$l: 5em;
$d: $l*sqrt(2);
$b: 1.75*$l;

@function xor($a, $b) {
	@return if($a*$b == 0 and $a + $b == 1, 1, 0);
}

@mixin paint($c, $dir) {
	$dtxt: if($dir == 0, right, left);
	background: linear-gradient(to $dtxt bottom, 
		transparent 49%, 
		currentColor 50%);
	color: $c;
}

@mixin cube($ixo, $izo, $state: 'final') {
	$f: if($state == 'final', .25, .5);
	transform: 
		translate3d(
			$ixo*$b - (1 - $izo)*$l*$f, 
			-.5*$l, 
			(1 + $izo)*$l*$f
		)
		if(
			$izo < 0, 
			rotateY(90deg),
			rotate(-90deg)
		) 
		rotateX($izo*90deg);
}

@mixin pyramid($k, $izo, $state: 'final') {
	$f: if($state == 'final', 1, 1.5);
	transform: 
		translate3d(0, 0, 2*$izo*$b) 
		rotateY(($k - .5)*90deg) 
		translate(-.5*$l*sqrt(2)*$f) 
		rotateY(-45deg);
}

html, body { height: 100%; }

body {
	overflow: hidden;
	margin: 0; 
	perspective: 40em;
	background: #191919;
}

.assembly {
	&, * {
		position: absolute;
		bottom: 50%; left: 50%;
		transform-style: preserve-3d;
	}
	
	transform: translateY(.5*$l) 
		rotateX(-22.5deg) rotateY(30deg);
}

.pyramid {
	@for $i from 0 to 12 {
		$j1: $i%3;
		$k1: floor($i/3);
		$ixo: ($k1 - 1.5);
		$izo: ($j1 - 1);
		$lightb: ($k1 + $j1 + 1)*8%;
		$lightl1: ($k1 + 5)*8%;
		
		&:nth-child(#{$i + 1}) {
			transform: 
				translate3d($ixo*$b, 0, $izo*$b);
			animation: pos#{$i + 1} 4s linear infinite;

			@if $izo != 0 {
				/* 2 classes because specificity */
				.pyramid__face.pyramid__face--base {
					animation-name: baseshade#{$i + 1};
				}
			}
			
			.pyramid__face--lateral {
				@for $li from 0 to 4 {
					$lj: $li%2;
					$lk: floor($li/2);
					$xor: xor($lj, $lk);
					$lightl2: ($j1*4 + $k1 - $li + 5)*5%;
					
					&:nth-child(#{$li + 1}) {
						color: hsl(0, 0%, if($xor == 1, $lightl2, $lightl1));
					}
				}
			}
			
			@at-root {
				@keyframes pos#{$i + 1} {
					0%, 5%, 45%, 55%, 95%, 100% {
						transform: 
							translate3d($ixo*$b, 0, $izo*$b);
					}
					@if $izo != 0 {
						15%, 35% {
							@include cube($ixo, $izo, 'mid');
						}
						20%, 30% {
							@include cube($ixo, $izo);
						}
					}
					65%, 85% {
						@include pyramid($k1, $izo, 'mid');
					}
					70%, 80% {
						@include pyramid($k1, $izo);
					}
				}
				
				@if $izo != 0 {
					@keyframes baseshade#{$i + 1} {
						20%, 30% {
							background: hsl(0, 0%, $lightb);
						}
					}
				}
			}
		}
	}
	
	&__face {
		margin: 0 (-.5*$l);
		width: $l; height: $l;
		backface-visibility: hidden;
		
		&--lateral {
			transform-origin: 50% 100%;
			
			@for $i from 0 to 4 {
				$j: $i%2;
				$k: floor($i/2);
				$xor: xor($j, $k);
				
				&:nth-child(#{$i + 1}) {
					@if $xor == 1 {
						height: $d;
					}
					@else {
						animation: inherit;
						animation-name: no-flick;
					}
					
					transform: rotateY((1 - $i)*90deg) 
						translateZ(.5*$l) 
						if($xor == 1, rotateX(45deg), ());
					@include paint(
						darken(silver, random(50)), $k
					);
				}
			}
		}
		
		&--base {
			transform: 
				rotateX(-90deg) translateZ(.5*$l);
			background: #000;
			
			.pyramid:not(:nth-child(3n + 2)) & {
				animation: inherit;
			}
		}
	}
}

@keyframes no-flick {
	0%, 69.99%, 80.01%, 100% { opacity: .999; }
	70%, 80% { opacity: .001; }
}