<template>
  <div class="container">
    <div class="node-container">
      <div v-for="(item, index) in nodeList"
           :key="index"
           class="source-node"
           draggable="true"
           @dragstart="dragStart(item)">
        {{ item }}
      </div>
    </div>
    <div class="tree-container"
         @dragover="allowDrop"
         @drop="handleDrop">
      <tree-node v-if="nodeData"
                 ref="node"
                 :nodeData="nodeData"
                 @delete-node="deleteTree" />
    </div>
  </div>
</template>
<script>
import TreeNode from './treeNode.vue'
import { Node } from './config.js'
export default {
  name: 'vue-tree',
  components: {
    TreeNode
  },
  // 后代节点无法获取节点数据，即无法独立创建节点，所以将祖先节点的创建节点方法暴露给后代节点
  provide () {
    return {
      createNode: this.createNode
    }
  },
  data () {
    return {
      nodeList: ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'],
      currNode: null,
      nodeData: null
    }
  },
  methods: {
    // 开始拖拽，获取节点数据
    dragStart (item) {
      this.currNode = item
    },
    // 若未生成跟节点，则允许拖拽
    allowDrop (event) {
      if (!this.nodeData) {
        event.preventDefault()
      }
    },
    // 拖拽结束，生成节点
    handleDrop () {
      if (!this.nodeData) {
        this.nodeData = this.createNode()
      }
    },
    createNode () {
      let node = new Node(this.currNode)
      return node
    },
    // 根节点删除，删除整个树
    deleteTree () {
      this.nodeData = null
    }
  }
}
</script>
<style lang="scss" scoped>
.container {
  padding: 20px;
  width: calc(100% - 40px);
  height: calc(100% - 40px);
  .node-container {
    height: 100px;
    border: 1px dashed red;
    display: flex;
    .source-node {
      width: 50px;
      height: 30px;
      background: #fff;
      border: 1px solid blue;
      text-align: center;
      line-height: 30px;
      margin: 10px;
      cursor: pointer;
    }
  }
  .tree-container {
    height: calc(100% - 122px);
    margin-top: 20px;
  }
}
</style>

export class Node{
  constructor(name){
    this.name = name,
    this.children = []
  }
}

<template>
  <!-- 
    结构：最外层是node-inner，每个node-inner中有一个node与node-box，node存放当前节点，node-box存放当前节点的全部子节点，当前节点有几个子节点则node-box中就会有几个node-inner，以此循环
      <node-inner>
        <node></node>
        <node-box>
          <node-inner>
            <node></node>
            <node-box>...</node-box>
          </node-inner>
          <node-inner>
            <node></node>
            <node-box>...</node-box>
          </node-inner>
          ...
        </node-box>
      </node-inner>
   -->
  <div class="node-inner">
    <div class="node"
         :class="{ 'drag-over-node': isDragover }"
         @dragover="dragOver"
         @dragleave="dragLeave"
         @drop="nodeDrop">
      <span class="name">{{nodeData.name}}</span>
      <span class="del"
            @click="deleteNode">删除</span>
    </div>
    <div v-show="nodeData.children.length > 0"
         class="node-box">
      <tree-node v-for="(item,index) in nodeData.children"
                 :key="index"
                 :nodeData="item"
                 @delete-node="deleteChild(index)" />
    </div>
  </div>
</template>
<script>
export default {
  name: 'tree-node',
  props: {
    nodeData: {
      type: Object,
      default: () => { }
    }
  },
  // 获取祖先节点传递的数据
  inject: ['createNode'],
  data () {
    return {
      isDragover: false
    }
  },
  methods: {
    // 节点允许拖拽添加子节点
    dragOver (event) {
      event.preventDefault()
      if (!this.isDragover) {
        this.isDragover = true
      }
    },
    dragLeave () {
      if (this.isDragover) {
        this.isDragover = false
      }
    },
    // 为节点添加子节点
    nodeDrop () {
      let node = this.createNode()
      this.nodeData.children.push(node)
      this.isDragover = false
    },
    // 删除当前节点，本质是交给父级删除子节点
    deleteNode () {
      this.$emit("delete-node")
    },
    // 接收删除子节点的指令并执行删除功能
    deleteChild (index) {
      this.nodeData.children.splice(index, 1)
    }
  }
}
</script>
<style lang="scss" scoped>
.node {
  border: 1px solid orange;
  border-radius: 4px;
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: space-between;
  background-color: #fff;
  height: 36px;
  padding: 0 12px 0 16px;
  line-height: 36px;
  margin-bottom: 10px;
  .name {
    font-size: 16px;
    margin-right: 12px;
  }
  .del {
    color: red;
    font-size: 12px;
    cursor: pointer;
  }
  &.drag-over-node {
    box-shadow: 6px 6px 12px rgba(106, 20, 134, 0.15);
  }
}
.node-box {
  display: inline-flex;
  flex-direction: column;
  .node-inner {
    margin-left: 80px;
    // 连接竖条
    &:not(:last-child):before {
      position: absolute;
      left: -70px;
      top: 22px;
      border: 1px solid orange;
      content: "";
      width: 8px;
      background-color: #fff;
      border-bottom-color: #fff;
      height: 100%;
      border-top-color: #fff;
      z-index: 3;
    }
    // 连接横条
    &:after {
      left: -61px;
      width: 60px;
      content: "";
      position: absolute;
      top: 14px;
      height: 8px;
      border: 1px solid orange;
      content: "";
      background-color: #fff;
      border-right-color: #fff;
      border-left-color: #fff;
      z-index: 3;
    }
    // 最后一个竖条圆滑拐角
    &:nth-last-child(2):before {
      border-bottom-left-radius: 6px;
      border-bottom-color: orange;
    }
    // 第一个横条拉长
    &:first-child:after {
      left: -81px;
      width: 80px;
      z-index: 2;
    }
  }
}
.node-inner {
  position: relative;
}
</style>