import {
warn,nextTick,devtools
} from '../util/index'

const queue: Array = []
let has: { [key: number]: ?true } = {}
let circular: { [key: number]: number } = {}
let waiting = false
let flushing = false
let index = 0

/**

• Reset the scheduler's state.
  */
  function resetSchedulerState () {
  queue.length = 0
  has = {}
  if (process.env.NODE_ENV !== 'production') {
  circular = {}
  }
  waiting = flushing = false
  }

/**

• Flush both queues and run the watchers.
  */
  function flushSchedulerQueue () {
  flushing = true
  let watcher,id,vm

// Sort queue before flush.
// This ensures that:
// 1. Components are updated from parent to child. (because parent is always
// created before the child)
// 2. A component's user watchers are run before its render watcher (because
// user watchers are created before the render watcher)
// 3. If a component is destroyed during a parent component's watcher run,// its watchers can be skipped.
queue.sort((a,b) => a.id - b.id)

// do not cache length because more watchers might be pushed
// as we run existing watchers
for (index = 0; index < queue.length; index++) {
watcher = queue[index]
id = watcher.id
has[id] = null
watcher.run()
// in dev build,check and stop circular updates.
if (process.env.NODE_ENV !== 'production' && has[id] != null) {
circular[id] = (circular[id] || 0) + 1
if (circular[id] > config._maxUpdateCount) {
warn(
'You may have an infinite update loop ' + (
watcher.user
? in watcher with expression "${watcher.expression}"
: in a component render function.
),watcher.vm
)
break
}
}
}

// reset scheduler before updated hook called
const oldQueue = queue.slice()
resetSchedulerState()

// call updated hooks
index = oldQueue.length
while (index--) {
watcher = oldQueue[index]
vm = watcher.vm
if (vm._watcher === watcher && vm._isMounted) {
callHook(vm,'updated')
}
}

// devtool hook
/ istanbul ignore if /
if (devtools && config.devtools) {
devtools.emit('flush')
}
}

/**

• Push a watcher into the watcher queue.
• Jobs with duplicate IDs will be skipped unless it's
• pushed when the queue is being flushed.
  */
  export function queueWatcher (watcher: Watcher) {
  const id = watcher.id
  if (has[id] == null) {
  has[id] = true
  if (!flushing) {
  queue.push(watcher)
  } else {
  // if already flushing,splice the watcher based on its id
  // if already past its id,it will be run next immediately.
  let i = queue.length - 1
  while (i >= 0 && queue[i].id > watcher.id) {
  i--
  }
  queue.splice(Math.max(i,index) + 1,watcher)
  }
  // queue the flush
  if (!waiting) {
  waiting = true
  nextTick(flushSchedulerQueue)
  }
  }
  }