import atob from './atob'

const b64DecodeUnicode = (str: string) => {
  return decodeURIComponent(atob(str).replace(/(.)/g, function (m, p) {
    var code = p.charCodeAt(0).toString(16).toUpperCase()
    if (code.length < 2) {
      code = '0' + code
    }
    return '%' + code
  }))
}

export default (str: string) => {
  var output = str.replace(/-/g, '+').replace(/_/g, '/')
  switch (output.length % 4) {
    case 0:
      break
    case 2:
      output += '=='
      break
    case 3:
      output += '='
      break
    default:
      throw 'Illegal base64url string!'
  }

  try {
    return b64DecodeUnicode(output)
  } catch (err) {
    return atob(output)
  }
}