/**
 * BuildState — the player's build progress (pure data, no scene).
 *
 * The run's build records, held by the GameScene (js/scenes/GameScene.js)
 * so they outlive the surface stay (SurfaceScene) and save with the run
 * (js/save/SaveData.js) — the same split as ResearchState:
 *
 *   - `built`  — which builds are installed on which planets
 *                (Map<planetName, Set<buildId>>); one-off builds land here
 *                on completion and are never built twice on a planet;
 *   - `active` — the single in-progress build (data/builds.json →
 *                maxConcurrent: one at a time): { planet, build,
 *                startedAt, durationMs }.
 *
 * The build is ticked by whichever scene is awake — the SurfaceScene
 * while on the surface (the GameScene sleeps then), the GameScene in
 * space — both with the game-loop clock (game.loop.now), the one clock
 * that keeps running across scene switches:
 *   progress(time) → { planet, build, fraction, remainingMs } | null
 *   tick(time)     → [ { planet, build, durationMs }, … ] (marks built)
 *
 * `remainingMs` is captured at save time; on load restoreActive() rebuilds
 * `startedAt` so the build finishes at the same wall time (the loop clock
 * is global, so a build started on the surface finishes in space too).
 */
export class BuildState {
  constructor() {
    this.built = new Map(); // planetName → Set<buildId>
    this.active = null;     // { planet, build, startedAt, durationMs }
  }

  // ── built records ────────────────────────────────────────────────────────
  markBuilt(planet, build) {
    if (!planet || !build) return;
    let set = this.built.get(planet);
    if (!set) {
      set = new Set();
      this.built.set(planet, set);
    }
    set.add(build);
  }

  isBuilt(planet, build) {
    const set = this.built.get(planet);
    return !!(set && build && set.has(build));
  }

  buildsOn(planet) {
    return [...(this.built.get(planet) ?? [])];
  }

  // ── the single in-progress build ─────────────────────────────────────────
  getActive() {
    return this.active;
  }

  /**
   * Claim the build slot. Fails when one is already running, the build is
   * already installed on this planet, or the duration is invalid.
   */
  start(planet, build, durationMs, now) {
    if (this.active) return false;
    if (this.isBuilt(planet, build)) return false;
    if (typeof durationMs !== 'number' || !(durationMs > 0)) return false;
    const t = Number.isFinite(now) ? now : 0;
    this.active = { planet, build, startedAt: t, durationMs };
    return true;
  }

  /**
   * Progress readout (0…1) for the active build.
   * @param {number} time ms on the ticking scene's clock (SurfaceScene)
   */
  progress(time) {
    if (!this.active) return null;
    const { startedAt, durationMs } = this.active;
    return {
      planet: this.active.planet,
      build: this.active.build,
      fraction: Math.max(0, Math.min(1, (time - startedAt) / durationMs)),
      remainingMs: Math.max(0, durationMs - (time - startedAt)),
    };
  }

  /**
   * Complete every build whose deadline has passed (marks it built on the
   * planet) and return the completions — the caller applies the effects
   * (the scene owns world state).
   */
  tick(time) {
    const out = [];
    if (this.active && time - this.active.startedAt >= this.active.durationMs) {
      const a = this.active;
      this.active = null;
      this.markBuilt(a.planet, a.build);
      out.push({ planet: a.planet, build: a.build, durationMs: a.durationMs });
    }
    return out;
  }

  // ── save / restore ───────────────────────────────────────────────────────
  /**
   * @param {number} now ms — capture remainingMs for the active build
   */
  toJSON(now) {
    return {
      built: Object.fromEntries([...this.built.entries()].map(([p, s]) => [p, [...s]])),
      active: this.active ? {
        planet: this.active.planet,
        build: this.active.build,
        startedAt: this.active.startedAt,
        durationMs: this.active.durationMs,
        remainingMs: this.progress(now)?.remainingMs ?? 0,
      } : null,
    };
  }

  fromJSON(json) {
    const j = json ?? {};
    for (const [p, ids] of Object.entries(j.built ?? {})) {
      for (const b of ids ?? []) this.markBuilt(p, b);
    }
    this.active = null; // restoreActive() re-claims it with the live clock
    return this;
  }

  /**
   * Rebuild the in-progress build so it finishes at the same wall time.
   * Skipped when the build is already installed on the planet (or when
   * the save predates the build system).
   */
  restoreActive(spec, now) {
    if (!spec || !spec.planet || !spec.build) return;
    if (this.isBuilt(spec.planet, spec.build)) return;
    const remaining = spec.remainingMs;
    if (typeof remaining !== 'number' || !(remaining > 0)) return;
    const t = Number.isFinite(now) ? now : 0;
    this.active = {
      planet: spec.planet,
      build: spec.build,
      startedAt: t - (spec.durationMs - remaining),
      durationMs: spec.durationMs,
    };
  }

  reset() {
    this.built.clear();
    this.active = null;
  }
}