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]: any;
}

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

// In-memory caches with expiration
const emailListCache: EmailCache = {};
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;
}

export async function GET(request: Request) {
  try {
    const session = await getServerSession(authOptions);
    if (!session?.user?.id) {
      return NextResponse.json(
        { error: 'Unauthorized' },
        { status: 401 }
      );
    }

    // 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';
    
    // 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) {
        return NextResponse.json(data);
      }
    }

    // Get credentials from cache or database
    const credentials = await getCredentialsWithCache(session.user.id);

    if (!credentials) {
      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;

    // Connect to IMAP server
    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();
      
      // Get list of all mailboxes first
      const mailboxes = await client.list();
      const availableFolders = mailboxes.map(box => box.path);
      
      // Open the requested mailbox
      const mailbox = await client.mailboxOpen(folder);
      
      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);
        
        // 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'];
        }
        
        const messages = await client.fetch(`${adjustedStart}:${adjustedEnd}`, fetchOptions);
        
        for await (const message of messages) {
          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);
        }
      }

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

      return NextResponse.json(responseData);
    } finally {
      try {
        await client.logout();
      } 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 }
    );
  }
}