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

// Initialize Redis client
let redisClient: Redis | null = null;

/**
 * Get a Redis client instance (singleton pattern)
 */
export function getRedisClient(): Redis {
  if (!redisClient) {
    // 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) => {
        const delay = Math.min(times * 100, 5000);
        return delay;
      },
      maxRetriesPerRequest: 5,
      enableOfflineQueue: true
    };
    
    console.log('Connecting to Redis using environment variables');
    redisClient = new Redis(redisOptions);
    
    redisClient.on('error', (err) => {
      console.error('Redis connection error:', err);
    });
    
    redisClient.on('connect', () => {
      console.log('Successfully connected to Redis');
    });
    
    redisClient.on('reconnecting', () => {
      console.log('Reconnecting to Redis...');
    });
  }
  
  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) => `email:credentials:${userId}`,
  SESSION: (userId: string) => `email:session:${userId}`,
  EMAIL_LIST: (userId: string, folder: string, page: number, perPage: number) => 
    `email:list:${userId}:${folder}:${page}:${perPage}`,
  EMAIL_CONTENT: (userId: string, emailId: string) => 
    `email:content:${userId}:${emailId}`
};

// TTL constants in seconds
export const TTL = {
  CREDENTIALS: 60 * 60 * 24, // 24 hours
  SESSION: 60 * 30,          // 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;
}

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

/**
 * Cache email credentials in Redis
 */
export async function cacheEmailCredentials(
  userId: string, 
  credentials: EmailCredentials
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.CREDENTIALS(userId);
  
  // Validate credentials before caching
  if (!credentials.email || !credentials.host || !credentials.password) {
    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
    };
    
    // Encrypt password
    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);
        // Don't proceed with caching if encryption fails
        return;
      }
    } else {
      console.warn(`No password provided for user ${userId}, skipping credential caching`);
      return;
    }
    
    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 cached email credentials from Redis
 */
export async function getCachedEmailCredentials(
  userId: string
): Promise<EmailCredentials | null> {
  const redis = getRedisClient();
  const key = KEYS.CREDENTIALS(userId);
  
  try {
    const cachedData = await redis.get(key);
    if (!cachedData) {
      console.log(`No cached credentials found for user ${userId}`);
      return null;
    }
    
    console.log(`Found cached credentials for user ${userId}, attempting to decrypt`);
    const credentials = JSON.parse(cachedData) as EmailCredentials;
    
    // Check if we have encrypted password
    if (!credentials.encryptedPassword) {
      console.warn(`Cached credentials for user ${userId} missing encrypted password`);
      return null;
    }
    
    try {
      // Decrypt password with error handling
      credentials.password = decryptData(credentials.encryptedPassword);
      delete credentials.encryptedPassword;
      
      // Validate the credentials to ensure they're complete
      if (!credentials.password || !credentials.email || !credentials.host) {
        console.warn(`Incomplete credentials in cache for user ${userId}, missing required fields`);
        return null;
      }
      
      console.log(`Successfully retrieved and decrypted credentials for ${userId}`);
      return credentials;
    } catch (decryptError) {
      console.error(`Failed to decrypt password for user ${userId}:`, decryptError);
      return null;
    }
  } catch (error) {
    console.error(`Error retrieving credentials from Redis 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,
  folder: string,
  page: number,
  perPage: number,
  data: any
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_LIST(userId, 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,
  folder: string,
  page: number,
  perPage: number
): Promise<any | null> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_LIST(userId, 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,
  emailId: string,
  data: any
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, emailId);
  
  await redis.set(key, JSON.stringify(data), 'EX', TTL.EMAIL_CONTENT);
}

/**
 * Get cached email content from Redis
 */
export async function getCachedEmailContent(
  userId: string,
  emailId: string
): Promise<any | null> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, 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,
  folder: string
): Promise<void> {
  const redis = getRedisClient();
  const pattern = `email:list:${userId}:${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,
  emailId: string
): Promise<void> {
  const redis = getRedisClient();
  const key = KEYS.EMAIL_CONTENT(userId, emailId);
  
  await redis.del(key);
}

/**
 * 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');
  }
}