// World generation and settlement placement: laying out capitals and cities,
// spawning their starting units, seeding population and budgets, and the small
// terrain predicates the rest of the model leans on.

import { ECONOMY } from "../data/economy.js";
import { RESOURCE_RULES } from "../data/resources.js";
import { transportImprovement } from "../data/improvements.js";
import { buildRoadNetwork } from "../roads.js";
import { MapTopology, key, parseKey } from "../hex.js";
import { MapGenerator } from "../map_generator.js";
import { TerrainStats } from "../terrain_stats.js";
import { Random } from "../rng.js";

// World generation is a pure function of (seed, mapConfig): the same inputs
// always produce the same terrain, city sites and road network. Caching the
// shape lets a new game with a known seed -- a server restart, or one test
// fixture after another -- skip regenerating the whole world every time. Only
// the immutable terrain pieces are shared; every mutable collection is rebuilt
// per GameState.
const WORLD_CACHE_LIMIT = 16;
const terrainCache = new Map();
const settlementCache = new Map();

function cachePut(cache, cacheKey, value) {
  cache.set(cacheKey, value);
  if (cache.size > WORLD_CACHE_LIMIT) cache.delete(cache.keys().next().value);
}

function copyCoords(coords) {
  return { x: coords.x, y: coords.y };
}

export const worldMethods = {
  // Builds or reuses the topology, tiles and terrain stats for `this.seed` and
  // `this.mapConfig`.
  _buildTerrain() {
    const cacheKey = `${this.seed}|${JSON.stringify(this.mapConfig)}`;
    const cached = terrainCache.get(cacheKey);
    if (cached) {
      this.topology = cached.topology;
      this.tiles = cached.tiles;
      this.landCells = cached.landCells;
      this.terrainStats = cached.terrainStats;
      this._generator = cached.generator;
      this._minMovementCost = cached.minMovementCost;
      this._maxStepLength = cached.maxStepLength;
      return;
    }
    this.topology = new MapTopology(
      this.mapConfig.mapSize,
      this.mapConfig.topology === "cylindrical"
    );
    this._generator = new MapGenerator(this.mapConfig, this.topology);
    this._generator.generate(this.seed);
    this.tiles = this._generator.tiles;
    this.landCells = this._generator.landCells;
    this.terrainStats = new TerrainStats(this.tiles);
    this._minMovementCost = this.terrainStats.minMovementCostMultiplier();
    this._maxStepLength = this._computeMaxStepLength();
    cachePut(terrainCache, cacheKey, {
      topology: this.topology,
      tiles: this.tiles,
      landCells: this.landCells,
      terrainStats: this.terrainStats,
      generator: this._generator,
      minMovementCost: this._minMovementCost,
      maxStepLength: this._maxStepLength,
    });
  },

  _placeSettlements() {
    // City sites and the road network depend only on the seed, the map config
    // and how many nations are playing, so they are cached alongside the
    // terrain and reused when a known world is started again.
    const cacheKey = `${this.seed}|${JSON.stringify(this.mapConfig)}|${this.civilisations.length}`;
    const cached = settlementCache.get(cacheKey);
    const capitals = cached
      ? cached.capitals.map(copyCoords)
      : this._placeCapitals(this.civilisations.length);
    const sites = cached
      ? cached.sites.map((site) => ({ ...site, coords: copyCoords(site.coords) }))
      : this._placeCities(capitals);
    for (const site of sites) this._spawnCity(site);
    this._rebuildCityIndex();
    this._seedCityPorts();
    this._generateRoads(cached ? cached.roads : null);
    if (!cached) {
      cachePut(settlementCache, cacheKey, {
        capitals: capitals.map(copyCoords),
        sites: sites.map((site) => ({ ...site, coords: copyCoords(site.coords) })),
        roads: new Set(this.roads),
      });
    }
    for (let i = 0; i < Math.min(this.civilisations.length, capitals.length); i++) {
      this._spawnUnit(capitals[i], i, this.protoUnits[0]);
    }
    this._recomputeTerritory();
    this._generatePopulation();
    this._initPolitics();
    this._generateEthnicMakeup();
    this._balanceStartingEconomy();
    // Every nation opens with the resource works its economy needs, laid out
    // before the budgets are founded so the opening treasury already reflects
    // them.
    this._seedResourceBuildings();
    // The terrain and where the starter industry landed give each region a
    // different income per head. Unworked land is not what makes a region rich
    // (food comes from the land, not the headcount), so people now move out of
    // the poor regions until every region of a nation is level.
    this._equalizeRegionIncomes();
    // The starter industry lifts raw GDP unevenly; restore the equal starting
    // production per head without disturbing the grid demand the seeding planned.
    this._rebalanceProduction();
    // Budgets are founded once the balanced economy is known, so every nation
    // opens on 1 January 2000 with a tenth of its own starting GDP.
    this._initBudgets();
  },

  _placeCapitals(count) {
    const rng = new Random(this.seed);
    return this._generator.pickCapitals(count, rng);
  },

  _placeCities(capitals) {
    return this._generator.pickCities(capitals, this.mapConfig.citiesPerCiv, this.mapConfig.citySpacing);
  },

  _spawnCity(site) {
    const civIndex = site.civIndex;
    if (civIndex < 0 || civIndex >= this.civilisations.length) return;
    const civ = this.civilisations[civIndex];
    const coords = site.coords;
    const isCapital = site.isCapital;
    const name = this._nextCityName(civ, civIndex);
    const population = 500000 +
      (Math.abs((coords.x * 92837111) ^ (coords.y * 689287499)) % 3500000);
    const city = {
      id: this._nextCityId,
      civ: civIndex,
      coords,
      name,
      isCapital,
      population,
      improvements: [],
      buildings: {},
      statuses: [],
    };
    this.cities.push(city);
    this._cityById.set(this._nextCityId, city);
    this._nextCityId += 1;
  },

  _rebuildCityIndex() {
    this._cityByCoords = new Map();
    this._cityAdjacent = new Map();
    for (const city of this.cities) {
      this._cityByCoords.set(key(city.coords.x, city.coords.y), city);
      const owner = city.civ;
      if (!this._cityAdjacent.has(owner)) this._cityAdjacent.set(owner, new Set());
      const adjacent = this._cityAdjacent.get(owner);
      for (const neighbour of this._neighbours(city.coords)) {
        adjacent.add(key(neighbour.x, neighbour.y));
      }
    }
  },

  // Every naval city opens the game with a port. It is the only way a nation can
  // reach resources on other continents, so a coastal city is never landlocked
  // in trade from the first turn.
  _seedCityPorts() {
    const index = this.protoBuildings.findIndex((proto) => proto.id === "port");
    if (index < 0) return;
    for (const city of this.cities) {
      if (this.isCoastalCity(city)) city.buildings[index] = 1;
    }
  },

  // Picks the civilisation's next city name, skipping any a city elsewhere has
  // already taken, and falls back to a numbered name so the whole world never
  // has two cities called the same thing.
  _nextCityName(civ, index) {
    const start = this._cityNamesUsed.get(index) || 0;
    for (let i = start; i < civ.cityNames.length; i++) {
      const candidate = civ.cityNames[i];
      if (this._usedCityNames.has(candidate)) continue;
      this._cityNamesUsed.set(index, i + 1);
      this._usedCityNames.add(candidate);
      return candidate;
    }
    let suffix = Math.max(start, civ.cityNames.length) + 1;
    let candidate = `${civ.name} ${suffix}`;
    while (this._usedCityNames.has(candidate)) {
      suffix += 1;
      candidate = `${civ.name} ${suffix}`;
    }
    this._cityNamesUsed.set(index, suffix);
    this._usedCityNames.add(candidate);
    return candidate;
  },

  // Lays the pre-generated road network. Cities are founded on a railway (they
  // improve themselves), so they are free nodes while the network is drawn; the
  // chosen links are the greedy spanner over every possible city-to-city route.
  _generateRoads(roadKeys = null) {
    const railwayName = transportImprovement("railway").name;
    // A cached world hands back the (read-only) road tiles; copy them so no
    // state can alter the cache.
    this.roads = roadKeys
      ? new Set(roadKeys)
      : buildRoadNetwork(this.cities, this.topology, this.tiles);
    // A city always stands on a railway, so no player has to improve it.
    for (const city of this.cities) {
      if (!city.improvements.includes(railwayName)) city.improvements.push(railwayName);
      const k = key(city.coords.x, city.coords.y);
      this.roads.delete(k);
      this.railways.add(k);
    }
  },

  _spawnUnit(center, civIndex, proto, homeCityId = null) {
    let index = this.protoUnits.indexOf(proto);
    if (index < 0) {
      this.protoUnits.push(proto);
      index = this.protoUnits.length - 1;
    }
    const unit = {
      id: this._nextUnitId,
      civ: civIndex,
      proto: index,
      coords: center,
      hp: proto.maxHp,
      maxHp: proto.maxHp,
      path: [],
      pathIndex: 0,
      progressHours: 0,
      moveSpeed: null,
      waypoints: [],
      invader: false,
      statuses: [],
      // A standing bombardment target (ground batteries) or a pending bomb run
      // (aircraft), plus the hour an aircraft may strike again.
      strikeTarget: null,
      strikeReadyHour: 0,
      missionFlown: false,
      // A transport's cargo and any boarding under way.
      cargo: [],
      embarking: null,
      // A land unit's carried food, in days. Air and naval units use their own
      // endurance models instead.
      foodDays: RESOURCE_RULES.unitSupplyDays,
    };
    if (proto.air) {
      unit.homeCityId = homeCityId;
      unit.airHours = proto.enduranceHours;
      unit.airborne = false;
      unit.autoReturn = false;
    }
    this.units.push(unit);
    this._unitById.set(this._nextUnitId, unit);
    this._nextUnitId += 1;
    return unit;
  },

  _generatePopulation() {
    this.tilePopulation = new Map();
    for (const k in this.tiles) {
      if (this._isLand(parseKey(k))) this.tilePopulation.set(k, this._basePopulation(parseKey(k)));
    }
    for (const city of this.cities) {
      this.tilePopulation.set(key(city.coords.x, city.coords.y), city.population);
    }
  },

  _basePopulation(coords) {
    return Math.round(ECONOMY.basePopulation * this.terrainStats.populationMultiplier(coords));
  },

  _initBudgets() {
    for (let i = 0; i < this.civilisations.length; i++) {
      this.budgets.set(i, this.getPlayerGdp(i) * ECONOMY.startingBudgetFraction);
    }
  },

  // Map generation should not hand one civilisation a richer start than
  // another. Terrain makes the raw territories unequal, so after the world is
  // populated we scale each civ's population to the common mean and then its
  // production per head to the mean of the raw figures. Total population
  // and total GDP are preserved; from here on the factors are constants and
  // terrain, buildings, technology and war move the numbers normally.
  _balanceStartingEconomy() {
    const count = this.civilisations.length;
    this._populationBalance = new Map();
    this._productionBalance = new Map();
    if (count <= 1) return;
    const bases = [];
    let totalPopulation = 0;
    let totalGdp = 0;
    for (let i = 0; i < count; i++) {
      const base = this._basePlayerAggregates(i);
      bases.push(base);
      totalPopulation += base.population;
      totalGdp += base.gdp;
    }
    if (totalPopulation <= 0) return;
    const targetPopulation = totalPopulation / count;
    const targetPerHead = totalGdp / totalPopulation;
    // Kept so the production balance can be restored once the starter industry
    // has been laid out and the raw figures have moved.
    this._targetProductionPerHead = targetPerHead;
    for (let i = 0; i < count; i++) {
      const base = bases[i];
      if (base.population <= 0) continue;
      const perHead = base.gdp / base.population;
      this._populationBalance.set(i, targetPopulation / base.population);
      this._productionBalance.set(i, perHead > 0 ? targetPerHead / perHead : 1);
    }
  },

  // Seeding the starter resource works changes every nation's raw GDP, but the
  // production balance must still hold: nations should not open richer just
  // because their land happens to host more industry. Re-derive the production
  // factor from the post-seeding figures against the same target, which also
  // leaves each nation's balanced GDP (and so its grid demand) exactly where
  // the seeding planned it.
  _rebalanceProduction() {
    if (!(this._targetProductionPerHead > 0)) return;
    for (let i = 0; i < this.civilisations.length; i++) {
      const base = this._basePlayerAggregates(i);
      if (base.population <= 0) continue;
      const perHead = base.gdp / base.population;
      this._productionBalance.set(i, perHead > 0 ? this._targetProductionPerHead / perHead : 1);
    }
    this._gdpPerCapitaCache.clear();
  },

  _isLand(coords) {
    const tile = this.tiles[key(coords.x, coords.y)];
    return !!tile && tile.terrainClass === "Land";
  },

  _isNextToCity(coords, owner) {
    const adjacent = this._cityAdjacent.get(owner);
    return adjacent ? adjacent.has(key(coords.x, coords.y)) : false;
  },
};