// Authoritative game server, ported from scripts/server/game_server.gd. Owns
// the GameState, turns player orders into state changes and pushes snapshots
// back to every connected client. The `network` adapter supplies getPeerIds()
// and send(peerId, message); everything else is transport-agnostic.

import { EventEmitter } from "node:events";
import { GameState } from "../shared/game_state.js";
import { LoginManager } from "../shared/login_manager.js";
import { CIVILISATIONS } from "../shared/data.js";
import { dateString } from "../shared/game_clock.js";

// The large collections a delta snapshot may leave out when their version has
// not moved since the last one sent to that peer. The viewer keeps the previous
// copy until it changes. Each entry pairs the collection with the version key
// that reports its changes; for `tileEthnicity` the version is named
// `ethnicity`. A mismatch here silently ships a whole collection every
// broadcast -- the opening production baseline is static, and shipping its
// several thousand entries on every 10 Hz snapshot was pure waste.
const DELTA_COLLECTIONS = [
  ["territory", "territory"],
  ["regions", "regions"],
  ["population", "population"],
  ["productionBaseline", "productionBaseline"],
  ["tileEthnicity", "ethnicity"],
  ["cities", "cityList"],
  ["cityStats", "cityStats"],
  ["visible", "visible"],
  ["resourceGraph", "resourceGraph"],
  // `resourceMarket` is small but is priced by the simple economy's global
  // stock and carries its supply/demand in the hard one, so it re-ships when
  // the market version moves rather than on every 10 Hz broadcast.
  ["resourceMarket", "market"],
  ["migrationGraph", "migrationGraph"],
];

// A wire move order carrying more units than this is split into chunks that
// each run in their own tick. One army move can otherwise run dozens of A*
// searches back to back and stall the simulation.
const MOVE_ORDER_CHUNK = 4;

export class GameServer extends EventEmitter {
  constructor(network) {
    super();
    this.network = network;
    this.state = null;
    this.hostCiv = 0;
    // True for a local test game, where free, instant orders are allowed.
    this.testing = false;
    this.peerCiv = new Map();
    // Peers whose page runs on the local machine. They may use the free, instant
    // testing orders even when the game as a whole is not a test game.
    this._localPeers = new Set();
    this.login = new LoginManager();
    this.adminName = "";
    this.peerNames = new Map();
    this.identityCiv = new Map();
    this._configured = false;
    this._stateDirty = false;
    // Orders wait here between the socket callback and the next simulation
    // tick, so a burst from several players is spread over time instead of
    // running every pathfinding search back to back on the event loop.
    this._orderQueue = [];
    // Per-peer delta bookkeeping: the versions last sent, how many explored
    // tiles the viewer already has, and which civ those were for (so a civ
    // change, whose per-viewer collections differ, forces a full snapshot).
    this._peerSnapshotVersions = new Map();
    this._peerExploredSent = new Map();
    this._peerCivSent = new Map();
    // Per-peer fingerprint of every unit last sent, so a delta ships only the
    // units that changed rather than the whole army. On a large world the unit
    // list is the bulk of a snapshot and most units are idle on any given
    // broadcast, so re-sending all of them dominated the loop.
    this._peerUnitSignatures = new Map();
  }

  isConfigured() {
    return this._configured;
  }

  gameList() {
    if (!this._configured || !this.state) return [];
    return [this.gameSummary()];
  }

  gameSummary() {
    return {
      id: this.state.seed,
      name: `Game ${this.state.seed}`,
      seed: this.state.seed,
      players: this.peerNames.size,
      civs: this.state.civilisations.map((c) => c.name),
      date: dateString(this.state.totalHours),
    };
  }

  authenticate(peerId, playerName, password) {
    const name = String(playerName || "").trim();
    if (name.length === 0) return { ok: false, reason: "Enter a player name." };
    if (String(password || "").length === 0) return { ok: false, reason: "Enter a password." };
    if (Array.from(this.peerNames.values()).includes(name)) {
      return { ok: false, reason: `${name} is already playing.` };
    }
    if (!this.login.login(name, password)) {
      return { ok: false, reason: `Wrong password for ${name}.` };
    }
    const isAdmin = this.adminName.length === 0;
    if (isAdmin) this.adminName = name;
    this.peerNames.set(peerId, name);
    return { ok: true, name, admin: name === this.adminName };
  }

  configureGame(setup) {
    if (this._configured) return;
    this.hostCiv = Number(setup.player_civ || 0);
    this.testing = !!setup.testing;
    this.state = new GameState();
    if (setup.mapConfig) this.state.mapConfig = setup.mapConfig;
    this.state.configure(this._loadCivs(setup.civilisations || []), Number(setup.seed || 0), {
      // The model the launcher chose; `configure` coerces an unknown value to
      // the "simple" default, so the setup may pass anything.
      economyModel: setup.economyModel,
    });
    this.state.testing = this.testing;
    this.state.onChanged(() => {
      this._stateDirty = true;
    });
    // A fresh world can be settled before the first player joins, so the game
    // opens with its economy and reserves already established rather than at a
    // cold start. The settle runs until commodity prices hold steady (over a
    // seven-day window) instead of for a fixed number of days, capped by the
    // launcher's `warmupDays` so an unsettled world cannot run away. Off when
    // the cap is zero. This is a hard-economy concept: the simple economy's
    // scenario is authored as its opening state, so it skips the settle
    // entirely and `settledDays` stays 0 whatever the cap says.
    const warmupDays = this.state.isSimpleEconomy() ? 0 : Number(setup.warmupDays || 0);
    this.settledDays = warmupDays > 0
      ? this.state.warmUpToStability({ maxDays: warmupDays })
      : 0;
    // Lay out every nation's opening forces and reserves only after the settle,
    // so the warm-up cannot spend the year of stores the game is meant to open
    // with. This is the state the first player joins.
    this.state.applyStartingScenario();
    this._configured = true;
    for (const peerId of this.network.getPeerIds()) {
      this._assignCiv(peerId, this.peerNames.get(peerId) || "");
    }
    this._broadcastState();
    this.emit("game_configured");
    return this.settledDays;
  }

  _loadCivs(ids) {
    const civs = [];
    for (const id of ids) {
      const civ = CIVILISATIONS.find((c) => c.id === id);
      if (civ) civs.push(civ);
    }
    // An empty list means the project's full roster.
    return civs.length === 0 ? CIVILISATIONS.slice() : civs;
  }

  // Queues an order from the wire. The socket callback must stay cheap: a
  // single group move can run hundreds of A* searches, and several players
  // sending at once would otherwise freeze the tick loop (and every client's
  // snapshot) until the whole burst finished.
  enqueueOrder(peerId, order) {
    // A large group move becomes several chunks so no single tick runs a whole
    // army's pathfinding at once. The chunks share the pace computed for the
    // full group, so a split stack still moves at its slowest member's speed.
    const type = String(order.t || order.type || "");
    if (type === "move" && Array.isArray(order.units) && order.units.length > MOVE_ORDER_CHUNK) {
      const civ = this.peerCiv.has(peerId) ? this.peerCiv.get(peerId) : -1;
      if (civ >= 0 && this.state && this._ownUnitIds(civ, order, true)) {
        const moveable = this.state._moveableUnits(order.units);
        const speed = moveable.length > 1
          ? Math.min(...moveable.map((unit) => this.state._unitSpeed(unit)))
          : null;
        for (let i = 0; i < order.units.length; i += MOVE_ORDER_CHUNK) {
          this._orderQueue.push({
            peerId,
            order: { ...order, units: order.units.slice(i, i + MOVE_ORDER_CHUNK), speed },
          });
        }
        return;
      }
    }
    this._orderQueue.push({ peerId, order });
  }

  // Applies queued orders until `budgetMs` is spent; the remainder waits for a
  // later tick. At least one order runs per call so the queue always drains.
  processOrders(budgetMs = 8) {
    if (this._orderQueue.length === 0) return 0;
    const deadline = Date.now() + budgetMs;
    let processed = 0;
    do {
      const next = this._orderQueue.shift();
      this.handleOrder(next.peerId, next.order);
      processed += 1;
    } while (this._orderQueue.length > 0 && Date.now() < deadline);
    return processed;
  }

  handleOrder(peerId, order) {
    if (!this._configured) return false;
    const civ = this.peerCiv.has(peerId) ? this.peerCiv.get(peerId) : -1;
    if (civ < 0) return false;
    const type = String(order.t || order.type || "");
    switch (type) {
      case "move":
        return this._handleMove(civ, order);
      case "attack":
        return this._handleAttack(civ, order);
      case "schedule":
        return this._handleSchedule(civ, order);
      case "pillage":
        return this._handlePillage(civ, order);
      case "sabotage":
        return this._handleSabotage(civ, order);
      case "spy_city":
        return this._handleSpyCity(civ, order);
      case "spy_comms":
        return this._handleSpyComms(civ, order);
      case "launch_satellite":
        return this._handleLaunchSatellite(civ, order);
      case "train":
        return this._handleTrain(peerId, civ, order);
      case "cancel_train":
        return this._handleCancelTrain(civ, order);
      case "build":
        return this._handleBuild(peerId, civ, order);
      case "build_improvement":
        return this._handleBuildImprovement(peerId, civ, order);
      case "remove_improvement":
        return this._handleRemoveImprovement(civ, order);
      case "dig_trench":
        return this._handleDigTrench(civ, order);
      case "build_tile_improvement":
        return this._handleBuildTileImprovement(civ, order);
      case "remove_tile_improvement":
        return this._handleRemoveTileImprovement(civ, order);
      case "cancel_site":
        return this._handleCancelSite(civ, order);
      case "embark":
        return this._handleEmbark(civ, order);
      case "disembark":
        return this._handleDisembark(civ, order);
      case "demolish":
        return this._handleDemolish(civ, order);
      case "government":
        return this._handleGovernment(civ, order);
      case "focus_technology":
        return this._handleFocusTechnology(civ, order);
      case "unlock_technology":
        return this._handleUnlockTechnology(peerId, civ, order);
      case "declare_war":
        return this._handleDeclareWar(civ, order);
      case "propose_treaty":
        return this._handleProposeTreaty(civ, order);
      case "respond_treaty":
        return this._handleRespondTreaty(civ, order);
      case "cancel_treaty":
        return this._handleCancelTreaty(civ, order);
      case "campaign":
        return this._handleCampaign(civ, order);
      case "cancel_campaign":
        return this._handleCancelCampaign(civ, order);
      case "campaign_spending":
        return this._handleCampaignSpending(civ, order);
      case "policy":
        return this._handlePolicy(civ, order);
      case "revoke_policy":
        return this._handleRevokePolicy(civ, order);
      case "set_interest_rate":
        // The simple economy has no central bank and no tax controls: its one
        // revenue is the per-inhabitant approval tax, so both orders are refused
        // before they reach the state.
        if (this.state.isSimpleEconomy()) return false;
        return this.state.requestSetInterestRate(civ, Number(order.rate));
      case "set_tax_rate":
        if (this.state.isSimpleEconomy()) return false;
        return this.state.requestSetTaxRate(
          civ, order.kind, Number(order.rate), order.resource || null
        );
      case "market_trade":
        // The global market is a simple-economy institution: the hard model's
        // reference prices are not buyable, so its server has no such order.
        if (!this.state.isSimpleEconomy()) return false;
        return this.state.requestMarketTrade(
          civ,
          String(order.resource || ""),
          String(order.side || ""),
          Number(order.lot)
        );
      default:
        return false;
    }
  }

  _handleMove(civ, order) {
    const units = this._ownUnitIds(civ, order, true);
    if (!units) return false;
    return this.state.requestGroupMove(units, coordsOf(order.coords), order.speed);
  }

  _handleAttack(civ, order) {
    const units = this._ownUnitIds(civ, order);
    if (units.length === 0) return false;
    const coords = coordsOf(order.coords);
    // A missile is a one-use rocket: firing it consumes the unit and lands its
    // warhead where it lands, whether that is conventional or nuclear.
    if (units.every((id) => this.state._isMissileUnit(this.state.findUnit(id)))) {
      return this.state.requestMissileStrike(units, coords, { nuclear: !!order.nuclear });
    }
    // Aircraft fly to a hostile unit and bomb it on arrival, then return to a
    // friendly airport. A ground/naval battery (artillery, warships) instead
    // opens a sustained hourly bombardment from where it stands. Anything else
    // -- or an attack on a tile with no unit on it, an undefended city say --
    // is a charge.
    if (units.every((id) => this.state._isAirUnit(this.state.findUnit(id)))) {
      return this.state.requestAirStrike(units, coords);
    }
    const ground = units.filter((id) => !this.state._isAirUnit(this.state.findUnit(id)));
    const allRanged =
      ground.length > 0 && ground.every((id) => this.state._isStrikeUnit(this.state.findUnit(id)));
    if (allRanged && this.state._strikeTargetAt(coords, civ)) {
      return this.state.requestBombard(ground, coords);
    }
    return this.state.requestAttack(units, coords);
  }

  _handleSchedule(civ, order) {
    const units = this._ownUnitIds(civ, order);
    if (units.length === 0) return false;
    const goals = (Array.isArray(order.goals) ? order.goals : [])
      .filter((goal) => Array.isArray(goal) && goal.length >= 2)
      .map(coordsOf);
    return this.state.requestScheduledMove(units, goals, !!order.append);
  }

  // The caller's own unit ids. With `strict`, a single id that is unknown or
  // owned by another civilisation rejects the whole order (null); otherwise the
  // foreign ids are simply dropped.
  _ownUnitIds(civ, order, strict = false) {
    const ids = Array.isArray(order.units) ? order.units : [order.unit];
    const units = [];
    for (const id of ids) {
      const unit = this.state.findUnit(Number(id));
      if (!unit || unit.civ !== civ) {
        if (strict) return null;
        continue;
      }
      units.push(unit.id);
    }
    return units;
  }

  _handlePillage(civ, order) {
    const units = this._ownUnitIds(civ, order, true);
    if (!units) return false;
    return this.state.requestPillage(units);
  }

  _handleSabotage(civ, order) {
    const units = this._ownUnitIds(civ, order, true);
    if (!units) return false;
    const frame = Number.isInteger(order.frame) ? order.frame : null;
    return this.state.requestSabotage(units, { frame });
  }

  _handleSpyCity(civ, order) {
    const units = this._ownUnitIds(civ, order, true);
    if (!units) return false;
    return this.state.requestCitySpy(units, coordsOf(order.coords));
  }

  _handleSpyComms(civ, order) {
    const units = this._ownUnitIds(civ, order, true);
    if (!units) return false;
    return this.state.requestCommsSpy(units, coordsOf(order.coords));
  }

  _handleLaunchSatellite(civ, order) {
    const city = this.state.findCity(Number(order.city));
    if (!city || city.civ !== civ) return false;
    return this.state.requestSatellite(civ, city);
  }

  _handleTrain(peerId, civ, order) {
    const city = this.state.findCity(Number(order.city));
    if (!city || city.civ !== civ) return false;
    const free = !!order.free && this._freeAllowed(peerId);
    return this.state.requestTrain(city.id, Number(order.proto), free);
  }

  _handleCancelTrain(civ, order) {
    const city = this.state.findCity(Number(order.city));
    if (!city || city.civ !== civ) return false;
    return this.state.cancelTrain(city.id, Number(order.index));
  }

  _handleBuild(peerId, civ, order) {
    const city = this.state.findCity(Number(order.city));
    if (!city || city.civ !== civ) return false;
    const free = !!order.free && this._freeAllowed(peerId);
    return this.state.requestBuild(city.id, Number(order.building), free);
  }

  _handleDemolish(civ, order) {
    const city = this.state.findCity(Number(order.city));
    if (!city || city.civ !== civ) return false;
    return this.state.requestDemolish(city.id, Number(order.building));
  }

  // Lays a road or railway on a tile the player controls. GameState enforces
  // ownership, terrain and cost; the testing shortcut is only honoured locally.
  _handleBuildImprovement(peerId, civ, order) {
    const free = !!order.free && this._freeAllowed(peerId);
    return this.state.requestBuildImprovement(
      civ,
      coordsOf(order.coords),
      String(order.improvement || ""),
      free
    );
  }

  // Tears a road or railway off a tile the player controls.
  _handleRemoveImprovement(civ, order) {
    return this.state.requestRemoveImprovement(civ, coordsOf(order.coords));
  }

  _handleDigTrench(civ, order) {
    const units = this._ownUnitIds(civ, order);
    if (units.length === 0) return false;
    return this.state.requestDigTrench(units);
  }

  _handleBuildTileImprovement(civ, order) {
    return this.state.requestBuildTileImprovement(
      civ,
      coordsOf(order.coords),
      String(order.improvement || "")
    );
  }

  _handleRemoveTileImprovement(civ, order) {
    return this.state.requestRemoveTileImprovement(civ, coordsOf(order.coords));
  }

  _handleCancelSite(civ, order) {
    return this.state.requestCancelSite(civ, coordsOf(order.coords));
  }

  _handleEmbark(civ, order) {
    const units = this._ownUnitIds(civ, order);
    if (units.length === 0) return false;
    return this.state.requestEmbark(units, Number(order.launch));
  }

  _handleDisembark(civ, order) {
    const units = this._ownUnitIds(civ, order);
    if (units.length === 0) return false;
    return this.state.requestDisembark(units, coordsOf(order.coords));
  }

  _handleGovernment(civ, order) {
    return this.state.requestSetGovernment(civ, Number(order.government));
  }

  _handleFocusTechnology(civ, order) {
    return this.state.requestFocusTechnology(civ, Number(order.technology));
  }

  // The testing shortcut: grants a technology outright. Honoured only for a
  // local page or a `--testing` game, exactly like the free build and train
  // orders; a normal client's `free` flag is ignored.
  _handleUnlockTechnology(peerId, civ, order) {
    if (!(!!order.free && this._freeAllowed(peerId))) return false;
    return this.state.unlockTechnology(civ, Number(order.technology));
  }

  _handleDeclareWar(civ, order) {
    const target = Number(order.target !== undefined ? order.target : order.civ);
    return this.state.requestDeclareWar(civ, target);
  }

  _handleProposeTreaty(civ, order) {
    const to = Number(order.to);
    const type = String(order.treaty || order.treatyType || "");
    return this.state.requestProposeTreaty(civ, to, type, order.payload || {});
  }

  _handleRespondTreaty(civ, order) {
    return this.state.requestRespondTreaty(civ, Number(order.proposal), !!order.accept);
  }

  _handleCancelTreaty(civ, order) {
    return this.state.requestCancelTreaty(civ, Number(order.treatyId));
  }

  _handleCampaign(civ, order) {
    const observer = Number(order.observer);
    const target = Number(order.target);
    const direction = Number(order.direction) < 0 ? -1 : 1;
    return this.state.requestCampaign(
      civ,
      observer,
      String(order.targetKind || ""),
      target,
      direction
    );
  }

  _handleCancelCampaign(civ, order) {
    return this.state.requestCancelCampaign(civ, Number(order.campaign));
  }

  _handleCampaignSpending(civ, order) {
    return this.state.requestSetCampaignSpending(
      civ,
      Number(order.campaign),
      Number(order.amount)
    );
  }

  _handlePolicy(civ, order) {
    return this.state.requestPolicy(civ, String(order.policy || ""), Number(order.ethnicity));
  }

  _handleRevokePolicy(civ, order) {
    return this.state.requestRevokePolicy(civ, Number(order.policy));
  }

  // Marks a peer as connected from a page on the local machine. Local peers may
  // use the free, instant testing orders even in a normal game.
  setPeerLocal(peerId, local) {
    if (local) this._localPeers.add(peerId);
    else this._localPeers.delete(peerId);
  }

  // Whether a peer may spend the testing shortcut.
  _freeAllowed(peerId) {
    return this.testing || this._localPeers.has(peerId);
  }

  onPeerJoined(peerId, playerName = "") {
    // A fresh connection must receive a full snapshot, never a delta against a
    // previous peer that happened to reuse the id.
    this._peerSnapshotVersions.delete(peerId);
    this._peerExploredSent.delete(peerId);
    this._peerCivSent.delete(peerId);
    this._peerUnitSignatures.delete(peerId);
    if (!this._configured) return;
    // A returning player keeps the nation they claimed before.
    if (this._reclaimIdentity(peerId, playerName)) {
      this.network.send(peerId, { t: "game_state", state: this.state.snapshot(this.peerCiv.get(peerId)) });
      return;
    }
    // Otherwise offer every nation no one has claimed yet and let the player
    // pick. They stay a spectator (civ -1) until they answer.
    this.peerCiv.set(peerId, -1);
    const options = this.availableCivs();
    this.network.send(peerId, { t: "choose_civ", civs: options });
    if (options.length === 0) {
      this.network.send(peerId, { t: "game_state", state: this.state.snapshot(-1) });
    }
  }

  onPeerLeft(peerId) {
    this.peerCiv.delete(peerId);
    this.peerNames.delete(peerId);
    this._localPeers.delete(peerId);
    // A departed player's queued orders must not land after they are gone.
    if (this._orderQueue.length > 0) {
      this._orderQueue = this._orderQueue.filter((entry) => entry.peerId !== peerId);
    }
    this._peerSnapshotVersions.delete(peerId);
    this._peerExploredSent.delete(peerId);
    this._peerCivSent.delete(peerId);
    this._peerUnitSignatures.delete(peerId);
  }

  // Indices of the civilisations no connected peer has claimed.
  availableCivs() {
    if (!this._configured || !this.state) return [];
    const used = new Set(this.peerCiv.values());
    const options = [];
    for (let i = 0; i < this.state.civilisations.length; i++) {
      if (used.has(i)) continue;
      const civ = this.state.civilisations[i];
      options.push({ index: i, id: civ.id, name: civ.name });
    }
    return options;
  }

  // Claims one of the offered civilisations for a joining peer. Rejects an
  // index that is out of range or already taken by someone else.
  claimCiv(peerId, index) {
    if (!this._configured || !this.state) return false;
    const choice = Number(index);
    if (!Number.isInteger(choice) || choice < 0 || choice >= this.state.civilisations.length) {
      return false;
    }
    if (Array.from(this.peerCiv.values()).includes(choice)) return false;
    this.peerCiv.set(peerId, choice);
    const name = this.peerNames.get(peerId);
    if (name) this.identityCiv.set(name, choice);
    this.network.send(peerId, { t: "civ_assigned", civ: choice });
    this.state.addControlNews(choice, name);
    this._broadcastState();
    return true;
  }

  // Re-attaches a known player to the nation they held before, as long as no
  // one else has claimed it in the meantime.
  _reclaimIdentity(peerId, playerName) {
    if (!playerName || !this.identityCiv.has(playerName)) return false;
    const choice = this.identityCiv.get(playerName);
    if (choice < 0 || choice >= this.state.civilisations.length) return false;
    if (Array.from(this.peerCiv.values()).includes(choice)) return false;
    this.peerCiv.set(peerId, choice);
    this.network.send(peerId, { t: "civ_assigned", civ: choice });
    this.state.addControlNews(choice, playerName);
    return true;
  }

  _assignCiv(peerId, playerName = "") {
    if (this._configured === false || this.state == null) return;
    const used = Array.from(this.peerCiv.values());
    let choice = -1;
    if (playerName && this.identityCiv.has(playerName)) choice = this.identityCiv.get(playerName);
    if (choice < 0 && peerId === this._adminPeerId()) choice = this.hostCiv;
    if (choice < 0 || used.includes(choice)) {
      choice = -1;
      for (let i = 0; i < this.state.civilisations.length; i++) {
        if (!used.includes(i)) {
          choice = i;
          break;
        }
      }
    }
    this.peerCiv.set(peerId, choice);
    if (playerName && choice >= 0) this.identityCiv.set(playerName, choice);
  }

  _adminPeerId() {
    for (const [peerId, name] of this.peerNames) {
      if (name === this.adminName) return peerId;
    }
    return 0;
  }

  tickHour() {
    if (!this._configured || !this.state) return;
    this.state.tickHour();
  }

  advanceMovement(hours) {
    if (!this._configured || !this.state) return;
    this.state.advanceMovement(hours);
  }

  flushIfDirty() {
    if (!this._stateDirty) return;
    this._stateDirty = false;
    this._broadcastState();
  }

  _broadcastState() {
    if (!this.state) return;
    // This snapshot reflects the state right now, so anything the change
    // listener recorded before it is already included. Clearing first means a
    // change raised while serialising still marks the next snapshot dirty.
    this._stateDirty = false;
    // One economy figure per city for the whole broadcast: the shared city
    // stats and every viewer's budget breakdown both need it.
    this.state.beginSnapshotCache();
    try {
      const shared = this.state.serializeShared();
      // One fingerprint pass for the whole broadcast. Units are shared by every
      // viewer, so their signatures are computed once and each peer is sent only
      // the units that changed for it since its last snapshot. The signature is
      // a hash so the per-peer bookkeeping stays a few numbers, not a second
      // copy of the army.
      const unitSignatures = new Map();
      for (const unit of shared.units) unitSignatures.set(unit.id, hashValue(JSON.stringify(unit)));
      const statsCache = new Map();
      for (const peerId of this.network.getPeerIds()) {
        const civ = this.peerCiv.has(peerId) ? this.peerCiv.get(peerId) : -1;
        if (!statsCache.has(civ)) statsCache.set(civ, this.state.viewerStats(civ));
        const snapshot = this.state.viewerSnapshot(shared, civ, statsCache.get(civ));
        this.network.send(peerId, {
          t: "game_state",
          state: this._deltaState(peerId, snapshot, unitSignatures),
        });
      }
    } finally {
      this.state.endSnapshotCache();
    }
  }

  // Trims a viewer snapshot down to what changed since the last one sent to this
  // peer: the large per-tile arrays are left out while their version is
  // unchanged, only the newly explored tiles are shipped, and units are sent one
  // by one as they change rather than as a whole army every broadcast. The first
  // snapshot to a peer (and after a reconnect) is always full.
  _deltaState(peerId, snapshot, unitSignatures) {
    // A viewer does not necessarily see every unit -- a hidden submarine is
    // omitted from its snapshot -- so the per-peer bookkeeping is keyed to the
    // units in this viewer's own snapshot.
    const viewerSignatures = new Map();
    for (const unit of snapshot.units || []) {
      const signature = unitSignatures.get(unit.id);
      if (signature !== undefined) viewerSignatures.set(unit.id, signature);
    }
    const versions = snapshot.versions;
    const previous = this._peerSnapshotVersions.get(peerId);
    // A viewer that changed civilisation sees different per-viewer collections
    // (explored, visible), so a delta against the old nation would be wrong.
    if (!previous || this._peerCivSent.get(peerId) !== snapshot.viewer) {
      this._peerSnapshotVersions.set(peerId, versions);
      this._peerExploredSent.set(peerId, (snapshot.explored || []).length);
      this._peerCivSent.set(peerId, snapshot.viewer);
      this._peerUnitSignatures.set(peerId, viewerSignatures);
      return { ...snapshot, delta: false };
    }
    const state = { ...snapshot, delta: true };
    for (const [key, versionKey] of DELTA_COLLECTIONS) {
      if (previous[versionKey] === versions[versionKey]) delete state[key];
    }
    const explored = snapshot.explored || [];
    const sent = this._peerExploredSent.get(peerId) || 0;
    if (explored.length > sent) {
      state.exploredAdded = explored.slice(sent);
      this._peerExploredSent.set(peerId, explored.length);
    }
    delete state.explored;
    const sentUnits = this._peerUnitSignatures.get(peerId);
    if (sentUnits) {
      const units = snapshot.units || [];
      const updated = [];
      for (const unit of units) {
        if (sentUnits.get(unit.id) !== viewerSignatures.get(unit.id)) updated.push(unit);
      }
      const removed = [];
      for (const id of sentUnits.keys()) {
        if (!viewerSignatures.has(id)) removed.push(id);
      }
      delete state.units;
      if (updated.length > 0) state.unitsUpdated = updated;
      if (removed.length > 0) state.unitsRemoved = removed;
    }
    this._peerUnitSignatures.set(peerId, viewerSignatures);
    this._peerSnapshotVersions.set(peerId, versions);
    this._peerCivSent.set(peerId, snapshot.viewer);
    return state;
  }
}

function coordsOf(value) {
  if (Array.isArray(value) && value.length >= 2) {
    return { x: Number(value[0]), y: Number(value[1]) };
  }
  return { x: -1, y: -1 };
}

// A cheap FNV-1a hash of a serialised value, used to tell one broadcast's unit
// list from the next without keeping a string per unit. A collision would only
// skip one update, and the next change to that unit hashes differently.
function hashValue(text) {
  let hash = 2166136261;
  for (let i = 0; i < text.length; i++) {
    hash = Math.imul(hash ^ text.charCodeAt(i), 16777619);
  }
  return hash >>> 0;
}