/**
 * 边滚动边加载的列表控件
 *
 * Created by GUY on 2017/5/23.
 * @class BI.ListView
 * @extends BI.Widget
 */
import { Widget, shortcut } from "../../core";
@shortcut()
export class ListView extends Widget {
  props() {
    return {
        baseCls: "bi-list-view",
        overscanHeight: 100,
        blockSize: 10,
        scrollTop: 0,
        el: {},
        items: [],
        itemFormatter: (item, index) => {
            return item;
        },
    };
  }

  init() {
      this.renderedIndex = -1;
      this.cache = {};
  }

  static xtype = "bi.list_view";

  render() {
      const { el } = this.options;

      return {
          type: "bi.vertical",
          items: [BI.extend({
              type: "bi.vertical",
              scrolly: false,
              ref: (_ref) => {
                  this.container = _ref;
              },
          }, el)],
          element: this,
      };
  }

  // mounted之后绑定事件
  mounted() {
    const o = this.options;
    //  这里无法进行结构，因为存在赋值操作，如果使用结构则this.options的值不会跟随变化
    o.items = BI.isFunction(o.items) ? this.__watch(o.items, (context, newValue) => {
        this.populate(newValue);
    }) : o.items;
    this._populate();
    this.element.scroll((e) => {
        o.scrollTop = this.element.scrollTop();
        this._calculateBlocksToRender();
    });
    let lastWidth = this.element.width(),
        lastHeight = this.element.height();
    BI.ResizeDetector.addResizeListener(this, () => {
        if (!this.element.is(":visible")) {
            return;
        }
        const width = this.element.width(),
            height = this.element.height();
        if (width !== lastWidth || height !== lastHeight) {
            lastWidth = width;
            lastHeight = height;
            this._calculateBlocksToRender();
        }
    });
  }

  _renderMoreIf() {
    const { scrollTop, overscanHeight, blockSize, items, itemFormatter } = this.options;
    const height = this.element.height();
    const minContentHeight = scrollTop + height + overscanHeight;
    let index = (this.cache[this.renderedIndex] && (this.cache[this.renderedIndex].index + blockSize)) || 0;
    let cnt = this.renderedIndex + 1;
    let lastHeight;

    const getElementHeight = () => {
      return this.container.element.height();
    }

    lastHeight = getElementHeight();
    while ((lastHeight) < minContentHeight && index < items.length) {
        const itemsArr = items.slice(index, index + blockSize);
        this.container.addItems(itemsArr.map((item, i) => {
            return itemFormatter(item, index + i);
        }), this);
        const addedHeight = getElementHeight() - lastHeight;
        this.cache[cnt] = {
            index: index,
            scrollTop: lastHeight,
            height: addedHeight,
        };
        this.renderedIndex = cnt;
        cnt++;
        index += blockSize;
        lastHeight = getElementHeight();
    }
  }
  _calculateBlocksToRender() {
    // BI-115750 不可见状态下依赖元素实际尺寸构造的线段树会分段错误，所以不进行后续计算和线段树的初始化。
    // 这样从不可见状态变为可见状态能够重新触发线段树初始化
    if (!this.element.is(":visible")) {
        return;
    }
    this._renderMoreIf();
  }

  _populate(items) {
      const { scrollTop } = this.options;
      if (items && this.options.items !== items) {
          this.options.items = items;
      }
      this._calculateBlocksToRender();
      this.element.scrollTop(scrollTop);
  }

  restore() {
      this.renderedIndex = -1;
      this.container.empty();
      this.cache = {};
  }

  scrollTo(scrollTop) {
    this.options.scrollTop = scrollTop;
    this._calculateBlocksToRender();
    this.element.scrollTop(scrollTop);
  }

  populate(items) {
    if (items && this.options.items !== items) {
      this.restore();
    }
    this._populate(items);
  }

  beforeDestroy() {
    BI.ResizeDetector.removeResizeListener(this);
    this.restore();
  }

}