export function compress (fileObj, callback) {
  try {
    const image = new Image()
    image.src = URL.createObjectURL(fileObj)
    image.onload = function () {
      const that = this
      // 默认按比例压缩
      let w = that.width
      let h = that.height
      const scale = w / h
      w = fileObj.width || w
      h = fileObj.height || (w / scale)
      let quality = 0.7 // 默认图片质量为0.7
      // 生成canvas
      const canvas = document.createElement('canvas')
      const ctx = canvas.getContext('2d')
      // 创建属性节点
      const anw = document.createAttribute('width')
      anw.nodeValue = w
      const anh = document.createAttribute('height')
      anh.nodeValue = h
      canvas.setAttributeNode(anw)
      canvas.setAttributeNode(anh)
      ctx.drawImage(that, 0, 0, w, h)
      // 图像质量
      if (fileObj.quality && fileObj.quality <= 1 && fileObj.quality > 0) {
        quality = fileObj.quality
      }
      // quality值越小，所绘制出的图像越模糊
      const data = canvas.toDataURL('image/jpeg', quality)
      // 压缩完成执行回调
      const newFile = convertBase64UrlToBlob(data)
      callback(newFile)
    }
  } catch (e) {
    console.log('压缩失败!')
  }
}

function convertBase64UrlToBlob (urlData) {
  const bytes = window.atob(urlData.split(',')[1]) // 去掉url的头，并转换为byte
  // 处理异常,将ascii码小于0的转换为大于0
  const ab = new ArrayBuffer(bytes.length)
  const ia = new Uint8Array(ab)
  for (let i = 0; i < bytes.length; i++) {
    ia[i] = bytes.charCodeAt(i)
  }
  return new Blob([ab], { type: 'image/png' })
}