<template>
    <el-color-picker
      v-model="theme"
      :predefine="['#409EFF', '#1890ff', '#304156','#212121','#11a983', '#13c2c2', '#6959CD', '#f5222d', ]"
      class="theme-picker"
      popper-class="theme-picker-dropdown"
    />
  </template>
  
  <script>
  const version = require('element-ui/package.json').version // element-ui version from node_modules
  const ORIGINAL_THEME = '#409EFF' // default color
  
  export default {
    data() {
      return {
        chalk: '', // content of theme-chalk css
        theme: ''
      }
    },
    computed: {
      defaultTheme() {
        return this.$store.state.settings.theme
      }
    },
    watch: {
      defaultTheme: {
        handler: function(val, oldVal) {
          this.theme = val
        },
        immediate: true
      },
      async theme(val) {
        const oldVal = this.chalk ? this.theme : ORIGINAL_THEME
        if (typeof val !== 'string') return
        const themeCluster = this.getThemeCluster(val.replace('#', ''))
        const originalCluster = this.getThemeCluster(oldVal.replace('#', ''))
        console.log(themeCluster, originalCluster)
  
        const $message = this.$message({
          message: '  Compiling the theme',
          customClass: 'theme-message',
          type: 'success',
          duration: 0,
          iconClass: 'el-icon-loading'
        })
  
        const getHandler = (variable, id) => {
          return () => {
            const originalCluster = this.getThemeCluster(ORIGINAL_THEME.replace('#', ''))
            const newStyle = this.updateStyle(this[variable], originalCluster, themeCluster)
  
            let styleTag = document.getElementById(id)
            if (!styleTag) {
              styleTag = document.createElement('style')
              styleTag.setAttribute('id', id)
              document.head.appendChild(styleTag)
            }
            styleTag.innerText = newStyle
          }
        }
  
        if (!this.chalk) {
          const url = `https://unpkg.com/element-ui@${version}/lib/theme-chalk/index.css`
          await this.getCSSString(url, 'chalk')
        }
  
        const chalkHandler = getHandler('chalk', 'chalk-style')
  
        chalkHandler()
  
        const styles = [].slice.call(document.querySelectorAll('style'))
          .filter(style => {
            const text = style.innerText
            return new RegExp(oldVal, 'i').test(text) && !/Chalk Variables/.test(text)
          })
        styles.forEach(style => {
          const { innerText } = style
          if (typeof innerText !== 'string') return
          style.innerText = this.updateStyle(innerText, originalCluster, themeCluster)
        })
  
        this.$emit('change', val)
  
        $message.close()
      }
    },
  
    methods: {
      updateStyle(style, oldCluster, newCluster) {
        let newStyle = style
        oldCluster.forEach((color, index) => {
          newStyle = newStyle.replace(new RegExp(color, 'ig'), newCluster[index])
        })
        return newStyle
      },
  
      getCSSString(url, variable) {
        return new Promise(resolve => {
          const xhr = new XMLHttpRequest()
          xhr.onreadystatechange = () => {
            if (xhr.readyState === 4 && xhr.status === 200) {
              this[variable] = xhr.responseText.replace(/@font-face{[^}]+}/, '')
              resolve()
            }
          }
          xhr.open('GET', url)
          xhr.send()
        })
      },
  
      getThemeCluster(theme) {
        const tintColor = (color, tint) => {
          let red = parseInt(color.slice(0, 2), 16)
          let green = parseInt(color.slice(2, 4), 16)
          let blue = parseInt(color.slice(4, 6), 16)
  
          if (tint === 0) { // when primary color is in its rgb space
            return [red, green, blue].join(',')
          } else {
            red += Math.round(tint * (255 - red))
            green += Math.round(tint * (255 - green))
            blue += Math.round(tint * (255 - blue))
  
            red = red.toString(16)
            green = green.toString(16)
            blue = blue.toString(16)
  
            return `#${red}${green}${blue}`
          }
        }
  
        const shadeColor = (color, shade) => {
          let red = parseInt(color.slice(0, 2), 16)
          let green = parseInt(color.slice(2, 4), 16)
          let blue = parseInt(color.slice(4, 6), 16)
  
          red = Math.round((1 - shade) * red)
          green = Math.round((1 - shade) * green)
          blue = Math.round((1 - shade) * blue)
  
          red = red.toString(16)
          green = green.toString(16)
          blue = blue.toString(16)
  
          return `#${red}${green}${blue}`
        }
  
        const clusters = [theme]
        for (let i = 0; i <= 9; i++) {
          clusters.push(tintColor(theme, Number((i / 10).toFixed(2))))
        }
        clusters.push(shadeColor(theme, 0.1))
        return clusters
      }
    }
  }
  </script>
  
  <style>
  .theme-message,
  .theme-picker-dropdown {
    z-index: 99999 !important;
  }
  
  .theme-picker .el-color-picker__trigger {
    height: 26px !important;
    width: 26px !important;
    padding: 2px;
  }
  
  .theme-picker-dropdown .el-color-dropdown__link-btn {
    display: none;
  }
  </style>