daidiplomat.c

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/***********************************************************************
 Freeciv - Copyright (C) 2002 - The Freeciv Project
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
***********************************************************************/
 
#ifdef HAVE_CONFIG_H
#include <fc_config.h>
#endif
 
/* utility */
#include "bitvector.h"
#include "log.h"
#include "mem.h"
#include "shared.h"
#include "timing.h"
 
/* common */
#include "actions.h"
#include "city.h"
#include "combat.h"
#include "game.h"
#include "government.h"
#include "map.h"
#include "movement.h"
#include "nation.h"
#include "packets.h"
#include "player.h"
#include "research.h"
#include "unit.h"
#include "unitlist.h"
 
/* aicore */
#include "aiactions.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 "advdata.h"
#include "advgoto.h"
 
/* ai */
#include "handicaps.h"
 
/* ai/default */
#include "daiactions.h"
#include "daicity.h"
#include "daidata.h"
#include "daiguard.h"
#include "daihand.h"
#include "dailog.h"
#include "daimilitary.h"
#include "daiplayer.h"
#include "daitools.h"
#include "daiunit.h"
 
#include "daidiplomat.h"
 
 
#define LOG_DIPLOMAT LOG_DEBUG
#define LOG_DIPLOMAT_BUILD LOG_DEBUG
 
/* 3000 is just a large number, but not hilariously large as the
 * previously used one. This is important for diplomacy. - Per */
#define DIPLO_DEFENSE_WANT 3000
 
static bool is_city_surrounded_by_our_spies(struct player *pplayer,
                                            struct city *pcity);
 
static void find_city_to_diplomat(struct player *pplayer, struct unit *punit,
                                  struct city **ctarget, int *move_dist,
                                  struct pf_map *pfm);
 
/************************************************************************/
static int count_diplomats_on_tile(struct tile *ptile)
{
  int count = 0;
 
  unit_list_iterate((ptile)->units, punit) {
    if (unit_has_type_flag(punit, UTYF_DIPLOMAT)) {
      count++;
    }
  } unit_list_iterate_end;
 
  return count;
}
 
/**************************************************************************/
static int count_stealable_techs(struct player *pplayer, struct player *tplayer)
{
  struct research *presearch = research_get(pplayer);
  struct research *tresearch = research_get(tplayer);
  int count = 0;
 
  advance_index_iterate(A_FIRST, idx) {
    if (research_invention_state(presearch, idx) != TECH_KNOWN
        && research_invention_state(tresearch, idx) == TECH_KNOWN) {
      count++;
    }
  } advance_index_iterate_end;
 
  return count;
}
 
/**************************************************************************/
void dai_choose_diplomat_defensive(struct ai_type *ait,
                                   struct player *pplayer,
                                   struct city *pcity,
                                   struct adv_choice *choice, int def)
{
  /* Build a diplomat if our city is threatened by enemy diplomats, and
     we have other defensive troops, and we don't already have a diplomat
     to protect us. If we see an enemy diplomat and we don't have diplomat
     tech... race it! */
  struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
  if (def != 0 && city_data->diplomat_threat
      && !city_data->has_diplomat) {
    struct unit_type *ut = best_role_unit(pcity, UTYF_DIPLOMAT);
 
    if (ut) {
       log_base(LOG_DIPLOMAT_BUILD,
                "A defensive diplomat will be built in city %s.",
                city_name_get(pcity));
       choice->want = 16000; /* diplomat more important than soldiers */
       city_data->urgency = 1;
       choice->type = CT_DEFENDER;
       choice->value.utype = ut;
       choice->need_boat = FALSE;
       adv_choice_set_use(choice, "defensive diplomat");
    } else if (num_role_units(UTYF_DIPLOMAT) > 0) {
      /* We don't know diplomats yet... */
      log_base(LOG_DIPLOMAT_BUILD,
               "A defensive diplomat is wanted badly in city %s.",
               city_name_get(pcity));
      ut = get_role_unit(UTYF_DIPLOMAT, 0);
      if (ut) {
        struct ai_plr *plr_data = def_ai_player_data(pplayer, ait);
 
        unit_tech_reqs_iterate(ut, padv) {
          plr_data->tech_want[advance_index(padv)]
            += DIPLO_DEFENSE_WANT;
          TECH_LOG(ait, LOG_DEBUG, pplayer, padv,
                   "ai_choose_diplomat_defensive() + %d for %s",
                   DIPLO_DEFENSE_WANT,
                   utype_rule_name(ut));
        } unit_tech_reqs_iterate_end;
      }
    }
  }
}
 
/**************************************************************************/
void dai_choose_diplomat_offensive(struct ai_type *ait,
                                   const struct civ_map *nmap,
                                   struct player *pplayer,
                                   struct city *pcity,
                                   struct adv_choice *choice)
{
  struct unit_type *ut = best_role_unit(pcity, UTYF_DIPLOMAT);
  struct ai_plr *ai = def_ai_player_data(pplayer, ait);
  int expenses;
 
  dai_calc_data(pplayer, nullptr, &expenses, nullptr);
 
  if (!ut) {
    /* We don't know diplomats yet! */
    return;
  }
 
  if (has_handicap(pplayer, H_DIPLOMAT)) {
    /* Diplomats are too tough on newbies */
    return;
  }
 
  /* Do we have a good reason for building diplomats? */
  {
    const struct research *presearch = research_get(pplayer);
    struct pf_map *pfm;
    struct pf_parameter parameter;
    struct city *acity;
    adv_want want;
    int loss, p_success, p_failure, time_to_dest;
    int gain_incite = 0, gain_theft = 0, gain = 1;
    int incite_cost;
    struct unit *punit = unit_virtual_create(
      pplayer, pcity, ut,
      city_production_unit_veteran_level(pcity, ut));
 
    pft_fill_unit_parameter(&parameter, nmap, punit);
    parameter.omniscience = !has_handicap(pplayer, H_MAP);
    pfm = pf_map_new(&parameter);
 
    find_city_to_diplomat(pplayer, punit, &acity, &time_to_dest, pfm);
 
    pf_map_destroy(pfm);
    unit_virtual_destroy(punit);
 
    if (acity == nullptr
        || BV_ISSET(ai->stats.diplomat_reservations, acity->id)) {
      /* Found no target or city already considered */
      return;
    }
    incite_cost = city_incite_cost(pplayer, acity);
    if (POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, city_owner(acity))
        && (is_action_possible_on_city(ACTION_SPY_INCITE_CITY,
                                       pplayer, acity)
            || is_action_possible_on_city(ACTION_SPY_INCITE_CITY_ESC,
                                          pplayer, acity))
        && (incite_cost < INCITE_IMPOSSIBLE_COST)
        && (incite_cost < pplayer->economic.gold - expenses)) {
      /* incite gain (FIXME: we should count wonders too but need to
         cache that somehow to avoid CPU hog -- Per) */
      gain_incite = acity->prod[O_FOOD] * FOOD_WEIGHTING
                    + acity->prod[O_SHIELD] * SHIELD_WEIGHTING
                    + (acity->prod[O_LUXURY]
                       + acity->prod[O_GOLD]
                       + acity->prod[O_SCIENCE]) * TRADE_WEIGHTING;
      gain_incite *= SHIELD_WEIGHTING; /* WAG cost to take city otherwise */
      gain_incite -= incite_cost * TRADE_WEIGHTING;
    }
    if ((research_get(city_owner(acity))->techs_researched
         > presearch->techs_researched)
        && (is_action_possible_on_city(ACTION_SPY_TARGETED_STEAL_TECH,
                                       pplayer, acity)
            || is_action_possible_on_city(ACTION_SPY_TARGETED_STEAL_TECH_ESC,
                                          pplayer, acity)
            || is_action_possible_on_city(ACTION_SPY_STEAL_TECH,
                                          pplayer, acity)
            || is_action_possible_on_city(ACTION_SPY_STEAL_TECH_ESC,
                                          pplayer, acity))
        && !pplayers_allied(pplayer, city_owner(acity))) {
      /* Tech theft gain */
      /* FIXME: This value is right only when
       * 'game.info.game.info.tech_cost_style' is set to
       * TECH_COST_CIV1CIV2. */
      gain_theft =
          (research_total_bulbs_required(presearch, presearch->researching,
                                         FALSE) * TRADE_WEIGHTING);
    }
    gain = MAX(gain_incite, gain_theft);
    loss = utype_build_shield_cost(pcity, nullptr, ut) * SHIELD_WEIGHTING;
 
    /* Probability to succeed, assuming no defending diplomat */
    p_success = game.server.diplchance;
    /* Probability to lose our unit */
    p_failure = (utype_can_do_action(ut, ACTION_SPY_TARGETED_STEAL_TECH_ESC)
                 || utype_can_do_action(ut, ACTION_SPY_STEAL_TECH_ESC) ?
                   100 - p_success :
                   100);
 
    /* Get the time to dest in turns (minimum 1 turn) */
    time_to_dest = (time_to_dest + ut->move_rate - 1) / ut->move_rate;
    /* Discourage long treks */
    time_to_dest *= ((time_to_dest + 1) / 2);
 
    /* Almost kill_desire() */
    want = (adv_want)(p_success * gain - p_failure * loss) / 100
           - SHIELD_WEIGHTING * time_to_dest;
    if (want <= 0) {
      return;
    }
 
    want = military_amortize(pplayer, pcity, want, time_to_dest,
                             utype_build_shield_cost(pcity, nullptr, ut));
 
    if (!player_has_embassy(pplayer, city_owner(acity))
        && want < 99
        && (is_action_possible_on_city(ACTION_ESTABLISH_EMBASSY,
                                       pplayer, acity)
            || is_action_possible_on_city(ACTION_ESTABLISH_EMBASSY_STAY,
                                          pplayer, acity))) {
        log_base(LOG_DIPLOMAT_BUILD,
                 "A diplomat desired in %s to establish an embassy with %s "
                 "in %s",
                 city_name_get(pcity),
                 player_name(city_owner(acity)),
                 city_name_get(acity));
        want = 99;
    }
    if (want > choice->want) {
      log_base(LOG_DIPLOMAT_BUILD,
               "%s, %s: %s is desired with want " ADV_WANT_PRINTF
               " to spy in %s (incite want %d cost %d gold %d, "
               "tech theft want %d, ttd %d)",
               player_name(pplayer),
               city_name_get(pcity),
               utype_rule_name(ut),
               want,
               city_name_get(acity),
               gain_incite,
               incite_cost,
               pplayer->economic.gold - expenses,
               gain_theft,
               time_to_dest);
      choice->want = want;
      choice->type = CT_CIVILIAN; /* so we don't build barracks for it */
      choice->value.utype = ut;
      choice->need_boat = FALSE;
      adv_choice_set_use(choice, "offensive diplomat");
      BV_SET(ai->stats.diplomat_reservations, acity->id);
    }
  }
}
 
/**************************************************************************/
static void dai_diplomat_city(struct ai_type *ait, struct unit *punit,
                              struct city *ctarget)
{
  struct action *chosen_action;
  adv_want chosen_action_utility;
  int chosen_sub_tgt_id;
  struct player *pplayer = unit_owner(punit);
  struct player *tplayer = city_owner(ctarget);
  int count_tech = count_stealable_techs(pplayer, tplayer);
  const struct civ_map *nmap = &(wld.map);
 
  fc_assert_ret(is_ai(pplayer));
 
  if (punit->moves_left == 0) {
    UNIT_LOG(LOG_ERROR, punit, "no moves left in ai_diplomat_city()!");
  }
 
  unit_activity_handling(punit, ACTIVITY_IDLE, ACTION_NONE);
 
  /* Select the best potentially legal action. */
  /* FIXME: What if it is illegal? */
  chosen_action = nullptr;
  chosen_action_utility = -1;
  chosen_sub_tgt_id = 0;
  action_iterate(act_id) {
    struct action *paction = action_by_number(act_id);
    adv_want action_utility;
    int sub_tgt_id;
 
    if (action_get_actor_kind(paction) != AAK_UNIT
        || action_get_target_kind(paction) != ATK_CITY) {
      /* Not relevant here. */
      continue;
    }
 
    if (!action_prob_possible(
            action_prob_vs_city(nmap, punit, action_number(paction),ctarget))) {
      /* Not possible. */
      continue;
    }
 
    if (paction->target_complexity == ACT_TGT_COMPL_SIMPLE) {
      /* No sub target */
      sub_tgt_id = 0;
    } else {
      /* Pick a suitable sub target. */
      sub_tgt_id = dai_action_choose_sub_tgt_unit_vs_city(paction,
                                                          punit, ctarget);
    }
 
    action_utility = dai_action_value_unit_vs_city(paction, punit,
                                                   ctarget, sub_tgt_id,
                                                   count_tech);
 
    if (chosen_action_utility < action_utility) {
      chosen_action = paction;
      chosen_action_utility = action_utility;
      chosen_sub_tgt_id = sub_tgt_id;
    }
  } action_iterate_end;
 
  if (chosen_action != nullptr) {
    /* An action has been selected. */
 
    if (action_prob_possible(
          action_prob_vs_city(nmap, punit, action_number(chosen_action),
                              ctarget))) {
      log_base(LOG_DIPLOMAT, "%s %s[%d] does %s at %s",
               nation_rule_name(nation_of_unit(punit)),
               unit_rule_name(punit), punit->id,
               action_rule_name(chosen_action),
               city_name_get(ctarget));
      unit_do_action(pplayer, punit->id,
                     ctarget->id, chosen_sub_tgt_id, "",
                     action_number(chosen_action));
      return;
    }
  }
 
  /* This can happen for a number of odd and esoteric reasons  */
  UNIT_LOG(LOG_DIPLOMAT, punit,
           "decides to stand idle outside enemy city %s!",
           city_name_get(ctarget));
  dai_unit_new_task(ait, punit, AIUNIT_NONE, nullptr);
}
 
/**************************************************************************/
static bool is_city_surrounded_by_our_spies(struct player *pplayer,
                                            struct city *enemy_city)
{
  adjc_iterate(&(wld.map), city_tile(enemy_city), ptile) {
    if (has_handicap(pplayer, H_FOG)
        && !map_is_known_and_seen(ptile, pplayer, V_MAIN)) {
      /* We cannot see danger at (ptile) => assume there is none. */
      continue;
    }
    unit_list_iterate(ptile->units, punit) {
      if (unit_owner(punit) == pplayer
          && aia_utype_is_considered_spy(unit_type_get(punit))) {
        return TRUE;
      }
    } unit_list_iterate_end;
  } adjc_iterate_end;
 
  return FALSE;
}
 
/**************************************************************************/
static void find_city_to_diplomat(struct player *pplayer, struct unit *punit,
                                  struct city **ctarget, int *move_dist,
                                  struct pf_map *pfm)
{
  bool has_embassy;
  int incite_cost = 0; /* Incite cost */
  int expenses;
  bool dipldef; /* Whether target is protected by diplomats */
 
  fc_assert_ret(punit != nullptr);
 
  *ctarget = nullptr;
  *move_dist = -1;
  dai_calc_data(pplayer, nullptr, &expenses, nullptr);
 
  pf_map_move_costs_iterate(pfm, ptile, move_cost, FALSE) {
    struct city *acity;
    struct player *aplayer;
    bool can_incite;
    bool can_steal;
 
    acity = tile_city(ptile);
 
    if (!acity) {
      continue;
    }
    aplayer = city_owner(acity);
 
    has_embassy = player_has_embassy(pplayer, aplayer);
 
    if (aplayer == pplayer || is_barbarian(aplayer)
        || (pplayers_allied(pplayer, aplayer) && has_embassy)) {
      continue;
    }
 
    incite_cost = city_incite_cost(pplayer, acity);
    can_incite = (incite_cost < INCITE_IMPOSSIBLE_COST)
        && (is_action_possible_on_city(ACTION_SPY_INCITE_CITY,
                                       pplayer, acity)
            || is_action_possible_on_city(ACTION_SPY_INCITE_CITY_ESC,
                                          pplayer, acity));
 
    can_steal = is_action_possible_on_city(ACTION_SPY_STEAL_TECH,
                                           pplayer, acity)
        || is_action_possible_on_city(ACTION_SPY_STEAL_TECH_ESC,
                                      pplayer, acity)
        || is_action_possible_on_city(ACTION_SPY_TARGETED_STEAL_TECH,
                                      pplayer, acity)
        || is_action_possible_on_city(ACTION_SPY_TARGETED_STEAL_TECH_ESC,
                                      pplayer, acity);
 
    dipldef = (count_diplomats_on_tile(acity->tile) > 0);
    /* Three actions to consider:
     * 1. establishing embassy OR
     * 2. stealing techs OR
     * 3. inciting revolt */
    if ((!has_embassy
         && (is_action_possible_on_city(ACTION_ESTABLISH_EMBASSY,
                                        pplayer, acity)
             || is_action_possible_on_city(ACTION_ESTABLISH_EMBASSY_STAY,
                                           pplayer, acity)))
        || (diplomats_unignored_tech_stealings(punit, acity) == 0
            && !dipldef && can_steal
            && (research_get(pplayer)->techs_researched
                < research_get(aplayer)->techs_researched))
        || (incite_cost < (pplayer->economic.gold - expenses)
            && can_incite && !dipldef)) {
      if (!is_city_surrounded_by_our_spies(pplayer, acity)) {
        /* We have the closest enemy city on the continent */
        *ctarget = acity;
        *move_dist = move_cost;
        break;
      }
    }
  } pf_map_move_costs_iterate_end;
}
 
/**************************************************************************/
static struct city *dai_diplomat_defend(struct ai_type *ait,
                                        struct player *pplayer,
                                        struct unit *punit,
                                        const struct unit_type *utype,
                                        struct pf_map *pfm)
{
  int best_dist = 30; /* Any city closer than this is better than none */
  int best_urgency = 0;
  struct city *ctarget = nullptr;
  struct city *pcity = tile_city(unit_tile(punit));
 
  if (pcity
      && count_diplomats_on_tile(pcity->tile) == 1
      && def_ai_city_data(pcity, ait)->urgency > 0) {
    /* Danger and we are only diplomat present - stay. */
    return pcity;
  }
 
  pf_map_move_costs_iterate(pfm, ptile, move_cost, FALSE) {
    struct city *acity;
    struct player *aplayer;
    int dipls, urgency;
    struct ai_city *city_data;
 
    acity = tile_city(ptile);
    if (!acity) {
      continue;
    }
    aplayer = city_owner(acity);
    if (aplayer != pplayer) {
      continue;
    }
 
    city_data = def_ai_city_data(acity, ait);
    urgency = city_data->urgency;
    dipls = (count_diplomats_on_tile(ptile)
             - (same_pos(ptile, unit_tile(punit)) ? 1 : 0));
    if (dipls == 0 && city_data->diplomat_threat) {
      /* We are _really_ needed there */
      urgency = (urgency + 1) * 5;
    } else if (dipls > 0) {
      /* We are probably not needed there... */
      urgency /= 3;
    }
 
    /* This formula may not be optimal, but it works. */
    if (move_cost > best_dist) {
      /* punish city for being so far away */
      urgency /= (float) (move_cost / best_dist);
    }
 
    if (urgency > best_urgency) {
      /* Found something worthy of our presence */
      ctarget = acity;
      best_urgency = urgency;
      /* squelch divide-by-zero */
      best_dist = MAX(move_cost, 1);
    }
  } pf_map_move_costs_iterate_end;
 
  return ctarget;
}
 
/**************************************************************************/
static bool dai_diplomat_bribe_nearby(struct ai_type *ait,
                                      struct player *pplayer,
                                      struct unit *punit, struct pf_map *pfm)
{
  int gold_avail, expenses;
  const struct civ_map *nmap = &(wld.map);
 
  dai_calc_data(pplayer, nullptr, &expenses, nullptr);
  gold_avail = pplayer->economic.gold - expenses;
 
  pf_map_positions_iterate(pfm, pos, FALSE) {
    struct tile *ptile = pos.tile;
    bool threat = FALSE;
    int newval, bestval = 0, cost;
    struct unit *pvictim = tile_other_players_unit(ptile, pplayer);
    int sanity = punit->id;
    const struct unit_type *ptype;
 
    if (pos.total_MC > punit->moves_left) {
      /* Didn't find anything within range. */
      break;
    }
 
    if (!pvictim
        || !POTENTIALLY_HOSTILE_PLAYER(ait, pplayer, unit_owner(pvictim))
        || unit_list_size(ptile->units) > 1
        || tile_city(ptile)
        || !is_action_enabled_unit_on_unit(nmap, ACTION_SPY_BRIBE_UNIT,
                                           punit, pvictim)) {
      continue;
    }
 
    /* Calculate if enemy is a threat */
    /* First find best defender on our tile */
    unit_list_iterate(ptile->units, aunit) {
      const struct unit_type *atype = unit_type_get(aunit);
 
      newval = DEFENSE_POWER(atype);
      if (bestval < newval) {
        bestval = newval;
      }
    } unit_list_iterate_end;
    /* Compare with victim's attack power */
    ptype = unit_type_get(pvictim);
    newval = ATTACK_POWER(ptype);
    if (newval > bestval
        && unit_move_rate(pvictim) > pos.total_MC) {
      /* Enemy can probably kill us */
      threat = TRUE;
    } else {
      /* Enemy cannot reach us or probably not kill us */
      threat = FALSE;
    }
 
    if (has_handicap(pplayer, H_NOBRIBE_WF)) {
      /* Don't bribe workers or city founders! */
      if (aia_utype_is_considered_worker(unit_type_get(pvictim))
          || unit_can_do_action_result(pvictim, ACTRES_FOUND_CITY)) {
        continue;
      }
    }
 
    /* Should we make the expense? */
    cost = unit_bribe_cost(pvictim, pplayer, punit);
    if (!threat) {
      /* Don't empty our treasure without good reason! */
      gold_avail = pplayer->economic.gold - dai_gold_reserve(pplayer);
    }
    if (cost > gold_avail) {
      /* Can't afford */
      continue;
    }
 
    /* Found someone! */
    {
      struct tile *bribee_tile;
      struct pf_path *path;
 
      bribee_tile = mapstep(nmap, pos.tile, DIR_REVERSE(pos.dir_to_here));
      path = pf_map_path(pfm, bribee_tile);
      if (!path || !adv_unit_execute_path(punit, path)
          || punit->moves_left <= 0) {
        pf_path_destroy(path);
        return FALSE;
      }
      pf_path_destroy(path);
    }
 
    if (action_prob_possible(action_prob_vs_unit(nmap, punit,
                                 ACTION_SPY_BRIBE_UNIT,
                                 pvictim))) {
      unit_do_action(pplayer, punit->id,
                     pvictim->id, -1, "",
                     ACTION_SPY_BRIBE_UNIT);
      /* Autoattack might kill us as we move in */
      if (game_unit_by_number(sanity) && punit->moves_left > 0) {
        return TRUE;
      } else {
        return FALSE;
      }
    } else if (action_prob_possible(action_prob_vs_unit(nmap, punit,
                                        ACTION_SPY_SABOTAGE_UNIT_ESC,
                                        pvictim))
               && threat) {
      /* don't stand around waiting for the final blow */
      unit_do_action(pplayer, punit->id,
                     pvictim->id, -1, "",
                     ACTION_SPY_SABOTAGE_UNIT_ESC);
      /* autoattack might kill us as we move in */
      if (game_unit_by_number(sanity) && punit->moves_left > 0) {
        return TRUE;
      } else {
        return FALSE;
      }
    } else {
      /* usually because we ended move early due to another unit */
      UNIT_LOG(LOG_DIPLOMAT, punit, "could not bribe target (%d, %d), "
               " %d moves left", TILE_XY(pos.tile), punit->moves_left);
      return FALSE;
    }
  } pf_map_positions_iterate_end;
 
  return (punit->moves_left > 0);
}
 
/**************************************************************************/
void dai_manage_diplomat(struct ai_type *ait, struct player *pplayer,
                         struct unit *punit)
{
  struct city *pcity, *ctarget = nullptr;
  struct pf_parameter parameter;
  struct pf_map *pfm;
  struct pf_position pos;
  struct unit_ai *unit_data;
  const struct civ_map *nmap = &(wld.map);
 
  CHECK_UNIT(punit);
 
  /* Generate map */
  pft_fill_unit_parameter(&parameter, nmap, punit);
  parameter.omniscience = !has_handicap(pplayer, H_MAP);
  parameter.get_zoc = nullptr; /* Kludge */
  parameter.get_TB = no_intermediate_fights;
  pfm = pf_map_new(&parameter);
 
  /* Look for someone to bribe */
  if (!dai_diplomat_bribe_nearby(ait, pplayer, punit, pfm)) {
    /* Died or ran out of moves */
    pf_map_destroy(pfm);
    return;
  }
 
  /* If we are the only diplomat in a threatened city, then stay to defend */
  pcity = tile_city(unit_tile(punit)); /* We may have moved */
  if (pcity) {
    struct ai_city *city_data = def_ai_city_data(pcity, ait);
 
    if (count_diplomats_on_tile(unit_tile(punit)) == 1
        && (city_data->diplomat_threat
            || city_data->urgency > 0)) {
      UNIT_LOG(LOG_DIPLOMAT, punit, "stays to protect %s (urg %d)",
               city_name_get(pcity), city_data->urgency);
      dai_unit_new_task(ait, punit, AIUNIT_NONE, nullptr); /* Abort mission */
      def_ai_unit_data(punit, ait)->done = TRUE;
      pf_map_destroy(pfm);
      return;
    }
  }
 
  unit_data = def_ai_unit_data(punit, ait);
 
  /* Check if existing target still makes sense */
  if (unit_data->task == AIUNIT_ATTACK
      || unit_data->task == AIUNIT_DEFEND_HOME) {
    bool failure = FALSE;
 
    ctarget = tile_city(punit->goto_tile);
    if (pf_map_position(pfm, punit->goto_tile, &pos)
        && ctarget) {
      if (same_pos(ctarget->tile, unit_tile(punit))) {
        failure = TRUE;
      } else if (pplayers_allied(pplayer, city_owner(ctarget))
          && unit_data->task == AIUNIT_ATTACK
          && player_has_embassy(pplayer, city_owner(ctarget))) {
        /* We probably incited this city with another diplomat */
        failure = TRUE;
      } else if (!pplayers_allied(pplayer, city_owner(ctarget))
                 && unit_data->task == AIUNIT_DEFEND_HOME) {
        /* We probably lost the city */
        failure = TRUE;
      }
    } else {
      /* City vanished! */
      failure = TRUE;
    }
    if (failure) {
      UNIT_LOG(LOG_DIPLOMAT, punit, "mission aborted");
      dai_unit_new_task(ait, punit, AIUNIT_NONE, nullptr);
    }
  }
 
  /* We may need a new map now. Both because we cannot get paths from an
   * old map, and we need paths to move, and because fctd below requires
   * a new map for its iterator. */
  if (!same_pos(parameter.start_tile, unit_tile(punit))
      || unit_data->task == AIUNIT_NONE) {
    pf_map_destroy(pfm);
    pft_fill_unit_parameter(&parameter, nmap, punit);
    parameter.omniscience = !has_handicap(pplayer, H_MAP);
    parameter.get_zoc = nullptr; /* Kludge */
    parameter.get_TB = no_intermediate_fights;
    pfm = pf_map_new(&parameter);
  }
 
  /* If we are not busy, acquire a target. */
  if (unit_data->task == AIUNIT_NONE) {
    enum ai_unit_task task;
    int move_dist; /* dummy */
 
    find_city_to_diplomat(pplayer, punit, &ctarget, &move_dist, pfm);
 
    if (ctarget) {
      task = AIUNIT_ATTACK;
      aiguard_request_guard(ait, punit);
      UNIT_LOG(LOG_DIPLOMAT, punit, "going on attack");
    } else if ((ctarget = dai_diplomat_defend(ait, pplayer, punit,
                                              unit_type_get(punit), pfm))
               != nullptr) {
      task = AIUNIT_DEFEND_HOME;
      UNIT_LOG(LOG_DIPLOMAT, punit, "going to defend %s",
               city_name_get(ctarget));
    } else if ((ctarget = find_closest_city(unit_tile(punit), nullptr, pplayer,
                                            TRUE, FALSE, FALSE, TRUE, FALSE,
                                            nullptr))
               != nullptr) {
      /* This should only happen if the entire continent was suddenly
       * conquered. So we head for closest coastal city and wait for someone
       * to code ferrying for diplomats, or hostile attacks from the sea. */
      task = AIUNIT_DEFEND_HOME;
      UNIT_LOG(LOG_DIPLOMAT, punit, "going idle");
    } else {
      UNIT_LOG(LOG_DIPLOMAT, punit, "could not find a job");
      def_ai_unit_data(punit, ait)->done = TRUE;
      pf_map_destroy(pfm);
      return;
    }
 
    dai_unit_new_task(ait, punit, task, ctarget->tile);
    fc_assert(punit->moves_left > 0 && ctarget
              && unit_data->task != AIUNIT_NONE);
  }
 
  CHECK_UNIT(punit);
  if (ctarget == nullptr) {
    UNIT_LOG(LOG_ERROR, punit, "ctarget not set (task == %d)",
             unit_data->task);
    pf_map_destroy(pfm);
    return;
  }
 
  /* GOTO unless we want to stay */
  if (!same_pos(unit_tile(punit), ctarget->tile)) {
    struct pf_path *path;
 
    path = pf_map_path(pfm, punit->goto_tile);
    if (path && adv_unit_execute_path(punit, path) && punit->moves_left > 0) {
      /* Check if we can do something with our destination now. */
      if (unit_data->task == AIUNIT_ATTACK) {
        int dist  = real_map_distance(unit_tile(punit), punit->goto_tile);
 
        UNIT_LOG(LOG_DIPLOMAT, punit, "attack, dist %d to %s",
                 dist, ctarget ? city_name_get(ctarget) : "(none)");
        if (dist <= 1) {
          /* Do our stuff */
          dai_unit_new_task(ait, punit, AIUNIT_NONE, nullptr);
          dai_diplomat_city(ait, punit, ctarget);
        }
      }
    }
    pf_path_destroy(path);
  } else {
    def_ai_unit_data(punit, ait)->done = TRUE;
  }
  pf_map_destroy(pfm);
}