import axios from 'axios';

/**
 * 公共文件下载工具（blob 请求 + 触发浏览器保存）
 *
 * - 成功：解析响应头 Content-Disposition 的 filename（RFC 5987 `filename*=UTF-8''` 优先），兜底用 fallbackName
 * - 失败兜底：后端业务错误也以 blob 返回（JSON），blob.type 为 application/json 时解析 msg 提示
 * - 401：清 token 跳登录页（与 createAxios 行为一致）
 */
export async function downloadBlob(
  url: string,
  params: Record<string, unknown>,
  fallbackName: string
): Promise<void> {
  const token = localStorage.getItem('token');

  let blob: Blob;
  let disposition = '';
  try {
    const response = await axios.get(url, {
      baseURL: import.meta.env.VITE_BASE_URL || '',
      params,
      responseType: 'blob',
      headers: token ? { Authorization: `Bearer ${token}` } : {},
    });
    blob = response.data as Blob;
    disposition = (response.headers['content-disposition'] as string) || '';
  } catch (err: any) {
    const status = err?.response?.status;
    const errBlob: Blob | undefined = err?.response?.data;

    if (status === 401) {
      window.$message?.error('您未登录，或者登录已经超时，请先登录！');
      localStorage.removeItem('token');
      localStorage.removeItem('auth-storage');
      window.location.href = '/login';
      return;
    }
    if (errBlob instanceof Blob) {
      await showBlobError(errBlob);
      return;
    }
    window.$message?.error('下载失败，请稍后重试');
    return;
  }

  // 后端业务错误以 JSON blob 返回
  if (blob.type.includes('application/json')) {
    await showBlobError(blob);
    return;
  }

  const filename = parseFilename(disposition) || fallbackName;
  const objectUrl = URL.createObjectURL(blob);
  const link = document.createElement('a');
  link.href = objectUrl;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  link.remove();
  URL.revokeObjectURL(objectUrl);
}

/**
 * 解析 blob 形式的错误响应并提示
 */
async function showBlobError(blob: Blob): Promise<void> {
  try {
    const body = JSON.parse(await blob.text());
    window.$message?.error(body?.msg || '导出失败');
  } catch {
    window.$message?.error('导出失败');
  }
}

/**
 * 从 Content-Disposition 解析文件名：RFC 5987 filename*=UTF-8'' 优先，其次 filename="..."
 */
function parseFilename(disposition: string): string | null {
  if (!disposition) {
    return null;
  }
  const rfc5987 = disposition.match(/filename\*\s*=\s*(?:UTF-8|utf-8)''([^;]+)/i);
  if (rfc5987?.[1]) {
    try {
      return decodeURIComponent(rfc5987[1].trim());
    } catch {
      return null;
    }
  }
  const plain = disposition.match(/filename\s*=\s*"?([^";]+)"?/i);
  if (plain?.[1]) {
    try {
      return decodeURIComponent(plain[1].trim());
    } catch {
      return plain[1].trim();
    }
  }
  return null;
}