import UI_ListItem from "./UI_ListItem";

export default class VirtualList{
    constructor(){}
    private scroll:cc.ScrollView;
    /**不能使用layout */
    private itemContainer:cc.Node;
    private mListData:any[];
    private viewPortItemCount:number;
    private copyeeItem:cc.Node;
    private viewPortFirstItem: cc.Node = null;

    initVirtualList(viewCount:number,listDatas:any[],itemContainer:cc.Node,scroller:cc.ScrollView,
        copyItem:cc.Node) {
        
        this.scroll = scroller;
        this.itemContainer = itemContainer;
        this.mListData = listDatas;
        this.viewPortItemCount = viewCount;
        this.copyeeItem = copyItem;

        let _data = listDatas.slice(0, viewCount + 1);
        this.addVirtualItems(_data,copyItem,itemContainer);
        this.viewPortFirstItem = itemContainer.children[0];

        scroller.node.on("scrolling", this.onScrolling, this);
    }

    private addVirtualItems(data: any[],copyItem:cc.Node,itemContainer:cc.Node) {
        let _itemHeight:number = copyItem.height;
        let _len = data.length;
        for (let i = 0; i < _len; i++) {
            let _item = cc.instantiate(copyItem);
            _item.y = -_itemHeight*i;
            let _dataItem = data[i];
            let _itemCls = _item.getComponent(UI_ListItem);
            _itemCls.showInfo(_dataItem);
            _itemCls.itemData = _dataItem;

            itemContainer.addChild(_item);
        }
    }

    onScrolling() {
        this.calcPosAndSwapItem();
    }
    
    calcPosAndSwapItem() {
        let _itemData = this.viewPortFirstItem.getComponent(UI_ListItem).itemData;
        let _offsetY = this.scroll.getScrollOffset().y;
        let _idx: number = _itemData["_list_idx_"];
        if (_offsetY > this.viewPortFirstItem.height
            ) {
            let _lastItem = this.itemContainer.children[this.itemContainer.childrenCount - 1];
            let _nextDataIdx: number = _lastItem.getComponent(UI_ListItem).itemData["_list_idx_"]+1;
            if (_nextDataIdx < this.mListData.length) {
                this.swapItem(0,_nextDataIdx, true);
            }
        } else if (_offsetY < 0
            ) {
            if (_idx > 0) {
                this.swapItem(this.viewPortItemCount, _idx-1,false);
            }
        }
    }
    
    swapItem(deleteBeginIdx: number,dataIdx:number, isToEnd: boolean = false) {
        let _el = this.itemContainer.children[deleteBeginIdx];
        let _top: number = 0;
        if (_el) {
            let _insertIdx: number = isToEnd ? this.viewPortItemCount : 0;

            let _itemData = this.mListData[dataIdx];
            _el.getComponent(UI_ListItem).showInfo(_itemData);

            this.itemContainer.insertChild(_el, _insertIdx);
            
            this.refreshItemsY();
            _top = isToEnd ? 0 : _el.height;
            this.scroll.setContentPosition(new cc.Vec2(0, _top));
            this.viewPortFirstItem = this.itemContainer.children[0];
        }
    }

    refreshItemsY(){
        this.itemContainer.children.forEach((item,idx)=>{
            item.y = -idx * this.copyeeItem.height;

        })
    }
}