const targetMap = new WeakMap<any, KeyToDepMap>()
export let activeEffect: ReactiveEffect | undefined
export let shouldTrack = true
const trackStack: boolean[] = []

// 暫停收集
export function pauseTracking() {
  trackStack.push(shouldTrack)
  shouldTrack = false
}
// 恢復(fù)收集
export function enableTracking() {
  trackStack.push(shouldTrack)
  shouldTrack = true
}
// 重置為上一次的狀態(tài)
export function resetTracking() {
  const last = trackStack.pop()
  shouldTrack = last === undefined ? true : last
}

export class ReactiveEffect<T = any> {
  active = true
  deps: Dep[] = []
  parent: ReactiveEffect | undefined = undefined
  /**
   * Can be attached after creation
   * @internal
   */
  computed?: ComputedRefImpl<T>
  /**
   * @internal
   */
  allowRecurse?: boolean
  /**
   * @internal
   */
  private deferStop?: boolean
  onStop?: () => void
  // dev only
  onTrack?: (event: DebuggerEvent) => void
  // dev only
  onTrigger?: (event: DebuggerEvent) => void
  constructor(
    public fn: () => T,
    public scheduler: EffectScheduler | null = null,
    scope?: EffectScope
  ) {
    recordEffectScope(this, scope)
  }
  run() {
    if (!this.active) {
      return this.fn()
    }
    // 當前活躍的effect
    let parent: ReactiveEffect | undefined = activeEffect
    let lastShouldTrack = shouldTrack
    // 如果當前活躍的effect就是這個effect本身，則直接返回
    while (parent) {
      if (parent === this) {
        return
      }
      parent = parent.parent
    }
    // 依次活躍的effect形成鏈表，由parent屬性連接
    try {
      this.parent = activeEffect
      activeEffect = this
      shouldTrack = true
      trackOpBit = 1 << ++effectTrackDepth
      if (effectTrackDepth <= maxMarkerBits) {
        // 遍歷 this.deps 將其中的effect設(shè)置為已捕獲 tracked
        initDepMarkers(this)
      } else {
        // 層級溢出則清除當前副作用
        cleanupEffect(this)
      }
      // 尾調(diào)用傳入的fn
      return this.fn()
    } finally {
      // 因為前面有return，因此當 try 的代碼塊發(fā)生異常時執(zhí)行
      if (effectTrackDepth <= maxMarkerBits) {
        // 該方法遍歷 this.deps，將其中過氣的effect刪除，未捕獲的effect加入
        // effect 就是其中的 dep
        finalizeDepMarkers(this)
      }
      trackOpBit = 1 << --effectTrackDepth
      // 復(fù)原一些狀態(tài)
      activeEffect = this.parent
      shouldTrack = lastShouldTrack
      this.parent = undefined
      // 若設(shè)置了延遲停止，則執(zhí)行stop，進行延遲清理
      if (this.deferStop) {
        this.stop()
      }
    }
  }
  // 清除副作用
  stop() {
    // stopped while running itself - defer the cleanup
    if (activeEffect === this) {
      this.deferStop = true
    } else if (this.active) {
      cleanupEffect(this)
      if (this.onStop) {
        this.onStop()
      }
      this.active = false
    }
  }
}

function cleanupEffect(effect: ReactiveEffect) {
  const { deps } = effect
  if (deps.length) {
    for (let i = 0; i < deps.length; i++) {
      deps[i].delete(effect)
    }
    deps.length = 0
  }
}

export interface DebuggerOptions {
  onTrack?: (event: DebuggerEvent) => void
  onTrigger?: (event: DebuggerEvent) => void
}
export interface ReactiveEffectOptions extends DebuggerOptions {
  lazy?: boolean
  scheduler?: EffectScheduler
  scope?: EffectScope
  allowRecurse?: boolean
  onStop?: () => void
}
export interface ReactiveEffectRunner<T = any> {
  (): T
  effect: ReactiveEffect
}

export function effect<T = any>(
  fn: () => T,
  options?: ReactiveEffectOptions
): ReactiveEffectRunner {
  // 處理fn
  if ((fn as ReactiveEffectRunner).effect) {
    fn = (fn as ReactiveEffectRunner).effect.fn
  }
  // 根據(jù) fn 創(chuàng)建一個 _effect 
  const _effect = new ReactiveEffect(fn)
  if (options) {
    // 用 options 覆蓋 _effect 上的屬性
    extend(_effect, options)
    if (options.scope) recordEffectScope(_effect, options.scope)
  }
  // 沒有 lazy , 則 _effect 立即執(zhí)行一次 run()
  if (!options || !options.lazy) {
    _effect.run()
  }
  // runner：拿到 _effect.run 并掛上 effect 屬性，包裝成 ReactiveEffectRunner 類型
  const runner = _effect.run.bind(_effect) as ReactiveEffectRunner
  // effect屬性指回 _effect 自身，方便使用 runner 調(diào)用 run 和 stop
  runner.effect = _effect
  // 返回 runner
  return runner
}

export function stop(runner: ReactiveEffectRunner) {
  runner.effect.stop()
}

// 全局變量 targetMap
const targetMap = new WeakMap<any, KeyToDepMap>()
export function track(target: object, type: TrackOpTypes, key: unknown) {
  if (shouldTrack && activeEffect) {
    let depsMap = targetMap.get(target)
    if (!depsMap) {
      targetMap.set(target, (depsMap = new Map()))
    }
    let dep = depsMap.get(key)
    if (!dep) {
      depsMap.set(key, (dep = createDep()))
    }
    const eventInfo = __DEV__
      ? { effect: activeEffect, target, type, key }
      : undefined
    trackEffects(dep, eventInfo)
  }
}

export const createDep = (effects?: ReactiveEffect[]): Dep => {
  const dep = new Set<ReactiveEffect>(effects) as Dep
  dep.w = 0
  dep.n = 0
  return dep
}

export function trackEffects(
  dep: Dep,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  let shouldTrack = false
  if (effectTrackDepth <= maxMarkerBits) {
    if (!newTracked(dep)) {
      dep.n |= trackOpBit // set newly tracked
      shouldTrack = !wasTracked(dep)
    }
  } else {
    // Full cleanup mode.
    shouldTrack = !dep.has(activeEffect!)
  }
  // 當前依賴 dep 還未被捕獲 / 當前依賴 dep 中，還沒有當前活躍的副作用時，
  // 將當前活躍的副作用 effect 添加進 dep 里，同時在把 dep 加入受副作用影響的依賴集合 activeEffect.deps 中
  if (shouldTrack) {
    dep.add(activeEffect!)
    activeEffect!.deps.push(dep)
    if (__DEV__ && activeEffect!.onTrack) {
      activeEffect!.onTrack({
        effect: activeEffect!,
        ...debuggerEventExtraInfo!
      })
    }
  }
}

function triggerEffect(
  effect: ReactiveEffect,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  if (effect !== activeEffect || effect.allowRecurse) {
    if (__DEV__ && effect.onTrigger) {
      effect.onTrigger(extend({ effect }, debuggerEventExtraInfo))
    }
    // 實際觸發(fā)更新的地方
    if (effect.scheduler) {
      effect.scheduler()
    } else {
      effect.run()
    }
  }
}

export function triggerEffects(
  dep: Dep | ReactiveEffect[],
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  // spread into array for stabilization
  const effects = isArray(dep) ? dep : [...dep]
  // 兩者互斥，但是執(zhí)行的操作相同？而且為什么不寫在一個 for...of... 里 ？
  for (const effect of effects) {
    if (effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
  for (const effect of effects) {
    if (!effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
}

export function trigger(
  target: object,
  type: TriggerOpTypes,
  key?: unknown,
  newValue?: unknown,
  oldValue?: unknown,
  oldTarget?: Map<unknown, unknown> | Set<unknown>
) {
  const depsMap = targetMap.get(target)
  if (!depsMap) {
    // never been tracked
    return
  }
  // 用于聚集所有相關(guān)依賴
  let deps: (Dep | undefined)[] = []
  if (type === TriggerOpTypes.CLEAR) {
    // 調(diào)用了Set、Map實例的clear方法，將觸發(fā)全部相關(guān)的副作用
    // collection being cleared
    // trigger all effects for target
    deps = [...depsMap.values()]
  } else if (key === 'length' && isArray(target)) {
    // 目標對象是數(shù)組，且修改了length屬性時，會觸發(fā)全部相關(guān)的副作用
    depsMap.forEach((dep, key) => {
      if (key === 'length' || key >= (newValue as number)) {
        deps.push(dep)
      }
    })
  } else {
    // schedule runs for SET | ADD | DELETE
    if (key !== void 0) {
      deps.push(depsMap.get(key))
    }
    // also run for iteration key on ADD | DELETE | Map.SET
    switch (type) {
      case TriggerOpTypes.ADD:
        if (!isArray(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
          if (isMap(target)) {
            deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
          }
        } else if (isIntegerKey(key)) {
          // 數(shù)組下標成員的更改 會引起 length 屬性相關(guān)的更新
          // new index added to array -> length changes
          deps.push(depsMap.get('length'))
        }
        break
      case TriggerOpTypes.DELETE:
        if (!isArray(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
          if (isMap(target)) {
            deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
          }
        }
        break
      case TriggerOpTypes.SET:
        if (isMap(target)) {
          deps.push(depsMap.get(ITERATE_KEY))
        }
        break
    }
  }
  const eventInfo = __DEV__
    ? { target, type, key, newValue, oldValue, oldTarget }
    : undefined
  if (deps.length === 1) {
    if (deps[0]) {
      if (__DEV__) {
        triggerEffects(deps[0], eventInfo)
      } else {
        triggerEffects(deps[0])
      }
    }
  } else {
    const effects: ReactiveEffect[] = []
    for (const dep of deps) {
      if (dep) {
        effects.push(...dep)
      }
    }
    // 這里triggerEffects接受的參數(shù)類型為Set，之前的是數(shù)組
    if (__DEV__) {
      triggerEffects(createDep(effects), eventInfo)
    } else {
      triggerEffects(createDep(effects))
    }
  }
}