/**
 * 前端下载工具：
 * 1) 先调用 validate=1 做权限/文件可用性校验
 * 2) 再通过浏览器原生附件下载，避免 blob: 协议兼容性问题
 */

export interface DownloadValidationError {
  code?: string
  error?: string
  details?: string
}

/**
 * 为下载 URL 追加校验参数
 */
export function buildValidateDownloadUrl(downloadUrl: string): string {
  const url = new URL(downloadUrl, window.location.origin)
  url.searchParams.set('validate', '1')
  return `${url.pathname}${url.search}${url.hash}`
}

/**
 * 触发浏览器原生下载（使用服务端 Content-Disposition）
 */
export function triggerAttachmentDownload(downloadUrl: string): void {
  const link = document.createElement('a')
  link.href = downloadUrl
  link.style.display = 'none'
  document.body.appendChild(link)
  link.click()

  // 延迟移除，确保浏览器已经接管下载任务
  setTimeout(() => {
    link.remove()
  }, 500)
}

/**
 * 先校验再下载，失败时抛出后端错误对象
 */
export async function validateAndTriggerDownload(downloadUrl: string): Promise<void> {
  const validateUrl = buildValidateDownloadUrl(downloadUrl)
  const response = await fetch(validateUrl, {
    method: 'GET',
    cache: 'no-store',
    credentials: 'include',
  })

  if (!response.ok) {
    const fallbackError: DownloadValidationError = {
      code: 'UNKNOWN_ERROR',
      error: '下载失败',
    }

    let errorData: DownloadValidationError = fallbackError
    try {
      errorData = await response.json()
    } catch {}
    throw errorData
  }

  triggerAttachmentDownload(downloadUrl)
}