Battle-for-Tismo/shared/game_state/territory.js

// Territory: which civilisation owns each land tile, how ownership spreads
// from cities, and how it is redrawn when a city changes hands.

import { key, parseKey } from "../hex.js";
import { NEWS_CAPTURE } from "../data/relations.js";
import { serializeCells } from "./helpers.js";

export const territoryMethods = {
  civAt(coords) {
    const k = key(coords.x, coords.y);
    return this.territory.has(k) ? this.territory.get(k) : -1;
  },

  terrainTypeAt(coords) {
    const tile = this.tiles[key(coords.x, coords.y)];
    return tile ? tile.terrainType : "Unknown";
  },

  getTilePopulation(coords) {
    return Math.round(this.tilePopulation.get(key(coords.x, coords.y)) || 0);
  },

  getTileInfo(coords) {
    const city = this.cityAt(coords);
    return {
      coords,
      owner: this.civAt(coords),
      terrainType: this.terrainTypeAt(coords),
      population: this.getTilePopulation(coords),
      improvements: city ? city.improvements : [],
    };
  },

  _recomputeTerritory() {
    this.territory = new Map();
    this._gdpPerCapitaCache = new Map();
    const ownerByCell = new Map();
    let frontier = [];
    for (const city of this.cities) {
      const k = key(city.coords.x, city.coords.y);
      ownerByCell.set(k, city.civ);
      this.territory.set(k, city.civ);
      frontier.push(city.coords);
    }
    while (frontier.length > 0) {
      const next = [];
      for (const coords of frontier) {
        const owner = ownerByCell.get(key(coords.x, coords.y));
        for (const neighbour of this._neighbours(coords)) {
          const nk = key(neighbour.x, neighbour.y);
          if (ownerByCell.has(nk) || !this._isLand(neighbour)) continue;
          ownerByCell.set(nk, owner);
          this.territory.set(nk, owner);
          next.push(neighbour);
        }
      }
      frontier = next;
    }
    this._rebuildRegionIndex();
    this._indexTerritory();
  },

  // Subdivides each nation's territory into the regions of its own cities: a
  // multi-source BFS grown from every city, but never crossing into another
  // nation's land. Ties between equally close cities are settled by city order,
  // so the result is deterministic and identical on both sides of the wire.
  _rebuildRegionIndex() {
    this._regionVersion += 1;
    this.tileRegion = new Map();
    this._regionByCity = new Map();
    const cityByCell = new Map();
    let frontier = [];
    for (const city of this.cities) {
      const k = key(city.coords.x, city.coords.y);
      cityByCell.set(k, city);
      this.tileRegion.set(k, city.id);
      frontier.push(city.coords);
    }
    while (frontier.length > 0) {
      const next = [];
      for (const coords of frontier) {
        const city = cityByCell.get(key(coords.x, coords.y));
        for (const neighbour of this._neighbours(coords)) {
          const nk = key(neighbour.x, neighbour.y);
          if (cityByCell.has(nk) || !this._isLand(neighbour)) continue;
          if (this.territory.get(nk) !== city.civ) continue;
          cityByCell.set(nk, city);
          this.tileRegion.set(nk, city.id);
          next.push(neighbour);
        }
      }
      frontier = next;
    }
    for (const [k, cityId] of this.tileRegion) {
      if (!this._regionByCity.has(cityId)) this._regionByCity.set(cityId, []);
      this._regionByCity.get(cityId).push(parseKey(k));
    }
  },

  // The city whose region the tile belongs to, or null on unclaimed land.
  regionCityAt(coords) {
    const id = this.tileRegion.get(key(coords.x, coords.y));
    return id !== undefined ? this._cityById.get(id) || null : null;
  },

  // The land tiles a city's region covers that are still owned by the city's
  // civilisation. A freshly captured city only taxes the land that came with it.
  regionTiles(city) {
    const tiles = this._regionByCity.get(city.id) || [];
    return tiles.filter((coords) => this.civAt(coords) === city.civ);
  },

  _indexTerritory() {
    this._territoryVersion += 1;
    this._territoryByCiv = new Map();
    for (const [k, owner] of this.territory) {
      if (!this._territoryByCiv.has(owner)) this._territoryByCiv.set(owner, []);
      this._territoryByCiv.get(owner).push(parseKey(k));
    }
    this._serializedTerritory = serializeCells(this.territory);
    this._gdpPerCapitaCache = new Map();
    // Which tiles a nation holds changes whose people count toward approval,
    // so a territory redraw invalidates the memoised approval figures.
    this._touchPolitics();
  },

  // Rebuilds the owner index, the regions, the serialised territory and the
  // GDP-per-capita cache after `this.territory` changes outside a full
  // recompute.
  _reindexTerritory() {
    this._rebuildRegionIndex();
    this._indexTerritory();
  },

  // Transfers `city` to `newCiv` and, with it, every tile of the old owner's
  // territory that is strictly closer (through land) to the captured city than
  // to any of their remaining cities. Ties stay with the old owner.
  _captureCity(city, newCiv) {
    const oldCiv = city.civ;
    if (oldCiv === newCiv) return false;
    const region = (this._territoryByCiv.get(oldCiv) || []).slice();
    const claim = this._nearestCityOwner(city, oldCiv, newCiv);
    city.civ = newCiv;
    for (const coords of region) {
      const k = key(coords.x, coords.y);
      if (claim.get(k) === newCiv) this.territory.set(k, newCiv);
    }
    // The captured city's own tile always changes hands, ties or not.
    this.territory.set(key(city.coords.x, city.coords.y), newCiv);
    this.training.delete(city.id);
    this._reindexTerritory();
    this._rebuildCityIndex();
    this._visibilityDirty = true;
    this._addNews({ type: NEWS_CAPTURE, city: city.name, from: oldCiv, to: newCiv });
    this._emitChanged();
    return true;
  },

  // Multi-source BFS over land from the captured city and every remaining city
  // of the old owner. Each tile records the civ of the nearest city; a tile
  // reached at the same distance from both sides is credited to the old owner.
  _nearestCityOwner(captured, oldCiv, newCiv) {
    const claim = new Map();
    const visited = new Set();
    let frontier = [];
    const sources = [{ coords: captured.coords, civ: newCiv }];
    for (const city of this.cities) {
      if (city !== captured && city.civ === oldCiv) {
        sources.push({ coords: city.coords, civ: oldCiv });
      }
    }
    for (const source of sources) {
      const k = key(source.coords.x, source.coords.y);
      if (visited.has(k)) continue;
      visited.add(k);
      claim.set(k, source.civ);
      frontier.push(source.coords);
    }
    while (frontier.length > 0) {
      const nextFrontier = [];
      const nextClaim = new Map();
      for (const coords of frontier) {
        const civ = claim.get(key(coords.x, coords.y));
        for (const neighbour of this._neighbours(coords)) {
          const nk = key(neighbour.x, neighbour.y);
          if (visited.has(nk) || !this._isLand(neighbour)) continue;
          if (nextClaim.has(nk)) {
            if (nextClaim.get(nk) === newCiv && civ === oldCiv) nextClaim.set(nk, oldCiv);
            continue;
          }
          nextClaim.set(nk, civ);
          nextFrontier.push(neighbour);
        }
      }
      for (const [k, civ] of nextClaim) {
        claim.set(k, civ);
        visited.add(k);
      }
      frontier = nextFrontier;
    }
    return claim;
  },
};