import type { VercelRequest, VercelResponse } from '@vercel/node';
import fetch from 'node-fetch'; // Ensure fetch is available

export default async function handler(req: VercelRequest, res: VercelResponse) {
    // Allow CORS
    res.setHeader('Access-Control-Allow-Credentials', 'true');
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Methods', 'GET,OPTIONS,PATCH,DELETE,POST,PUT');
    res.setHeader(
        'Access-Control-Allow-Headers',
        'X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5, Content-Type, Date, X-Api-Version'
    );

    if (req.method === 'OPTIONS') {
        res.status(200).end();
        return;
    }

    try {
        // 1. Reconstruct the Target Dropbox URL
        // The incoming request is to /api/dropbox/scl/fi/...
        // We want to fetch https://www.dropbox.com/scl/fi/...

        // req.url in Vercel function might be just the suffix or full path depending on routing
        // Typically: /api/dropbox/scl/fi/xyz?dl=1

        // We need to strip '/api/dropbox' from the start to get the dropbox path
        const requestPath = req.url || '';
        const dropboxPath = requestPath.replace(/^\/api\/dropbox/, ''); // e.g. /scl/fi/xyz?dl=1

        let targetUrl = `https://www.dropbox.com${dropboxPath}`;

        // Ensure dl=1 is present to force download
        if (targetUrl.includes('?')) {
            if (!targetUrl.includes('dl=1')) {
                targetUrl = targetUrl.replace('dl=0', 'dl=1');
                if (!targetUrl.includes('dl=1')) {
                    targetUrl += '&dl=1';
                }
            }
        } else {
            targetUrl += '?dl=1';
        }

        console.log(`[Proxy] Incoming: ${req.url}`);
        console.log(`[Proxy] Target: ${targetUrl}`);

        const response = await fetch(targetUrl);

        if (!response.ok) {
            throw new Error(`Dropbox responded with ${response.status} ${response.statusText}`);
        }

        // Forward the content type (likely text/csv)
        const contentType = response.headers.get('content-type');
        if (contentType) {
            res.setHeader('Content-Type', contentType);
        }

        const data = await response.text();
        res.status(200).send(data);

    } catch (error: any) {
        console.error('Proxy Error:', error);
        res.status(500).json({ error: 'Failed to fetch data from Dropbox', details: error.message });
    }
}