<template>
    <div class="main-box">
        <button @click="add">添加</button>
        <div class="main-box-tab">
            <i @click="previous"><<</i>
            <i @click="next">>></i>
            <div class="main-box-tab-content" ref="tabs">
                <div class="main-box-tab-roll">
                    <div v-for="(item,index) in tabs" :key="index"
                         :class="{'tab-item-action':actionName === item.name ,'tab-item':actionName !== item.name}"
                         @click.stop="clickTab(item.name,index)">
                        <span>{{item.meta.title}}</span>
                        <i class="el-icon-close" @click.stop="close(item.name)"></i>
                    </div>
                </div>
            </div>
        </div>
        <div class="main-box-content">
            <div>{{actionName}}</div>
        </div>
    </div>
</template>
<script>
    export default {
        name: "index",
        data() {
            return {
                tabs: [],
                moveX: 0,
                count: 1,
                unoccupied: 0,
                tabsCount: 0,
                actionName: 'test1'
            }
        },
        watch: {
            actionName(val) {
                let len = this.tabs.length
                // 如有重复数据退出后续函数执行
                for (let i = 0; i < len; i++) {
                    if (this.tabs[i].name === val) {
                        this.$nextTick(() => {
                            this.translateX((i + 1 - this.tabsCount) * this.width - this.unoccupied)
                        })
                        return
                    }
                }

                this.tabs.push({
                    name: `test${this.count}`,
                    meta: {
                        title: `test${this.count}`
                    }
                })
                this.$nextTick(() => {
                  // (总共有多少个tabs - 未偏移时可见的元素个数) * 单个tab标签元素长度 - 被遮挡tab元素的可见部分的宽度
                    this.translateX((this.tabs.length - this.tabsCount) * this.width - this.unoccupied)
                })
            }
        },
        mounted() {
            this.tabs.push({
                name: `test${this.count}`,
                meta: {
                    title: `test${this.count}`
                }
            })
            this.$nextTick(() => {
                let tabs = this.$refs.tabs
                let getStyle = getComputedStyle(tabs.children[0].children[0], null)
                let marginLeft = parseFloat(getStyle.marginLeft.substr(0, getStyle.marginLeft.length - 2))
                let marginRight = parseFloat(getStyle.marginRight.substr(0, getStyle.marginRight.length - 2))
                // 元素实际宽度 = 元素的宽度 + 外边距
                this.width = marginLeft + marginRight + tabs.children[0].children[0].offsetWidth

                /**
                 * 以下注释计算方式用于理解实现逻辑
                 **/
                // // 可视区域能放入多少个元素 = 可视区域的宽度 / 子元素实际宽度
                // let num = tabs.offsetWidth / this.width

                // // 被遮挡tab元素的可见部分的宽度 = 可见区域的宽度 - (子元素实际宽度 * num转为整数)
                // this.unoccupied = tabs.offsetWidth - (this.width * parseInt(num))

                // 最终精简为取余（得数跟上面的计算是一样的）
                this.unoccupied = tabs.offsetWidth % this.width
                // 转为整数
                this.tabsCount = parseInt(tabs.offsetWidth / this.width)
            })
        },
        methods: {
            add() {
                this.count++
                this.actionName = `test${this.count}`
            },

            /**
             * 切换tab标签页
             **/
            clickTab(name) {
                if (this.actionName !== name) {
                    this.actionName = name
                }
            },

            /**
             * 关闭tab标签页
             **/
            close(name) {
                let len = this.tabs.length
                let jumpName = null
                if (len > 1) {
                    for (let i = 0; i < len; i++) {
                        if (this.tabs[i].name === name) {
                            this.tabs.splice(i, 1)

                            jumpName = this.tabs[i ? i - 1 : 0].name
                            if (this.actionName !== jumpName && name === this.actionName) {
                                this.actionName = jumpName
                            }

                            this.$nextTick(() => {
                                this.previous()
                            })
                            return
                        }
                    }
                }
            },

            /**
             * 往右偏移
             **/
            next() {
                // scrollWidth获取不准确
                // 使用this.width * this.tabs.length计算出总长度
                let totalWidth = this.width * this.tabs.length

                this.$nextTick(() => {
                    let dom = this.$refs.tabs
                    // 可视区域 < 滚动区域（滚动区域大于可视区域才可以移动）
                    // 移动距离 + 可视区域 = 滚动区域的宽度（上一次的宽度，当点击时才是实际宽度）< 滚动区域
                    if (dom.clientWidth < totalWidth && this.moveX + dom.clientWidth < totalWidth) {
                        // this.moveX为0减去空余空间的宽度
                        this.moveX += this.moveX ? this.width : this.width - this.unoccupied
                        this.translateX(this.moveX)
                    }
                })
            },

            /**
             * 往左偏移
             **/
            previous() {
                if (this.moveX > 0) {
                    this.moveX -= this.width
                    this.translateX(this.moveX)
                }
            },

            /**
             * 开始移动dom
             **/
            translateX(x) {
                this.moveX = x < 0 ? 0 : x
                this.$refs.tabs.children[0].style.transform = `translateX(-${this.moveX}px)`
            }
        }
    }
</script>

<style lang="scss" scoped>
    .main-box {
        height: 500px;
        width: 500px;
        padding: 10px 20px 20px 20px;

        .main-box-tab {
            position: relative;
            padding: 10px 20px;
            overflow: hidden;

            & > i {
                position: absolute;
                cursor: pointer;
                bottom: 15px;

                &:nth-child(1) {
                    left: 0;
                }

                &:nth-child(2) {
                    right: 0;
                }
            }

            .main-box-tab-content {
                overflow: hidden;

                .main-box-tab-roll {
                    transition: transform .5s;
                    display: flex;
                    align-items: center;

                    div {
                        flex-shrink: 0;
                        cursor: pointer;
                        width: 130px;
                        height: 25px;
                        margin: 0 5px;
                        display: flex;
                        align-items: center;
                        justify-content: space-between;

                        span, i {
                            font-size: 12px;
                        }

                        span {
                            margin-left: 10px;
                            overflow: hidden;
                            white-space: nowrap;
                            text-overflow: ellipsis;
                        }

                        i {
                            margin-right: 10px;
                        }
                    }
                }
            }

            .tab-item {
                color: #cccccc;
                background-color: rgba(255, 255, 255, .5);
                border-radius: 0 1px 0 1px;
                border: 1px solid #052141;
            }

            .tab-item-action {
                color: #ffffff;
                background: rgba(0, 180, 255, 0.8);
                border-radius: 0 1px 0 1px;
                border: 1px solid #1E2088;
            }

        }

        .main-box-content {
            height: calc(100% - 70px);
            padding: 10px;
            border: 1px saddlebrown solid;
            background-size: 100% 100%;
        }
    }
</style>