SOURCE

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

function reactive(obj) {
  return createReactive(obj)
}
function shallowReactive(obj) {
  return createReactive(obj, true)
}

function readonly(obj) {
  return createReactive(obj, false, true)
}

function shallowReadonly(obj) {
  return createReactive(obj, true, true)
}


function createReactive(obj, isShallow = false, isReadonly = false) {
  return new Proxy(obj, {
    // 拦截读取操作
    get(target, key, receiver) {
    //   console.log('get: ', key)
      if (key === 'raw') {
        return target
      }
      // 非只读的时候才需要建立响应联系
      if (!isReadonly) {
        track(target, key)
      }

      const res = Reflect.get(target, key, receiver)

      if (isShallow) {
        return res
      }

      if (typeof res === 'object' && res !== null) {
        // 深只读/响应
        return isReadonly ? readonly(res) : reactive(res)
      }

      return res
    },
    // 拦截设置操作
    set(target, key, newVal, receiver) {
    //   console.log('set: ', key )
      if (isReadonly) {
        // console.warn(`属性 ${key} 是只读的`)
        return true
      }
      const oldVal = target[key]
      // 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 = Array.isArray(target)
        ? Number(key) < target.length ? 'SET' : 'ADD'
        : Object.prototype.hasOwnProperty.call(target, key) ? 'SET' : 'ADD'
      // 设置属性值
      const res = Reflect.set(target, key, newVal, receiver)
      if (target === receiver.raw) {
        if (oldVal !== newVal && (oldVal === oldVal || newVal === newVal)) {
          trigger(target, key, type, newVal)
        }
      }

      return res
    },
    has(target, key) {
      track(target, key)
      return Reflect.has(target, key)
    },
    ownKeys(target) {
      track(target, ITERATE_KEY)
      return Reflect.ownKeys(target)
    },
    deleteProperty(target, key) {
      if (isReadonly) {
        // console.warn(`属性 ${key} 是只读的`)
        return true
      }
      const hadKey = Object.prototype.hasOwnProperty.call(target, key)
      const res = Reflect.deleteProperty(target, key)

      if (res && hadKey) {
        trigger(target, key, 'DELETE')
      }

      return res
    }
  })
}

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, newVal) {
  const depsMap = bucket.get(target)
  if (!depsMap) return
  const effects = depsMap.get(key)

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

  if (type === 'ADD' && Array.isArray(target)) {
    const lengthEffects = depsMap.get('length')
    lengthEffects && lengthEffects.forEach(effectFn => {
      if (effectFn !== activeEffect) {
        effectsToRun.add(effectFn)
      }
    })
  }

  if (Array.isArray(target) && key === 'length') {
    depsMap.forEach((effects, key) => {
      if (key >= newVal) {
        effects.forEach(effectFn => {
          if (effectFn !== activeEffect) {
            effectsToRun.add(effectFn)
          }
        })
      }
    })
  }

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


// =================================================================
// const arr = reactive(['foo'])

// effect(() => {
//   console.log(arr.length)
// })

// arr[1] = 'bar'

// // =================================================================


const arr = reactive(['foo','abc','def'])

effect(() => {
  console.log(arr[2]) // foo
})

arr.length = 2