ractive-ez-table/lib/Virtualization.js

Ractive Ez UI Table

import utils from './utils.js';

class Virtualization {
	
	constructor(viewport, labelHeight, itemHeight) {
		this._viewport = viewport;
		this._labelHeight = labelHeight;
		this._itemHeight = itemHeight;
	}
	
	getGroupsHeight(groups) {
		return groups.reduce((height, group) => height + this.getGroupHeight(group), 0);
	}
	
	getItemsHeight(items) {
		return items.length * this._itemHeight;
	}
	
	getItemHeight(item) {
		return this._itemHeight;
	}
	
	getGroupHeight(group) {
		const contentHeight = group.subGroups
			? this.getGroupsHeight(group.subGroups)
			: this.getItemsHeight(group.items);
			
		return this._labelHeight + contentHeight;
	}
	
	isVisible(top, height) {
		const vpBottom = this._viewport.top + this._viewport.height;
		const bottom = top + height;
		
		return top <= vpBottom
			&& bottom >= this._viewport.top;
	}
	
	virtualize(grouping, virtualizationEnabled, top = 0) {
		
		const visibleItems = [];
		let itemOffset = top;
		let groupingOffsetTop = top;
		let groupingOffsetBottom = 0;
		let skipMode = -1;
		
		const action = grouping.subGroups
			? group => this.virtualize(group, virtualizationEnabled, itemOffset + this._labelHeight)
			: item => item;
		const getHeight = grouping.subGroups 
			? group => this.getGroupHeight(group)
			: item => this.getItemHeight(item);
		const collection = grouping.subGroups
			? grouping.subGroups
			: grouping.items;
			
		if (!collection) return grouping;
		if (!collection.length) return grouping;
		
		for (let i = 0; i < collection.length; i++) {
			const item = collection[i];
			const itemHeight = getHeight(item);
			const itemVisible = (!virtualizationEnabled) || this.isVisible(itemOffset, itemHeight);
			
			if (itemVisible) visibleItems.push(action(item));
			
			if (skipMode == -1 && itemVisible) skipMode = 0;
			if (skipMode == 0 && !itemVisible) skipMode = 1;
			
			itemOffset += itemHeight;
			
			if (skipMode == -1) groupingOffsetTop += itemHeight;
			if (skipMode ==  1) groupingOffsetBottom += itemHeight;
		}
		
		grouping.top = groupingOffsetTop - top;
		grouping.bottom = groupingOffsetBottom;
		
		if (grouping.subGroups) {
			grouping.subGroups = visibleItems;
		} else {
			grouping.virtualItems = visibleItems;
		}
				
		return grouping;
		
	}
	
};

export default Virtualization;