//针对阿里小程序Scroll控件定制的补充事件的插件类
//阿里小程序要求Scroll控件内必须有一个class为scroll-list的元素，这里我们的插件对scroll-list也有一定要求，scroll-list相对于父级元素不要有高度的padding或margin的情况，否则
//会导致滚动计算不准确导致无法命中事件的情况

class ScrollEventPlugin {
    constructor() {
		this.eventLock = false;
		this.widget = null;
		this.dom = null;

    this.onToBottomCallback = null;
    this.onToTopCallback = null;
	}

    bind(widget){
        this.widget = widget;
        this.dom = widget.con;
        this.widget.on('scrollend', ()=>{
            if(this.eventLock) { return; }

            let wTop = this.dom.getElementsByClassName('scroll-list')[0].style.top;
            wTop = parseFloat(wTop.replace('px' , ''));

            let scrollHeight = this.dom.clientHeight;
            let listHeight = this.dom.getElementsByClassName('scroll-list')[0].clientHeight;
            let maxOffset = listHeight - scrollHeight;

            if(wTop == 0 && this.onToTopCallback){
                this.onToTopCallback();
                this.eventLock = true;
                return;
            }

            if(wTop == maxOffset * -1 && this.onToBottomCallback){
                this.onToBottomCallback();
                this.eventLock = true;
            }
        });
    }

    onScrollToBottom(callback){
        this.onToBottomCallback = callback;
    }

    onScrollToTop(callback){
        this.onToTopCallback = callback;
    }

    releaseEventLock(){
	    this.eventLock = false;
    }
}

module.exports = ScrollEventPlugin;