// packages/reactivity/src/computed.ts
export function computed<T>(
  getterOrOptions: ComputedGetter<T> | WritableComputedOptions<T>,
  debugOptions?: DebuggerOptions,
  isSSR = false
) {
  let getter: ComputedGetter<T>
  let setter: ComputedSetter<T>
  const onlyGetter = isFunction(getterOrOptions)
  if (onlyGetter) {
    getter = getterOrOptions
    setter = __DEV__
      ? () => {
          console.warn('Write operation failed: computed value is readonly')
        }
      : NOOP
  } else {
    getter = getterOrOptions.get
    setter = getterOrOptions.set
  }
  // new ComputedRefImpl
  const cRef = new ComputedRefImpl(getter, setter, onlyGetter || !setter, isSSR)
  if (__DEV__ && debugOptions && !isSSR) {
    cRef.effect.onTrack = debugOptions.onTrack
    cRef.effect.onTrigger = debugOptions.onTrigger
  }
  // 返回ComputedRefImpl實例
  return cRef as any
}

// packages/reactivity/src/computed.ts
export class ComputedRefImpl<T> {
  public dep?: Dep = undefined // 存儲effect的集合
  private _value!: T
  public readonly effect: ReactiveEffect<T>
  public readonly __v_isRef = true
  public readonly [ReactiveFlags.IS_READONLY]: boolean = false
  public _dirty = true // 是否需要重新更新value
  public _cacheable: boolean
  constructor(
    getter: ComputedGetter<T>,
    private readonly _setter: ComputedSetter<T>,
    isReadonly: boolean,
    isSSR: boolean
  ) {
    // 創(chuàng)建effect
    this.effect = new ReactiveEffect(getter, () => {
      // 調(diào)度器執(zhí)行 重新賦值_dirty為true
      if (!this._dirty) {
        this._dirty = true
        // 觸發(fā)effect
        triggerRefValue(this)
      }
    })
    // 用于區(qū)分effect是否是computed
    this.effect.computed = this
    this.effect.active = this._cacheable = !isSSR
    this[ReactiveFlags.IS_READONLY] = isReadonly
  }
  get value() {
    // the computed ref may get wrapped by other proxies e.g. readonly() #3376
    // computed ref可能被其他代理包裝，例如readonly() #3376
    // 通過toRaw()獲取原始值
    const self = toRaw(this)
    // 收集effect
    trackRefValue(self)
    // 如果是臟的，重新執(zhí)行effect.run()，并且將_dirty設(shè)置為false
    if (self._dirty || !self._cacheable) {
      self._dirty = false
      // run()方法會執(zhí)行g(shù)etter方法 值會被緩存到self._value
      self._value = self.effect.run()!
    }
    return self._value
  }
  set value(newValue: T) {
    this._setter(newValue)
  }
}

// packages/reactivity/src/effect.ts
export function triggerEffects(
  dep: Dep | ReactiveEffect[],
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  // spread into array for stabilization
  const effects = isArray(dep) ? dep : [...dep]
  // computed的effect會先執(zhí)行
  // 防止render獲取computed值得時候_dirty還沒有置為true
  for (const effect of effects) {
    if (effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
  for (const effect of effects) {
    if (!effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
}

// packages/runtime-core/src/apiWatch.ts
export function watch<T = any, Immediate extends Readonly<boolean> = false>(
  source: T | WatchSource<T>,
  cb: any,
  options?: WatchOptions<Immediate>
): WatchStopHandle {
  if (__DEV__ && !isFunction(cb)) {
    warn(...)
  }
  // watch 具體實現(xiàn)
  return doWatch(source as any, cb, options)
}

function doWatch(
  source: WatchSource | WatchSource[] | WatchEffect | object,
  cb: WatchCallback | null,
  { immediate, deep, flush, onTrack, onTrigger }: WatchOptions = EMPTY_OBJ
): WatchStopHandle {
  if (__DEV__ && !cb) {
    ...
  }
  const warnInvalidSource = (s: unknown) => {
    warn(...)
  }
  const instance =
    getCurrentScope() === currentInstance?.scope ? currentInstance : null
  // const instance = currentInstance
  let getter: () => any
  let forceTrigger = false
  let isMultiSource = false
  // 根據(jù)不同source 創(chuàng)建不同的getter函數(shù)
  // getter 函數(shù)與computed的getter函數(shù)作用類似
  if (isRef(source)) {
    getter = () => source.value
    forceTrigger = isShallow(source)
  } else if (isReactive(source)) {
    // source是reactive對象時 自動開啟deep=true
    getter = () => source
    deep = true
  } else if (isArray(source)) {
    isMultiSource = true
    forceTrigger = source.some(s => isReactive(s) || isShallow(s))
    getter = () =>
      source.map(s => {
        if (isRef(s)) {
          return s.value
        } else if (isReactive(s)) {
          return traverse(s)
        } else if (isFunction(s)) {
          return callWithErrorHandling(s, instance, ErrorCodes.WATCH_GETTER)
        } else {
          __DEV__ && warnInvalidSource(s)
        }
      })
  } else if (isFunction(source)) {
    if (cb) {
      // getter with cb
      getter = () =>
        callWithErrorHandling(source, instance, ErrorCodes.WATCH_GETTER)
    } else {
      // no cb -> simple effect
      getter = () => {
        if (instance && instance.isUnmounted) {
          return
        }
        if (cleanup) {
          cleanup()
        }
        return callWithAsyncErrorHandling(
          source,
          instance,
          ErrorCodes.WATCH_CALLBACK,
          [onCleanup]
        )
      }
    }
  } else {
    getter = NOOP
    __DEV__ && warnInvalidSource(source)
  }
  // 2.x array mutation watch compat
  // 兼容vue2
  if (__COMPAT__ && cb && !deep) {
    const baseGetter = getter
    getter = () => {
      const val = baseGetter()
      if (
        isArray(val) &&
        checkCompatEnabled(DeprecationTypes.WATCH_ARRAY, instance)
      ) {
        traverse(val)
      }
      return val
    }
  }
  // 深度監(jiān)聽
  if (cb && deep) {
    const baseGetter = getter
    // traverse會遞歸遍歷對象的所有屬性 以達(dá)到深度監(jiān)聽的目的
    getter = () => traverse(baseGetter())
  }
  let cleanup: () => void
  // watch回調(diào)的第三個參數(shù) 可以用此注冊一個cleanup函數(shù) 會在下一次watch cb調(diào)用前執(zhí)行
  // 常用于競態(tài)問題的處理
  let onCleanup: OnCleanup = (fn: () => void) => {
    cleanup = effect.onStop = () => {
      callWithErrorHandling(fn, instance, ErrorCodes.WATCH_CLEANUP)
    }
  }
  // in SSR there is no need to setup an actual effect, and it should be noop
  // unless it's eager or sync flush
  let ssrCleanup: (() => void)[] | undefined
  if (__SSR__ && isInSSRComponentSetup) {
    // ssr處理 ...
  }
  // oldValue 聲明 多個source監(jiān)聽則初始化為數(shù)組
  let oldValue: any = isMultiSource
    ? new Array((source as []).length).fill(INITIAL_WATCHER_VALUE)
    : INITIAL_WATCHER_VALUE
  // 調(diào)度器調(diào)用時執(zhí)行
  const job: SchedulerJob = () => {
    if (!effect.active) {
      return
    }
    if (cb) {
      // watch(source, cb)
      // 獲取newValue
      const newValue = effect.run()
      if (
        deep ||
        forceTrigger ||
        (isMultiSource
          ? (newValue as any[]).some((v, i) =>
              hasChanged(v, (oldValue as any[])[i])
            )
          : hasChanged(newValue, oldValue)) ||
        (__COMPAT__ &&
          isArray(newValue) &&
          isCompatEnabled(DeprecationTypes.WATCH_ARRAY, instance))
      ) {
        // cleanup before running cb again
        if (cleanup) {
          // 執(zhí)行onCleanup傳過來的函數(shù)
          cleanup()
        }
        // 調(diào)用cb 參數(shù)為newValue、oldValue、onCleanup
        callWithAsyncErrorHandling(cb, instance, ErrorCodes.WATCH_CALLBACK, [
          newValue,
          // pass undefined as the old value when it's changed for the first time
          oldValue === INITIAL_WATCHER_VALUE
            ? undefined
            : isMultiSource && oldValue[0] === INITIAL_WATCHER_VALUE
            ? []
            : oldValue,
          onCleanup
        ])
        // 更新oldValue
        oldValue = newValue
      }
    } else {
      // watchEffect
      effect.run()
    }
  }
  // important: mark the job as a watcher callback so that scheduler knows
  // it is allowed to self-trigger (#1727)
  job.allowRecurse = !!cb
  let scheduler: EffectScheduler
  if (flush === 'sync') {
    // 同步更新 即每次響應(yīng)式數(shù)據(jù)改變都會回調(diào)一次cb 通常不使用
    scheduler = job as any // the scheduler function gets called directly
  } else if (flush === 'post') {
    // job放入pendingPostFlushCbs隊列中
    // pendingPostFlushCbs隊列會在queue隊列執(zhí)行完畢后執(zhí)行 函數(shù)更新effect通常會放在queue隊列中
    // 所以pendingPostFlushCbs隊列執(zhí)行時組件已經(jīng)更新完畢
    scheduler = () => queuePostRenderEffect(job, instance && instance.suspense)
  } else {
    // default: 'pre'
    job.pre = true
    if (instance) job.id = instance.uid
    // 默認(rèn)異步更新 關(guān)于異步更新會和nextTick放在一起詳細(xì)講解
    scheduler = () => queueJob(job)
  }
  // 創(chuàng)建effect effect.run的時候建立effect與getter內(nèi)響應(yīng)式數(shù)據(jù)的關(guān)系
  const effect = new ReactiveEffect(getter, scheduler)
  if (__DEV__) {
    effect.onTrack = onTrack
    effect.onTrigger = onTrigger
  }
  // initial run
  if (cb) {
    if (immediate) {
      // 立馬執(zhí)行一次job
      job()
    } else {
      // 否則執(zhí)行effect.run() 會執(zhí)行g(shù)etter 獲取oldValue
      oldValue = effect.run()
    }
  } else if (flush === 'post') {
    queuePostRenderEffect(
      effect.run.bind(effect),
      instance && instance.suspense
    )
  } else {
    effect.run()
  }
  // 返回一個取消監(jiān)聽的函數(shù)
  const unwatch = () => {
    effect.stop()
    if (instance && instance.scope) {
      remove(instance.scope.effects!, effect)
    }
  }
  if (__SSR__ && ssrCleanup) ssrCleanup.push(unwatch)
  return unwatch
}