<template>
  <div class="hue">
    <div 
      class="hue-container"
      ref="hueRef"
      @mousedown="$event => handleMouseDown($event)"
    >
      <div 
        class="hue-pointer"
        :style="{ left: pointerLeft }"
      >
        <div class="hue-picker"></div>
      </div>
    </div>
  </div>
</template>

<script lang="ts">
import { computed, defineComponent, onUnmounted, PropType, ref, watch } from 'vue'
import tinycolor, { ColorFormats } from 'tinycolor2'

export default defineComponent({
  name: 'hue',
  props: {
    value: {
      type: Object as PropType<ColorFormats.RGBA>,
      required: true,
    },
    hue: {
      type: Number,
      required: true,
    },
  },
  setup(props, { emit }) {
    const oldHue = ref(0)
    const pullDirection = ref('')
    
    const color = computed(() => {
      const hsla = tinycolor(props.value).toHsl()
      if(hsla.s === 0) hsla.h = props.hue
      return hsla
    })

    const pointerLeft = computed(() => {
      if(color.value.h === 0 && pullDirection.value === 'right') return '100%'
      return color.value.h * 100 / 360 + '%'
    })

    watch(() => props.value, () => {
      const hsla = tinycolor(props.value).toHsl()
      const h = hsla.s === 0 ? props.hue : hsla.h
      if(h !== 0 && h - oldHue.value > 0) pullDirection.value = 'right'
      if(h !== 0 && h - oldHue.value < 0) pullDirection.value = 'left'
      oldHue.value = h
    })

    const hueRef = ref<HTMLElement>()
    const handleChange = (e: MouseEvent) => {
      e.preventDefault()
      if(!hueRef.value) return

      const containerWidth = hueRef.value.clientWidth
      const xOffset = hueRef.value.getBoundingClientRect().left + window.pageXOffset
      const left = e.pageX - xOffset
      let h, percent
      
      if(left < 0) h = 0
      else if(left > containerWidth) h = 360
      else {
        percent = left * 100 / containerWidth
        h = (360 * percent / 100)
      }
      if(color.value.h !== h) {
        emit('change', {
          h,
          l: color.value.l,
          s: color.value.s,
          a: color.value.a,
        })
      }
    }

    const unbindEventListeners = () => {
      window.removeEventListener('mousemove', handleChange)
      window.removeEventListener('mouseup', unbindEventListeners)
    }
    const handleMouseDown = (e: MouseEvent) => {
      handleChange(e)
      window.addEventListener('mousemove', handleChange)
      window.addEventListener('mouseup', unbindEventListeners)
    }

    onUnmounted(unbindEventListeners)

    return {
      hueRef,
      handleMouseDown,
      pointerLeft,
    }
  },
})
</script>

<style lang="scss" scoped>
.hue {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background: linear-gradient(to right, #f00 0%, #ff0 17%, #0f0 33%, #0ff 50%, #00f 67%, #f0f 83%, #f00 100%);
}
.hue-container {
  cursor: pointer;
  margin: 0 2px;
  position: relative;
  height: 100%;
}
.hue-pointer {
  z-index: 2;
  position: absolute;
  top: 0;
}
.hue-picker {
  cursor: pointer;
  margin-top: 1px;
  width: 4px;
  height: 8px;
  box-shadow: 0 0 2px rgba(0, 0, 0, .6);
  background: #fff;
  transform: translateX(-2px);
}
</style>