import { promises as fs } from 'fs';
import path from 'path';
import type { VercelRequest, VercelResponse } from '@vercel/node';

export default async function handler(req: VercelRequest, res: VercelResponse) {
    try {
        const filePath = path.join(process.cwd(), 'BSR.xlsx');

        try {
            await fs.access(filePath);
        } catch {
            return res.status(404).json({ error: 'BSR data file not found' });
        }

        const fileBuffer = await fs.readFile(filePath);

        res.setHeader('Content-Type', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
        res.setHeader('Content-Disposition', 'attachment; filename="BSR.xlsx"');
        res.setHeader('Cache-Control', 'public, max-age=3600');

        // Convert Buffer to ArrayBuffer before sending for fetch compatibility on client
        res.send(fileBuffer);
    } catch (error) {
        console.error('Error serving BSR Excel file:', error);
        res.status(500).json({ error: 'Failed to serve BSR file' });
    }
}