let isFlushPending = false

const resolvedPromise = Promise.resolve() as Promise<any>

let currentFlushPromise: Promise<void> | null = null

const pendingPreFlushCbs: Function[] = []
export function queuePreFlushCb(cb: Function) {
  queueCb(cb, pendingPreFlushCbs)
}
function queueCb(cb: Function, pendingQueue: Function[]) {
  pendingQueue.push(cb)
  queueFlush()
}

function queueFlush() {
  if (!isFlushPending) {
    isFlushPending = true
    currentFlushPromise = resolvedPromise.then(flushJobs)
  }
}
function flushJobs() {
  isFlushPending = false
  flushPreFlushCbs()
}
export function flushPreFlushCbs() {
  if (pendingPreFlushCbs.length) {
    //拷贝去重,类似深拷贝
    let activePreFlushCbs = [...new Set(pendingPreFlushCbs)]
    pendingPreFlushCbs.length = 0
    for (let i = 0; i < activePreFlushCbs.length; i++) {
      activePreFlushCbs[i]()
    }
  }
}