.has-slider
  .slider#slider
    .slider-panel{ style: 'background-color: #faaf34; background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/40288/65d721_4dfa47a05152487fb3bc45ca2ec8fd1e.png)' }
    .slider-panel{ style: 'background-color: #aca680; background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/40288/65d721_761db9a0c113407f924a824ed173ed26.png)' }
    .slider-panel{ style: 'background-color: #d8daa6; background-image: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/40288/tumblr_njkn6kp0kE1qgsw73o1_500.png)' }
  .slider-pagination

.colophon
  Artwork ©
  %a{ href: 'https://sachinteng.tumblr.com/' } Sachin Teng

$sliderCards: 3

*
  background-position: center center
  background-repeat: no-repeat
  background-size: auto 100%

body
  background-color: black
  font-family: sans-serif
  margin: 0
  padding: 0

.slider
  display: flex
  width: 100% * $sliderCards
  &.is-animating
    transition: transform 400ms cubic-bezier( 0.5, 0, 0.5, 1 )
    
.slider-pagination
  bottom: 6.25%
  left: 0
  pointer-events: none
  position: absolute
  text-align: center
  width: 100%
  > *
    border-radius: 50%
    box-shadow: 0 0 0 2px rgba( white, 0.75 )
    display: inline-block
    height: 6px
    margin-left: 4px
    margin-right: 4px
    transition: background-color 250ms
    width: 6px
    &.is-active
      background-color: rgba( white, 0.75 )
 
.slider-panel
  padding-top: 10%
  width: 100%

.has-slider
  overflow: hidden
  position: relative
  width: 100%

.colophon
  color: #808080
  padding-bottom: 1em
  padding-top: 1em
  text-align: center
  
a
  color: white
  font-size: 14px
  letter-spacing: 0.125em
  text-decoration: none
  text-transform: uppercase

// 1. Basic object for our stuff
window.slider = {};

// 2. Settings
slider.sliderPanelSelector = '.slider-panel';
slider.sliderPaginationSelector = '.slider-pagination';
slider.sensitivity = 25 // horizontal % needed to trigger swipe

// 2. Placeholder to remember which slide we’re on
slider.activeSlide = 0;

// 3. Slide counter
slider.slideCount = 0;

// 4. Initialization + event listener
slider.init = function( selector ) {
  
  // 4a. Find the container
  slider.sliderEl = document.querySelector( selector );
  
  // 4b. Count stuff
  slider.slideCount = slider.sliderEl.querySelectorAll( slider.sliderPanelSelector ).length;
  
  // 4c. Populate pagination
  var n = 0;
  for( n; n < slider.slideCount; n++ ) {
    var activeStatus = n == slider.activeSlide ? ' class="is-active"' : '';
    slider.sliderEl.parentElement.querySelector( slider.sliderPaginationSelector ).innerHTML += '<div ' + activeStatus + '></div>';
  }
  
  // 4d. Set up HammerJS
  var sliderManager = new Hammer.Manager( slider.sliderEl );
  sliderManager.add( new Hammer.Pan({ threshold: 0, pointers: 0 }) );
  sliderManager.on( 'pan', function( e ) {
    
    // 4e. Calculate pixel movements into 1:1 screen percents so gestures track with motion
    var percentage = 100 / slider.slideCount * e.deltaX / window.innerWidth;
    
    // 4f. Multiply percent by # of slide we’re on
    var percentageCalculated = percentage - 100 / slider.slideCount * slider.activeSlide;
    
    // 4g. Apply transformation
    slider.sliderEl.style.transform = 'translateX( ' + percentageCalculated + '% )';
    
    // 4h. Snap to slide when done
    if( e.isFinal ) {
      if( e.velocityX > 1 ) {
        slider.goTo( slider.activeSlide - 1 );
      } else if( e.velocityX < -1 ) {
        slider.goTo( slider.activeSlide + 1 )
      } else {
        if( percentage <= -( slider.sensitivity / slider.slideCount ) )
          slider.goTo( slider.activeSlide + 1 );
        else if( percentage >= ( slider.sensitivity / slider.slideCount ) )
          slider.goTo( slider.activeSlide - 1 );
        else
          slider.goTo( slider.activeSlide );
      }
    }
  });
};

// 5. Update current slide
slider.goTo = function( number ) {
  
  // 5a. Stop it from doing weird things like moving to slides that don’t exist
  if( number < 0 )
    slider.activeSlide = 0;
  else if( number > slider.slideCount - 1 )
    slider.activeSlide = slider.slideCount - 1
  else
    slider.activeSlide = number;
    
 // 5b. Apply transformation & smoothly animate via .is-animating CSS
 slider.sliderEl.classList.add( 'is-animating' );
 var percentage = -( 100 / slider.slideCount ) * slider.activeSlide;
 slider.sliderEl.style.transform = 'translateX( ' + percentage + '% )';
 clearTimeout( slider.timer );
 slider.timer = setTimeout( function() {
   slider.sliderEl.classList.remove( 'is-animating' );
 }, 400 );
  
 // 5c. Update the counters
 var pagination = slider.sliderEl.parentElement.querySelectorAll( slider.sliderPaginationSelector + ' > *' );
 var n = 0;
 for( n; n < pagination.length; n++ ) {
   var className = n == slider.activeSlide ? 'is-active' : '';
   pagination[n].className = className;
 }
};

// Initialize
slider.init( '#slider' );