<!-- tab组件: <me-tabs v-model="tabIndex" :tabs="tabs" @change="tabChange"></me-tabs> -->
<template>
	<view class="me-tabs bg-white" :class="{'tabs-fixed': fixed}" :style="{height: tabHeightVal}">
		<scroll-view v-if="tabs.length" :id="viewId" :scroll-left="scrollLeft" scroll-x scroll-with-animation
		 :scroll-animation-duration="300">
			<view class="tabs-item" :class="{'tabs-flex':!isScroll, 'tabs-scroll':isScroll}">
				<!-- tab -->
				<view class="tab-item lf-font-28" :style="{width: tabWidthVal, height: tabHeightVal1, 'line-height':tabHeightVal1}" v-for="(tab, i) in tabs"
				 :class="{'active': value===i}" :key="i" @click="tabClick(i)">
					{{getTabName(tab)}}
				</view>
				<!-- 下划线 -->
				<view class="tabs-line" :style="{left:lineLeft}"></view>
			</view>
		</scroll-view>
	</view>
</template>

<script>
	export default {
		props: {
			tabs: { // 支持格式: ['全部', '待付款'] 或 [{name:'全部'}, {name:'待付款'}]
				type: Array,
				default () {
					return []
				}
			},
			nameKey: { // 取name的字段
				type: String,
				default: 'name'
			},
			value: { // 当前显示的下标 (使用v-model语法糖: 1.props需为value; 2.需回调input事件)
				type: [String, Number],
				default: 0
			},
			fixed: Boolean, // 是否悬浮,默认false
			tabWidth: Number, // 每个tab的宽度,默认不设置值,为flex平均分配; 如果指定宽度,则不使用flex,每个tab居左,超过则水平滑动(单位默认rpx)
			height: { // 高度,单位rpx
				type: Number,
				default: 60
			}
		},
		data() {
			return {
				viewId: 'id_' + Math.random().toString(36).substr(2, 16),
				scrollLeft: 0
			}
		},
		computed: {
			isScroll() {
				return this.tabWidth && this.tabs.length // 指定了tabWidth的宽度,则支持水平滑动
			},
			tabHeightPx() {
				return uni.upx2px(this.height)
			},
			tabHeightPx1() {
				return uni.upx2px(60)
			},
			tabHeightVal() {
				return this.tabHeightPx + 'px'
			},
			tabHeightVal1() {
				return this.tabHeightPx1 + 'px'
			},
			tabWidthPx() {
				return uni.upx2px(this.tabWidth)
			},
			tabWidthVal() {
				return this.isScroll ? this.tabWidthPx + 'px' : ''
			},
			lineLeft() {
				if (this.isScroll) {
					return this.tabWidthPx * this.value + this.tabWidthPx / 2 + 'px' // 需转为px (用rpx的话iOS真机显示有误差)
				} else {
					return 100 / this.tabs.length * (this.value + 1) - 100 / (this.tabs.length * 2) + '%'
				}
			}
		},
		watch: {
			tabs() {
				this.warpWidth = null; // 重新计算容器宽度
				this.scrollCenter(); // 水平滚动到中间
			},
			value() {
				this.scrollCenter(); // 水平滚动到中间
			}
		},
		methods: {
			getTabName(tab) {
				return typeof tab === "object" ? tab[this.nameKey] : tab
			},
			tabClick(i) {
				if (this.value != i) {
					this.$emit("input", i);
					this.$emit("change", i);
				}
			},
			async scrollCenter() {
				if (!this.isScroll) return;
				if (!this.warpWidth) { // tabs容器的宽度
					let rect = await this.initWarpRect()
					this.warpWidth = rect ? rect.width : uni.getSystemInfoSync().windowWidth; // 某些情况下取不到宽度,暂时取屏幕宽度
				}
				let tabLeft = this.tabWidthPx * this.value + this.tabWidthPx / 2; // 当前tab中心点到左边的距离
				let diff = tabLeft - this.warpWidth / 2 // 如果超过tabs容器的一半,则滚动差值
				this.scrollLeft = diff;
				// #ifdef MP-TOUTIAO
				this.scrollTimer && clearTimeout(this.scrollTimer)
				this.scrollTimer = setTimeout(() => { // 字节跳动小程序,需延时再次设置scrollLeft,否则tab切换跨度较大时不生效
					this.scrollLeft = Math.ceil(diff)
				}, 400)
				// #endif
			},
			initWarpRect() {
				return new Promise(resolve => {
					setTimeout(() => { // 延时确保dom已渲染, 不使用$nextclick
						let query = uni.createSelectorQuery();
						// #ifndef MP-ALIPAY
						query = query.in(this) // 支付宝小程序不支持in(this),而字节跳动小程序必须写in(this), 否则都取不到值
						// #endif
						query.select('#' + this.viewId).boundingClientRect(data => {
							resolve(data)
						}).exec();
					}, 20)
				})
			}
		},
		mounted() {
			this.scrollCenter() // 滚动到当前下标
		}
	}
</script>

<style lang="scss">
	.me-tabs {
		position: relative;
		box-sizing: border-box;
		overflow-y: hidden;
		background-color: #FE9903;
		border-radius: 18rpx;
		// box-shadow: 0 0.06rem 0.3rem rgba(0, 0, 0, .1);

		&.tabs-fixed {
			width: 100%;
		}

		.tabs-item {
			margin:0 4rpx;
			border-radius: 16px;
			display: flex;
			position: relative;
			white-space: nowrap;
			padding-bottom: 30rpx; // 撑开高度,再配合me-tabs的overflow-y: hidden,以达到隐藏滚动条的目的
			box-sizing: border-box;

			&::after {
				position: absolute;
				bottom: 31rpx;
				left: 0;
				width: 100%;
				height: 1rpx;
				content: '';
				// border-bottom: 1rpx solid rgba(255, 255, 255, 0.2);
			}

			.tab-item {
				flex: 1;
				position: relative;
				text-align: center;
				box-sizing: border-box;
				color: white;

				&.active {
					// font-weight: bold;
					color: black;
					background-color: white;
					border-radius: 14rpx;
					height: 26px!important;
					line-height: 26px!important;
				}
			}
		}

		// 平分的方式显示item
		.tabs-flex {
			display: flex;
			align-items: center;
			.tab-item {
				flex: 1;
				background-color: #FE9903;
			}
		}

		// 居左显示item,支持水平滑动
		.tabs-scroll {
			.tab-item {
				display: inline-block;
			}
		}

		// 选中tab的线
		.tabs-line {
			z-index: 1;
			position: absolute;
			bottom: 30rpx; // 至少与.tabs-item的padding-bottom一致,才能保证在底部边缘
			width: 100rpx;
			height: 5rpx;
			transform: translateX(-50%);
			border-radius: 4rpx;
			transition: left .3s;
			// background: red;
		}
	}
</style>
