<div id="app">
  <div class="container">
    <article>
      <header>
        <div class="progress">
          <div class="progress-step"
               :class="{'active': index === activeStep}"
               v-for="(step, index) in formSteps"
               :key="'step'+index">
            {{ index + 1 }}
          </div>
        </div>
      </header>
      <section :class="animation">
        <h2>{{ formSteps[activeStep].title }}</h2>
        <div class="input-fields">
          <div class="input-container"
               v-for="(field, index) in formSteps[activeStep].fields" :key="'field'+index">
            <input type="text" :class="{'wrong-input': !field.valid}" v-model="field.value" required />
            <label class="input-label">{{ field.label }}</label>
          </div>
        </div>
        <div class="actions">
          <button v-if="activeStep + 1 < formSteps.length -1" @click="checkFields">next</button>
          <button v-if="activeStep + 1 === formSteps.length -1" @click="checkFields">done</button>
        </div>
      </section>
    </article>
  </div>

  <!-- Youtube Link -->
  <a id="yt_link" target="_blank" href="https://www.youtube.com/watch?v=8S5a7wM0DUw&list=PLINmvGGUwYc2FVxImTwT66Phi4hQ2embf">Watch on YouTube</a>
</div>

body {
  margin: 0; padding: 0;
}

#app {
  width: 100%;
  height: 100vh;
  overflow: hidden;
}

@mixin flexbox() {
  display: flex;
  justify-content: center;
  align-items: center;
}

.container {
  @include flexbox();
  width: 100%;
  min-height: 100vh;
  font-family: 'Noto Sans', sans-serif;
  background: radial-gradient(#DF5C2E, #A43227);
}

article {
  display: flex;
  margin: 10px;
  width: calc(100% - 20px);
  max-width: 720px;
  min-height: 480px;
  perspective: 1000px;

  header {
    @include flexbox();
    width: 60px;
    height: 480px;
    background-color: #fff;
    border-right: 2px dotted #DF5C2E;
    box-shadow: 0 15px 30px rgba(0,0,0,0.2),
      0 10px 10px rgba(0,0,0,0.2);
  }

  .progress-step {
    @include flexbox();
    position: relative;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    margin-bottom: 20px;
    color: #fff;
    background-color: #DF5C2E;
    font-weight: bold;

    &.active {
      background-color: #DF5C2E;

      ~ .progress-step {
        color: #555;
        background-color: #ccc;
      }

      ~ .progress-step::before {
        background-color: #ccc;
      }
    }

    &:before {
      content: '';
      position: absolute;
      top: -20px;
      width: 2px;
      height: 20px;
      background: #DF5C2E;
      z-index: 10;
    }

    &:first-child::before {
      display: none;
    }
  }

  section {
    @include flexbox();
    flex-direction: column;
    width: 100%;
    background-color: #fff;
    box-shadow: 0 15px 30px rgba(0,0,0,0.2),
      0 10px 10px rgba(0,0,0,0.2);

    h2 {
      font-size: 1.6rem;
      color: #DF5C2E;
      margin: 0;
      padding: 20px;
    }

    .input-fields {
      @include flexbox();
      flex-direction: column;
      width: 100%;
    }

    .input-container {
      position: relative;
      padding: 30px 20px 20px 20px;
      width: calc(100% - 40px);
      max-width: 400px;

      input {
        position: relative;
        width: 100%;
        font-family: 'Noto Sans', sans-serif;
        font-size: 1.35rem;
        outline: 0;
        background: transparent;
        box-shadow: none;
        border: none;
        border-bottom: 2px dashed #DF5C2E;

        &:valid + .input-label {
          top: 10px;
          left: 20px;
          font-size: .7rem;
          font-weight: normal;
          color: #999;
        }

        &.wrong-input + .input-label {
          color: #B92938;
        }
      }
    }

    .input-label {
      position: absolute;
      top: 32px;
      left: 20px;
      font-size: 1.35rem;
      pointer-events: none;
      transition: .2s ease-in-out;
    }

    .actions {
      margin: 30px 0 0 0;

      button {
        font-family: 'Noto Sans', sans-serif;
        outline: none;
        border: none;
        color: #fff;
        background-color: #DF5C2E;
        font-size: 1.35rem;
        padding: 5px 20px;
        margin: 0 10px;
        text-transform: uppercase;
        border-radius: 3px;
        cursor: pointer;
      }
    }

  }
}

.animate-out {
  transform-origin: bottom left;
  animation: out .6s ease-in-out;
}

.animate-in {
  transform-origin: left;
  animation: in .6s ease-in-out;
}

.animate-wrong {
  animation: wrong .4s ease-in-out;
}

@keyframes out {
  0% { transform: translateY(0px) rotate(0deg); }
  60% { transform: rotate(10deg); }
  100% { transform: translateY(1000px); }
}

@keyframes in {
  0% {
    opacity: 0;
    transform: rotateY(90deg);
  }
  100% {
    opacity: 1;
    transform: rotateY(0deg);
  }
}

@keyframes wrong {
  0% { transform: translateX(0); }
  20% { transform: translateX(40px); }
  40% { transform: translateX(20px); }
  60% { transform: translateX(40px); }
  80% { transform: translateX(20px); }
  100% { transform: translateX(0); }
}

/* Youtube Link */
#yt_link
{
  position: absolute;
  right: 0;
  left: 0;
  bottom: -200px;
  display: block;
  width: 160px;
  text-align: center;
  color: red;
  font-size: 15px;
  text-decoration: none;
  font-family: Verdana, Geneva, Tahoma, sans-serif;
  padding: 10px;
  margin: 0 auto;
  background-color: #fff;
  border-radius: 2px;
  animation: showYtLink 1.5s ease 3s forwards;
}

@keyframes showYtLink
{
  0%{ bottom: -200px; }
  100%{ bottom: 20px; }
}

new Vue({
  el: '#app',
  data: {
    activeStep: 0,
    animation: 'animate-in',
    formSteps: [
      {
        title: "HTML Quiz",
        fields: [
          { label: "What does HTML stand for?", value: '', valid: true, pattern: /.+/ },
          { label: "Who is making the Web standards?", value: '', valid: true, pattern: /.+/ },
          { label: "Element for the largest heading?", value: '', valid: true, pattern: /.+/ }
        ]
      },
      {
        title: "CSS Quiz",
        fields: [
          { label: "What does CSS stand for?", value: '', valid: true, pattern: /.+/ },
          { label: "HTML tag for an internal style sheet?", value: '', valid: true, pattern: /.+/ },
          { label: "Property for the background color?", value: '', valid: true, pattern: /.+/ }
        ]
      },
      {
        title: "Your data",
        fields: [
          { label: "Your first name?", value: '', valid: true, pattern: /.+/ },
          { label: "Your last name?", value: '', valid: true, pattern: /.+/ },
          { label: "Your email?", value: '', valid: true, pattern: /^[^\s@]+@[^\s@]+\.[^\s@]+$/ }
        ]
      },
      {
        title: "Thank you for participating!",
      }
    ],
  },
  methods: {
    nextStep() {
      this.animation = 'animate-out';
      setTimeout(() => {
        this.animation = 'animate-in';
        this.activeStep += 1;
      }, 600);
    },
    checkFields() {
      let valid = true;
      this.formSteps[this.activeStep].fields.forEach(field => {
        if (!field.pattern.test(field.value)) {
          valid = false;
          field.valid = false;
        }
        else {
          field.valid = true;
        }
      });

      if(valid) {
        this.nextStep();
      }
      else {
        this.animation = 'animate-wrong';
        setTimeout(() => {
          this.animation = '';
        }, 400);
      }
    }
  }
})