<template>
 <div class="transition-container">
   <div class="item" v-for="(item, index) in items" :key="index"
    draggable="true"
    @dragstart="handleDragStart($event, item)"
    @dragover.prevent="handleDragOver($event, item)"
    @dragenter="handleDragEnter($event, item)"
    @dragend="handleDragEnd($event, item)" 
    @click="chooseNav(item)"
    >
    <p class="trans-btn">
     <span v-if="item.problemId">
      <b class="id">
        {{item.problemId}}
      </b>
       {{item.key}}
     </span>
     <span v-else>
       {{item.key}}
     </span>
     <span>
      <i-button v-if="btn" size="small" type="error" style="margin-right: 10px;" @click="deleteItem(item, index)">删除</i-button>
     </span>
    </p>
   </div>
 </div>
</template>
<script>
import './index.less';

export default {
  name: 'transition',
  props: {
    dataSource: Array,
    btn: Boolean,
  },
  data() {
    return {
      items: [],
      dragging: null,
    };
  },
  watch: {
    dataSource(val) {
      this.items = val;
    },
    dragging(val) {
      if (this.dataSource.includes(val)) {
        this.dragging = val;
      } else {
        this.dragging = null;
      }
    },
  },
  methods: {
    handleDragStart(e, item) {
      this.dragging = item;
    },
    handleDragEnd() {
      this.dragging = null;
      this.$emit('hasChanged', this.items);
    },
    // 首先把div变成可以放置的元素，即重写dragenter/dragover
    handleDragOver(e) {
      e.dataTransfer.dropEffect = 'move';// e.dataTransfer.dropEffect="move";//在dragenter中针对放置目标来设置!
    },
    handleDragEnter(e, item) {
      if (this.dragging) {
        e.dataTransfer.effectAllowed = 'move';// 为需要移动的元素设置dragstart事件
        if (item === this.dragging) {
          return;
        }
        const newItems = [...this.items];
        console.log(newItems);
        const src = newItems.indexOf(this.dragging);
        const dst = newItems.indexOf(item);
        newItems.splice(dst, 0, ...newItems.splice(src, 1));
        this.items = newItems;
      }
    },
    chooseNav(val) {
      this.$emit('selectItem', val);
    },
    deleteItem(item, index) {
      this.$emit('deleteItem', item, index);
    },
    editor(item, index) {
      this.$emit('editorItem', item, index);
    },
  },
};
</script>