// clientX 鼠标相对于浏览器左上角x轴的坐标； 不随滚动条滚动而改变；
// clientY 鼠标相对于浏览器左上角y轴的坐标； 不随滚动条滚动而改变；
// element.offsetTop 指 element距离上方或上层控件的位置，整型，单位像素。
// element.offsetLeft 指 element距离左方或上层控件的位置，整型，单位像素。
// element.offsetWidth 指 element控件自身的宽度，整型，单位像素。
// element.offsetHeight 指 element控件自身的高度，整型，单位像素。
//  clientHeigh = height + 上下padding
//   clientWidth = width+左右padding

<template>
  <div class="to-do-list" ref="parentBox">
    <div class="search-title">
      <h1 class="add-bold left-box" style="margin-left:35px">
        <a-icon type="unordered-list" style="margin-right: 10px;" />元素拖动
      </h1>
    </div>
    <a-button ref="moveBtn" style="width: 100px;height: 40px;transition:none" class="move-btn" type="primary"
      >拖动按钮</a-button
    >
  </div>
</template>

<script lang="ts">
import { Component, Emit, Inject, Prop, Ref, Vue, Watch } from 'vue-property-decorator';

@Component({
  components: {},
})
export default class BriberyInformation extends Vue {
  @Ref() readonly moveBtn;
  @Ref() readonly parentBox;

  btnDown() {
    let box = this.moveBtn.$el; //获取button的盒子dom元素
    let parentBox = this.parentBox; //获取button父级元素的dom元素
    let parentH = parentBox.clientHeight; //获取button父级元素的height
    let parentW = parentBox.clientWidth; //获取button父级元素的width

    let x, y;
    let moveX, moveY; //移动距离
    let maxX, maxY; //最大移动距离
    let isDrop = false;

    box.onmousedown = e => {
      x = e.clientX - box.offsetLeft; // e.clientX鼠标相对于浏览器左上角x轴的坐标-button上层控件的位置
      y = e.clientY - box.offsetTop;
      isDrop = true;
    };
    document.onmousemove = e => {
      if (isDrop) {
        e.preventDefault();
        moveX = e.clientX - x; //得到距离左边移动距离
        moveY = e.clientY - y; //得到距离上边移动距离

        //可移动最大距离
        maxX = parentW - box.offsetWidth;
        maxY = parentH - box.offsetHeight;

        //移动的有效距离计算
        //console.log(Math.min(-1, 4, 6, 12));//输出-1-----多个参数，返回最小值
        moveX = Math.min(maxX, Math.max(0, moveX));

        moveY = Math.min(maxY, Math.max(0, moveY));
        box.style.left = moveX + 'px';
        box.style.top = moveY + 'px';
      } else {
        return;
      }
    };
    document.onmouseup = e => {
      e.preventDefault();
      isDrop = false;
    };
  }

  mounted() {
    this.btnDown();
  }
}
</script>
<style scoped lang="less">
.to-do-list {
  position: relative;
  min-height: 600px;
  max-height: 600px;
  width: 600px;
  overflow: hidden;
  border: 2px solid black;
  .move-btn {
    position: absolute;
  }
}
</style>