export function sendJson(response, status, payload, headers = {}) {
  response.writeHead(status, { 'Content-Type': 'application/json; charset=utf-8', 'Cache-Control': 'no-store', ...headers });
  response.end(JSON.stringify(payload));
}

export function sendError(response, status, message, details) {
  sendJson(response, status, { ok: false, message, ...(details ? { details } : {}) });
}

export async function readJson(request) {
  const chunks = [];
  let size = 0;
  for await (const chunk of request) {
    size += chunk.length;
    if (size > 1024 * 1024) throw Object.assign(new Error('请求内容过大'), { status: 413 });
    chunks.push(chunk);
  }
  if (!chunks.length) return {};
  try {
    return JSON.parse(Buffer.concat(chunks).toString('utf8'));
  } catch {
    throw Object.assign(new Error('请求数据格式不正确'), { status: 400 });
  }
}

export async function readBodyBuffer(request, maxBytes = 12 * 1024 * 1024) {
  const chunks = [];
  let size = 0;
  for await (const chunk of request) {
    size += chunk.length;
    if (size > maxBytes) throw Object.assign(new Error('Excel 文件不能超过 12 MB'), { status: 413 });
    chunks.push(chunk);
  }
  if (!chunks.length) throw Object.assign(new Error('请选择要导入的 Excel 文件'), { status: 400 });
  return Buffer.concat(chunks);
}

export function sendWorkbook(response, buffer, filename) {
  response.writeHead(200, {
    'Content-Type': 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
    'Content-Disposition': `attachment; filename*=UTF-8''${encodeURIComponent(filename)}`,
    'Content-Length': buffer.length,
    'Cache-Control': 'no-store'
  });
  response.end(buffer);
}