import { NextResponse } from 'next/server';
import { ImapFlow } from 'imapflow';
import { getServerSession } from 'next-auth';
import { authOptions } from '@/app/api/auth/[...nextauth]/route';
import { prisma } from '@/lib/prisma';

// Email cache structure
interface EmailCache {
  [key: string]: {
    data: any;
    timestamp: number;
  };
}

// Credentials cache to reduce database queries
interface CredentialsCache {
  [userId: string]: {
    credentials: any;
    timestamp: number;
  }
}

// In-memory caches with expiration
// Make emailListCache available globally for other routes
if (!global.emailListCache) {
  global.emailListCache = {};
}
const emailListCache: EmailCache = global.emailListCache;
const credentialsCache: CredentialsCache = {};

// Cache TTL in milliseconds (5 minutes)
const CACHE_TTL = 5 * 60 * 1000;

// Helper function to get credentials with caching
async function getCredentialsWithCache(userId: string) {
  // Check if we have fresh cached credentials
  const cachedCreds = credentialsCache[userId];
  const now = Date.now();
  
  if (cachedCreds && now - cachedCreds.timestamp < CACHE_TTL) {
    return cachedCreds.credentials;
  }
  
  // Otherwise fetch from database
  const credentials = await prisma.mailCredentials.findUnique({
    where: { userId }
  });
  
  // Cache the result
  if (credentials) {
    credentialsCache[userId] = {
      credentials,
      timestamp: now
    };
  }
  
  return credentials;
}

// Retry logic for IMAP operations
async function retryOperation<T>(operation: () => Promise<T>, maxAttempts = 3, delay = 1000): Promise<T> {
  let lastError: Error;
  
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await operation();
    } catch (error) {
      lastError = error as Error;
      console.warn(`Operation failed (attempt ${attempt}/${maxAttempts}):`, error);
      
      if (attempt < maxAttempts) {
        // Exponential backoff
        const backoffDelay = delay * Math.pow(2, attempt - 1);
        console.log(`Retrying in ${backoffDelay}ms...`);
        await new Promise(resolve => setTimeout(resolve, backoffDelay));
      }
    }
  }
  
  throw lastError!;
}

export async function GET(request: Request) {
  try {
    console.log('Courrier API call received');
    const session = await getServerSession(authOptions);
    if (!session?.user?.id) {
      console.log('No authenticated session found');
      return NextResponse.json(
        { error: 'Unauthorized' },
        { status: 401 }
      );
    }
    console.log('User authenticated:', session.user.id);

    // Get URL parameters
    const url = new URL(request.url);
    const folder = url.searchParams.get('folder') || 'INBOX';
    const page = parseInt(url.searchParams.get('page') || '1');
    const limit = parseInt(url.searchParams.get('limit') || '20');
    const preview = url.searchParams.get('preview') === 'true';
    const skipCache = url.searchParams.get('skipCache') === 'true';
    console.log('Request parameters:', { folder, page, limit, preview, skipCache });
    
    // Generate cache key based on request parameters
    const cacheKey = `${session.user.id}:${folder}:${page}:${limit}:${preview}`;
    
    // Check cache first if not explicitly skipped
    if (!skipCache && emailListCache[cacheKey]) {
      const { data, timestamp } = emailListCache[cacheKey];
      // Return cached data if it's fresh (less than 1 minute old)
      if (Date.now() - timestamp < 60000) {
        console.log('Returning cached email data');
        return NextResponse.json(data);
      }
    }

    // Get credentials from cache or database
    const credentials = await getCredentialsWithCache(session.user.id);
    console.log('Credentials retrieved:', credentials ? 'yes' : 'no');

    if (!credentials) {
      console.log('No mail credentials found for user');
      return NextResponse.json(
        { error: 'No mail credentials found. Please configure your email account.' },
        { status: 401 }
      );
    }

    // Calculate start and end sequence numbers
    const start = (page - 1) * limit + 1;
    const end = start + limit - 1;
    console.log('Fetching emails from range:', { start, end });

    // Connect to IMAP server
    console.log('Connecting to IMAP server:', credentials.host, credentials.port);
    const client = new ImapFlow({
      host: credentials.host,
      port: credentials.port,
      secure: true,
      auth: {
        user: credentials.email,
        pass: credentials.password,
      },
      logger: false,
      emitLogs: false,
      tls: {
        rejectUnauthorized: false
      }
    });

    try {
      await client.connect();
      console.log('Connected to IMAP server');
      
      // Get list of all mailboxes first
      const mailboxes = await client.list();
      const availableFolders = mailboxes.map(box => box.path);
      console.log('Available folders:', availableFolders);
      
      // Open the requested mailbox
      console.log('Opening mailbox:', folder);
      const mailbox = await client.mailboxOpen(folder);
      console.log('Mailbox stats:', { 
        exists: mailbox.exists, 
        name: mailbox.path,
        flags: mailbox.flags
      });
      
      const result = [];
      
      // Only try to fetch if the mailbox has messages
      if (mailbox.exists > 0) {
        // Adjust start and end to be within bounds
        const adjustedStart = Math.min(start, mailbox.exists);
        const adjustedEnd = Math.min(end, mailbox.exists);
        console.log('Adjusted fetch range:', { adjustedStart, adjustedEnd });
        
        // Fetch both metadata and preview content
        const fetchOptions: any = { 
          envelope: true,
          flags: true,
          bodyStructure: true
        };
        
        // Only fetch preview content if requested
        if (preview) {
          fetchOptions.bodyParts = ['TEXT'];
        }
        
        console.log('Fetching messages with options:', fetchOptions);
        const fetchPromises = [];
        for (let i = adjustedStart; i <= adjustedEnd; i++) {
          // Convert to string sequence number as required by ImapFlow
          fetchPromises.push(client.fetchOne(`${i}`, fetchOptions));
        }
        
        try {
          const results = await Promise.all(fetchPromises);
          
          for (const message of results) {
            if (!message) continue; // Skip undefined messages
            
            console.log('Processing message ID:', message.uid);
            const emailData: any = {
              id: message.uid,
              from: message.envelope.from?.[0]?.address || '',
              fromName: message.envelope.from?.[0]?.name || message.envelope.from?.[0]?.address?.split('@')[0] || '',
              to: message.envelope.to?.map(addr => addr.address).join(', ') || '',
              subject: message.envelope.subject || '(No subject)',
              date: message.envelope.date?.toISOString() || new Date().toISOString(),
              read: message.flags.has('\\Seen'),
              starred: message.flags.has('\\Flagged'),
              folder: mailbox.path,
              hasAttachments: message.bodyStructure?.type === 'multipart',
              flags: Array.from(message.flags)
            };
            
            // Include preview content if available
            if (preview && message.bodyParts && message.bodyParts.has('TEXT')) {
              emailData.preview = message.bodyParts.get('TEXT')?.toString() || null;
            }
            
            result.push(emailData);
          }
        } catch (fetchError) {
          console.error('Error fetching emails:', fetchError);
          // Continue with any successfully fetched messages
        }
      } else {
        console.log('No messages in mailbox');
      }

      const responseData = {
        emails: result,
        folders: availableFolders,
        total: mailbox.exists,
        hasMore: end < mailbox.exists
      };
      
      console.log('Response summary:', { 
        emailCount: result.length, 
        folderCount: availableFolders.length,
        total: mailbox.exists,
        hasMore: end < mailbox.exists
      });
      
      // Cache the result
      emailListCache[cacheKey] = {
        data: responseData,
        timestamp: Date.now()
      };

      return NextResponse.json(responseData);
    } catch (error) {
      console.error('Error in IMAP operations:', error);
      let errorMessage = 'Failed to fetch emails';
      let statusCode = 500;
      
      // Type guard for Error objects
      if (error instanceof Error) {
        errorMessage = error.message;
        
        // Handle specific error cases
        if (errorMessage.includes('authentication') || errorMessage.includes('login')) {
          statusCode = 401;
          errorMessage = 'Authentication failed. Please check your email credentials.';
        } else if (errorMessage.includes('connect')) {
          errorMessage = 'Failed to connect to email server. Please check your settings.';
        } else if (errorMessage.includes('timeout')) {
          errorMessage = 'Connection timed out. Please try again later.';
        }
      }
      
      return NextResponse.json(
        { error: errorMessage },
        { status: statusCode }
      );
    } finally {
      try {
        await client.logout();
        console.log('IMAP client logged out');
      } catch (e) {
        console.error('Error during logout:', e);
      }
    }
  } catch (error) {
    console.error('Error in courrier route:', error);
    return NextResponse.json(
      { error: 'An unexpected error occurred' },
      { status: 500 }
    );
  }
}

export async function POST(request: Request) {
  try {
    const session = await getServerSession(authOptions);
    if (!session?.user?.id) {
      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
    }
    
    const { emailId, folderName, action } = await request.json();
    
    if (!emailId) {
      return NextResponse.json({ error: 'Missing emailId parameter' }, { status: 400 });
    }
    
    // Invalidate cache entries for this folder
    const userId = session.user.id;
    
    // If folder is specified, only invalidate that folder's cache
    if (folderName) {
      Object.keys(emailListCache).forEach(key => {
        if (key.includes(`${userId}:${folderName}`)) {
          delete emailListCache[key];
        }
      });
    } else {
      // Otherwise invalidate all cache entries for this user
      Object.keys(emailListCache).forEach(key => {
        if (key.startsWith(`${userId}:`)) {
          delete emailListCache[key];
        }
      });
    }
    
    return NextResponse.json({ success: true });
  } catch (error) {
    console.error('Error in POST handler:', error);
    return NextResponse.json({ error: 'An unexpected error occurred' }, { status: 500 });
  }
}