import { nextTick } from 'vue'

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms))

/**
 * 串行挂载：每隔 stepMs 增加 1 个可见项，避免同时挂大量观察器/解码。
 */
export function createSequentialMount() {
  let token = 0

  const cancel = () => {
    token += 1
  }

  /**
   * @param {{ total: number, stepMs?: number, settleMs?: number, setCount: (n: number) => void }} opts
   * @returns {Promise<{ cancelled: boolean }>}
   */
  const run = async ({ total, stepMs = 220, settleMs = 300, setCount }) => {
    const t = ++token
    const n = Math.max(0, Number(total) || 0)
    setCount(0)
    await nextTick()
    if (t !== token) return { cancelled: true }

    if (!n) return { cancelled: false }

    for (let i = 0; i < n; i += 1) {
      if (t !== token) return { cancelled: true }
      await sleep(stepMs)
      if (t !== token) return { cancelled: true }
      setCount(i + 1)
      await nextTick()
    }

    if (t !== token) return { cancelled: true }
    if (settleMs > 0) {
      await sleep(settleMs)
      if (t !== token) return { cancelled: true }
    }
    return { cancelled: false }
  }

  return { run, cancel }
}