import { Injectable, Inject, Logger } from '@nestjs/common';
import { CACHE_MANAGER } from '@nestjs/cache-manager';
import type { Cache } from 'cache-manager';
import { Redis } from 'ioredis';
import { CacheService } from './cacheService';

export interface MultiLevelCacheOptions {
  l1Ttl?: number; // L1 缓存时间（秒）
  l2Ttl?: number; // L2 缓存时间（秒）
  prefix?: string;
}

@Injectable()
export class MultiLevelCacheService {
  private readonly logger = new Logger(MultiLevelCacheService.name);
  private readonly appPrefix = 'wwjcloud'; // 使用固定前缀，避免硬编码

  constructor(
    @Inject(CACHE_MANAGER) private l1Cache: Cache, // 内存缓存
    @Inject('REDIS_CLIENT') private l2Cache: Redis, // Redis 缓存
    private cacheService: CacheService,
  ) {}

  /**
   * 获取缓存（多级）
   */
  async get<T>(key: string, options?: MultiLevelCacheOptions): Promise<T | null> {
    try {
      const fullKey = this.buildKey(key, options?.prefix);
      
      // L1: 内存缓存
      const l1Value = await this.l1Cache.get<T>(fullKey);
      if (l1Value !== undefined && l1Value !== null) {
        this.logger.debug(`L1 cache hit: ${fullKey}`);
        return l1Value as T;
      }
      
      // L2: Redis 缓存
      const l2Value = await this.l2Cache.get(fullKey);
      if (l2Value !== null && l2Value !== undefined) {
        const parsedValue = JSON.parse(l2Value) as T;
        // 回填到 L1 缓存
        await this.l1Cache.set(fullKey, parsedValue, options?.l1Ttl || 60);
        this.logger.debug(`L2 cache hit: ${fullKey}`);
        return parsedValue;
      }
      
      this.logger.debug(`Cache miss: ${fullKey}`);
      return null;
    } catch (error) {
      this.logger.error(`Cache get error: ${error.message}`, error.stack);
      return null;
    }
  }

  /**
   * 设置缓存（多级）
   */
  async set<T>(key: string, value: T, options?: MultiLevelCacheOptions): Promise<void> {
    const fullKey = this.buildKey(key, options?.prefix);
    
    try {
      // 并行设置 L1 和 L2 缓存
      await Promise.all([
        this.l1Cache.set(fullKey, value, options?.l1Ttl || 60),
        this.l2Cache.setex(fullKey, options?.l2Ttl || 300, JSON.stringify(value)),
      ]);
      
      this.logger.debug(`Multi-level cache set: ${fullKey}`);
    } catch (error) {
      this.logger.error(`Multi-level cache set error: ${error.message}`, error.stack);
    }
  }

  /**
   * 删除缓存（多级）
   */
  async del(key: string, options?: MultiLevelCacheOptions): Promise<void> {
    const fullKey = this.buildKey(key, options?.prefix);
    
    try {
      // 并行删除 L1 和 L2 缓存
      await Promise.all([
        this.l1Cache.del(fullKey),
        this.l2Cache.del(fullKey),
      ]);
      
      this.logger.debug(`Multi-level cache del: ${fullKey}`);
    } catch (error) {
      this.logger.error(`Multi-level cache del error: ${error.message}`, error.stack);
    }
  }

  /**
   * 批量删除缓存
   */
  async delPattern(pattern: string): Promise<void> {
    try {
      // 获取匹配的键
      const keys = await this.l2Cache.keys(pattern);
      
      if (keys.length > 0) {
        // 删除 L2 缓存
        await this.l2Cache.del(...keys);
        
        // 删除 L1 缓存
        const l1Promises = keys.map(key => this.l1Cache.del(key));
        await Promise.allSettled(l1Promises);
        
        this.logger.debug(`Multi-level cache del pattern: ${pattern}, deleted ${keys.length} keys`);
      }
    } catch (error) {
      this.logger.error(`Multi-level cache del pattern error: ${error.message}`, error.stack);
    }
  }

  /**
   * 获取或设置缓存（缓存穿透保护）
   */
  async getOrSet<T>(
    key: string,
    factory: () => Promise<T>,
    options?: MultiLevelCacheOptions
  ): Promise<T> {
    const fullKey = this.buildKey(key, options?.prefix);
    
    try {
      // 先尝试获取缓存
      let value = await this.get<T>(fullKey, options);
      
      if (value !== null) {
        return value;
      }

      // 缓存未命中，执行工厂函数
      value = await factory();
      
      // 设置缓存
      await this.set(key, value, options);
      
      return value;
    } catch (error) {
      this.logger.error(`Multi-level cache getOrSet error: ${error.message}`, error.stack);
      throw error;
    }
  }

  /**
   * 预热缓存
   */
  async warmup<T>(
    keys: string[],
    factory: (key: string) => Promise<T>,
    options?: MultiLevelCacheOptions
  ): Promise<void> {
    this.logger.log(`Starting cache warmup for ${keys.length} keys`);
    
    const promises = keys.map(async (key) => {
      try {
        const value = await factory(key);
        await this.set(key, value, options);
        this.logger.debug(`Cache warmed up: ${key}`);
      } catch (error) {
        this.logger.error(`Cache warmup failed for key ${key}: ${error.message}`);
      }
    });

    await Promise.allSettled(promises);
    this.logger.log('Cache warmup completed');
  }

  /**
   * 获取缓存统计信息
   */
  async getStats(): Promise<{
    l1Stats: { size: number; hitRate: number };
    l2Stats: { size: number; hitRate: number };
    totalHitRate: number;
  }> {
    try {
      // 获取 L2 缓存统计
      const l2Info = await this.l2Cache.info('memory');
      const l2Keys = await this.l2Cache.dbsize();
      
      // 解析 L2 内存使用
      const memoryMatch = l2Info.match(/used_memory_human:(\S+)/);
      const l2Memory = memoryMatch ? memoryMatch[1] : '0B';
      
      return {
        l1Stats: {
          size: 0, // 需要实现 L1 缓存大小统计
          hitRate: 0, // 需要实现命中率统计
        },
        l2Stats: {
          size: this.parseMemoryUsage(l2Memory),
          hitRate: 0, // 需要实现命中率统计
        },
        totalHitRate: 0, // 需要实现总命中率统计
      };
    } catch (error) {
      this.logger.error(`Multi-level cache stats error: ${error.message}`, error.stack);
      return {
        l1Stats: { size: 0, hitRate: 0 },
        l2Stats: { size: 0, hitRate: 0 },
        totalHitRate: 0,
      };
    }
  }

  /**
   * 清空所有缓存
   */
  async clear(): Promise<void> {
    try {
      // 直接使用 Redis 的 FLUSHDB 命令清空 L2 缓存
      // L1 缓存会在下次访问时自动失效
      await this.l2Cache.flushdb();
      
      this.logger.debug('Multi-level cache cleared');
    } catch (error) {
      this.logger.error(`Multi-level cache clear error: ${error.message}`, error.stack);
    }
  }

  /**
   * 构建缓存键
   */
  private buildKey(key: string, prefix?: string): string {
    const finalPrefix = prefix ? `${this.appPrefix}:ml:${prefix}` : `${this.appPrefix}:ml`;
    return `${finalPrefix}:${key}`;
  }

  /**
   * 解析内存使用量
   */
  private parseMemoryUsage(memoryStr: string): number {
    const match = memoryStr.match(/^(\d+(?:\.\d+)?)([KMGT]?B)$/);
    if (!match) return 0;
    
    const [, value, unit] = match;
    const numValue = parseFloat(value);
    
    switch (unit) {
      case 'KB': return numValue * 1024;
      case 'MB': return numValue * 1024 * 1024;
      case 'GB': return numValue * 1024 * 1024 * 1024;
      case 'TB': return numValue * 1024 * 1024 * 1024 * 1024;
      default: return numValue;
    }
  }
}