import fs from 'fs';
import path from 'path';
import { NextResponse } from 'next/server';

const BACKEND_SERVER_URL = process.env.BACKEND_SERVER_URL || '';
const PUBLIC_FILES_DIR = path.join(process.cwd(), 'public/files');

function getContentType(filePath) {
  const ext = path.extname(filePath).toLowerCase();
  switch (ext) {
    case '.jpg':
    case '.jpeg':
      return 'image/jpeg';
    case '.png':
      return 'image/png';
    case '.gif':
      return 'image/gif';
    case '.svg':
      return 'image/svg+xml';
    case '.webp':
      return 'image/webp';
    case '.mp4':
      return 'video/mp4';
    case '.pdf':
      return 'application/pdf';
    default:
      return 'application/octet-stream';
  }
}

export async function GET(req, { params }) {
  try {
    const parts = params.path || [];
    const fileName = parts.join('/');
    if (!fileName) return new NextResponse('Not Found', { status: 404 });

    const localPath = path.join(PUBLIC_FILES_DIR, fileName);

    if (fs.existsSync(localPath)) {
      const data = fs.readFileSync(localPath);
      return new NextResponse(data, {
        status: 200,
        headers: { 'Content-Type': getContentType(localPath), 'Cache-Control': 'public, max-age=31536000, immutable' }
      });
    }

    const remoteUrl = `${BACKEND_SERVER_URL}/files/${fileName}`;
    const res = await fetch(remoteUrl);
    if (!res.ok) {
    // 占位图（SVG），避免前端空白
    const placeholder = `<svg xmlns="http://www.w3.org/2000/svg" width="800" height="450" viewBox="0 0 800 450"><rect width="800" height="450" fill="#f3f4f6"/><text x="50%" y="50%" dominant-baseline="middle" text-anchor="middle" fill="#9ca3af" font-size="20" font-family="Arial, Helvetica, sans-serif">Image unavailable</text></svg>`;
    return new NextResponse(placeholder, { status: 200, headers: { 'Content-Type': 'image/svg+xml', 'Cache-Control': 'no-store' } });
    }
    const arrayBuffer = await res.arrayBuffer();
    const buffer = Buffer.from(arrayBuffer);

    // 确保目录存在并写入本地
    fs.mkdirSync(path.dirname(localPath), { recursive: true });
    fs.writeFileSync(localPath, buffer);

    return new NextResponse(buffer, {
      status: 200,
      headers: { 'Content-Type': getContentType(localPath), 'Cache-Control': 'public, max-age=31536000, immutable' }
    });
  } catch (e) {
    return new NextResponse('Server Error', { status: 500, headers: { 'Cache-Control': 'no-store' } });
  }
}