/**
 * 创建一个简单倒计时控制器，适配 Vue2 Options API。
 * @param {object} options
 * @param {number} options.duration 倒计时总秒数
 * @param {(value:number)=>void} options.onChange 每次变化回调
 */
export function createCountdown(options = {}) {
  const {
    duration = 60,
    onChange = () => {}
  } = options

  let timer = null
  let current = 0

  function emit() {
    onChange(current)
  }

  function clear() {
    if (timer) {
      clearInterval(timer)
      timer = null
    }
  }

  function start() {
    clear()
    current = duration
    emit()

    timer = setInterval(() => {
      current -= 1
      if (current <= 0) {
        current = 0
        emit()
        clear()
        return
      }

      emit()
    }, 1000)
  }

  return {
    start,
    clear
  }
}