/**
 * ResourceManager.js
 * Handles preloading of image resources using wx.createImage.
 * Provides progress callback and cached access to loaded images.
 */

class ResourceManager {
  constructor() {
    /** @type {Map<string, Image>} */
    this._cache = new Map();
    this._totalAssets = 0;
    this._loadedAssets = 0;
  }

  /**
   * Preload a list of image assets.
   * @param {Array<{key: string, src: string}>} assetList - Assets to load.
   * @param {Function} [onProgress] - Called with (loaded, total) on each load.
   * @returns {Promise<void>} Resolves when all assets are loaded.
   */
  loadImages(assetList, onProgress) {
    this._totalAssets = assetList.length;
    this._loadedAssets = 0;

    if (this._totalAssets === 0) {
      return Promise.resolve();
    }

    const promises = assetList.map(({ key, src }) => {
      return new Promise((resolve, reject) => {
        // If already cached, skip
        if (this._cache.has(key)) {
          this._loadedAssets++;
          if (onProgress) onProgress(this._loadedAssets, this._totalAssets);
          resolve();
          return;
        }

        const img = wx.createImage();
        img.onload = () => {
          this._cache.set(key, img);
          this._loadedAssets++;
          if (onProgress) onProgress(this._loadedAssets, this._totalAssets);
          resolve();
        };
        img.onerror = (err) => {
          console.warn(`[ResourceManager] Failed to load: ${src}`, err);
          // Resolve anyway so other assets continue loading
          this._loadedAssets++;
          if (onProgress) onProgress(this._loadedAssets, this._totalAssets);
          resolve();
        };
        img.src = src;
      });
    });

    return Promise.all(promises).then(() => {});
  }

  /**
   * Get a loaded image by key.
   * @param {string} key
   * @returns {Image|null}
   */
  getImage(key) {
    return this._cache.get(key) || null;
  }

  /**
   * Check if an image is loaded.
   * @param {string} key
   * @returns {boolean}
   */
  hasImage(key) {
    return this._cache.has(key);
  }

  /**
   * Clear all cached images.
   */
  clear() {
    this._cache.clear();
    this._totalAssets = 0;
    this._loadedAssets = 0;
  }

  /** Current loading progress (0 to 1). */
  get progress() {
    if (this._totalAssets === 0) return 1;
    return this._loadedAssets / this._totalAssets;
  }
}

module.exports = ResourceManager;