SOURCE

// 存储副作用函数的桶
const bucket = new WeakMap()
const ITERATE_KEY = Symbol()

function track(target, key) {
  if (!activeEffect) return
  let depsMap = bucket.get(target)
  if (!depsMap) {
    bucket.set(target, (depsMap = new Map()))
  }
  let deps = depsMap.get(key)
  if (!deps) {
    depsMap.set(key, (deps = new Set()))
  }
  deps.add(activeEffect)
  activeEffect.deps.push(deps)
}

function trigger(target, key,type) {
  const depsMap = bucket.get(target)
  if (!depsMap) return
  const effects = depsMap.get(key)
  const iterateEffects = depsMap.get(ITERATE_KEY)

  const effectsToRun = new Set()
  effects && effects.forEach(effectFn => {
    if (effectFn !== activeEffect) {
      effectsToRun.add(effectFn)
    }
  })
if (type === 'ADD' || type === 'DELETE') {
  iterateEffects && iterateEffects.forEach(effectFn => {
    if (effectFn !== activeEffect) {
      effectsToRun.add(effectFn)
    }
  })
}

  effectsToRun.forEach(effectFn => {
    if (effectFn.options.scheduler) {
      effectFn.options.scheduler(effectFn)
    } else {
      effectFn()
    }
  })
  // effects && effects.forEach(effectFn => effectFn())
}

// 用一个全局变量存储当前激活的 effect 函数
let activeEffect
// effect 栈
const effectStack = []

function effect(fn, options = {}) {
  const effectFn = () => {
    cleanup(effectFn)
    // 当调用 effect 注册副作用函数时，将副作用函数复制给 activeEffect
    activeEffect = effectFn
    // 在调用副作用函数之前将当前副作用函数压栈
    effectStack.push(effectFn)
    const res = fn()
    // 在当前副作用函数执行完毕后，将当前副作用函数弹出栈，并还原 activeEffect 为之前的值
    effectStack.pop()
    activeEffect = effectStack[effectStack.length - 1]

    return res
  }
  // 将 options 挂在到 effectFn 上
  effectFn.options = options
  // activeEffect.deps 用来存储所有与该副作用函数相关的依赖集合
  effectFn.deps = []
  // 执行副作用函数
  if (!options.lazy) {
    effectFn()
  }

  return effectFn
}

function cleanup(effectFn) {
  for (let i = 0; i < effectFn.deps.length; i++) {
    const deps = effectFn.deps[i]
    deps.delete(effectFn)
  }
  effectFn.deps.length = 0
}



// 原始数据
const obj = { foo: 1 }

// 对原始数据的代理
const p = new Proxy(obj, {
  // 拦截读取操作
  get(target, key) {
    // 将副作用函数 activeEffect 添加到存储副作用函数的桶中
    track(target, key,reciever)
    // 返回属性值
    return Reflect.get(target,key,reciever)
  },
  // 拦截设置操作
  set(target, key, newVal,receiver) {
    // 如果属性不存在，则说明是在添加新的属性，否则是设置已存在的属性
    const type = Object.prototype.hasOwnProperty.call(target, key) ? 'SET' : 'ADD'
    // 设置属性值
    const res = Reflect.set(target, key, newVal, receiver)
    trigger(target, key, type)
  },
  has(target, key) {
    track(target, key)
    return Reflect.has(target, key)
  },
  ownKeys(target) {
    track(target, ITERATE_KEY)
    return Reflect.ownKeys(target)
  }
})

// effect(() => {
//   console.log('foo' in p)
// })


effect(() => {
  for (const key in p) {
    console.log('key: ', key)
  }
})

p.foo = 2