/* global Blob, FileReader */

module.exports = function blobToBuffer (blob, cb) {
  if (typeof Blob === 'undefined' || !(blob instanceof Blob)) {
    throw new Error('first argument must be a Blob')
  }
  if (typeof cb !== 'function') {
    throw new Error('second argument must be a function')
  }

  var reader = new FileReader()

  function onLoadEnd (e) {
    reader.removeEventListener('loadend', onLoadEnd, false)
    if (e.error) cb(e.error)
    else cb(null, new Buffer(reader.result))
  }

  reader.addEventListener('loadend', onLoadEnd, false)
  reader.readAsArrayBuffer(blob)
}