import Redis from 'ioredis';
import CryptoJS from 'crypto-js';

// Initialize Redis client
let redisClient: Redis | null = null;
let isConnecting = false;
let connectionAttempts = 0;
const MAX_RECONNECT_ATTEMPTS = 5;

/**
 * Get a Redis client instance (singleton pattern) with improved connection management
 */
export function getRedisClient(): Redis {
  if (redisClient && redisClient.status === 'ready') {
    return redisClient;
  }
  
  if (isConnecting) {
    // If we're already trying to connect, return the existing client
    // This prevents multiple simultaneous connection attempts
    if (redisClient) return redisClient;
    
    // This is a fallback in case we're connecting but don't have a client yet
    console.warn('Redis connection in progress, creating temporary client');
  }
  
  if (!redisClient) {
    isConnecting = true;
    connectionAttempts = 0;
    
    // Set Redis connection parameters from environment variables only
    const redisOptions = {
      host: process.env.REDIS_HOST,
      port: process.env.REDIS_PORT ? parseInt(process.env.REDIS_PORT) : undefined,
      password: process.env.REDIS_PASSWORD,
      retryStrategy: (times: number) => {
        connectionAttempts = times;
        if (times > MAX_RECONNECT_ATTEMPTS) {
          console.error(`Redis connection failed after ${times} attempts, giving up`);
          return null; // Stop trying to reconnect
        }
        const delay = Math.min(times * 100, 5000);
        console.log(`Redis reconnect attempt ${times}, retrying in ${delay}ms`);
        return delay;
      },
      maxRetriesPerRequest: 5,
      enableOfflineQueue: true,
      connectTimeout: 10000, // 10 seconds
      disconnectTimeout: 2000, // 2 seconds
      keepAlive: 10000, // 10 seconds
      keyPrefix: '' // No prefix to keep keys clean
    };
    
    console.log('Connecting to Redis using environment variables');
    redisClient = new Redis(redisOptions);
    
    redisClient.on('error', (err) => {
      console.error('Redis connection error:', err);
      
      // Only set to null if we've exceeded max attempts
      if (connectionAttempts > MAX_RECONNECT_ATTEMPTS) {
        console.error('Redis connection failed permanently, will create new client on next request');
        redisClient = null;
        isConnecting = false;
      }
    });
    
    redisClient.on('connect', () => {
      console.log('Successfully connected to Redis');
      isConnecting = false;
      connectionAttempts = 0;
    });
    
    redisClient.on('reconnecting', () => {
      console.log('Reconnecting to Redis...');
      isConnecting = true;
    });
    
    redisClient.on('ready', () => {
      console.log('Redis connection warmed up');
      isConnecting = false;
    });
    
    redisClient.on('end', () => {
      console.log('Redis connection ended');
      // Don't set to null here - let the error handler decide
    });
  }
  
  return redisClient;
}

/**
 * Close Redis connection (useful for serverless environments)
 */
export async function closeRedisConnection(): Promise<void> {
  if (redisClient) {
    await redisClient.quit();
    redisClient = null;
  }
}

// Encryption key from environment variable or fallback
const getEncryptionKey = () => {
  return process.env.REDIS_ENCRYPTION_KEY || 'default-encryption-key-change-in-production';
};

/**
 * Encrypt sensitive data before storing in Redis
 */
export function encryptData(data: string): string {
  return CryptoJS.AES.encrypt(data, getEncryptionKey()).toString();
}

/**
 * Decrypt sensitive data retrieved from Redis
 */
export function decryptData(encryptedData: string): string {
  const bytes = CryptoJS.AES.decrypt(encryptedData, getEncryptionKey());
  return bytes.toString(CryptoJS.enc.Utf8);
}

// Cache key definitions
export const KEYS = {
  CREDENTIALS: (userId: string, accountId: string) => `email:credentials:${userId}:${accountId}`,
  SESSION: (userId: string) => `email:session:${userId}`,
  EMAIL_LIST: (userId: string, accountId: string, folder: string, page: number, perPage: number) => 
    `email:list:${userId}:${accountId}:${folder}:${page}:${perPage}`,
  EMAIL_CONTENT: (userId: string, accountId: string, emailId: string) => 
    `email:content:${userId}:${accountId}:${emailId}`
};

// TTL constants in seconds
export const TTL = {
  CREDENTIALS: 60 * 60 * 24, // 24 hours
  SESSION: 60 * 60 * 4,      // 4 hours (increased from 30 minutes)
  EMAIL_LIST: 60 * 5,        // 5 minutes
  EMAIL_CONTENT: 60 * 15     // 15 minutes
};

interface EmailCredentials {
  email: string;
  password?: string;
  host: string;
  port: number;
  secure?: boolean;
  encryptedPassword?: string;
  smtp_host?: string;
  smtp_port?: number;
  smtp_secure?: boolean;
  display_name?: string;
  color?: string;
  useOAuth?: boolean;
  accessToken?: string;
  refreshToken?: string;
  tokenExpiry?: number;
}

interface ImapSessionData {
  connectionId?: string;
  lastActive: number;
  mailboxes?: string[];
  lastVisit?: number;
  defaultAccountId?: string;
}

/**
 * Cache email credentials in Redis
 */
export async function cacheEmailCredentials(
  userId: string,
  accountId: string,
  credentials: EmailCredentials
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.CREDENTIALS(userId, accountId);
  
  // Validate credentials before caching
  if (!credentials.email || !credentials.host || (!credentials.password && !credentials.useOAuth)) {
    console.error(`Cannot cache incomplete credentials for user ${userId}`);
    return;
  }
  
  try {
    console.log(`Caching credentials for user ${userId}`);
    
    // Create a copy without the password to store
    const secureCredentials: EmailCredentials = {
      email: credentials.email,
      host: credentials.host,
      port: credentials.port,
      secure: credentials.secure ?? true,
      // Include the extended fields
      ...(credentials.smtp_host && { smtp_host: credentials.smtp_host }),
      ...(credentials.smtp_port && { smtp_port: credentials.smtp_port }),
      ...(credentials.smtp_secure !== undefined && { smtp_secure: credentials.smtp_secure }),
      ...(credentials.display_name && { display_name: credentials.display_name }),
      ...(credentials.color && { color: credentials.color }),
      // Include OAuth fields
      ...(credentials.useOAuth !== undefined && { useOAuth: credentials.useOAuth }),
      ...(credentials.accessToken && { accessToken: credentials.accessToken }),
      ...(credentials.refreshToken && { refreshToken: credentials.refreshToken }),
      ...(credentials.tokenExpiry && { tokenExpiry: credentials.tokenExpiry })
    };
    
    // Encrypt password if provided
    if (credentials.password) {
      try {
        const encrypted = encryptData(credentials.password);
        console.log(`Successfully encrypted password for user ${userId}`);
        secureCredentials.encryptedPassword = encrypted;
      } catch (encryptError) {
        console.error(`Failed to encrypt password for user ${userId}:`, encryptError);
        // Continue anyway since we might have OAuth tokens
      }
    }
    
    await redis.set(key, JSON.stringify(secureCredentials), 'EX', TTL.CREDENTIALS);
    console.log(`Credentials cached for user ${userId}`);
  } catch (error) {
    console.error(`Error caching credentials for user ${userId}:`, error);
  }
}

/**
 * Get email credentials from Redis
 */
export async function getEmailCredentials(
  userId: string,
  accountId: string
): Promise<EmailCredentials | null> {
  const redis = getRedisClient();
  const key = KEYS.CREDENTIALS(userId, accountId);
  
  try {
    const credStr = await redis.get(key);
    
    if (!credStr) {
      return null;
    }
    
    const creds = JSON.parse(credStr) as EmailCredentials;
    
    let password: string | undefined;
    
    // Handle OAuth accounts (they might not have a password)
    if (creds.encryptedPassword) {
      try {
        // Decrypt the password
        password = decryptData(creds.encryptedPassword);
      } catch (decryptError) {
        console.error(`Failed to decrypt password for user ${userId}:`, decryptError);
        // For OAuth accounts, we can continue without a password
        if (!creds.useOAuth) {
          return null;
        }
      }
    }
    
    // Return the full credentials with decrypted password if available
    const result: EmailCredentials = {
      email: creds.email,
      host: creds.host,
      port: creds.port,
      secure: creds.secure ?? true,
      ...(password && { password }),
      ...(creds.smtp_host && { smtp_host: creds.smtp_host }),
      ...(creds.smtp_port && { smtp_port: creds.smtp_port }),
      ...(creds.smtp_secure !== undefined && { smtp_secure: creds.smtp_secure }),
      ...(creds.display_name && { display_name: creds.display_name }),
      ...(creds.color && { color: creds.color }),
      // Include OAuth fields
      ...(creds.useOAuth !== undefined && { useOAuth: creds.useOAuth }),
      ...(creds.accessToken && { accessToken: creds.accessToken }),
      ...(creds.refreshToken && { refreshToken: creds.refreshToken }),
      ...(creds.tokenExpiry && { tokenExpiry: creds.tokenExpiry })
    };
    
    return result;
  } catch (error) {
    console.error(`Error getting credentials for user ${userId}:`, error);
    return null;
  }
}

/**
 * Cache IMAP session data for quick reconnection
 */
export async function cacheImapSession(
  userId: string,
  sessionData: ImapSessionData
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.SESSION(userId);
  
  // Always update the lastActive timestamp
  sessionData.lastActive = Date.now();
  
  await redis.set(key, JSON.stringify(sessionData), 'EX', TTL.SESSION);
}

/**
 * Get cached IMAP session data
 */
export async function getCachedImapSession(
  userId: string
): Promise<ImapSessionData | null> {
  const redis = getRedisClient();
  const key = KEYS.SESSION(userId);
  
  const cachedData = await redis.get(key);
  if (!cachedData) return null;
  
  return JSON.parse(cachedData) as ImapSessionData;
}

/**
 * Cache email list in Redis
 */
export async function cacheEmailList(
  userId: string,
  accountId: string,
  folder: string,
  page: number,
  perPage: number,
  data: any
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_LIST(userId, accountId, folder, page, perPage);
  
  await redis.set(key, JSON.stringify(data), 'EX', TTL.EMAIL_LIST);
}

/**
 * Get cached email list from Redis
 */
export async function getCachedEmailList(
  userId: string,
  accountId: string,
  folder: string,
  page: number,
  perPage: number
): Promise<any | null> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_LIST(userId, accountId, folder, page, perPage);
  
  const cachedData = await redis.get(key);
  if (!cachedData) return null;
  
  return JSON.parse(cachedData);
}

/**
 * Cache email content in Redis
 */
export async function cacheEmailContent(
  userId: string,
  accountId: string,
  emailId: string,
  data: any
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, accountId, emailId);
  
  await redis.set(key, JSON.stringify(data), 'EX', TTL.EMAIL_CONTENT);
}

/**
 * Get cached email content from Redis
 */
export async function getCachedEmailContent(
  userId: string,
  accountId: string,
  emailId: string
): Promise<any | null> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, accountId, emailId);
  
  const cachedData = await redis.get(key);
  if (!cachedData) return null;
  
  return JSON.parse(cachedData);
}

/**
 * Invalidate all email caches for a folder
 */
export async function invalidateFolderCache(
  userId: string,
  accountId: string,
  folder: string
): Promise<void> {
  const redis = getRedisClient();
  const pattern = `email:list:${userId}:${accountId}:${folder}:*`;
  
  // Use SCAN to find and delete keys matching the pattern
  let cursor = '0';
  do {
    const [nextCursor, keys] = await redis.scan(cursor, 'MATCH', pattern, 'COUNT', 100);
    cursor = nextCursor;
    
    if (keys.length > 0) {
      await redis.del(...keys);
    }
  } while (cursor !== '0');
}

/**
 * Invalidate email content cache
 */
export async function invalidateEmailContentCache(
  userId: string,
  accountId: string,
  emailId: string
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, accountId, emailId);
  
  await redis.del(key);
}

/**
 * Warm up Redis connection to avoid cold starts
 */
export async function warmupRedisCache(): Promise<boolean> {
  try {
    // Ping Redis to establish connection early
    const redis = getRedisClient();
    await redis.ping();
    console.log('Redis connection warmed up');
    return true;
  } catch (error) {
    console.error('Error warming up Redis:', error);
    return false;
  }
}

/**
 * Get Redis connection status
 */
export async function getRedisStatus(): Promise<{
  status: 'connected' | 'error';
  ping?: string;
  error?: string;
}> {
  try {
    const redis = getRedisClient();
    const pong = await redis.ping();
    return {
      status: 'connected',
      ping: pong
    };
  } catch (error) {
    return {
      status: 'error',
      error: error instanceof Error ? error.message : String(error)
    };
  }
}

/**
 * Invalidate all user email caches (email lists and content)
 */
export async function invalidateUserEmailCache(
  userId: string
): Promise<void> {
  const redis = getRedisClient();
  
  // Patterns to delete
  const patterns = [
    `email:list:${userId}:*`,
    `email:content:${userId}:*`
  ];
  
  for (const pattern of patterns) {
    let cursor = '0';
    do {
      const [nextCursor, keys] = await redis.scan(cursor, 'MATCH', pattern, 'COUNT', 100);
      cursor = nextCursor;
      
      if (keys.length > 0) {
        await redis.del(...keys);
      }
    } while (cursor !== '0');
  }
}

/**
 * Get cached email credentials from Redis
 * @deprecated Use getEmailCredentials instead
 */
export async function getCachedEmailCredentials(
  userId: string,
  accountId: string
): Promise<EmailCredentials | null> {
  return getEmailCredentials(userId, accountId);
}