/* src/styles/element-variables.scss */

/* 改變主題色變量 */
$--color-primary: #256DCB;
$--color-success: #7AC800;
$--color-danger: #EC4242;
$--color-info: #999999;

/* 改變 icon 字體路徑變量，必需 */
$--font-path: '~element-ui/lib/theme-chalk/fonts';

@import "~element-ui/packages/theme-chalk/src/index";

/* 如遇到導(dǎo)出的變量值為 undefined 則本文件名需要改成 element-variables.module.scss */
:export {
  theme: $--color-primary
}

/* main.js */

import Vue from 'vue'
import Element from 'element-ui'
import './element-variables.scss'
 
Vue.use(Element)

/* src/store/modules/settings.js */

import variables from '@/styles/element-variables.module.scss'
import * as Types from '../mutation-types'

const state = {
  theme: variables.theme
}

const mutations = {
  CHANGE_SETTING: (state, { key, value }) => {
    localStorage.setItem('theme', value) // 緩存起來(lái)，刷新的時(shí)候重新取用
    // eslint-disable-next-line no-prototype-builtins
    if (state.hasOwnProperty(key)) {
      state[key] = value
    }
  }
}

const actions = {
  changeSetting ({ commit }, data) {
    commit('CHANGE_SETTING', data)
  }
}

export default {
  namespaced: true,
  state,
  mutations,
  actions
}

/* src/components/ThemePicker/index.vue */

<template>
  <el-color-picker
    v-model="theme"
    :predefine="['#256DCB', '#409EFF', '#1890ff', '#304156','#212121','#11a983', '#13c2c2', '#6959CD', '#f5222d', '#F80', ]"
    class="theme-picker"
    popper-class="theme-picker-dropdown"
  />
</template>

<script>

import { chalkCss } from './chalk.js' // 就是 getCSSString 接口中獲取的 css，這里我將版本號(hào)固定并且把 css 緩存到本地，記得處理 \ 轉(zhuǎn)義問(wèn)題

// const version = require('element-ui/package.json').version // element-ui version from node_modules
const ORIGINAL_THEME = '#409EFF' // default color  chalk.js 中的 primary color，根據(jù)此顏色計(jì)算出一系列顏色進(jìn)行正則替換

export default {
  name: 'ThemePicker',
  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: this.$t('theme_compiling'),
        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')
        this.chalk = chalkCss.replace(/@font-face{[^}]+}/, '') // 本地緩存，如果需要獲取線上的就用上面那種方式，優(yōu)點(diǎn)：切換無(wú)延遲，缺點(diǎn)：需要手動(dòng)維護(hù) css string
      }

      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>

// template
<theme-picker @change="themeChange" />
// js
import ThemePicker from '@/components/ThemePicker'
// methods
themeChange (val) {
  this.$store.dispatch('settings/changeSetting', {
    key: 'theme',
    value: val
  })
}

/* src/App.vue */

<template>
  <div id="app" :style="{'--color': defaultTheme}">
    <theme-picker @change="themeChange" v-show="false" />
    <router-view />
  </div>
</template>

<script>
import ThemePicker from '@/components/ThemePicker'

export default {
  name: 'App',
  components: { ThemePicker },
  computed: {
    defaultTheme () {
      return this.$store.state.settings.theme
    }
  },
  mounted () {
    if (localStorage.getItem('theme')) {
      this.themeChange(localStorage.getItem('theme'))
    }
  },
  methods: {
    themeChange (val) {
      this.$store.dispatch('settings/changeSetting', {
        key: 'theme',
        value: val
      })
    }
  }
}
</script>

<div class="box"></div>

.box {
  width: 100px;
  height: 100px;
  background-color: var(--color);
}