<template>
  <div :ref="ref" class="dv-border-box-8-reverse">
    <svg class="dv-border-svg-container" :width="width" :height="height">
      <defs>
        <path
          :id="path"
          :d="pathD"
          fill="transparent"
        />
        <radialGradient
          :id="gradient"
          cx="50%"
          cy="50%"
          r="50%"
        >
          <stop
            offset="0%"
            stop-color="#fff"
            stop-opacity="1"
          />
          <stop
            offset="100%"
            stop-color="#fff"
            stop-opacity="0"
          />
        </radialGradient>

        <mask :id="mask">
          <circle cx="0" cy="0" r="150" :fill="`url(#${gradient})`">
            <animateMotion
              :dur="`${dur}s`"
              :path="pathD"
              rotate="auto"
              repeatCount="indefinite"
            />
          </circle>
        </mask>
      </defs>

      <polygon :fill="backgroundColor" :points="`5, 5 ${width - 5}, 5 ${width - 5} ${height - 5} 5, ${height - 5}`" />

      <use
        :stroke="mergedColor[0]"
        stroke-width="1"
        :xlink:href="`#${path}`"
      />

      <use
        :stroke="mergedColor[1]"
        stroke-width="3"
        :xlink:href="`#${path}`"
        :mask="`url(#${mask})`"
      >
        <animate
          attributeName="stroke-dasharray"
          :from="`0, ${length}`"
          :to="`${length}, 0`"
          :dur="`${dur}s`"
          repeatCount="indefinite"
        />
      </use>
    </svg>

    <div class="border-box-content">
      <slot />
    </div>
  </div>
</template>

<script>
export default {
  name: 'BorderBox8Reverse',
  props: {
    width: {
      type: Number,
      default: 0
    },
    height: {
      type: Number,
      default: 0
    }
  },
  data() {
    const id = new Date().getTime()
    return {
      ref: 'border-box-8-reverse',
      dur: 3,
      reverse: true,
      backgroundColor: 'transparent',
      mergedColor: ['#235fa7', '#4fd2dd'],
      path: `border-box-8-reverse-path-${id}`,
      gradient: `border-box-8-reverse-gradient-${id}`,
      mask: `border-box-8-reverse-mask-${id}`
    }
  },
  computed: {
    length() {
      const { width, height } = this
      return (width + height - 5) * 2
    },
    pathD() {
      const { reverse, width, height } = this
      if (reverse) return `M 2.5, 2.5 L 2.5, ${height - 2.5} L ${width - 2.5}, ${height - 2.5} L ${width - 2.5}, 2.5 L 2.5, 2.5`
      return `M2.5, 2.5 L${width - 2.5}, 2.5 L${width - 2.5}, ${height - 2.5} L2.5, ${height - 2.5} L2.5, 2.5`
    }
  }
}
</script>

<style lang="scss" scoped>
.dv-border-box-8-reverse {
  position: relative;
  width: 100%;
  height: 100%;

  .dv-border-svg-container {
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0px;
    top: 0px;
  }

  .border-box-content {
    position: relative;
    width: 100%;
    height: 100%;
  }
}
</style>
