export const getVideoCover = (data: string | Blob,  seekTo: number = 0.0, width?: number, height?: number) : Promise<string> => {
  const url = typeof data !== 'string' 
    ? URL.createObjectURL(data)
    : data

  return new Promise(function (resolve, reject) {
    const video = document.createElement('video')

    video.setAttribute('crossOrigin', 'anonymous')// 处理跨域,需要服务器支持跨域
    video.setAttribute('src', url)
    video.setAttribute('muted', '')
    if (width && height) {
      video.setAttribute('width', `${width}px`)
      video.setAttribute('height', `${height}px`)
      video.setAttribute('style', 'object-fit:scale-down')
    }
    video.load()
    video.addEventListener('loadedmetadata', function () {
      if (video.duration < seekTo) {
        reject(new Error('视频长度不够'));
        return;
      }

      setTimeout(() => video.currentTime = seekTo, 200);

      video.addEventListener('seeked', () => {
        const canvas = document.createElement('canvas')
        if (width && height) {
          canvas.width = width
          canvas.height = height
        } else {
          canvas.width = video.videoWidth
          canvas.height = video.videoHeight
        }
        canvas.getContext('2d')!.drawImage(video, 0, 0, width!, height!)

        const dataURL = canvas.toDataURL('image/jpeg') 

        if (typeof data !== 'string') {
          video.pause()
          URL.revokeObjectURL(url)
        }
        resolve(dataURL)
      })
    })
  })

}