<section id="flip" data-state="initial">
  <button id="prev">&lsaquo;</button>
  <div class="window">
    <div class="box"></div>
  </div>
  <div class="steps">
    <p data-flip-key="first">
      <strong>First:</strong> get the initial dimensions
    </p>
    <p data-flip-key="last">
      <strong>Last:</strong> get dimensions after change
    </p>
    <p data-flip-key="invert">
      <strong>Invert:</strong> calculate deltas to move element to its original position
    </p>
    <p data-flip-key="play">
      <strong>Play:</strong> animate from original position to final position
    </p>
  </div>
  <button id="next">&rsaquo;</button>
</section>

body, section {
  display: flex;
  flex-direction: row;
  justify-content: center;
  align-items: center;
}

section {
  width: 100vw;
  
  > .steps, > .window {
    flex-basis: 40%;
    flex-grow: 0;
    flex-shrink: 0;
  }
}

[data-state="initial"] {
  [data-flip-key] {
    display: none;
  }
  
  .box {
    outline-color: transparent;
  }
}

[data-state="initial"], [data-state="play"] {
  .box:before {
    opacity: 1;
  }
}

// First
[data-state="first"] {
  [data-flip-key]:nth-child(1) ~ [data-flip-key] {
    display: none
  }
}

// Last
[data-state="last"] {
  [data-flip-key]:nth-child(2) ~ [data-flip-key] {
    display: none
  }
  .box:before {
    transform:
      translate(
        calc(20vw - 5vmin - 1rem),
        calc(25vh - 5vmin - 1rem)
      );
  }
  
  .box:after {
    opacity: 1;
  }
}

// Invert
[data-state="invert"] {
  [data-flip-key]:nth-child(3) ~ [data-flip-key] {
    display: none
  }
  .box:after {
    opacity: 1;
  }
  .box:before {
    transform:
      translate(0, 0);
  }
}

// Play
[data-state="play"] {
  .box:after {
    opacity: 1;
  }
  .box:before {
    opacity: 1;
    transform:
      translate(0, 0);
    animation: play 2s ease-in-out both infinite;
    
    @keyframes play {
      from, 10% {
        transform: none;
      }
      50%, to {
        transform: translate(
          calc(20vw - 5vmin - 1rem),
          calc(25vh - 5vmin - 1rem)
        );
      }
      75% {
        opacity: 1;
      }
      to {
        opacity: 0;
      }
    }
  }
}

button {
  appearance: none;
  -webkit-appearance: none;
  background: transparent;
  border: none;
  color: white;
  font-size: 10vmin;
  font-weight: normal;
}

.steps {
  flex-basis: 50%;
  padding: 0 2rem;
  
  [data-state="initial"] &:before {
    content: "Let's smoothly animate the blue box to the center. Press the right arrow to begin."
  }
}

.box {
  position: absolute;
  top: 1rem;
  left: 1rem;
  height: 10vmin;
  width: 10vmin;
  outline: 2px dashed #16c72e;
  outline-offset: 1px;
  
  &:before, &:after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    transition: opacity .3s ease-out;
  }
  
  &:before {
    opacity: 0.5;
    background-color: #449dda;
    border-radius: .25rem;
    will-change: transform;
  }
  
  &:after {
    outline: 2px dashed #E8747E;
    outline-offset: inherit;
    opacity: 0;
    transform:
      translate(
        calc(20vw - 5vmin - 1rem),
        calc(25vh - 5vmin - 1rem)
      );
  }
}

.window {
  height: 70vh;
  width: 40vw;
  border-top: 2rem solid #C4C7C8;
  border-radius: .5rem;
  background-color: #fff;
  box-shadow: 0 0 5vw 0 rgba(black, 0.2);
}

body {
  background-image: linear-gradient(to bottom right, #636C91, #313A5C);
  color: #FEFEFE;
}

html, body {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
}

*, *:before, *:after {
  box-sizing: border-box;
  position: relative;
}

const flipContainer = document.getElementById('flip');

const machine = {
  initial: 'initial',
  states: {
    initial: {
      on: { NEXT: 'first' }
    },
    first: {
      on: { NEXT: 'last', PREV: 'initial' }
    },
    last: {
      on: { NEXT: 'invert', PREV: 'first' }
    },
    invert: {
      on: { NEXT: 'play', PREV: 'last' }
    },
    play: {
      on: { PREV: 'invert', NEXT: 'initial' }
    },
  }
};

const flipping = new Flipping();
let state = machine.initial;
const transition = (state, action) => {
  try {
    return machine.states[state].on[action];
  } catch (e) {
    return undefined;
  }
}
const update = flipping.wrap((nextState) => {
  state = nextState;
  flipContainer.setAttribute('data-state', nextState);
});
const emit = (action) => (e) => {
  const nextState = transition(state, action);
  console.log(action, state, nextState);
  if (nextState) {
    update(nextState);
  }
}

const prev = document.getElementById('prev');
const next = document.getElementById('next');

prev.addEventListener('click', emit('PREV'));
next.addEventListener('click', emit('NEXT'));