/**
 * 数字滚动工具 — 替代第三方库
 * 用 setTimeout(fn, 16) 模拟 60fps,兼容性最稳
 * 使用 easeOut 缓动: 1 - (1-t)^3
 *
 * 使用:
 *   const task = countUp({ from: 0, to: 30, duration: 800, onUpdate: setDisplayTime })
 *   // 不再需要时:
 *   task.cancel()
 */

function countUp({ from = 0, to, duration = 800, decimals = 0, onUpdate, onComplete } = {}) {
  // 边界:数值相同 或 时长 <= 0,跳过动画
  if (from === to || duration <= 0) {
    if (typeof onUpdate === 'function') onUpdate(to)
    if (typeof onComplete === 'function') onComplete()
    return { cancel: () => {} }
  }

  const start = Date.now()
  const delta = to - from
  let cancelled = false

  const tick = () => {
    if (cancelled) return
    const elapsed = Date.now() - start
    let t = Math.min(elapsed / duration, 1)
    // easeOut cubic
    t = 1 - Math.pow(1 - t, 3)
    const current = from + delta * t
    const value = decimals > 0
      ? Number(current.toFixed(decimals))
      : Math.round(current)
    if (typeof onUpdate === 'function') onUpdate(value)
    if (elapsed >= duration) {
      if (typeof onComplete === 'function') onComplete()
      return
    }
    setTimeout(tick, 16)
  }

  setTimeout(tick, 16)

  return {
    cancel() { cancelled = true }
  }
}

module.exports = { countUp }