
<template>
	<view class="u-waterfall">
		<view id="u-left-column" class="u-column"><slot name="left" :leftList="leftList"></slot></view>
		<view id="u-right-column" class="u-column"><slot name="right" :rightList="rightList"></slot></view>
	</view>
</template>
<script>
export default {
	props: {
		value: {
			type: Array,
			required: true,
			default: function() {
				return [];
			}
		},
		addTime: {
			type: [Number, String],
			default: 200
		},
		idKey: {
			type: String,
			default: 'id'
		}
	},
	data() {
		return {
			leftList: [],
			rightList: [],
			tempList: [],
		}
	},
	watch: {
		copyFlowList(nVal, oVal) {
			let startIndex = Array.isArray(oVal) && oVal.length > 0 ? oVal.length : 0;
			this.tempList = this.tempList.concat(this.cloneData(nVal.slice(startIndex)));
			this.splitData();
		}
	},
	mounted() {
		this.tempList = this.cloneData(this.copyFlowList);
		this.splitData();
	},
	computed: {
		copyFlowList() {
			return this.cloneData(this.value);
		}
	},
	methods: {
		async splitData() {
			if (!this.tempList.length) return;
			let leftRect = await this.$uGetRect('#u-left-column');
			let rightRect = await this.$uGetRect('#u-right-column');
			// 如果左边小于或等于右边，就添加到左边，否则添加到右边
			let item = this.tempList[0];
			if(!item) return;
			if (leftRect.height < rightRect.height) {
				this.leftList.push(item);
			} else if (leftRect.height > rightRect.height) {
				this.rightList.push(item);
			} else {
				// 这里是为了保证第一和第二张添加时，左右都能有内容
				// 因为添加第一张，实际队列的高度可能还是0，这时需要根据队列元素长度判断下一个该放哪边
				if (this.leftList.length <= this.rightList.length) {
					this.leftList.push(item);
				} else {
					this.rightList.push(item);
				}
			}
			// 移除临时列表的第一项
			this.tempList.splice(0, 1);
			// 如果临时数组还有数据，继续循环
			if (this.tempList.length) {
				setTimeout(() => {
					this.splitData();
				}, this.addTime)
			}
		},
		cloneData(data) {
			return JSON.parse(JSON.stringify(data));
		}
	}
}
</script>
 
<style lang="scss" scoped>
 
.u-waterfall {
	display: flex;
	flex-direction: row;
	align-items: flex-start;
}
 
.u-column {
	display: flex;
	flex: 1;
	flex-direction: column;
	height: auto;
}
 
.u-image {
	width: 100%;
}
</style>