export function get_suffix(filename) {
  var pos = filename.lastIndexOf('.')
  var suffix = ''
  if (pos !== -1) {
    suffix = filename.substring(pos)
  }
  return suffix
}

export function random_string(len) {
  len = len || 32
  var chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678'
  var maxPos = chars.length
  var pwd = ''
  for (let i = 0; i < len; i++) {
    pwd += chars.charAt(Math.floor(Math.random() * maxPos))
  }
  return pwd
}

export function random_filename(filename) {
  var suffix = get_suffix(filename)
  var time = new Date()
  var time2 = new Date('2020/01/01')
  return Math.ceil((time.getTime() - time2.getTime()) / 1000) + '_' + random_string(10) + suffix
}

export function utf8_to_b64(str) {
  return window.btoa(unescape(encodeURIComponent(str)))
}

export function b64_to_utf8(str) {
  return decodeURIComponent(escape(window.atob(str)))
}