 
/**********************************************************************/
bool find_beachhead(const struct player *pplayer, struct pf_map *ferry_map,
                    struct tile *dest_tile,
                    const struct unit_type *cargo_type,
                    struct tile **ferry_dest, struct tile **beachhead_tile)
{
  if (NULL == tile_city(dest_tile)
      || can_attack_from_non_native(cargo_type)) {
    /* Unit can directly go to 'dest_tile'. */
    struct tile *best_tile = NULL;
    int best_cost = PF_IMPOSSIBLE_MC, cost;
 
    if (NULL != beachhead_tile) {
      *beachhead_tile = dest_tile;
    }
 
    adjc_iterate(&(wld.map), dest_tile, ptile) {
      cost = pf_map_move_cost(ferry_map, ptile);
      if (cost != PF_IMPOSSIBLE_MC
          && (NULL == best_tile || cost < best_cost)) {
        best_tile = ptile;
        best_cost = cost;
      }
    } adjc_iterate_end;
 
    if (NULL != ferry_dest) {
      *ferry_dest = best_tile;
    }
 
    return (PF_IMPOSSIBLE_MC != best_cost);
  } else {
    /* We need to find a beach around 'dest_tile'. */
    struct tile *best_tile = NULL, *best_beach = NULL;
    struct tile_list *checked_tiles = tile_list_new();
    int best_cost = PF_IMPOSSIBLE_MC, cost;
 
    tile_list_append(checked_tiles, dest_tile);
    adjc_iterate(&(wld.map), dest_tile, beach) {
      if (is_native_tile(cargo_type, beach)) {
        /* Can land there. */
        adjc_iterate(&(wld.map), beach, ptile) {
          if (!tile_list_search(checked_tiles, ptile)
              && !is_non_allied_unit_tile(ptile, pplayer)) {
            tile_list_append(checked_tiles, ptile);
            cost = pf_map_move_cost(ferry_map, ptile);
            if (cost != PF_IMPOSSIBLE_MC
                && (NULL == best_tile || cost < best_cost)) {
              best_beach = beach;
              best_tile = ptile;
              best_cost = cost;
            }
          }
        } adjc_iterate_end;
      }
    } adjc_iterate_end;
 
    tile_list_destroy(checked_tiles);
 
    if (NULL != beachhead_tile) {
      *beachhead_tile = best_beach;
    }
    if (NULL != ferry_dest) {
      *ferry_dest = best_tile;
    }
    return (PF_IMPOSSIBLE_MC != best_cost);
  }
}
 
/**********************************************************************/
adv_want find_something_to_kill(struct ai_type *ait, struct player *pplayer,
                                struct unit *punit,
                                struct tile **pdest_tile, struct pf_path **ppath,
                                struct pf_map **pferrymap,
                                struct unit **pferryboat,
                                const struct unit_type **pboattype, int *pmove_time)
{
  const int attack_value = adv_unit_att_rating(punit);    /* basic attack. */
  struct pf_parameter parameter;
  struct pf_map *punit_map, *ferry_map;
  struct pf_position pos;
  struct unit_class *punit_class = unit_class_get(punit);
  const struct unit_type *punit_type = unit_type_get(punit);
  struct tile *punit_tile = unit_tile(punit);
  /* Type of our boat (a future one if ferryboat == NULL). */
  const struct unit_type *boattype = NULL;
  struct unit *ferryboat = NULL;
  struct city *pcity;
  struct ai_city *acity_data;
  int bcost, bcost_bal; /* Build cost of the attacker (+adjustments). */
  bool handicap = has_handicap(pplayer, H_TARGETS);
  bool unhap = FALSE;   /* Do we make unhappy citizen. */
  bool harbor = FALSE;  /* Do we have access to sea? */
  bool go_by_boat;      /* Whether we need a boat or not. */
  int vulnerability;    /* Enemy defense rating. */
  adv_want benefit;     /* Benefit from killing the target. */
  struct unit *pdefender;       /* Enemy city defender. */
  int move_time;        /* Turns needed to target. */
  int reserves;
  int attack;           /* Our total attack value with reinforcements. */
  int victim_count;     /* Number of enemies there. */
  int needferry;        /* Cost of building a ferry boat. */
  /* This is a kluge, because if we don't set x and y with !punit->id,
   * p_a_w isn't called, and we end up not wanting ironclads and therefore
   * never learning steam engine, even though ironclads would be very
   * useful. -- Syela */
  adv_want bk = 0;
  adv_want want;        /* Want (amortized) of the operaton. */
  adv_want best = 0;    /* Best of all wants. */
  struct tile *goto_dest_tile = NULL;
  bool can_occupy;
  struct civ_map *nmap = &(wld.map);
 
  /* Very preliminary checks. */
  *pdest_tile = punit_tile;
  if (NULL != pferrymap) {
    *pferrymap = NULL;
  }
  if (NULL != pferryboat) {
    *pferryboat = NULL;
  }
  if (NULL != pboattype) {
    *pboattype = NULL;
  }
  if (NULL != pmove_time) {
    *pmove_time = 0;
  }
  if (NULL != ppath) {
    *ppath = NULL;
  }
 
  if (0 == attack_value) {
    /* A very poor attacker... probably low on HP. */
    return 0;
  }
 
  TIMING_LOG(AIT_FSTK, TIMER_START);
 
 
  /*** Part 1: Calculate targets ***/
 
  /* This horrible piece of code attempts to calculate the attractiveness of
   * enemy cities as targets for our units, by checking how many units are
   * going towards it or are near it already. */
 
  /* Reset enemy cities data. */
  players_iterate(aplayer) {
    /* See comment below in next usage of POTENTIALLY_HOSTILE_PLAYER. */
    if ((punit->id == 0 && !POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, aplayer))
        || (punit->id != 0 && !pplayers_at_war(pplayer, aplayer))) {
      continue;
    }
    city_list_iterate(aplayer->cities, acity) {
      struct ai_city *city_data = def_ai_city_data(acity, ait);
 
      reinforcements_cost_and_value(punit, acity->tile,
                                    &city_data->attack,
                                    &city_data->bcost);
      city_data->invasion.attack = 0;
      city_data->invasion.occupy = 0;
    } city_list_iterate_end;
  } players_iterate_end;
 
  /* Second, calculate in units on their way there, and mark targets for
   * invasion */
  unit_list_iterate(pplayer->units, aunit) {
    const struct unit_type *atype;
 
    if (aunit == punit) {
      continue;
    }
 
    atype = unit_type_get(aunit);
 
    /* Dealing with invasion stuff */
    if (IS_ATTACKER(atype)) {
      if (aunit->activity == ACTIVITY_GOTO) {
        invasion_funct(ait, aunit, TRUE, 0,
                       (unit_can_take_over(aunit)
                        ? INVASION_OCCUPY : INVASION_ATTACK));
        if ((pcity = tile_city(aunit->goto_tile))) {
          struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
          city_data->attack += adv_unit_att_rating(aunit);
          city_data->bcost += unit_build_shield_cost_base(aunit);
        } 
      }
      invasion_funct(ait, aunit, FALSE, unit_move_rate(aunit) / SINGLE_MOVE,
                     (unit_can_take_over(aunit)
                      ? INVASION_OCCUPY : INVASION_ATTACK));
    } else if (def_ai_unit_data(aunit, ait)->passenger != 0
               && !same_pos(unit_tile(aunit), unit_tile(punit))) {
      /* It's a transport with reinforcements */
      if (aunit->activity == ACTIVITY_GOTO) {
        invasion_funct(ait, aunit, TRUE, 1, INVASION_OCCUPY);
      }
      invasion_funct(ait, aunit, FALSE, 2, INVASION_OCCUPY);
    }
  } unit_list_iterate_end;
  /* end horrible initialization subroutine */
 
 
  /*** Part 2: Now pick one target ***/
 
  /* We first iterate through all cities, then all units, looking
   * for a viable target. We also try to gang up on the target
   * to avoid spreading out attacks too widely to be inefficient.
   */
 
  pcity = tile_city(punit_tile);
  if (NULL != pcity && (0 == punit->id || pcity->id == punit->homecity)) {
    /* I would have thought unhappiness should be taken into account
     * irrespectfully the city in which it will surface... -- GB */
    unhap = dai_assess_military_unhappiness(pcity);
  }
 
  bcost = unit_build_shield_cost_base(punit);
  bcost_bal = build_cost_balanced(punit_type);
 
  pft_fill_unit_attack_param(&parameter, nmap, punit);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  punit_map = pf_map_new(&parameter);
 
  if (MOVE_NONE == punit_class->adv.sea_move) {
    /* We need boat to move over sea. */
    ferryboat = unit_transport_get(punit);
 
    /* First check if we can use the boat we are currently loaded to. */
    if (ferryboat == NULL || !is_boat_free(ait, ferryboat, punit, 0)) {
      /* No, we cannot control current boat */
      ferryboat = NULL;
    }
 
    if (NULL == ferryboat) {
      /* Try to find new boat */
      ferryboat = player_unit_by_number(pplayer,
                                        aiferry_find_boat(ait, punit, 1, NULL));
    }
 
    if (punit->id == 0 && is_terrain_class_near_tile(nmap, punit_tile, TC_OCEAN)) {
      harbor = TRUE;
    }
  }
 
  if (NULL != ferryboat) {
    boattype = unit_type_get(ferryboat);
    pft_fill_unit_overlap_param(&parameter, nmap, ferryboat);
    parameter.omniscience = !has_handicap(pplayer, H_MAP);
    ferry_map = pf_map_new(&parameter);
  } else {
    boattype = best_role_unit_for_player(pplayer, L_FERRYBOAT);
    if (NULL == boattype) {
      /* We pretend that we can have the simplest boat to stimulate tech. */
      boattype = get_role_unit(L_FERRYBOAT, 0);
    }
    if (NULL != boattype && harbor) {
      /* Let's simulate a boat at 'punit' position. */
      pft_fill_utype_overlap_param(&parameter, nmap, boattype,
                                   punit_tile, pplayer);
      parameter.omniscience = !has_handicap(pplayer, H_MAP);
      ferry_map = pf_map_new(&parameter);
    } else {
      ferry_map = NULL;
    }
  }
 
  can_occupy = unit_can_take_over(punit);
 
  players_iterate(aplayer) {
    /* For the virtual unit case, which is when we are called to evaluate
     * which units to build, we want to calculate in danger and which
     * players we want to make war with in the future. We do _not_ want
     * to do this when actually making attacks. */
    if ((punit->id == 0 && !POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, aplayer))
        || (punit->id != 0 && !pplayers_at_war(pplayer, aplayer))) {
      continue; /* Not an enemy. */
    }
 
    city_list_iterate(aplayer->cities, acity) {
      struct tile *atile = city_tile(acity);
 
      if (!is_native_tile(punit_type, atile)
          && !can_attack_non_native(punit_type)) {
        /* Can't attack this city. It is on land. */
        continue;
      }
 
      if (handicap && !map_is_known(atile, pplayer)) {
        /* Can't see it */
        continue;
      }
 
      if (pf_map_position(punit_map, atile, &pos)) {
        go_by_boat = FALSE;
        move_time = pos.turn;
      } else if (NULL == ferry_map) {
        continue;       /* Impossible to handle. */
      } else {
        struct tile *dest, *beach;
 
        if (!find_beachhead(pplayer, ferry_map, atile, punit_type,
                            &dest, &beach)) {
          continue;   /* Impossible to go by boat. */
        }
        if (!pf_map_position(ferry_map, dest, &pos)) {
          fc_assert(pf_map_position(ferry_map, dest, &pos));
          continue;
        }
        move_time = pos.turn;   /* Sailing time. */
        if (dest != beach) {
          move_time++;          /* Land time. */
        }
        if (NULL != ferryboat && unit_tile(ferryboat) != punit_tile) {
          if (pf_map_position(punit_map, unit_tile(ferryboat), &pos)) {
            move_time += pos.turn;      /* Time to reach the boat. */
          } else {
            continue;   /* Cannot reach the boat. */
          }
        }
        go_by_boat = TRUE;
      }
 
      if (can_unit_attack_tile(punit, NULL, city_tile(acity))
          && (pdefender = get_defender(nmap, punit, city_tile(acity)))) {
        vulnerability = unit_def_rating_squared(punit, pdefender);
        benefit = unit_build_shield_cost_base(pdefender);
      } else {
        pdefender = NULL;
        vulnerability = 0;
        benefit = 0;
      }
 
      if (1 < move_time) {
        struct unit_type *def_type = dai_choose_defender_versus(acity, punit);
 
        if (def_type) {
          int v = unittype_def_rating_squared(
            punit_type, def_type, aplayer, atile, FALSE,
            city_production_unit_veteran_level(acity, def_type));
          if (v > vulnerability) {
            /* They can build a better defender! */
            vulnerability = v;
            benefit = utype_build_shield_cost(acity, NULL, def_type);
          }
        }
      }
 
      acity_data = def_ai_city_data(acity, ait);
 
      reserves = (acity_data->invasion.attack
                  - unit_list_size(acity->tile->units));
 
      if (punit->id == 0) {
        /* Real unit would add to reserves once built. */
        if (utype_action_takes_all_mp(unit_type_get(punit),
                                      action_by_number(ACTION_ATTACK))) {
          reserves++;
        } else {
          reserves += punit_type->move_rate;
        }
      }
 
      if (0 < reserves && (can_occupy
                           || 0 < acity_data->invasion.occupy)) {
        /* There are units able to occupy the city after all defenders
         * are killed! */
        benefit += acity_data->worth * reserves / 5;
      }
 
      attack = attack_value + acity_data->attack;
      attack *= attack;
      /* Avoiding handling upkeep aggregation this way -- Syela */
 
      /* AI was not sending enough reinforcements to totally wipe out a city
       * and conquer it in one turn.
       * This variable enables total carnage. -- Syela */
      victim_count = unit_list_size(atile->units);
 
      if (!can_occupy && NULL == pdefender) {
        /* Nothing there to bash and we can't occupy!
         * Not having this check caused warships yoyoing */
        want = 0;
      } else if (10 < move_time) {
        /* Too far! */
        want = 0;
      } else if (can_occupy && 0 == acity_data->invasion.occupy
                 && (0 < acity_data->invasion.attack
                     || victim_count == 0)) {
        /* Units able to occupy really needed there! */
        want = bcost * SHIELD_WEIGHTING;
      } else {
        want = kill_desire(benefit, attack, bcost + acity_data->bcost,
                           vulnerability, victim_count + 1);
      }
      want -= move_time * (unhap ? SHIELD_WEIGHTING + 2 * TRADE_WEIGHTING 
                           : SHIELD_WEIGHTING);
      /* Build_cost of ferry. */
      needferry = (go_by_boat && NULL == ferryboat
                   ? utype_build_shield_cost(acity, NULL, boattype) : 0);
      /* FIXME: add time to build the ferry? */
      want = military_amortize(pplayer, game_city_by_number(punit->homecity),
                               want, MAX(1, move_time),
                               bcost_bal + needferry);
 
      /* BEGIN STEAM-ENGINES-ARE-OUR-FRIENDS KLUGE. */
      if (0 >= want && 0 == punit->id && 0 >= best) {
        adv_want bk_e = military_amortize(pplayer,
                                          game_city_by_number(punit->homecity),
                                          benefit * SHIELD_WEIGHTING,
                                          MAX(1, move_time),
                                          bcost_bal + needferry);
 
        if (bk_e > bk) {
          *pdest_tile = atile;
          if (NULL != pferrymap) {
            *pferrymap = go_by_boat ? ferry_map : NULL;
          }
          if (NULL != pferryboat) {
            *pferryboat = go_by_boat ? ferryboat : NULL;
          }
          if (NULL != pboattype) {
            *pboattype = go_by_boat ? boattype : NULL;
          }
          if (NULL != pmove_time) {
            *pmove_time = move_time;
          }
          goto_dest_tile = (go_by_boat && NULL != ferryboat
                            ? unit_tile(ferryboat) : atile);
          bk = bk_e;
        }
      }
      /* END STEAM-ENGINES KLUGE */
 
      if (0 != punit->id
          && NULL != ferryboat
          && punit_class->adv.sea_move == MOVE_NONE) {
        UNIT_LOG(LOG_DEBUG, punit,
                 "%s(): with boat %s@(%d, %d) -> %s@(%d, %d)"
                 " (go_by_boat = %d, move_time = %d, want = " ADV_WANT_PRINTF
                 ", best = " ADV_WANT_PRINTF ")",
                 __FUNCTION__, unit_rule_name(ferryboat),
                 TILE_XY(unit_tile(ferryboat)), city_name_get(acity),
                 TILE_XY(atile), go_by_boat, move_time, want, best);
      }
 
      if (want > best && ai_fuzzy(pplayer, TRUE)) {
        /* Yes, we like this target */
        best = want;
        *pdest_tile = atile;
        if (NULL != pferrymap) {
          *pferrymap = go_by_boat ? ferry_map : NULL;
        }
        if (NULL != pferryboat) {
          *pferryboat = go_by_boat ? ferryboat : NULL;
        }
        if (NULL != pboattype) {
          *pboattype = go_by_boat ? boattype : NULL;
        }
        if (NULL != pmove_time) {
          *pmove_time = move_time;
        }
        goto_dest_tile = (go_by_boat && NULL != ferryboat
                          ? unit_tile(ferryboat) : atile);
      }
    } city_list_iterate_end;
 
    attack = unit_att_rating_squared(punit);
    /* I'm not sure the following code is good but it seems to be adequate.
     * I am deliberately not adding ferryboat code to the unit_list_iterate.
     * -- Syela */
    unit_list_iterate(aplayer->units, aunit) {
      struct tile *atile = unit_tile(aunit);
 
      if (NULL != tile_city(atile)) {
        /* already dealt with it. */
        continue;
      }
 
      if (handicap && !map_is_known(atile, pplayer)) {
        /* Can't see the target. */
        continue;
      }
 
      if (!utype_acts_hostile(unit_type_get(aunit))
          && 0 == punit->id) {
        /* We will not build units just to chase caravans and
         * ambassadors. */
        continue;
      }
 
      /* We have to assume the attack is diplomatically ok.
       * We cannot use can_player_attack_tile, because we might not
       * be at war with aplayer yet */
      if (!can_unit_attack_tile(punit, NULL, atile)
          || aunit != get_defender(nmap, punit, atile)) {
        /* We cannot attack it, or it is not the main defender. */
        continue;
      }
 
      if (!pf_map_position(punit_map, atile, &pos)) {
        /* Cannot reach it. */
        continue;
      }
 
      vulnerability = unit_def_rating_squared(punit, aunit);
      benefit = unit_build_shield_cost_base(aunit);
 
      move_time = pos.turn;
      if (10 < move_time) {
        /* Too far. */
        want = 0;
      } else {
        want = kill_desire(benefit, attack, bcost, vulnerability, 1);
          /* Take into account maintainance of the unit. */
          /* FIXME: Depends on the government. */
        want -= move_time * SHIELD_WEIGHTING;
        /* Take into account unhappiness
         * (costs 2 luxuries to compensate). */
        want -= (unhap ? 2 * move_time * TRADE_WEIGHTING : 0);
      }
      want = military_amortize(pplayer, game_city_by_number(punit->homecity),
                               want, MAX(1, move_time), bcost_bal);
      if (want > best && ai_fuzzy(pplayer, TRUE)) {
        best = want;
        *pdest_tile = atile;
        if (NULL != pferrymap) {
          *pferrymap = NULL;
        }
        if (NULL != pferryboat) {
          *pferryboat = NULL;
        }
        if (NULL != pboattype) {
          *pboattype = NULL;
        }
        if (NULL != pmove_time) {
          *pmove_time = move_time;
        }
        goto_dest_tile = atile;
      }
    } unit_list_iterate_end;
  } players_iterate_end;
 
  if (NULL != ppath) {
    *ppath = (NULL != goto_dest_tile && goto_dest_tile != punit_tile
              ? pf_map_path(punit_map, goto_dest_tile) : NULL);
  }
 
  pf_map_destroy(punit_map);
  if (NULL != ferry_map
      && (NULL == pferrymap || *pferrymap != ferry_map)) {
    pf_map_destroy(ferry_map);
  }
 
  TIMING_LOG(AIT_FSTK, TIMER_STOP);
 
  return best;
}
 
/**********************************************************************/
struct city *find_nearest_safe_city(struct unit *punit)
{
  struct pf_parameter parameter;
  struct pf_map *pfm;
  struct player *pplayer = unit_owner(punit);
  struct city *pcity, *best_city = NULL;
  int best = FC_INFINITY, cur;
  const struct civ_map *nmap = &(wld.map);
 
  pft_fill_unit_parameter(&parameter, nmap, punit);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  pfm = pf_map_new(&parameter);
 
  pf_map_move_costs_iterate(pfm, ptile, move_cost, TRUE) {
    if (move_cost > best) {
      /* We already found a better city. No need to continue. */
      break;
    }
 
    pcity = tile_city(ptile);
    if (NULL == pcity || !pplayers_allied(pplayer, city_owner(pcity))) {
      continue;
    }
 
    /* Score based on the move cost. */
    cur = move_cost;
 
    /* Note the unit owner may be different from the city owner. */
    if (0 == get_unittype_bonus(unit_owner(punit), ptile,
                                unit_type_get(punit), NULL,
                                EFT_HP_REGEN)) {
      /* If we cannot regen fast our hit points here, let's make some
       * penalty. */
      cur *= 3;
    }
 
    if (cur < best) {
      best_city = pcity;
      best = cur;
    }
  } pf_map_move_costs_iterate_end;
 
  pf_map_destroy(pfm);
  return best_city;
}
 
/**********************************************************************/
static void dai_military_attack_barbarian(struct ai_type *ait,
                                          struct player *pplayer,
                                          struct unit *punit)
{
  struct city *pc;
  bool only_continent = TRUE;
 
  if (unit_transported(punit)) {
    /* If we are in transport, we can go to any continent.
     * Actually, we are not currently in a continent where to stay. */
    only_continent = FALSE;
  }
 
  if ((pc = find_closest_city(unit_tile(punit), NULL, pplayer, FALSE,
                              only_continent, FALSE, FALSE, TRUE, NULL))) {
    if (can_unit_exist_at_tile(&(wld.map), punit, unit_tile(punit))) {
      UNIT_LOG(LOG_DEBUG, punit, "Barbarian heading to conquer %s",
               city_name_get(pc));
      (void) dai_gothere(ait, pplayer, punit, pc->tile);
    } else {
      struct unit *ferry = NULL;
 
      if (unit_transported(punit)) {
        ferry = unit_transport_get(punit);
 
        /* We already are in a boat so it needs no
         * free capacity */
        if (!is_boat_free(ait, ferry, punit, 0)) {
          /* We cannot control our ferry. */
          ferry = NULL;
        }
      } else {
        /* We are not in a boat yet. Search for one. */
        unit_list_iterate(unit_tile(punit)->units, aunit) {
          if (is_boat_free(ait, aunit, punit, 1)
              && unit_transport_load(punit, aunit, FALSE)) {
            ferry = aunit;
            break;
          }
        } unit_list_iterate_end;
      }
 
      if (ferry) {
        UNIT_LOG(LOG_DEBUG, punit, "Barbarian sailing to conquer %s",
                 city_name_get(pc));
        (void) aiferry_goto_amphibious(ait, ferry, punit, pc->tile);
      } else {
        /* This is not an error. Somebody else might be in charge
         * of the ferry. */
        UNIT_LOG(LOG_DEBUG, punit, "unable to find barbarian ferry");
      }
    }
  } else {
    UNIT_LOG(LOG_DEBUG, punit, "Barbarian find no target city");
  }
}
 
/**********************************************************************/
static void dai_military_attack(struct ai_type *ait, struct player *pplayer,
                                struct unit *punit)
{
  struct tile *dest_tile;
  int id = punit->id;
  int ct = 10;
  struct city *pcity = NULL;
 
  CHECK_UNIT(punit);
 
  /* Barbarians pillage, and might keep on doing that so they sometimes
   * even finish it. */
  if (punit->activity == ACTIVITY_PILLAGE && is_barbarian(pplayer)
      && fc_rand(2) == 1) {
    return;
  }
 
  /* First find easy nearby enemies, anything better than pillage goes.
   * NB: We do not need to repeat dai_military_rampage, it is repeats itself
   * until it runs out of targets. */
  /* FIXME: 1. dai_military_rampage never checks if it should defend newly
   * conquered cities.
   * FIXME: 2. would be more convenient if it returned FALSE if we run out 
   * of moves too.*/
  if (!dai_military_rampage(punit, RAMPAGE_ANYTHING, RAMPAGE_ANYTHING)) {
    return; /* we died */
  }
  
  if (punit->moves_left <= 0) {
    return;
  }
 
  /* Main attack loop */
  do {
    struct tile *start_tile = unit_tile(punit);
    struct pf_path *path;
    struct unit *ferryboat;
 
    /* Then find enemies the hard way */
    find_something_to_kill(ait, pplayer, punit, &dest_tile, &path,
                           NULL, &ferryboat, NULL, NULL);
    if (!same_pos(unit_tile(punit), dest_tile)) {
      if (!is_tiles_adjacent(unit_tile(punit), dest_tile)
          || !can_unit_attack_tile(punit, NULL, dest_tile)) {
 
        /* Adjacent and can't attack usually means we are not marines
         * and on a ferry. This fixes the problem (usually). */
        UNIT_LOG(LOG_DEBUG, punit, "mil att gothere -> (%d, %d)",
                 TILE_XY(dest_tile));
 
        /* Set ACTIVITY_GOTO more permanently than just inside
         * adv_follow_path(). This way other units will know we're
         * on our way even if we don't reach target yet. */
        punit->goto_tile = dest_tile;
        unit_activity_handling(punit, ACTIVITY_GOTO);
        if (NULL != path && !adv_follow_path(punit, path, dest_tile)) {
          /* Died. */
          pf_path_destroy(path);
          return;
        }
        if (NULL != ferryboat) {
          /* Need a boat. */
          aiferry_gobyboat(ait, pplayer, punit, dest_tile, FALSE);
          pf_path_destroy(path);
          return;
        }
        if (0 >= punit->moves_left) {
          /* No moves left. */
          pf_path_destroy(path);
          return;
        }
 
        /* Either we're adjacent or we sitting on the tile. We might be
         * sitting on the tile if the enemy that _was_ sitting there 
         * attacked us and died _and_ we had enough movement to get there */
        if (same_pos(unit_tile(punit), dest_tile)) {
          UNIT_LOG(LOG_DEBUG, punit, "mil att made it -> (%d, %d)",
                   TILE_XY(dest_tile));
          pf_path_destroy(path);
          break;
        }
      }
 
      if (is_tiles_adjacent(unit_tile(punit), dest_tile)) {
        /* Close combat. fstk sometimes want us to attack an adjacent
         * enemy that rampage wouldn't */
        UNIT_LOG(LOG_DEBUG, punit, "mil att bash -> (%d, %d)",
                 TILE_XY(dest_tile));
        if (!dai_unit_attack(ait, punit, dest_tile)) {
          /* Died */
          pf_path_destroy(path);
          return;
        }
      } else if (!same_pos(start_tile, unit_tile(punit))) {
        /* Got stuck. Possibly because of adjacency to an
         * enemy unit. Perhaps we are in luck and are now next to a
         * tempting target? Let's find out... */
        (void) dai_military_rampage(punit,
                                    RAMPAGE_ANYTHING, RAMPAGE_ANYTHING);
        pf_path_destroy(path);
        return;
      }
 
    } else {
      /* FIXME: This happens a bit too often! */
      UNIT_LOG(LOG_DEBUG, punit, "fstk didn't find us a worthy target!");
      /* No worthy enemies found, so abort loop */
      ct = 0;
    }
    pf_path_destroy(path);
 
    ct--; /* infinite loops from railroads must be stopped */
  } while (punit->moves_left > 0 && ct > 0);
 
  /* Cleanup phase */
  if (punit->moves_left == 0) {
    return;
  }
  pcity = find_nearest_safe_city(punit);
  if (pcity != NULL
      && (dai_is_ferry(punit, ait)
          || punit->hp < unit_type_get(punit)->hp * 0.50)) { /* WAG */
    /* Go somewhere safe */
    UNIT_LOG(LOG_DEBUG, punit, "heading to nearest safe house.");
    (void) dai_unit_goto(ait, punit, pcity->tile);
  } else if (!is_barbarian(pplayer)) {
    /* Nothing else to do, so try exploring. */
    switch (manage_auto_explorer(punit)) {
    case MR_DEATH:
      /* don't use punit! */
      return;
    case MR_OK:
      UNIT_LOG(LOG_DEBUG, punit, "nothing else to do, so exploring");
      break;
    default:
      UNIT_LOG(LOG_DEBUG, punit, "nothing to do - no more exploring either");
      break;
    };
  } else {
    /* You can still have some moves left here, but barbarians should
       not sit helplessly, but advance towards nearest known enemy city */
    UNIT_LOG(LOG_DEBUG, punit, "attack: barbarian");
    dai_military_attack_barbarian(ait, pplayer, punit);
  }
  if ((punit = game_unit_by_number(id)) && punit->moves_left > 0) {
    UNIT_LOG(LOG_DEBUG, punit, "attack: giving up unit to defense");
    dai_military_defend(ait, pplayer, punit);
  }
}
 
/**********************************************************************/
static bool dai_find_boat_for_unit(struct ai_type *ait, struct unit *punit)
{
  bool alive = TRUE;
  int ferryboat = 0;
  struct pf_path *path_to_ferry = NULL;
 
  UNIT_LOG(LOG_CARAVAN, punit, "requesting a boat!");
  ferryboat = aiferry_find_boat(ait, punit, 1, &path_to_ferry);
  /* going to meet the boat */
  if ((ferryboat <= 0)) {
    UNIT_LOG(LOG_CARAVAN, punit, 
             "in find_boat_for_unit cannot find any boats.");
    /* if we are undefended on the country side go to a city */
    struct city *current_city = tile_city(unit_tile(punit));
    if (current_city == NULL) {
      struct city *city_near = find_nearest_safe_city(punit);
      if (city_near != NULL) {
        alive = dai_unit_goto(ait, punit, city_near->tile);
      }
    }
  } else {
    if (path_to_ferry != NULL) {
      if (!adv_unit_execute_path(punit, path_to_ferry)) { 
        /* Died. */
        pf_path_destroy(path_to_ferry);
        path_to_ferry = NULL;
        alive = FALSE;
      } else {
        pf_path_destroy(path_to_ferry);
        path_to_ferry = NULL;
        alive = TRUE;
      }
    }
  }
  return alive;
}
 
/**********************************************************************/
bool uclass_need_trans_between(struct unit_class *pclass,
                               struct tile *ctile, struct tile *ptile)
{
  /* We usually have Inaccessible terrain, so not testing MOVE_FULL == */
  bool lm = MOVE_NONE != pclass->adv.land_move,
    sm = MOVE_NONE != pclass->adv.sea_move;
  struct civ_map *pmap = &(wld.map);
 
  if (lm && sm) {
    return FALSE;
  }
 
  /* We could use adjc_iterate() but likely often tiles are on the same
   * continent and it will be more time to find where they connect */
  iterate_outward(pmap, ctile, 1, atile) {
    Continent_id acont = tile_continent(atile);
 
    if (is_ocean_tile(atile) ? sm : lm) {
      iterate_outward(pmap, ptile, 1, btile) {
        if (tile_continent(btile) == acont) {
          return FALSE;
        }
      } iterate_outward_end;
    }
  } iterate_outward_end;
 
  if (is_tiles_adjacent(ctile, ptile)) {
    return FALSE;
  }
 
  return TRUE;
}
 
/**********************************************************************/
static void dai_caravan_goto(struct ai_type *ait, struct player *pplayer,
                             struct unit *punit,
                             const struct city *dest_city,
                             bool help_wonder,
                             bool required_boat, bool request_boat)
{
  bool alive = TRUE;
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
  const struct civ_map *nmap = &(wld.map);
 
  fc_assert_ret(NULL != dest_city);
 
  /* if we're not there yet, and we can move, move... */
  if (!same_pos(dest_city->tile, unit_tile(punit))
      && punit->moves_left != 0) {
    log_base(LOG_CARAVAN, "%s %s[%d](%d,%d) task %s going to %s in %s %s",
             nation_rule_name(nation_of_unit(punit)),
             unit_rule_name(punit), punit->id, TILE_XY(unit_tile(punit)),
             dai_unit_task_rule_name(unit_data->task),
             help_wonder ? "help a wonder" : "trade", city_name_get(dest_city),
             required_boat ? "with a boat" : "");
    if (required_boat) {
      /* to trade with boat */
      if (request_boat) {
        /* Try to find new boat */
        alive = dai_find_boat_for_unit(ait, punit);
      } else {
        /* if we are not being transported then ask for a boat again */
        alive = TRUE;
        if (!unit_transported(punit)
            && uclass_need_trans_between(unit_class_get(punit),
                                         unit_tile(punit), dest_city->tile)) {
          alive = dai_find_boat_for_unit(ait, punit);
        }
      }
      if (alive)  {
        /* FIXME: sometimes we get FALSE here just because
         * a trireme that we've boarded can't go over an ocean. */
        alive = dai_gothere(ait, pplayer, punit, dest_city->tile);
      }
    } else {
      /* to trade without boat */
      alive = dai_unit_goto(ait, punit, dest_city->tile);
    }
  }
 
  /* if moving didn't kill us, and we got to the destination, handle it. */
  if (alive && real_map_distance(dest_city->tile, unit_tile(punit)) <= 1) {
    /* release the boat! */
    if (unit_transported(punit)) {
      aiferry_clear_boat(ait, punit);
    }
    if (help_wonder && is_action_enabled_unit_on_city(nmap, ACTION_HELP_WONDER,
                                                      punit, dest_city)) {
        /*
         * We really don't want to just drop all caravans in immediately.
         * Instead, we want to aggregate enough caravans to build instantly.
         * -AJS, 990704
         */
      log_base(LOG_CARAVAN, "%s %s[%d](%d,%d) helps build wonder in %s",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit),
               punit->id,
               TILE_XY(unit_tile(punit)),
               city_name_get(dest_city));
      unit_do_action(pplayer, punit->id, dest_city->id,
                     0, "", ACTION_HELP_WONDER);
    } else if (is_action_enabled_unit_on_city(nmap, ACTION_TRADE_ROUTE,
                                              punit, dest_city)) {
      log_base(LOG_CARAVAN, "%s %s[%d](%d,%d) creates trade route in %s",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit),
               punit->id,
               TILE_XY(unit_tile(punit)),
               city_name_get(dest_city));
      unit_do_action(pplayer, punit->id, dest_city->id,
                     0, "", ACTION_TRADE_ROUTE);
    } else if (is_action_enabled_unit_on_city(nmap, ACTION_MARKETPLACE,
                                              punit, dest_city)) {
      /* Get the one time bonus. */
      log_base(LOG_CARAVAN, "%s %s[%d](%d,%d) enters marketplace of %s",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit),
               punit->id,
               TILE_XY(unit_tile(punit)),
               city_name_get(dest_city));
      unit_do_action(pplayer, punit->id, dest_city->id,
                     0, "", ACTION_MARKETPLACE);
    } else {
      enum log_level level = LOG_NORMAL;
 
      if (help_wonder) {
        /* A Caravan ordered to help build wonder may arrive after
         * enough shields to build the wonder is produced. */
        level = LOG_VERBOSE;
      }
 
      log_base(level,
               "%s %s[%d](%d,%d) unable to trade with %s",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit),
               punit->id,
               TILE_XY(unit_tile(punit)),
               city_name_get(dest_city));
    }
  }
}
 
/**********************************************************************/
static void caravan_optimize_callback(const struct caravan_result *result,
                                      void *data)
{
  const struct unit *caravan = data;
 
  log_base(LOG_CARAVAN3, "%s %s[%d](%d,%d) %s: %s %s worth %g",
           nation_rule_name(nation_of_unit(caravan)),
           unit_rule_name(caravan),
           caravan->id,
           TILE_XY(unit_tile(caravan)),
           city_name_get(result->src),
           result->help_wonder ? "wonder in" : "trade to",
           city_name_get(result->dest),
           result->value);
}
 
/**********************************************************************/
static bool dai_is_unit_tired_waiting_boat(struct ai_type *ait,
                                           struct unit *punit)
{
  struct tile *src = NULL, *dest = NULL, *src_home_city = NULL;
  struct city *phome_city = NULL;
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
  
  if ((unit_data->task != AIUNIT_NONE)) {
    src = unit_tile(punit);
    phome_city = game_city_by_number(punit->homecity);
    if (phome_city != NULL) {
      src_home_city = city_tile(phome_city);
    }
    dest = punit->goto_tile;
 
    if (src == NULL || dest == NULL) {
      return FALSE;
    }
 
    /* If we have a home continent, and are not there.
     * (FIXME: well, why?)
     * (I guess because home continent is which we were supposed to leave,
     *  not the target continent) */
    if (src_home_city != NULL
        && tile_continent(src) != tile_continent(src_home_city)) {
      return FALSE;
    }
 
    if (!goto_is_sane(punit, dest)) {
      if (unit_transported(punit)) {
        /* if we're being transported */
        return FALSE;
      }
      if ((punit->server.birth_turn + 15 < game.info.turn)) {
        /* we are tired of waiting */
        int ferrys = aiferry_avail_boats(ait, punit->owner);
 
        if (ferrys <= 0) {
          /* there are no ferrys available... give up */
          return TRUE;
        } else {
          if (punit->server.birth_turn + 20 < game.info.turn) {
            /* we are feed up! */
            return TRUE;
          }
        }
      }
    }
  }
 
  return FALSE;
}
 
/**********************************************************************/
static bool dai_caravan_can_trade_cities_diff_cont(struct player *pplayer,
                                                   struct unit *punit)
{
  struct city *pcity = game_city_by_number(punit->homecity);
  Continent_id continent;
 
  fc_assert(pcity != NULL);
 
  if (unit_class_get(punit)->adv.ferry_types <= 0) {
    /* There is just no possible transporters. */
    return FALSE;
  }
  continent = tile_continent(pcity->tile);
 
  /* Look for proper destination city at different continent. */
  city_list_iterate(pplayer->cities, acity) {
    if (can_cities_trade(pcity, acity)) {
      if (tile_continent(acity->tile) != continent) {
        return TRUE;
      }
    }
  } city_list_iterate_end;
 
  players_iterate(aplayer) {
    if (aplayer == pplayer || !aplayer->is_alive) {
      continue;
    }
    if (pplayers_allied(pplayer, aplayer)) {      
      city_list_iterate(aplayer->cities, acity) {
        if (can_cities_trade(pcity, acity)) {
          if (tile_continent(acity->tile) != continent) {
            return TRUE;
          }
        }
      } city_list_iterate_end;
    } players_iterate_end;
  }
 
  return FALSE;
}
 
/**********************************************************************/
static bool search_homecity_for_caravan(struct ai_type *ait, struct unit *punit)
{
  struct city *nearest = NULL;
  int min_dist = FC_INFINITY;
  struct tile *current_loc = unit_tile(punit);
  Continent_id continent = tile_continent(current_loc);
  bool alive = TRUE;
 
  city_list_iterate(punit->owner->cities, pcity) {
    struct tile *ctile = city_tile(pcity);
 
    if (tile_continent(ctile) == continent) {
      int this_dist = map_distance(current_loc, ctile);
 
      if (this_dist < min_dist) {
        min_dist = this_dist;
        nearest = pcity;
      }
    }
  } city_list_iterate_end;
 
  if (nearest != NULL) {
    alive = dai_unit_goto(ait, punit, nearest->tile);
    if (alive && same_pos(unit_tile(punit), nearest->tile)) {
      dai_unit_make_homecity(punit, nearest);
    }
  }
 
  return alive;
}
 
/**********************************************************************/
static void dai_manage_caravan(struct ai_type *ait, struct player *pplayer,
                               struct unit *punit)
{
  struct caravan_parameter parameter;
  struct caravan_result result;
  const struct city *homecity;
  const struct city *dest = NULL;
  struct unit_ai *unit_data;
  struct unit_class *pclass = unit_class_get(punit);
  bool expect_boats = pclass->adv.ferry_types > 0;
  /* TODO: will pplayer have a boat for punit in a reasonable time? */
  bool help_wonder = FALSE;
  bool required_boat = FALSE;
  bool request_boat = FALSE;
  bool tired_of_waiting_boat = FALSE;
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
 
  if (!unit_can_do_action(punit, ACTION_TRADE_ROUTE)
      && !unit_can_do_action(punit, ACTION_MARKETPLACE)
      && !unit_can_do_action(punit, ACTION_HELP_WONDER)) {
    /* we only want units that can establish trade, enter marketplace or
     * help build wonders */
    return;
  }
 
  unit_data = def_ai_unit_data(punit, ait);
 
  log_base(LOG_CARAVAN2, "%s %s[%d](%d,%d) task %s to (%d,%d)",
           nation_rule_name(nation_of_unit(punit)),
           unit_rule_name(punit), punit->id, TILE_XY(unit_tile(punit)),
           dai_unit_task_rule_name(unit_data->task), 
           TILE_XY(punit->goto_tile));
 
  homecity = game_city_by_number(punit->homecity);
  if (homecity == NULL && unit_data->task == AIUNIT_TRADE) {
    if (!search_homecity_for_caravan(ait, punit)) {
      return;
    }
    homecity = game_city_by_number(punit->homecity);
    if (homecity == NULL) {
      return;
    }
  }
 
  if ((unit_data->task == AIUNIT_TRADE
       || unit_data->task == AIUNIT_WONDER)) {
    /* we are moving to our destination */
    /* we check to see if our current goal is feasible */
    struct city *city_dest = tile_city(punit->goto_tile);
 
    if ((city_dest == NULL) 
        || !pplayers_allied(unit_owner(punit), city_dest->owner)
        || (unit_data->task == AIUNIT_TRADE
            && !(can_cities_trade(homecity, city_dest)
                 && can_establish_trade_route(homecity, city_dest)))
        || (unit_data->task == AIUNIT_WONDER
            /* Helping the (new) production is illegal. */
            && !city_production_gets_caravan_shields(&city_dest->production))
        || (unit_data->task == AIUNIT_TRADE
            && real_map_distance(city_dest->tile, unit_tile(punit)) <= 1
            && !(is_action_enabled_unit_on_city(nmap, ACTION_TRADE_ROUTE,
                                                punit, city_dest)
                 || is_action_enabled_unit_on_city(nmap, ACTION_MARKETPLACE,
                                                   punit, city_dest)))
        || (unit_data->task == AIUNIT_WONDER
            && real_map_distance(city_dest->tile, unit_tile(punit)) <= 1
            && !is_action_enabled_unit_on_city(nmap, ACTION_HELP_WONDER,
                                               punit, city_dest))) {
      /* destination invalid! */
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
      log_base(LOG_CARAVAN2, "%s %s[%d](%d,%d) destination invalid!",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit), punit->id, TILE_XY(unit_tile(punit)));
    } else {
      /* destination valid, are we tired of waiting for a boat? */
      if (expect_boats && dai_is_unit_tired_waiting_boat(ait, punit)) {
        aiferry_clear_boat(ait, punit);
        dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
        log_base(LOG_CARAVAN2, "%s %s[%d](%d,%d) unit tired of waiting!",
                 nation_rule_name(nation_of_unit(punit)),
                 unit_rule_name(punit), punit->id, TILE_XY(unit_tile(punit)));
        tired_of_waiting_boat = TRUE;
      } else {
        dest = city_dest;
        help_wonder = (unit_data->task == AIUNIT_WONDER) ? TRUE : FALSE;
        required_boat = uclass_need_trans_between(pclass, unit_tile(punit), dest->tile);
        request_boat = FALSE;
      }
    }
  }
 
  if (unit_data->task == AIUNIT_NONE) {
    if (homecity == NULL) {
      /* FIXME: We shouldn't bother in getting homecity for
       * caravan that will then be used for wonder building. */
      if (!search_homecity_for_caravan(ait, punit)) {
        return;
      }
      homecity = game_city_by_number(punit->homecity);
      if (homecity == NULL) {
        return;
      }
    }
 
    caravan_parameter_init_from_unit(&parameter, punit);
    /* Make more trade with allies than other peaceful nations
     * by considering only allies 50% of the time.
     * (the other 50% allies are still considered, but so are other nations) */
    if (fc_rand(2)) {
      /* Be optimistic about development of relations with no-contact and
       * cease-fire nations. */
      parameter.allow_foreign_trade = FTL_NONWAR;
    } else {
      parameter.allow_foreign_trade = FTL_ALLIED;
    }
 
    if (log_do_output_for_level(LOG_CARAVAN2)) {
      parameter.callback = caravan_optimize_callback;
      parameter.callback_data = punit;
    }
    if (dai_caravan_can_trade_cities_diff_cont(pplayer, punit)) {
      parameter.ignore_transit_time = TRUE;
    }
    if (tired_of_waiting_boat) {
      parameter.allow_foreign_trade = FTL_NATIONAL_ONLY;
      parameter.ignore_transit_time = FALSE;
    }
    caravan_find_best_destination(nmap, punit, &parameter, &result,
                                  !has_handicap(pplayer, H_MAP));
    if (result.dest != NULL) {
      /* We did find a new destination for the unit */
      dest = result.dest;
      help_wonder = result.help_wonder;
      required_boat = uclass_need_trans_between(pclass, unit_tile(punit), dest->tile);
      request_boat = required_boat;
      dai_unit_new_task(ait, punit,
                        (help_wonder) ? AIUNIT_WONDER : AIUNIT_TRADE,
                        dest->tile);
    } else {
      dest = NULL;
    }
  }
 
  if (required_boat && !expect_boats) {
    /* Would require boat, but can't have them. Render destination invalid. */
    dest = NULL;
  }
 
  if (dest != NULL) {
    dai_caravan_goto(ait, pplayer, punit, dest, help_wonder, 
                     required_boat, request_boat);
    return; /* that may have clobbered the unit */
  } else {
    /* We have nowhere to go! */
     log_base(LOG_CARAVAN2, "%s %s[%d](%d,%d), nothing to do!",
              nation_rule_name(nation_of_unit(punit)),
              unit_rule_name(punit), punit->id,
              TILE_XY(unit_tile(punit)));
     /* Should we become a defensive unit? */
  }
}
 
/**********************************************************************/
static void dai_manage_hitpoint_recovery(struct ai_type *ait,
                                         struct unit *punit)
{
  struct player *pplayer = unit_owner(punit);
  struct city *pcity = tile_city(unit_tile(punit));
  struct city *safe = NULL;
  const struct unit_type *punittype = unit_type_get(punit);
  bool no_recovery;
 
  CHECK_UNIT(punit);
 
  if (pcity != NULL) {
    /* Rest in the city until the hitpoints are recovered, but attempt
     * to protect city from attack (and be opportunistic too)*/
    if (dai_military_rampage(punit, RAMPAGE_ANYTHING, 
                             RAMPAGE_FREE_CITY_OR_BETTER)) {
      UNIT_LOG(LOGLEVEL_RECOVERY, punit, "recovering hit points.");
    } else {
      return; /* We died heroically defending our city */
    }
  } else {
    /* Goto to nearest city to recover hit points */
    /* Just before, check to see if we can occupy an undefended enemy city */
    if (!dai_military_rampage(punit, RAMPAGE_FREE_CITY_OR_BETTER, 
                              RAMPAGE_FREE_CITY_OR_BETTER)) { 
      return; /* Oops, we died */
    }
 
    /* Find a city to stay and go there */
    safe = find_nearest_safe_city(punit);
    if (safe) {
      UNIT_LOG(LOGLEVEL_RECOVERY, punit, "going to %s to recover",
               city_name_get(safe));
      if (!dai_unit_goto(ait, punit, safe->tile)) {
        log_base(LOGLEVEL_RECOVERY, "died trying to hide and recover");
        return;
      }
    } else {
      /* Oops */
      UNIT_LOG(LOGLEVEL_RECOVERY, punit, "didn't find a city to recover in!");
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
      dai_military_attack(ait, pplayer, punit);
      return;
    }
  }
 
  /* Is the unit still damaged? If true, and could recover hit points, do so.
   * Don't wait if would be losing hitpoints that way! */
  no_recovery = FALSE;
  if (punit->hp == punittype->hp) {
    no_recovery = TRUE;
  } else {
    int gain = unit_gain_hitpoints(punit);
 
    if (gain < 0) {
      no_recovery = TRUE;
    } else if (gain == 0 && !punit->moved) {
      /* Isn't gaining even though has not moved. */
      no_recovery = TRUE;
    }
  }
  if (no_recovery) {
    /* We are ready to go out and kick ass again */
    UNIT_LOG(LOGLEVEL_RECOVERY, punit, "ready to kick ass again!");
    dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);  
    return;
  } else {
    def_ai_unit_data(punit, ait)->done = TRUE; /* Sit tight */
  }
}
 
/**********************************************************************/
void dai_manage_military(struct ai_type *ait, struct player *pplayer,
                         struct unit *punit)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
  int id = punit->id;
 
  CHECK_UNIT(punit);
 
  /* "Escorting" aircraft should not do anything. They are activated
   * by their transport or charge.  We do _NOT_ set them to 'done'
   * since they may need be activated once our charge moves. */
  if (unit_data->task == AIUNIT_ESCORT
      && utype_fuel(unit_type_get(punit))) {
    return;
  }
 
  if ((punit->activity == ACTIVITY_SENTRY
       || punit->activity == ACTIVITY_FORTIFIED)
      && has_handicap(pplayer, H_AWAY)) {
    /* Don't move sentried or fortified units controlled by a player
     * in away mode. */
    unit_data->done = TRUE;
    return;
  }
 
  /* Since military units re-evaluate their actions every turn,
     we must make sure that previously reserved ferry is freed. */
  aiferry_clear_boat(ait, punit);
 
  TIMING_LOG(AIT_HUNTER, TIMER_START);
  /* Try hunting with this unit */
  if (dai_hunter_qualify(pplayer, punit)) {
    int result, sanity = punit->id;
 
    UNIT_LOG(LOGLEVEL_HUNT, punit, "is qualified as hunter");
    result = dai_hunter_manage(ait, pplayer, punit);
    if (NULL == game_unit_by_number(sanity)) {
      TIMING_LOG(AIT_HUNTER, TIMER_STOP);
      return; /* died */
    }
    if (result == -1) {
      (void) dai_hunter_manage(ait, pplayer, punit); /* More carnage */
      TIMING_LOG(AIT_HUNTER, TIMER_STOP);
      return;
    } else if (result >= 1) {
      TIMING_LOG(AIT_HUNTER, TIMER_STOP);
      return; /* Done moving */
    } else if (unit_data->task == AIUNIT_HUNTER) {
      /* This should be very rare */
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
    }
  } else if (unit_data->task == AIUNIT_HUNTER) {
    dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
  }
  TIMING_LOG(AIT_HUNTER, TIMER_STOP);
 
  /* Do we have a specific job for this unit? If not, we default
   * to attack. */
  dai_military_findjob(ait, pplayer, punit);
 
  switch (unit_data->task) {
  case AIUNIT_AUTO_SETTLER:
  case AIUNIT_BUILD_CITY:
    fc_assert(FALSE); /* This is not the place for this role */
    break;
  case AIUNIT_DEFEND_HOME:
    TIMING_LOG(AIT_DEFENDERS, TIMER_START);
    dai_military_defend(ait, pplayer, punit);
    TIMING_LOG(AIT_DEFENDERS, TIMER_STOP);
    break;
  case AIUNIT_ATTACK:
  case AIUNIT_NONE:
    TIMING_LOG(AIT_ATTACK, TIMER_START);
    dai_military_attack(ait, pplayer, punit);
    TIMING_LOG(AIT_ATTACK, TIMER_STOP);
    break;
  case AIUNIT_ESCORT: 
    TIMING_LOG(AIT_BODYGUARD, TIMER_START);
    dai_military_bodyguard(ait, pplayer, punit);
    TIMING_LOG(AIT_BODYGUARD, TIMER_STOP);
    break;
  case AIUNIT_EXPLORE:
    switch (manage_auto_explorer(punit)) {
    case MR_DEATH:
      /* don't use punit! */
      return;
    case MR_OK:
      UNIT_LOG(LOG_DEBUG, punit, "more exploring");
      break;
    default:
      UNIT_LOG(LOG_DEBUG, punit, "no more exploring either");
      break;
    };
    def_ai_unit_data(punit, ait)->done = (punit->moves_left <= 0);
    break;
  case AIUNIT_RECOVER:
    TIMING_LOG(AIT_RECOVER, TIMER_START);
    dai_manage_hitpoint_recovery(ait, punit);
    TIMING_LOG(AIT_RECOVER, TIMER_STOP);
    break;
  case AIUNIT_HUNTER:
    fc_assert(FALSE); /* dealt with above */
    break;
  default:
    fc_assert(FALSE);
  }
 
  /* If we are still alive, either sentry or fortify. */
  if ((punit = game_unit_by_number(id))) {
    unit_data = def_ai_unit_data(punit, ait);
    struct city *pcity = tile_city(unit_tile(punit));
 
    if (unit_list_find(unit_tile(punit)->units,
                       unit_data->ferryboat)) {
      unit_activity_handling(punit, ACTIVITY_SENTRY);
    } else if (pcity || punit->activity == ACTIVITY_IDLE) {
      /* We do not need to fortify in cities - we fortify and sentry
       * according to home defense setup, for easy debugging. */
      if (!pcity || unit_data->task == AIUNIT_DEFEND_HOME) {
        if (punit->activity == ACTIVITY_IDLE
            || punit->activity == ACTIVITY_SENTRY) {
          unit_activity_handling(punit, ACTIVITY_FORTIFYING);
        }
      } else {
        unit_activity_handling(punit, ACTIVITY_SENTRY);
      }
    }
  }
}
 
/**********************************************************************/
static void dai_manage_settler(struct ai_type *ait, struct player *pplayer,
                               struct unit *punit)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  unit_server_side_agent_set(pplayer, punit, SSA_AUTOSETTLER);
  unit_data->done = TRUE; /* we will manage this unit later... ugh */
  /* if BUILD_CITY must remain BUILD_CITY, otherwise turn into autosettler */
  if (unit_data->task == AIUNIT_NONE) {
    adv_unit_new_task(punit, AUT_AUTO_SETTLER, NULL);
  }
  return;
}
 
/**********************************************************************/
void dai_manage_unit(struct ai_type *ait, struct player *pplayer,
                     struct unit *punit)
{
  struct unit_ai *unit_data;
  struct unit *bodyguard = aiguard_guard_of(ait, punit);
  bool is_ferry = FALSE;
  const struct unit_type *ptype;
 
  CHECK_UNIT(punit);
 
  /* Don't manage the unit if it is under human orders. */
  if (unit_has_orders(punit)) {
    unit_data = def_ai_unit_data(punit, ait);
 
    UNIT_LOG(LOG_VERBOSE, punit, "is under human orders, aborting AI control.");
    dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
    unit_data->done = TRUE;
    return;
  }
 
  /* Check if we have lost our bodyguard. If we never had one, all
   * fine. If we had one and lost it, ask for a new one. */
  if (!bodyguard && aiguard_has_guard(ait, punit)) {
    UNIT_LOG(LOGLEVEL_BODYGUARD, punit, "lost bodyguard, asking for new");
    aiguard_request_guard(ait, punit);
  }
 
  unit_data = def_ai_unit_data(punit, ait);
 
  if (punit->moves_left <= 0) {
    /* Can do nothing */
    unit_data->done = TRUE;
    return;
  }
 
  is_ferry = dai_is_ferry(punit, ait);
 
  ptype = unit_type_get(punit);
 
  if (utype_has_flag(ptype, UTYF_DIPLOMAT)) {
    TIMING_LOG(AIT_DIPLOMAT, TIMER_START);
    dai_manage_diplomat(ait, pplayer, punit);
    TIMING_LOG(AIT_DIPLOMAT, TIMER_STOP);
    return;
  } else if (ptype->adv.worker
             || unit_is_cityfounder(punit)) {
    dai_manage_settler(ait, pplayer, punit);
    return;
  } else if (unit_can_do_action(punit, ACTION_TRADE_ROUTE)
             || unit_can_do_action(punit, ACTION_MARKETPLACE)
             || unit_can_do_action(punit, ACTION_HELP_WONDER)) {
    TIMING_LOG(AIT_CARAVAN, TIMER_START);
    dai_manage_caravan(ait, pplayer, punit);
    TIMING_LOG(AIT_CARAVAN, TIMER_STOP);
    return;
  } else if (unit_has_type_role(punit, L_BARBARIAN_LEADER)) {
    dai_manage_barbarian_leader(ait, pplayer, punit);
    return;
  } else if (unit_can_do_action_result(punit, ACTRES_PARADROP)
             || unit_can_do_action_result(punit, ACTRES_PARADROP_CONQUER)) {
    dai_manage_paratrooper(ait, pplayer, punit);
    return;
  } else if (is_ferry && unit_data->task != AIUNIT_HUNTER) {
    TIMING_LOG(AIT_FERRY, TIMER_START);
    dai_manage_ferryboat(ait, pplayer, punit);
    TIMING_LOG(AIT_FERRY, TIMER_STOP);
    return;
  } else if (utype_fuel(ptype)
             && unit_data->task != AIUNIT_ESCORT) {
    TIMING_LOG(AIT_AIRUNIT, TIMER_START);
    dai_manage_airunit(ait, pplayer, punit);
    TIMING_LOG(AIT_AIRUNIT, TIMER_STOP);
    return;
  } else if (is_losing_hp(punit)) {
    /* This unit is losing hitpoints over time */
 
    /* TODO: We can try using air-unit code for helicopters, just
     * pretend they have fuel = HP / 3 or something. */
    unit_data->done = TRUE; /* we did our best, which was ... 
                                             nothing */
    return;
  } else if (is_military_unit(punit)) {
    TIMING_LOG(AIT_MILITARY, TIMER_START);
    UNIT_LOG(LOG_DEBUG, punit, "recruit unit for the military");
    dai_manage_military(ait, pplayer, punit); 
    TIMING_LOG(AIT_MILITARY, TIMER_STOP);
    return;
  } else {
    /* what else could this be? -- Syela */
    switch (manage_auto_explorer(punit)) {
    case MR_DEATH:
      /* don't use punit! */
      break;
    case MR_OK:
      UNIT_LOG(LOG_DEBUG, punit, "now exploring");
      break;
    default:
      UNIT_LOG(LOG_DEBUG, punit, "fell through all unit tasks, defending");
      dai_unit_new_task(ait, punit, AIUNIT_DEFEND_HOME, NULL);
      dai_military_defend(ait, pplayer, punit);
      break;
    };
    return;
  }
}
 
/**********************************************************************/
static void dai_set_defenders(struct ai_type *ait, struct player *pplayer)
{
  city_list_iterate(pplayer->cities, pcity) {
    /* The idea here is that we should never keep more than two
     * units in permanent defense. */
    int total_defense = 0;
    int total_attack = def_ai_city_data(pcity, ait)->danger;
    bool emergency = FALSE;
    int count = 0;
    int mart_max = get_city_bonus(pcity, EFT_MARTIAL_LAW_MAX);
    int mart_each = get_city_bonus(pcity, EFT_MARTIAL_LAW_EACH);
    int martless_unhappy = pcity->feel[CITIZEN_UNHAPPY][FEELING_NATIONALITY]
      + pcity->feel[CITIZEN_ANGRY][FEELING_NATIONALITY];
    int entertainers = 0;
    bool enough = FALSE;
 
    specialist_type_iterate(sp) {
      if (get_specialist_output(pcity, sp, O_LUXURY) > 0) {
        entertainers += pcity->specialists[sp];
      }
    } specialist_type_iterate_end;
 
    martless_unhappy += entertainers; /* We want to use martial law instead
                                       * of entertainers. */
 
    while (!enough
           && (total_defense <= total_attack
               || (count < mart_max && mart_each > 0
                   && martless_unhappy > mart_each * count))) {
      int best_want = 0;
      struct unit *best = NULL;
      bool defense_needed = total_defense <= total_attack; /* Defense or martial */
 
      unit_list_iterate(pcity->tile->units, punit) {
        struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
        if ((unit_data->task == AIUNIT_NONE || emergency)
            && unit_data->task != AIUNIT_DEFEND_HOME
            && unit_owner(punit) == pplayer) {
          int want = assess_defense_unit(ait, pcity, punit, FALSE);
 
          if (want > best_want) {
            best_want = want;
            best = punit;
          }
        }
      } unit_list_iterate_end;
      
      if (best == NULL) {
        if (defense_needed) {
          /* Ooops - try to grab any unit as defender! */
          if (emergency) {
            CITY_LOG(LOG_DEBUG, pcity, "Not defended properly");
            break;
          }
          emergency = TRUE;
        } else {
          break;
        }
      } else {
        const struct unit_type *btype = unit_type_get(best);
 
        if ((martless_unhappy < mart_each * count
             || count >= mart_max || mart_each <= 0)
            && ((count >= 2
                 && btype->attack_strength > btype->defense_strength)
                || (count >= 4
                    && btype->attack_strength == btype->defense_strength))) {
          /* In this case attack would be better defense than fortifying
           * to city. */
          enough = TRUE;
        } else {
          int loglevel = pcity->server.debug ? LOG_AI_TEST : LOG_DEBUG;
 
          total_defense += best_want;
          UNIT_LOG(loglevel, best, "Defending city");
          dai_unit_new_task(ait, best, AIUNIT_DEFEND_HOME, pcity->tile);
          count++;
        }
      }
    }
    CITY_LOG(LOG_DEBUG, pcity, "Evaluating defense: %d defense, %d incoming"
             ", %d defenders (out of %d)", total_defense, total_attack, count,
             unit_list_size(pcity->tile->units));
  } city_list_iterate_end;
}
 
/**********************************************************************/
void dai_manage_units(struct ai_type *ait, struct player *pplayer) 
{
  TIMING_LOG(AIT_AIRLIFT, TIMER_START);
  dai_airlift(ait, pplayer);
  TIMING_LOG(AIT_AIRLIFT, TIMER_STOP);
 
  /* Clear previous orders, if desirable, here. */
  unit_list_iterate(pplayer->units, punit) {
    struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
    unit_data->done = FALSE;
    if (unit_data->task == AIUNIT_DEFEND_HOME) {
      dai_unit_new_task(ait, punit, AIUNIT_NONE, NULL);
    }
  } unit_list_iterate_end;
 
  /* Find and set city defenders first - figure out which units are
   * allowed to leave home. */
  dai_set_defenders(ait, pplayer);
 
  unit_list_iterate_safe(pplayer->units, punit) {
    if ((!unit_transported(punit) || unit_owner(unit_transport_get(punit)) != pplayer)
         && !def_ai_unit_data(punit, ait)->done) {
      /* Though it is usually the passenger who drives the transport,
       * the transporter is responsible for managing its passengers. */
      dai_manage_unit(ait, pplayer, punit);
    }
  } unit_list_iterate_safe_end;
}
 
/**********************************************************************/
const struct impr_type *utype_needs_improvement(const struct unit_type *putype,
                                                const struct city *pcity)
{
  const struct impr_type *impr_req = NULL;
  const struct req_context context = {
    .player = city_owner(pcity),
    .city = pcity,
    .tile = city_tile(pcity),
    .unittype = putype,
  };
 
  requirement_vector_iterate(&putype->build_reqs, preq) {
    if (is_req_active(&context, NULL, preq, RPT_CERTAIN)) {
      /* Already there. */
      continue;
    }
    if (!dai_can_requirement_be_met_in_city(preq,
                                            city_owner(pcity), pcity)) {
      /* The unit type can't be built at all. */
      return NULL;
    }
    if (VUT_IMPROVEMENT == preq->source.kind && preq->present) {
      /* This is (one of) the building(s) required. */
      impr_req = preq->source.value.building;
    }
  } requirement_vector_iterate_end;
 
  return impr_req;
}
 
/**********************************************************************/
bool is_on_unit_upgrade_path(const struct unit_type *test,
                             const struct unit_type *base)
{
  /* This is the real function: */
  do {
    base = base->obsoleted_by;
    if (base == test) {
      return TRUE;
    }
  } while (base);
  return FALSE;
}
 
/**********************************************************************/
static void dai_manage_barbarian_leader(struct ai_type *ait,
                                        struct player *pplayer,
                                        struct unit *leader)
{
  struct tile *leader_tile = unit_tile(leader), *safest_tile;
  struct pf_parameter parameter;
  struct pf_map *pfm;
  struct pf_reverse_map *pfrm;
  struct unit *worst_danger;
  int move_cost, best_move_cost;
  int body_guards;
  bool alive = TRUE;
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(leader);
 
  if (leader->moves_left == 0
      || (can_unit_survive_at_tile(&(wld.map), leader, leader_tile)
          && 1 < unit_list_size(leader_tile->units))) {
    unit_activity_handling(leader, ACTIVITY_SENTRY);
 
    return;
  }
 
  if (is_boss_of_boat(ait, leader)) {
    /* We are in charge. Of course, since we are the leader...
     * But maybe somebody more militaristic should lead our ship to battle! */
 
    /* First release boat from leaders lead */
    aiferry_clear_boat(ait, leader);
 
    unit_list_iterate(leader_tile->units, warrior) {
      if (!unit_has_type_role(warrior, L_BARBARIAN_LEADER)
          && get_transporter_capacity(warrior) == 0
          && warrior->moves_left > 0) {
        /* This seems like a good warrior to lead us in to conquest! */
        dai_manage_unit(ait, pplayer, warrior);
 
        /* If we reached our destination, ferryboat already called
         * ai_manage_unit() for leader. So no need to continue here.
         * Leader might even be dead.
         * If this return is removed, surronding unit_list_iterate()
         * has to be replaced with unit_list_iterate_safe()*/
        return;
      }
    } unit_list_iterate_end;
  }
 
  /* If we are not in charge of the boat, continue as if we
   * were not in a boat - we may want to leave the ship now. */
 
  /* Check the total number of units able to protect our leader. */
  body_guards = 0;
  unit_list_iterate(pplayer->units, punit) {
    if (!unit_has_type_role(punit, L_BARBARIAN_LEADER)
        && goto_is_sane(punit, leader_tile)) {
      body_guards++;
    }
  } unit_list_iterate_end;
 
  if (0 < body_guards) {
    pft_fill_unit_parameter(&parameter, nmap, leader);
    parameter.omniscience = !has_handicap(pplayer, H_MAP);
    pfm = pf_map_new(&parameter);
 
    /* Find the closest body guard.
     * FIXME: maybe choose the strongest too? */
    pf_map_tiles_iterate(pfm, ptile, FALSE) {
      unit_list_iterate(ptile->units, punit) {
        if (unit_owner(punit) == pplayer
            && !unit_has_type_role(punit, L_BARBARIAN_LEADER)
            && goto_is_sane(punit, leader_tile)) {
          struct pf_path *path = pf_map_path(pfm, ptile);
 
          adv_follow_path(leader, path, ptile);
          pf_path_destroy(path);
          pf_map_destroy(pfm);
          return;
        }
      } unit_list_iterate_end;
    } pf_map_tiles_iterate_end;
 
    pf_map_destroy(pfm);
  }
 
  UNIT_LOG(LOG_DEBUG, leader, "Barbarian leader needs to flee");
 
  /* Check for units we could fear. */
  pfrm = pf_reverse_map_new(pplayer, leader_tile, 3,
                            !has_handicap(pplayer, H_MAP), &(wld.map));
  worst_danger = NULL;
  best_move_cost = FC_INFINITY;
 
  players_iterate(other_player) {
    if (other_player == pplayer) {
      continue;
    }
 
    unit_list_iterate(other_player->units, punit) {
      move_cost = pf_reverse_map_unit_move_cost(pfrm, punit);
      if (PF_IMPOSSIBLE_MC != move_cost && move_cost < best_move_cost) {
        best_move_cost = move_cost;
        worst_danger = punit;
      }
    } unit_list_iterate_end;
  } players_iterate_end;
 
  pf_reverse_map_destroy(pfrm);
 
  if (NULL == worst_danger) {
    unit_activity_handling(leader, ACTIVITY_IDLE);
    UNIT_LOG(LOG_DEBUG, leader, "Barbarian leader: no close enemy.");
    return;
  }
 
  pft_fill_unit_parameter(&parameter, nmap, worst_danger);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  pfm = pf_map_new(&parameter);
  best_move_cost = pf_map_move_cost(pfm, leader_tile);
 
  /* Try to escape. */
  do {
    safest_tile = leader_tile;
 
    UNIT_LOG(LOG_DEBUG, leader, "Barbarian leader: moves left: %d.",
             leader->moves_left);
 
    adjc_iterate(&(wld.map), leader_tile, near_tile) {
      if (adv_could_unit_move_to_tile(leader, near_tile) != 1) {
        continue;
      }
 
      move_cost = pf_map_move_cost(pfm, near_tile);
      if (PF_IMPOSSIBLE_MC != move_cost
          && move_cost > best_move_cost) {
        UNIT_LOG(LOG_DEBUG, leader,
                 "Barbarian leader: safest is (%d, %d), safeness %d",
                 TILE_XY(near_tile), best_move_cost);
        best_move_cost = move_cost;
        safest_tile = near_tile;
      }
    } adjc_iterate_end;
 
    UNIT_LOG(LOG_DEBUG, leader, "Barbarian leader: fleeing to (%d, %d).",
             TILE_XY(safest_tile));
    if (same_pos(unit_tile(leader), safest_tile)) {
      UNIT_LOG(LOG_DEBUG, leader, 
               "Barbarian leader: reached the safest position.");
      unit_activity_handling(leader, ACTIVITY_IDLE);
      pf_map_destroy(pfm);
      return;
    }
 
    alive = dai_unit_goto(ait, leader, safest_tile);
    if (alive) {
      if (same_pos(unit_tile(leader), leader_tile)) {
        /* Didn't move. No point to retry. */
        pf_map_destroy(pfm);
        return;
      }
      leader_tile = unit_tile(leader);
    }
  } while (alive && 0 < leader->moves_left);
 
  pf_map_destroy(pfm);
}
 
/**********************************************************************/
void dai_consider_tile_dangerous(struct ai_type *ait, struct tile *ptile,
                                 struct unit *punit,
                                 enum override_bool *result)
{
  int a = 0, d, db;
  struct player *pplayer = unit_owner(punit);
  struct city *pcity = tile_city(ptile);
  int extras_bonus = 0;
 
  if (is_human(pplayer)) {
    /* Use advisors code for humans. */
    return;
  }
 
  if (pcity && pplayers_allied(city_owner(pcity), unit_owner(punit))
      && !is_non_allied_unit_tile(ptile, pplayer)) {
    /* We will be safe in a friendly city */
    *result = OVERRIDE_FALSE;
    return;
  }
 
  /* Calculate how well we can defend at (x,y) */
  db = 10 + tile_terrain(ptile)->defense_bonus / 10;
  extras_bonus += tile_extras_defense_bonus(ptile, unit_type_get(punit));
 
  db += (db * extras_bonus) / 100;
  d = adv_unit_def_rating_basic_squared(punit) * db;
 
  adjc_iterate(&(wld.map), ptile, ptile1) {
    if (has_handicap(pplayer, H_FOG)
        && !map_is_known_and_seen(ptile1, unit_owner(punit), V_MAIN)) {
      /* We cannot see danger at (ptile1) => assume there is none */
      continue;
    }
    unit_list_iterate(ptile1->units, enemy) {
      if (pplayers_at_war(unit_owner(enemy), unit_owner(punit)) 
          && (unit_attack_unit_at_tile_result(enemy, NULL, punit, ptile)
              == ATT_OK)
          && (unit_attack_units_at_tile_result(enemy, NULL, ptile)
              == ATT_OK)) {
        a += adv_unit_att_rating(enemy);
        if ((a * a * 10) >= d) {
          /* The enemies combined strength is too big! */
          *result = OVERRIDE_TRUE;
          return;
        }
      }
    } unit_list_iterate_end;
  } adjc_iterate_end;
 
  *result = OVERRIDE_FALSE;
}
 
/**********************************************************************/
static void update_simple_ai_types(void)
{
  int i = 0;
 
  unit_type_iterate(punittype) {
    struct unit_class *pclass = utype_class(punittype);
 
    if (A_NEVER != punittype->require_advance
        && !utype_has_flag(punittype, UTYF_CIVILIAN)
        && !utype_can_do_action(punittype, ACTION_SUICIDE_ATTACK)
        && !(pclass->adv.land_move == MOVE_NONE
             && !can_attack_non_native(punittype))
        && !utype_fuel(punittype)
        && punittype->transport_capacity < 8) {
      simple_ai_types[i] = punittype;
      i++;
    }
  } unit_type_iterate_end;
 
  simple_ai_types[i] = NULL;
}
 
/**********************************************************************/
void dai_units_ruleset_init(struct ai_type *ait)
{
  /* TODO: remove the simple_ai_types cache or merge it with a general ai
   *       cache; see the comment to struct unit_type *simple_ai_types at
   *       the beginning of this file. */
  update_simple_ai_types();
 
  unit_type_iterate(ptype) {
    struct unit_type_ai *utai = fc_malloc(sizeof(*utai));
 
    utai->low_firepower = FALSE;
    utai->ferry = FALSE;
    utai->missile_platform = FALSE;
    utai->carries_occupiers = FALSE;
    utai->potential_charges = unit_type_list_new();
 
    utype_set_ai_data(ptype, ait, utai);
  } unit_type_iterate_end;
 
  unit_type_iterate(punittype) {
    struct unit_class *pclass = utype_class(punittype);
 
    /* Confirm firepower */
    combat_bonus_list_iterate(punittype->bonuses, pbonus) {
      if (pbonus->type == CBONUS_LOW_FIREPOWER) {
        unit_type_iterate(penemy) {
          if (utype_has_flag(penemy, pbonus->flag)) {
            struct unit_type_ai *utai = utype_ai_data(penemy, ait);
 
            utai->low_firepower = TRUE;
          }
        } unit_type_iterate_end;
      }
    } combat_bonus_list_iterate_end;
 
    /* Consider potential cargo */
    if (punittype->transport_capacity > 0) {
      struct unit_type_ai *utai = utype_ai_data(punittype, ait);
 
      unit_type_iterate(pctype) {
        struct unit_class *pcargo = utype_class(pctype);
 
        if (can_unit_type_transport(punittype, pcargo)) {
          if (utype_can_do_action(pctype, ACTION_SUICIDE_ATTACK)) {
            utai->missile_platform = TRUE;
          } else if (pclass->adv.sea_move != MOVE_NONE
              && pcargo->adv.land_move != MOVE_NONE) {
            if (pcargo->adv.sea_move != MOVE_FULL) {
              utai->ferry = TRUE;
            } else {
              if (0 != utype_fuel(pctype)) {
                utai->ferry = TRUE;
              }
            }
          }
 
          if (utype_can_take_over(pctype)) {
            utai->carries_occupiers = TRUE;
          }
        }
      } unit_type_iterate_end;
    }
 
    /* Consider potential charges */
    unit_type_iterate(pcharge) {
      bool can_move_like_charge = FALSE;
 
      if (0 < utype_fuel(punittype)
          && (0 == utype_fuel(pcharge)
              || utype_fuel(pcharge) > utype_fuel(punittype))) {
        continue;
      }
 
      unit_class_list_iterate(pclass->cache.subset_movers, chgcls) {
        if (chgcls == utype_class(pcharge)) {
          can_move_like_charge = TRUE;
        }
      } unit_class_list_iterate_end;
 
      if (can_move_like_charge) {
        struct unit_type_ai *utai = utype_ai_data(punittype, ait);
        unit_type_list_append(utai->potential_charges, pcharge);
      }
 
    } unit_type_iterate_end;
  } unit_type_iterate_end;
}
 
/**********************************************************************/
void dai_units_ruleset_close(struct ai_type *ait)
{
  unit_type_iterate(ptype) {
    struct unit_type_ai *utai = utype_ai_data(ptype, ait);
 
    if (utai == NULL) {
      continue;
    }
    utype_set_ai_data(ptype, ait, NULL);
 
    unit_type_list_destroy(utai->potential_charges);
    free(utai);
  } unit_type_iterate_end;
}
 
/**********************************************************************/
void dai_unit_init(struct ai_type *ait, struct unit *punit)
{
  /* Make sure that contents of unit_ai structure are correctly initialized,
   * if you ever allocate it by some other mean than fc_calloc() */
  struct unit_ai *unit_data = fc_calloc(1, sizeof(struct unit_ai));
 
  unit_data->done = FALSE;
  unit_data->cur_pos = NULL;
  unit_data->prev_pos = NULL;
  unit_data->target = 0;
  BV_CLR_ALL(unit_data->hunted);
  unit_data->ferryboat = 0;
  unit_data->passenger = 0;
  unit_data->bodyguard = 0;
  unit_data->charge = 0;
 
  unit_set_ai_data(punit, ait, unit_data);
}
 
/**********************************************************************/
void dai_unit_turn_end(struct ai_type *ait, struct unit *punit)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  fc_assert_ret(unit_data != NULL);
 
  BV_CLR_ALL(unit_data->hunted);
}
 
/**********************************************************************/
void dai_unit_close(struct ai_type *ait, struct unit *punit)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  fc_assert_ret(unit_data != NULL);
 
  aiguard_clear_charge(ait, punit);
  aiguard_clear_guard(ait, punit);
 
  if (unit_data != NULL) {
    unit_set_ai_data(punit, ait, NULL);
    FC_FREE(unit_data);
  }
}
 
/**********************************************************************/
void dai_unit_save(struct ai_type *ait, const char *aitstr,
                   struct section_file *file,
                   const struct unit *punit, const char *unitstr)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  secfile_insert_int(file, unit_data->passenger, "%s.%spassenger",
                     unitstr, aitstr);
  secfile_insert_int(file, unit_data->ferryboat, "%s.%sferryboat",
                     unitstr, aitstr);
  secfile_insert_int(file, unit_data->charge, "%s.%scharge",
                     unitstr, aitstr);
  secfile_insert_int(file, unit_data->bodyguard, "%s.%sbodyguard",
                     unitstr, aitstr);
}
 
/**********************************************************************/
void dai_unit_load(struct ai_type *ait, const char *aitstr,
                   const struct section_file *file,
                   struct unit *punit, const char *unitstr)
{
  struct unit_ai *unit_data = def_ai_unit_data(punit, ait);
 
  unit_data->passenger
    = secfile_lookup_int_default(file, 0, "%s.%spassenger",
                                 unitstr, aitstr);
  unit_data->ferryboat
    = secfile_lookup_int_default(file, 0, "%s.%sferryboat",
                                 unitstr, aitstr);
  unit_data->charge
    = secfile_lookup_int_default(file, 0, "%s.%scharge",
                                 unitstr, aitstr);
  unit_data->bodyguard
    = secfile_lookup_int_default(file, 0, "%s.%sbodyguard",
                                 unitstr, aitstr);
}
 
struct role_unit_cb_data
{
  enum terrain_class tc;
  struct city *build_city;
};
 
/**********************************************************************/
static bool role_unit_cb(struct unit_type *ptype, void *data)
{
  struct role_unit_cb_data *cb_data = (struct role_unit_cb_data *)data;
  struct unit_class *pclass = utype_class(ptype);
 
  if ((cb_data->tc == TC_LAND && pclass->adv.land_move == MOVE_NONE)
      || (cb_data->tc == TC_OCEAN && pclass->adv.sea_move == MOVE_NONE)) {
    return FALSE;
  }
 
  if (cb_data->build_city == NULL
      || can_city_build_unit_now(cb_data->build_city, ptype)) {
    return TRUE;
  }
 
  return FALSE;
}
 
/**********************************************************************/
struct unit_type *dai_role_utype_for_terrain_class(struct city *pcity, int role,
                                                   enum terrain_class tc)
{
  struct role_unit_cb_data cb_data = { .build_city = pcity, .tc = tc };
 
  return role_units_iterate_backwards(role, role_unit_cb, &cb_data);
}
 
/**********************************************************************/
bool dai_unit_can_strike_my_unit(const struct unit *attacker,
                                 const struct unit *defender)
{
  struct pf_parameter parameter;
  struct pf_map *pfm;
  const struct tile *ptarget = unit_tile(defender);
  int max_move_cost = attacker->moves_left;
  bool able_to_strike = FALSE;
  const struct civ_map *nmap = &(wld.map);
 
  pft_fill_unit_parameter(&parameter, nmap, attacker);
  parameter.omniscience = !has_handicap(unit_owner(defender), H_MAP);
  pfm = pf_map_new(&parameter);
 
  pf_map_move_costs_iterate(pfm, ptile, move_cost, FALSE) {
    if (move_cost > max_move_cost) {
      break;
    }
 
    if (ptile == ptarget) {
      able_to_strike = TRUE;
      break;
    }
  } pf_map_move_costs_iterate_end;
 
  pf_map_destroy(pfm);
 
  return able_to_strike;
}
 
/**********************************************************************/
void dai_switch_to_explore(struct ai_type *ait, struct unit *punit,
                           struct tile *target, enum override_bool *allow)
{
  struct unit_ai *udata = def_ai_unit_data(punit, ait);
 
  if (udata->task != AIUNIT_NONE && udata->task != AIUNIT_EXPLORE) {
    *allow = OVERRIDE_FALSE;
 
    return;
  }
}