let activeEffect
class Dep {
    subscribers = new Set()

    define() {
        if (activeEffect) {
            this.subscribers.add(activeEffect)
        }
    }

    notify() {
        this.subscribers.forEach((effect) => {
            effect()
        })
    }
}

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

const targetMap = new WeakMap()
function getDep(target, key) {
    let depsMap = targetMap.get(target)
    if (!depsMap) {
        depsMap = new Map()
        targetMap.set(target, depsMap)
    }

    let dep = depsMap.get(key)
    if (!dep) {
        dep = new Dep()
        depsMap.set(key, dep)
    }
    return dep
}
const reactiveHandlers = {
    get(target, key, receiver) {
        const dep = getDep(target, key)
        dep.define()
        return Reflect.get(target, key, receiver)
    },
    set(target, key, value, receiver) {
        const dep = getDep(target, key)
        const result = Reflect.set(target, key, value, receiver)
        dep.notify()
        return result
    },
}
function reactive(raw) {
    return new Proxy(raw, reactiveHandlers)
}

// 使用
const state = reactive({
    count: 0,
})
watchEffect(() => {
    console.log(state.count)
})
state.count++

<style>
  .red {
    color: red;
  }
  .green {
    color: green;
  }
</style>

<div id="app"></div>

<script>
  function h(tag, props, children) {
    return { tag, props, children }
  }

  function mount(vnode, container) {
    const el = (vnode.el = document.createElement(vnode.tag))
    // props
    if (vnode.props) {
      for (const key in vnode.props) {
        const value = vnode.props[key]
        el.setAttribute(key, value)
      }
    }
    // children
    if (vnode.children) {
      if (typeof vnode.children === "string") {
        el.textContent = vnode.children
      } else {
        vnode.children.forEach((child) => {
          mount(child, el)
        })
      }
    }
    container.appendChild(el)
  }

  const vdom = h("div", { id: "hello", class: "red" }, [h("span", null, "hello")])

  mount(vdom, document.getElementById("app"))

  function patch(n1, n2) {
    if (n1.tag === n2.tag) {
      const el = (n2.el = n1.el)
      // props
      const oldProps = n1.props || {}
      const newProps = n2.props || {}

      for (const key in newProps) {
        const oldVal = oldProps[key]
        const newVal = newProps[key]
        if (newVal !== oldVal) {
          el.setAttribute(key, newVal)
        }
      }

      for (const key in oldProps) {
        if (!(key in newProps)) {
          el.removeAttribute(key)
        }
      }

      // children
      const oldChildren = n1.children
      const newChildren = n2.children
      if (typeof newChildren === "string") {
        if (typeof oldChildren === "string") {
          if (newChildren !== oldChildren) {
            el.textContent = newChildren
          }
        } else {
          el.textContent = newChildren
        }
      } else {
        if (typeof oldChildren === "string") {
          el.innerHTML = ""
          newChildren.forEach((child) => {
            mount(child, el)
          })
        } else {
          const commonLength = Math.min(oldChildren.length, newChildren.length)
          for (let i = 0; i < commonLength; i++) {
            patch(oldChildren[i], newChildren[i])
          }
          if (newChildren.length > oldChildren.length) {
            newChildren.slice(oldChildren.length).forEach((child) => {
              mount(child, el)
            })
          }
          if (newChildren.length < oldChildren.length) {
            oldChildren.slice(newChildren.length).forEach((child) => {
              el.removeChild(child.el)
            })
          }
        }
      }
    } else {
      // replace
    }
  }

  const vdom2 = h("div", { id: "hello", class: "green" }, [h("span", null, "change!")])
  patch(vdom, vdom2)
</script>

<div id="app"></div>

<script>
  function h(tag, props, children) {
    return { tag, props, children }
  }

  function mount(vnode, container) {
    const el = (vnode.el = document.createElement(vnode.tag))
    // props
    if (vnode.props) {
      for (const key in vnode.props) {
        const value = vnode.props[key]
        if (key.startsWith("on")) {
          el.addEventListener(key.slice(2).toLowerCase(), value)
        } else {
          el.setAttribute(key, value)
        }
      }
    }
    // children
    if (vnode.children) {
      if (typeof vnode.children === "string") {
        el.textContent = vnode.children
      } else {
        vnode.children.forEach((child) => {
          mount(child, el)
        })
      }
    }
    container.appendChild(el)
  }

  function patch(n1, n2) {
    if (n1.tag === n2.tag) {
      const el = (n2.el = n1.el)
      // props
      const oldProps = n1.props || {}
      const newProps = n2.props || {}

      for (const key in newProps) {
        const oldVal = oldProps[key]
        const newVal = newProps[key]
        if (newVal !== oldVal) {
          el.setAttribute(key, newVal)
        }
      }

      for (const key in oldProps) {
        if (!(key in newProps)) {
          el.removeAttribute(key)
        }
      }

      // children
      const oldChildren = n1.children
      const newChildren = n2.children
      if (typeof newChildren === "string") {
        if (typeof oldChildren === "string") {
          if (newChildren !== oldChildren) {
            el.textContent = newChildren
          }
        } else {
          el.textContent = newChildren
        }
      } else {
        if (typeof oldChildren === "string") {
          el.innerHTML = ""
          newChildren.forEach((child) => {
            mount(child, el)
          })
        } else {
          const commonLength = Math.min(oldChildren.length, newChildren.length)
          for (let i = 0; i < commonLength; i++) {
            patch(oldChildren[i], newChildren[i])
          }
          if (newChildren.length > oldChildren.length) {
            newChildren.slice(oldChildren.length).forEach((child) => {
              mount(child, el)
            })
          }
          if (newChildren.length < oldChildren.length) {
            oldChildren.slice(newChildren.length).forEach((child) => {
              el.removeChild(child.el)
            })
          }
        }
      }
    } else {
      // replace
    }
  }

  // reactive
  let activeEffect
  class Dep {
    subscribers = new Set()

    depend() {
      if (activeEffect) {
        this.subscribers.add(activeEffect)
      }
    }

    notify() {
      this.subscribers.forEach((effect) => {
        effect()
      })
    }
  }

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

  const targetMap = new WeakMap()
  function getDep(target, key) {
    let depsMap = targetMap.get(target)
    if (!depsMap) {
      depsMap = new Map()
      targetMap.set(target, depsMap)
    }

    let dep = depsMap.get(key)
    if (!dep) {
      dep = new Dep()
      depsMap.set(key, dep)
    }
    return dep
  }
  const reactiveHandlers = {
    get(target, key, receiver) {
      const dep = getDep(target, key)
      dep.depend()
      return Reflect.get(target, key, receiver)
    },
    set(target, key, value, receiver) {
      const dep = getDep(target, key)
      const result = Reflect.set(target, key, value, receiver)
      dep.notify()
      return result
    },
  }
  function reactive(raw) {
    return new Proxy(raw, reactiveHandlers)
  }

  const App = {
    data: reactive({
      count: 22,
    }),
    render() {
      return h(
        "div",
        {
          onClick: () => {
            this.data.count++
          },
        },
        String(this.data.count)
      )
    },
  }
  function mountApp(component, container) {
    let isMounted = false
    let prevVdom
    watchEffect(() => {
      if (!isMounted) {
        prevVdom = component.render()
        mount(prevVdom, container)
        isMounted = true
      } else {
        const newVdom = component.render()
        patch(prevVdom, newVdom)
        prevVdom = newVdom
      }
    })
  }
  mountApp(App, document.getElementById("app"))
</script>