/**
 * SceneManager.js
 * Manages scene registration, switching, and lifecycle (enter/exit/update/render).
 */

class SceneManager {
  constructor() {
    /** @type {Map<string, object>} Registered scene instances */
    this._scenes = new Map();
    /** @type {object|null} Current active scene */
    this._currentScene = null;
    /** @type {string|null} Current scene name */
    this._currentName = null;
    /** @type {boolean} Whether a transition is in progress */
    this._transitioning = false;
  }

  /**
   * Register a scene.
   * A scene object should implement: enter(params), exit(), update(dt), render(ctx).
   * @param {string} name - Unique scene name.
   * @param {object} scene - Scene instance.
   */
  register(name, scene) {
    this._scenes.set(name, scene);
  }

  /**
   * Switch to a different scene.
   * @param {string} name - Target scene name.
   * @param {object} [params] - Optional parameters passed to the new scene's enter().
   */
  switchTo(name, params) {
    if (this._transitioning) return;
    if (!this._scenes.has(name)) {
      console.error(`[SceneManager] Scene "${name}" not registered.`);
      return;
    }

    this._transitioning = true;

    // Exit current scene
    if (this._currentScene && typeof this._currentScene.exit === 'function') {
      this._currentScene.exit();
    }

    // Enter new scene
    this._currentName = name;
    this._currentScene = this._scenes.get(name);
    if (typeof this._currentScene.enter === 'function') {
      this._currentScene.enter(params || {});
    }

    this._transitioning = false;
  }

  /**
   * Update the current scene.
   * @param {number} dt - Delta time in seconds.
   */
  update(dt) {
    if (this._currentScene && typeof this._currentScene.update === 'function') {
      this._currentScene.update(dt);
    }
  }

  /**
   * Render the current scene.
   * @param {CanvasRenderingContext2D} ctx
   */
  render(ctx) {
    if (this._currentScene && typeof this._currentScene.render === 'function') {
      this._currentScene.render(ctx);
    }
  }

  /**
   * Forward touch events to the current scene.
   * @param {string} eventType - 'touchstart' | 'touchmove' | 'touchend'
   * @param {TouchEvent} e
   */
  handleTouch(eventType, e) {
    if (this._currentScene && typeof this._currentScene.handleTouch === 'function') {
      this._currentScene.handleTouch(eventType, e);
    }
  }

  /** Get the current scene name. */
  get currentName() {
    return this._currentName;
  }

  /** Get the current scene instance. */
  get currentScene() {
    return this._currentScene;
  }
}

module.exports = SceneManager;