import { ElMessage, type MessageHandler } from 'element-plus'

let downloadBusy = false

export function isDownloadBusy(): boolean {
  return downloadBusy
}

export function formatDownloadSizeHint(size?: number | null): string {
  if (size == null || !Number.isFinite(size) || size <= 0) return ''
  if (size < 1024 * 1024) return `约 ${Math.max(1, Math.round(size / 1024))} KB`
  return `约 ${(size / (1024 * 1024)).toFixed(1)} MB`
}

export type DownloadFeedbackHandle = {
  setText: (text: string) => void
  close: () => void
}

/**
 * 下载过程中的轻量提示（非全屏）；若已有下载进行中则提示并返回 null。
 */
export function beginDownloadFeedback(
  fileName: string,
  size?: number | null,
  actionLabel = '下载',
): DownloadFeedbackHandle | null {
  if (downloadBusy) {
    ElMessage.warning(`附件正在${actionLabel}中，请勿重复点击`)
    return null
  }
  downloadBusy = true
  const name = fileName.trim() || '附件'
  const sizeHint = formatDownloadSizeHint(size)
  const text = sizeHint
    ? `正在准备${actionLabel}「${name}」（${sizeHint}），文件较大时请耐心等待…`
    : `正在准备${actionLabel}「${name}」，请稍候…`

  let handler: MessageHandler = ElMessage({
    type: 'info',
    message: text,
    duration: 0,
    showClose: true,
  })

  return {
    setText: (next: string) => {
      handler.close()
      handler = ElMessage({
        type: 'info',
        message: next,
        duration: 0,
        showClose: true,
      })
    },
    close: () => {
      handler.close()
      downloadBusy = false
    },
  }
}

export function notifyDownloadStarted(): void {
  ElMessage.success('下载已开始，请查看浏览器下载进度')
}