<div id="app">
  <div class="btn-container" :style="{'backgroundColor': selectedBgColor}">
    <div v-for="(button, index) in buttons" 
         :key="index" :ref="`button_${index}`"
         @click="selectButton(index)"
         class="btn">
      <i :class="['fas', `fa-${button.icon}`]"></i>
    </div>
  </div>
</div>

.btn-container {
  display: flex;
  background-color: black;
  
  /* center vertically */
  padding-top: 150px;
  padding-bottom: 150px;
  /* center horizontally */
  justify-content: center;
}

.btn {
  display: inline-block;
  cursor: pointer;
  width: 50px;
  height: 50px;
  margin: 5px;
  font-size: 25px;
  color: gray;
  
  /*  Circles  */
  border-radius: 25px;
  background-color: white;

  /* center icons */
  text-align: center;
  line-height: 50px;
  
  /* remove touch blue highlight on mobile */
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
}

new Vue({
  el: '#app',
  data: {
    buttons: [
      {icon: 'comment', bgColor: '#DE9B00', color: '#EDB205'},
      {icon: 'user', bgColor: '#3EAF6F', color: '#4BD389'},
      {icon: 'map-marker', bgColor: '#BE0031', color: '#E61753'},
      {icon: 'cog', bgColor: '#8E00AC', color: '#B32DD2'}
    ],
    selectedBgColor: '#DE9B00',
    selectedId: 0
  },
  mounted () {
    // initialize widget
    this.selectButton(0)
  },
  methods: {
    selectButton (id) {
      const previousButton = this.$refs[`button_${this.selectedId}`]
      const nextButton = this.$refs[`button_${id}`]
      
      this.selectedId = id
      this.animateBgColor()
      
      this.animateOut(previousButton)
      this.animateIn(nextButton)
    },
    animateBgColor () {
      TweenMax.to(this, 0.2, {
        selectedBgColor: this.selectedButton.bgColor
      })
    },
    animateIn (btn) {      
      // animate icon color
      TweenMax.to(btn, 0.3, {
        backgroundColor: this.selectedButton.color,
        color: 'white'
      })
                  
      // animate button width
      TweenMax.to(btn, 0.7, {
        width: 100,
        ease: Elastic.easeOut.config(1, 0.5)
      })
    },
    animateOut (btn) {
      // animate icon color
      TweenMax.to(btn, 0.3, {
        backgroundColor: 'white',
        color: 'gray'
      })
      
      // animate button width
      TweenMax.to(btn, 0.7, {
        width: 50,
        ease: Elastic.easeOut.config(1, 0.5)
      })
    }
  },
  computed: {
    selectedButton () {
      return this.buttons[this.selectedId]
    }
  }
})