const obj = reactive({count: 1})

const runner = effect(() => {
  console.log(obj.count)
})

obj.count++

// 先執(zhí)行
fun()  // 打印出1

const runner = new ReactiveEffect(fn)

return runner

runner： {
  run() {
    this.fun() //執(zhí)行fun
  },
  stop() {

  }
}

() => {
  console.log(obj.count)
}

const obj = reactive({count: 1})

const runner = effect(() => {
  console.log(obj.count)
}, {
  lazy: true
})
runner()
obj.count++

let events = []
const onTrack = (e) => {
  events.push(e)
}
const obj = reactive({ foo: 1, bar: 2 })
const runner = effect(
  () => {
    console.log(obj.foo)
  },
  { onTrack }
)
console.log('runner', runner)
obj.foo++
console.log("events", events)

[
  {
    effect: runner,  // effect 函數(shù)的返回值
    target: toRaw(obj),  // 表示的是哪個(gè)響應(yīng)式數(shù)據(jù)發(fā)生了變化
    type: TrackOpTypes.GET,  // 表示此次記錄操作的類型。 get 表示獲取值
    key: 'foo'
 }
]

// packages/reactivity/src/effect.ts
export interface ReactiveEffectOptions extends DebuggerOptions {
  lazy?: boolean
  scheduler?: EffectScheduler
  scope?: EffectScope
  allowRecurse?: boolean
  onStop?: () => void
}

export function effect<T = any>(
  fn: () => T, // 副作用函數(shù)
  options?: ReactiveEffectOptions // 結(jié)構(gòu)如上
): ReactiveEffectRunner {
  // 如果 fn 對(duì)象上有 effect 屬性
  if ((fn as ReactiveEffectRunner).effect) {
    // 那么就將 fn 替換為 fn.effect.fn
    fn = (fn as ReactiveEffectRunner).effect.fn
  }
  // 創(chuàng)建一個(gè)響應(yīng)式副作用函數(shù)
  const _effect = new ReactiveEffect(fn)
  if (options) {
    // 將配置項(xiàng)合并到響應(yīng)式副作用函數(shù)上
    extend(_effect, options)
    // 如果配置項(xiàng)中有 scope 屬性（該屬性的作用是指定副作用函數(shù)的作用域）
    if (options.scope) recordEffectScope(_effect, options.scope)
  }
  if (!options || !options.lazy) { // options.lazy 不為true
    _effect.run() // 執(zhí)行響應(yīng)式副作用函數(shù) 首次執(zhí)行fn()
  }
  // _effect.run作用域綁定到_effect
  const runner = _effect.run.bind(_effect) as ReactiveEffectRunner
  // 將響應(yīng)式副作用函數(shù)賦值給 runner.effect
  runner.effect = _effect
  return runner
}

if (!options || !options.lazy) { // options.lazy 不為true
  _effect.run() // 執(zhí)行響應(yīng)式副作用函數(shù) 首次執(zhí)行fn()
}

// _effect.run作用域綁定到_effect
  const runner = _effect.run.bind(_effect) as ReactiveEffectRunner

export class ReactiveEffect<T = any> {
  active = true
  deps: Dep[] = [] // 響應(yīng)式依賴項(xiàng)的集合
  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
  ) {
    // 記錄當(dāng)前 ReactiveEffect 對(duì)象的作用域
    recordEffectScope(this, scope)
  }

  run() {
    // 如果當(dāng)前 ReactiveEffect 對(duì)象不處于活動(dòng)狀態(tài)，直接返回 fn 的執(zhí)行結(jié)果
    if (!this.active) {
      return this.fn()
    }
    // 尋找當(dāng)前 ReactiveEffect 對(duì)象的最頂層的父級(jí)作用域
    let parent: ReactiveEffect | undefined = activeEffect
    let lastShouldTrack = shouldTrack // 是否要跟蹤
    while (parent) {
      if (parent === this) {
        return
      }
      parent = parent.parent
    }
    try {
      // 記錄父級(jí)作用域?yàn)楫?dāng)前活動(dòng)的 ReactiveEffect 對(duì)象
      this.parent = activeEffect
      activeEffect = this  // 將當(dāng)前活動(dòng)的 ReactiveEffect 對(duì)象設(shè)置為 “自己”
      shouldTrack = true // 將 shouldTrack 設(shè)置為 true （表示是否需要收集依賴）
      // effectTrackDepth 用于標(biāo)識(shí)當(dāng)前的 effect 調(diào)用棧的深度，執(zhí)行一次 effect 就會(huì)將 effectTrackDepth 加 1
      trackOpBit = 1 << ++effectTrackDepth

      if (effectTrackDepth <= maxMarkerBits) {
        // 初始依賴追蹤標(biāo)記
        initDepMarkers(this)
      } else {
        // 清除依賴追蹤標(biāo)記
        cleanupEffect(this)
      }
      // 返回副作用函數(shù)執(zhí)行結(jié)果
      return this.fn()
    } finally {
      // 如果 effect調(diào)用棧的深度 沒有超過(guò)閾值
      if (effectTrackDepth <= maxMarkerBits) {
        // 確定最終的依賴追蹤標(biāo)記
        finalizeDepMarkers(this)
      }
      // 執(zhí)行完畢會(huì)將 effectTrackDepth 減 1
      trackOpBit = 1 << --effectTrackDepth
      // 執(zhí)行完畢，將當(dāng)前活動(dòng)的 ReactiveEffect 對(duì)象設(shè)置為 “父級(jí)作用域”
      activeEffect = this.parent
      // 將 shouldTrack 設(shè)置為上一個(gè)值
      shouldTrack = lastShouldTrack
      // 將父級(jí)作用域設(shè)置為 undefined
      this.parent = undefined
      // 延時(shí)停止，這個(gè)標(biāo)志是在 stop 方法中設(shè)置的
      if (this.deferStop) {
        this.stop()
      }
    }
  }

  stop() {
    // stopped while running itself - defer the cleanup
    // 如果當(dāng)前 活動(dòng)的 ReactiveEffect 對(duì)象是 “自己”
    // 延遲停止，需要執(zhí)行完當(dāng)前的副作用函數(shù)之后再停止
    if (activeEffect === this) {
      // 在 run 方法中會(huì)判斷 deferStop 的值，如果為 true，就會(huì)執(zhí)行 stop 方法
      this.deferStop = true
    } else if (this.active) {// 如果當(dāng)前 ReactiveEffect 對(duì)象處于活動(dòng)狀態(tài)
      cleanupEffect(this) // 清除所有的依賴追蹤標(biāo)記
      if (this.onStop) { 
        this.onStop()
      }
      this.active = false // 將 active 設(shè)置為 false
    }
  }
}

const runner = effect(() => {
  console.log(obj.count) 
})

function createGetter(isReadonly = false, shallow = false) {
  // 閉包返回 get 攔截器方法
  return function get(target: Target, key: string | symbol, receiver: object) {
    // ...
    if (!isReadonly) {
      track(target, TrackOpTypes.GET, key)
    }
    // ...
  }

const targetMap = new WeakMap();
/**
 * 收集依賴
 * @param target target 觸發(fā)依賴的對(duì)象，例子中的obj
 * @param type 操作類型 比如obj.count就是get
 * @param key 指向?qū)ο蟮膋ey, 比如obj.count就是count
 */
export function track(target: object, type: TrackOpTypes, key: unknown) {
  if (shouldTrack && activeEffect) { // 是否應(yīng)該依賴收集 & 當(dāng)前的new ReactiveEffect()即指向的就是當(dāng)前正在執(zhí)行的副作用函數(shù)

    // 如果 targetMap 中沒有 target，就會(huì)創(chuàng)建一個(gè) Map
    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())) // createDep 生成dep = { w:0, n: 0}
    }

    const eventInfo = __DEV__
      ? { effect: activeEffect, target, type, key }
      : undefined

    trackEffects(dep, eventInfo)
  }
}

targetMap = {
  target: { 
    key: dep
  },
  // 比如：
  obj: { 
    count: {
       w: 0, 
       n: 0
    }
  }
}

const eventInfo = __DEV__
  ? { effect: activeEffect, target, type, key }
  : undefined

export function trackEffects(
  dep: Dep,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  let shouldTrack = false
  if (effectTrackDepth <= maxMarkerBits) {
    if (!newTracked(dep)) {
      // 執(zhí)行之前 dep = Set(0) {w: 0, n: 0}

      // 執(zhí)行之后 dep = Set(0) {w: 0, n: 2}
      dep.n |= trackOpBit // set newly tracked
  
      shouldTrack = !wasTracked(dep) 
    }
  } else {
    // Full cleanup mode.
    shouldTrack = !dep.has(activeEffect!)
  }

  if (shouldTrack) {
    // 將activeEffect添加到dep
    dep.add(activeEffect!)
    activeEffect!.deps.push(dep)
    if (__DEV__ && activeEffect!.onTrack) { // onTrack邏輯
      activeEffect!.onTrack(
        extend(
          {
            effect: activeEffect!
          },
          debuggerEventExtraInfo!
        )
      )
    }
  }
}

function createSetter(shallow = false) {
  return function set(
    target: object,
    key: string | symbol,
    value: unknown,
    receiver: object
  ): boolean {
    //...
    const result = Reflect.set(target, key, value, receiver)
    // don't trigger if target is something up in the prototype chain of original
    if (target === toRaw(receiver)) {
      if (!hadKey) {
        trigger(target, TriggerOpTypes.ADD, key, value) // 觸發(fā)ADD依賴更新
      } else if (hasChanged(value, oldValue)) {
        trigger(target, TriggerOpTypes.SET, key, value, oldValue) //觸發(fā)SET依賴更新
      }
    }
    //...
  }

// 路徑：packages/reactivity/src/effect.ts
export function trigger(
  target: object,
  type: TriggerOpTypes,
  key?: unknown,
  newValue?: unknown,
  oldValue?: unknown,
  oldTarget?: Map<unknown, unknown> | Set<unknown>
) {
  const depsMap = targetMap.get(target) // 獲取depsMap, targetMap是在track中創(chuàng)建的依賴
  if (!depsMap) {
    // never been tracked
    return
  }

  let deps: (Dep | undefined)[] = []
  if (type === TriggerOpTypes.CLEAR) {
    // collection being cleared
    // trigger all effects for target
    deps = [...depsMap.values()]
  } else if (key === 'length' && isArray(target)) {
    const newLength = Number(newValue)
    depsMap.forEach((dep, key) => {
      if (key === 'length' || key >= newLength) {
        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)) {
          // 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)
      }
    }
    if (__DEV__) {
      triggerEffects(createDep(effects), eventInfo)
    } else {
      triggerEffects(createDep(effects))
    }
  }
}

  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])
      }
    }
  }

export function triggerEffects(
  dep: Dep | ReactiveEffect[],
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  // spread into array for stabilization
  const effects = isArray(dep) ? dep : [...dep]
  for (const effect of effects) {
    if (effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
  for (const effect of effects) {
    if (!effect.computed) {
      triggerEffect(effect, debuggerEventExtraInfo)
    }
  }
}

function triggerEffect(
  effect: ReactiveEffect,
  debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
  if (effect !== activeEffect || effect.allowRecurse) {
     // 如果 effect.onTrigger 存在，就會(huì)執(zhí)行，只有開發(fā)模式下才會(huì)執(zhí)行
    if (__DEV__ && effect.onTrigger) {
      effect.onTrigger(extend({ effect }, debuggerEventExtraInfo))
    }
    // 如果 effect 是一個(gè)調(diào)度器，就會(huì)執(zhí)行 scheduler
    if (effect.scheduler) {
      effect.scheduler()
    } else {
      // 其它情況執(zhí)行 effect.run()
      effect.run()
    }
  }
}