//是否是第一次加載
let isMount = true;
//fiber 鏈表指針
let workInProgressHook = null;

//每個組件對應(yīng)一個fiber對象
let fiber = {
    //保存組件函數(shù)
    stateNode:App,
    //保存組件對應(yīng)的hooks 數(shù)據(jù)鏈表
    memoizedState:null

}

function useState(initialState){
    //生成一個hook 對象
    let hook;
    if(isMount){
       //第一次加載初始化hook對象
       hook = {
         memoizedState:initialState,
         next:null,
         queue:{
            pending:null
         }   
       }
       //當是第一個useState的時候     
       if(!fiber.memoizedState){
           fiber.memoizedState = hook;
       }else{
           //掛在到最后一個
            workInProgressHook.next = hook;
       }
       //移動指針到最后一個
       workInProgressHook = hook;
    }else{
        //更新阻星，非第一次加載
        //設(shè)置當前hook對象
        hook = workInProgressHook;
        //指針后移
        workInProgressHook = hook.next;
    }
    //獲取hook對應(yīng)的值
    let baseState = hook.memoizedState;

    //需要更新,環(huán)狀鏈表遍歷
    if(hook.queue.pending){
        // 獲取update環(huán)狀單向鏈表中第一個update
        let firstUpdate = hook.queue.pending.next;
        do {
            // 執(zhí)行update action
            const action = firstUpdate.action;
            baseState = action(baseState);
            firstUpdate = firstUpdate.next;
            // 最后一個update執(zhí)行完后跳出循環(huán)
          } while (firstUpdate !== hook.queue.pending.next);
    }
    //重新給hook 賦值
    hook.memoizedState = baseState;
    return [baseState,dispatchAction.bind(null,hook.queue)]

}

//memoizedState更新方法
function dispatchAction(queue,action){
    //創(chuàng)建要更新的鏈表(環(huán)狀)
     const update = {
         action:action,
         next:null
     }
     //與當前hook的操作對象queue關(guān)聯(lián)
     //當前hook沒有更新
     if(!queue.pending){
         //u0 -> u0
         update.next = update;
     }else{
         //u1 -> u0 ->u1
         update.next = queue.pending.next;
         queue.pending.next = update;
     }
     queue.pending = update;
    //模擬調(diào)度
    schedule();
}



//初始化調(diào)度render函數(shù)
function schedule(){
    //指針指到第一個節(jié)點
    workInProgressHook = fiber.memoizedState;
    isMount = false;
    //觸發(fā)組件render
    fiber.stateNode();
}






function App(){
    const [num,updateNum] = useState(0);
    const [num1,updateNum1] = useState(1);
    console.log(num,num1);
    return {
        click:()=>{
            updateNum(num=>num+1);
        }
    }
    
}
var test = App();
test.click();