/**
 * 头像缓存管理工具类
 * 实现头像图片的KV存储和缓存机制，避免重复下载相同图片
 */

class AvatarCache {
  private static instance: AvatarCache;
  private cache: Map<string, string> = new Map(); // KV存储：avatarUrl -> 本地图片路径
  private downloadingUrls: Set<string> = new Set(); // 正在下载的URL集合

  private constructor() {}

  public static getInstance(): AvatarCache {
    if (!AvatarCache.instance) {
      AvatarCache.instance = new AvatarCache();
    }
    return AvatarCache.instance;
  }

  /**
   * 获取头像图片路径
   * @param avatarUrl 头像URL
   * @returns 本地图片路径或Promise<string>
   */
  public async getAvatarPath(avatarUrl: string): Promise<string> {
    if (!avatarUrl) {
      return this.getDefaultAvatarPath();
    }

    // 如果缓存中已存在，直接返回
    if (this.cache.has(avatarUrl)) {
      return this.cache.get(avatarUrl)!;
    }

    // 如果正在下载中，等待下载完成
    if (this.downloadingUrls.has(avatarUrl)) {
      return await this.waitForDownload(avatarUrl);
    }

    // 开始下载图片
    return await this.downloadAndCacheAvatar(avatarUrl);
  }

  /**
   * 获取头像URL（用于存储和传递，不下载图片）
   * @param userId 用户ID
   * @param avatarUrl 头像URL
   * @returns 头像URL
   */
  public getAvatarUrl(avatarUrl: string): string {
    if (!avatarUrl) {
      return '/images/user-avatar.png';
    }

    // 如果缓存中已存在，直接返回URL（不下载）
    if (this.cache.has(avatarUrl)) {
      return avatarUrl;
    }

    // 如果不在缓存中，异步下载但不等待结果
    if (!this.downloadingUrls.has(avatarUrl)) {
      this.downloadAndCacheAvatar(avatarUrl).catch(() => {
        // 下载失败不影响主流程
      });
    }

    return avatarUrl;
  }

  /**
   * 下载并缓存头像图片
   * @param avatarUrl 头像URL
   * @returns 本地图片路径
   */
  private async downloadAndCacheAvatar(avatarUrl: string): Promise<string> {
    this.downloadingUrls.add(avatarUrl);

    try {
      // 下载图片到临时文件
      const tempFilePath = await this.downloadImage(avatarUrl);
      
      // 缓存到KV存储
      this.cache.set(avatarUrl, tempFilePath);
      
      return tempFilePath;
    } catch (error) {
      console.error(`下载头像失败: ${avatarUrl}`, error);
      return this.getDefaultAvatarPath();
    } finally {
      this.downloadingUrls.delete(avatarUrl);
    }
  }

  /**
   * 下载图片到本地临时文件
   * @param avatarUrl 头像URL
   * @returns 本地临时文件路径
   */
  private async downloadImage(avatarUrl: string): Promise<string> {
    return new Promise((resolve, reject) => {
      wx.downloadFile({
        url: avatarUrl,
        success: (res) => {
          if (res.statusCode === 200) {
            resolve(res.tempFilePath);
          } else {
            reject(new Error(`下载失败，状态码: ${res.statusCode}`));
          }
        },
        fail: (error) => {
          reject(error);
        }
      });
    });
  }

  /**
   * 等待下载完成
   * @param avatarUrl 头像URL
   * @returns 本地图片路径
   */
  private async waitForDownload(avatarUrl: string): Promise<string> {
    return new Promise((resolve) => {
      const checkInterval = setInterval(() => {
        if (!this.downloadingUrls.has(avatarUrl) && this.cache.has(avatarUrl)) {
          clearInterval(checkInterval);
          resolve(this.cache.get(avatarUrl)!);
        }
      }, 100);

      // 设置超时时间
      setTimeout(() => {
        clearInterval(checkInterval);
        resolve(this.getDefaultAvatarPath());
      }, 5000);
    });
  }

  /**
   * 获取默认头像路径
   * @returns 默认头像路径
   */
  private getDefaultAvatarPath(): string {
    return '/images/user-avatar.png';
  }

  /**
   * 预加载多个头像
   * @param avatarUrls 头像URL数组
   */
  public async preloadAvatars(avatarUrls: string[]): Promise<void> {
    const uniqueUrls = [...new Set(avatarUrls)];
    
    for (const url of uniqueUrls) {
      if (url && !this.cache.has(url) && !this.downloadingUrls.has(url)) {
        // 异步预加载，不等待结果
        this.downloadAndCacheAvatar(url).catch(() => {
          // 预加载失败不影响主流程
        });
      }
    }
  }

  /**
   * 预加载多个头像并等待所有加载完成
   * @param avatarUrls 头像URL数组
   */
  public async preloadAvatarsAndWait(avatarUrls: string[]): Promise<void> {
    const uniqueUrls = [...new Set(avatarUrls)];
    const downloadPromises: Promise<string>[] = [];
    
    for (const url of uniqueUrls) {
      if (url && !this.cache.has(url) && !this.downloadingUrls.has(url)) {
        // 同步预加载，等待结果
        downloadPromises.push(this.downloadAndCacheAvatar(url));
      }
    }
    
    if (downloadPromises.length > 0) {
      console.log(`🔄 [AvatarCache] 开始预加载 ${downloadPromises.length} 个头像`);
      await Promise.allSettled(downloadPromises);
      console.log(`✅ [AvatarCache] 头像预加载完成，缓存大小: ${this.cache.size}`);
    } else {
      console.log('ℹ️ [AvatarCache] 没有需要预加载的头像');
    }
  }

  /**
   * 清除缓存
   */
  public clearCache(): void {
    this.cache.clear();
  }

  /**
   * 获取缓存统计信息
   */
  public getCacheStats(): { size: number; downloading: number } {
    return {
      size: this.cache.size,
      downloading: this.downloadingUrls.size
    };
  }
}

// 导出单例实例
export const avatarCache = AvatarCache.getInstance();

export default AvatarCache;