const targetMap = new WeakMap() // 用原始对象作为key，依赖映射作为value
let activeEffect = null // 保存当前的需要订阅通知的effect

function track(target, key) {
  if(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=new Set()))
    }
    dep.add(activeEffect) // 将efect添加进通知set
  }
}

function trigger(target, key) {
  const depsMap = targetMap.get(target)
  if(!depsMap) return
  const deps = depsMap.get(key)
  deps.forEach(effect => {
    effect()
  });
}


function reactive(target){
  const hander = {
    get(target, key, receiver) {
      const result = Reflect.get(target, key, receiver)
      track(target, key)
      return result
    },

    set(target, key, value, receiver) {
      let oldValue = target[key]
      let result = Reflect.set(target, key, value, receiver)
      if (oldValue !== value){
        trigger(target, key)
      }
      return result
    }
  }

  return new Proxy(target, hander)
}

// 创建ref，为基本数据类型赋予响应式功能

function ref(raw) {
  const r = {
    get value(){
      track(r, 'value')
      return raw
    },

    set value(newVal){
      raw = newVal
      trigger(r, 'value')
    }
  }

  return r
}

function effect(effect){
  activeEffect = effect
  activeEffect()
  activeEffect = null
}

const product = new reactive({price: 5, quantity: 2})

let tax = ref(5) // 固定的商品税
let total = 0

effect(()=>{
  total = tax.value + product.price * product.quantity // price和quantity都被跟踪了
})

console.log(total);
product.quantity = 4
product.price = 5
console.log(total);
tax.value = 10 // 修改固定的商品税
console.log(total);