/**
 * Redis 缓存模块
 * 用于缓存聚合数据，减少数据库查询
 */
const Redis = require('ioredis');
const { getRuntimeRedisConfig } = require('../services/redisConfig');

let redis = null;
let connected = false;
let currentConfigSignature = '';
let unavailableUntil = 0;
let configCache = {
  expiresAt: 0,
  value: null,
};
const REDIS_FAILURE_COOLDOWN_MS = Number.parseInt(process.env.REDIS_FAILURE_COOLDOWN_MS || '30000', 10);
const REDIS_CONNECT_TIMEOUT_MS = Number.parseInt(process.env.REDIS_CONNECT_TIMEOUT_MS || '1000', 10);
const REDIS_OPERATION_TIMEOUT_MS = Math.min(
  Math.max(Number.parseInt(process.env.REDIS_OPERATION_TIMEOUT_MS || '500', 10), 100),
  2000
);
const REDIS_CONFIG_RESOLVE_TIMEOUT_MS = Math.min(
  Math.max(Number.parseInt(process.env.REDIS_CONFIG_RESOLVE_TIMEOUT_MS || '1500', 10), 300),
  3000
);

function withTimeout(promise, timeoutMs, fallback) {
  let timer;
  const timeout = new Promise((resolve) => {
    timer = setTimeout(() => resolve(fallback), timeoutMs);
  });

  return Promise.race([promise, timeout]).finally(() => {
    if (timer) {
      clearTimeout(timer);
    }
  });
}

function buildRedisClientConfig(config) {
  return {
    host: config.host,
    port: parseInt(config.port || '6379', 10),
    username: config.username || process.env.REDIS_USERNAME || process.env.REDIS_USER || undefined,
    password: config.password || undefined,
    db: parseInt(config.db || '0', 10),
    tls: config.tls ? { servername: config.tlsServerName || config.host } : undefined,
    connectTimeout: REDIS_CONNECT_TIMEOUT_MS,
    retryStrategy: (times) => (times > 1 ? null : 200),
    maxRetriesPerRequest: 1,
    enableOfflineQueue: false,
    enableReadyCheck: false,
    lazyConnect: true,
  };
}

function getConfigSignature(config) {
  if (!config?.host) {
    return '';
  }

  return JSON.stringify({
    host: config.host,
    port: parseInt(config.port || '6379', 10),
    db: parseInt(config.db || '0', 10),
    username: config.username || process.env.REDIS_USERNAME || process.env.REDIS_USER || '',
    password: config.password || '',
    tls: Boolean(config.tls),
    tlsServerName: config.tlsServerName || '',
  });
}

async function resolveRedisConfig(force = false) {
  const now = Date.now();
  if (!force && configCache.expiresAt > now) {
    return configCache.value;
  }

  const config = await getRuntimeRedisConfig();
  configCache = {
    value: config,
    expiresAt: now + 5000,
  };
  return config;
}

async function closeCurrentClient() {
  if (!redis) {
    connected = false;
    currentConfigSignature = '';
    return;
  }

  const client = redis;
  redis = null;
  connected = false;
  currentConfigSignature = '';

  try {
    await client.quit();
  } catch (_error) {
    client.disconnect();
  }
}

async function ensureRedisConnection(client) {
  if (!client) {
    return false;
  }

  if (unavailableUntil > Date.now()) {
    return false;
  }

  // `connect` only means that the socket is being opened. Sending a command
  // in that state can wait for ioredis' retry window, so only ready is usable.
  if (client.status === 'ready') {
    return true;
  }

  if (client.status === 'wait' || client.status === 'end') {
    try {
      await client.connect();
      unavailableUntil = 0;
      return true;
    } catch (error) {
      unavailableUntil = Date.now() + REDIS_FAILURE_COOLDOWN_MS;
      connected = false;
      console.warn('[Redis] 连接失败，进入冷却期:', error.message);
      return false;
    }
  }

  return false;
}

/**
 * 获取 Redis 实例
 */
const getRedis = async () => {
  const redisConfig = await withTimeout(
    resolveRedisConfig(),
    REDIS_CONFIG_RESOLVE_TIMEOUT_MS,
    null
  );
  if (!redisConfig) {
    await closeCurrentClient();
    return null;
  }

  const nextSignature = getConfigSignature(redisConfig);
  if (redis && currentConfigSignature !== nextSignature) {
    await closeCurrentClient();
  }

  if (!redis) {
    redis = new Redis(buildRedisClientConfig(redisConfig));
    currentConfigSignature = nextSignature;

    redis.on('connect', () => {
      connected = true;
      unavailableUntil = 0;
      console.log('[Redis] 连接成功');
    });

    redis.on('error', (err) => {
      connected = false;
      unavailableUntil = Date.now() + REDIS_FAILURE_COOLDOWN_MS;
      console.error('[Redis] 连接错误:', err.message);
    });

    redis.on('close', () => {
      connected = false;
      unavailableUntil = Date.now() + REDIS_FAILURE_COOLDOWN_MS;
      console.log('[Redis] 连接关闭');
    });
  }
  return redis;
};

/**
 * 安全获取缓存，Redis 不可用时返回 null
 */
const get = async (key) => {
  try {
    const r = await getRedis();
    if (!r) {
      return null;
    }
    if (!(await ensureRedisConnection(r))) {
      return null;
    }
    const value = await withTimeout(r.get(key), REDIS_OPERATION_TIMEOUT_MS, null);
    return value ? JSON.parse(value) : null;
  } catch (error) {
    console.warn('[Redis] GET 失败:', error.message);
    return null;
  }
};

/**
 * 原子读取并删除缓存。用于一次性票据，避免并发请求重复消费。
 */
const take = async (key) => {
  try {
    const r = await getRedis();
    if (!r) {
      return null;
    }
    if (!(await ensureRedisConnection(r))) {
      return null;
    }

    const value = await withTimeout(
      r.eval(
        "local value = redis.call('GET', KEYS[1]); if value then redis.call('DEL', KEYS[1]); end; return value",
        1,
        key
      ),
      REDIS_OPERATION_TIMEOUT_MS,
      null
    );
    return value ? JSON.parse(value) : null;
  } catch (error) {
    console.warn('[Redis] TAKE 失败:', error.message);
    return null;
  }
};

/**
 * 安全设置缓存，Redis 不可用时静默失败
 */
const setex = async (key, ttl, value) => {
  try {
    const r = await getRedis();
    if (!r) {
      return false;
    }
    if (!(await ensureRedisConnection(r))) {
      return false;
    }
    const stringValue = typeof value === 'string' ? value : JSON.stringify(value);
    const result = await withTimeout(r.setex(key, ttl, stringValue), REDIS_OPERATION_TIMEOUT_MS, null);
    return result === 'OK';
  } catch (error) {
    console.warn('[Redis] SETEX 失败:', error.message);
    return false;
  }
};

/**
 * 删除缓存
 */
const del = async (key) => {
  try {
    const r = await getRedis();
    if (!r) {
      return false;
    }
    if (!(await ensureRedisConnection(r))) {
      return false;
    }
    await withTimeout(r.del(key), REDIS_OPERATION_TIMEOUT_MS, null);
    return true;
  } catch (error) {
    console.warn('[Redis] DEL 失败:', error.message);
    return false;
  }
};

/**
 * 批量删除匹配的 key
 */
const delPattern = async (pattern) => {
  try {
    const r = await getRedis();
    if (!r) {
      return 0;
    }
    if (!(await ensureRedisConnection(r))) {
      return 0;
    }

    let cursor = '0';
    let deleted = 0;
    do {
      const [nextCursor, keys] = await r.scan(cursor, 'MATCH', pattern, 'COUNT', 100);
      cursor = nextCursor;
      if (Array.isArray(keys) && keys.length > 0) {
        deleted += await r.del(...keys);
      }
    } while (cursor !== '0');

    return deleted;
  } catch (error) {
    console.warn('[Redis] DEL PATTERN 失败:', error.message);
    return 0;
  }
};

/**
 * 测试连接
 */
const test = async () => {
  try {
    const r = await getRedis();
    if (!r) {
      return { success: false, message: '未配置 Redis' };
    }
    if (!(await ensureRedisConnection(r))) {
      return { success: false, message: '连接失败: Redis 当前不可用' };
    }
    const pong = await r.ping();
    return { success: pong === 'PONG', message: pong === 'PONG' ? 'Redis 连接成功' : `连接失败: ${pong}` };
  } catch (error) {
    return { success: false, message: `连接失败: ${error.message}` };
  }
};

/**
 * 关闭连接
 */
const close = async () => {
  await closeCurrentClient();
  console.log('[Redis] 连接已关闭');
};

/**
 * 应用已保存的运行时配置，无需重启后端进程。
 */
const reload = async () => {
  configCache = {
    expiresAt: 0,
    value: null,
  };
  unavailableUntil = 0;
  await closeCurrentClient();
  const client = await getRedis();
  if (client) {
    await ensureRedisConnection(client);
  }
  return client;
};

module.exports = {
  getRedis,
  get,
  take,
  setex,
  del,
  delPattern,
  test,
  close,
  reload,
  get connected() {
    return connected;
  },
};