<form class="fr" action="">
	<label class="fr__label" for="face-rating">How was your experience?</label>
	<div class="fr__face" role="img" aria-label="Straight face">
		<div class="fr__face-right-eye" data-right></div>
		<div class="fr__face-left-eye" data-left></div>
		<div class="fr__face-mouth-lower" data-mouth-lower></div>
		<div class="fr__face-mouth-upper" data-mouth-upper></div>
	</div>
	<input class="fr__input" id="face-rating" type="range" value="2.5" min="0" max="5" step="0.1">
</form>

* {
	border: 0;
	box-sizing: border-box;
	margin: 0;
	padding: 0;
}
:root {
	--hue: 223;
	--white: hsl(var(--hue),10%,100%);
	--lt-gray: hsl(var(--hue),10%,95%);
	--gray1: hsl(var(--hue),10%,90%);
	--gray2: hsl(var(--hue),10%,80%);
	--gray7: hsl(var(--hue),10%,30%);
	--gray9: hsl(var(--hue),10%,10%);
	--primary: hsl(var(--hue),90%,55%);
	--trans-dur: 0.3s;
	font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body,
input {
	font: 1em/1.5 "DM Sans", sans-serif;
}
body {
	background-color: var(--white);
	color: var(--gray9);
	height: 100vh;
	display: grid;
	place-items: center;
	transition:
		background-color var(--trans-dur),
		color var(--trans-dur);
}

/* Main styles */
.fr {
	animation: fade-slide-in 0.6s ease-out;
	padding: 0 1.5em;
	max-width: 20em;
}
.fr__face {
	--face-hue1: 60;
	--face-hue2: 30;
	background-image:
		linear-gradient(
			135deg,
			hsl(var(--face-hue1),90%,55%),
			hsl(var(--face-hue2),90%,45%)
		);
	border-radius: 50%;
	box-shadow: 0 0.5em 0.75em hsla(var(--face-hue2),90%,55%,0.3);
	margin: 0 auto 2em;
	position: relative;
	width: 3em;
	height: 3em;
}
.fr__face-right-eye,
.fr__face-left-eye,
.fr__face-mouth-lower,
.fr__face-mouth-upper {
	position: absolute;
	transition:
		background-color var(--trans-dur),
		box-shadow var(--trans-dur),
		color var(--trans-dur);
}
.fr__face-right-eye,
.fr__face-left-eye {
	background-color: var(--white);
	border-radius: 50%;
	top: 0.75em;
	width: 0.6em;
	height: 0.6em;
}
.fr__face-right-eye {
	--delay-right: 0s;
	animation: right-eye 1s var(--delay-right) linear paused;
	clip-path: polygon(0 75%,100% 0,100% 100%,0 100%);
	left: 0.6em;
}
.fr__face-left-eye {
	--delay-left: 0s;
	animation: left-eye 1s var(--delay-left) linear paused;
	clip-path: polygon(0 0,100% 75%,100% 100%,0 100%);
	right: 0.6em;
}
.fr__face-mouth-lower,
.fr__face-mouth-upper {
	color: var(--white);
	top: 1.75em;
	left: 0.75em;
	width: 1.5em;
	height: 0.75em;
}
.fr__face-mouth-lower {
	--delay-mouth-lower: 0s;
	animation: mouth-lower 1s var(--delay-mouth-lower) linear paused;
	border-radius: 50% 50% 0 0 / 100% 100% 0 0;
	box-shadow: 0 0.125em 0 inset;
}
.fr__face-mouth-upper {
	--delay-mouth-upper: 0s;
	animation: mouth-upper 1s var(--delay-mouth-upper) linear paused;
	border-radius: 0 0 50% 50% / 0 0 100% 100%;
	box-shadow: 0 -0.125em 0 inset;
}
.fr__label {
	display: block;
	margin-bottom: 1.5em;
	text-align: center;
}
.fr__input {
	--input-hue: 60;
	--percent: 50%;
	background-color: var(--gray1);
	background-image: linear-gradient(hsl(var(--input-hue),90%,45%),hsl(var(--input-hue),90%,45%));
	background-size: var(--percent) 100%;
	background-repeat: no-repeat;
	border-radius: 0.25em;
	display: block;
	margin: 0.5em auto;
	width: 100%;
	max-width: 10em;
	height: 0.5em;
	transition: background-color var(--trans-dur);
	-webkit-appearance: none;
	appearance: none;
	-webkit-tap-highlight-color: transparent;
}
.fr__input:focus {
	outline: transparent;
}

/* WebKit */
.fr__input::-webkit-slider-thumb {
	background-color: var(--white);
	border: 0;
	border-radius: 50%;
	box-shadow: 0 0.125em 0.5em hsl(0,0%,0%,0.3);
	width: 1.5em;
	height: 1.5em;
	transition: background-color 0.15s linear;
	-webkit-appearance: none;
	appearance: none;
}
.fr__input:focus::-webkit-slider-thumb,
.fr__input::-webkit-slider-thumb:hover {
	background-color: var(--lt-gray);
}

/* Firefox */
.fr__input::-moz-range-thumb {
	background-color: var(--white);
	border: 0;
	border-radius: 50%;
	box-shadow: 0 0.125em 0.5em hsl(0,0%,0%,0.3);
	width: 1.5em;
	height: 1.5em;
	transition: background-color 0.15s linear;
}
.fr__input:focus::-moz-range-thumb,
.fr__input::-moz-range-thumb:hover {
	background-color: var(--lt-gray);
}

/* `:focus-visible` support */
@supports selector(:focus-visible) {
	.fr__input:focus::-webkit-slider-thumb {
		background-color: var(--white);
	}
	.fr__input:focus-visible::-webkit-slider-thumb,
	.fr__input::-webkit-slider-thumb:hover {
		background-color: var(--lt-gray);
	}
	.fr__input:focus::-moz-range-thumb {
		background-color: var(--white);
	}
	.fr__input:focus-visible::-moz-range-thumb,
	.fr__input::-moz-range-thumb:hover {
		background-color: var(--lt-gray);
	}
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
	body {
		background-color: var(--gray9);
		color: var(--gray1);
	}
	.fr__face-right-eye,
	.fr__face-left-eye {
		background-color: var(--gray9);
	}
	.fr__face-mouth-lower,
	.fr__face-mouth-upper {
		color: var(--gray9);
	}
	.fr__input {
		background-color: var(--gray7);
	}
}

/* Animations */
@keyframes fade-slide-in {
	from,
	16.67% {
		opacity: 0;
		transform: translateY(25%);
	}
	to {
		opacity: 1;
		transform: translateY(0);
	}
}
@keyframes right-eye {
	from { clip-path: polygon(0 75%,100% 0,100% 100%,0 100%); }
	50%, to { clip-path: polygon(0 0,100% 0,100% 100%,0 100%); }
}
@keyframes left-eye {
	from { clip-path: polygon(0 0,100% 75%,100% 100%,0 100%); }
	50%, to { clip-path: polygon(0 0,100% 0,100% 100%,0 100%); }
}
@keyframes mouth-lower {
	from {
		border-radius: 50% 50% 0 0 / 100% 100% 0 0;
		top: 1.75em;
		height: 0.75em;
		visibility: visible;
	}
	40% {
		border-radius: 50% 50% 0 0 / 100% 100% 0 0;
		top: 1.95em;
		height: 0.25em;
		visibility: visible;
	}
	50%,
	to {
		border-radius: 0;
		top: 2em;
		height: 0.125em;
		visibility: hidden;
	}
}
@keyframes mouth-upper {
	from,
	50% {
		border-radius: 0;
		box-shadow: 0 -0.125em 0 inset;
		top: 2em;
		height: 0.125em;
		visibility: hidden;
	}
	62.5% {
		border-radius: 0 0 50% 50% / 0 0 100% 100%;
		box-shadow: 0 -0.125em 0 inset;
		top: 1.95em;
		height: 0.25em;
		visibility: visible;
	}
	75% {
		border-radius: 0 0 50% 50% / 0 0 100% 100%;
		box-shadow: 0 -0.125em 0 inset;
		top: 1.825em;
		height: 0.5em;
		visibility: visible;
	}
	to {
		border-radius: 0 0 50% 50% / 0 0 100% 100%;
		box-shadow: 0 -0.8em 0 inset;
		top: 1.75em;
		height: 0.75em;
		visibility: visible;
	}
}

window.addEventListener("DOMContentLoaded",() => {
	const fr = new FaceRating("#face-rating");
});

class FaceRating {
	constructor(qs) {
		this.input = document.querySelector(qs);
		this.input?.addEventListener("input",this.update.bind(this));
		this.face = this.input?.previousElementSibling;
		this.update();
	}
	update(e) {
		let value = this.input.defaultValue;

		// when manually set
		if (e) value = e.target?.value;
		// when initiated
		else this.input.value = value;

		const min = this.input.min || 0;
		const max = this.input.max || 100;
		const percentRaw = (value - min) / (max - min) * 100;
		const percent = +percentRaw.toFixed(2);

		this.input?.style.setProperty("--percent",`${percent}%`);

		// face and range fill colors
		const maxHue = 120;
		const hueExtend = 30;
		const hue = Math.round(maxHue * percent / 100);

		let hue2 = hue - hueExtend;
		if (hue2 < 0) hue2 += 360;

		const hues = [hue,hue2];
		hues.forEach((h,i) => {
			this.face?.style.setProperty(`--face-hue${i + 1}`,h);
		});

		this.input?.style.setProperty("--input-hue",hue);

		// emotions
		const duration = 1;
		const delay = -(duration * 0.99) * percent / 100;
		const parts = ["right","left","mouth-lower","mouth-upper"];

		parts.forEach(p => {
			const el = this.face?.querySelector(`[data-${p}]`);
			el?.style.setProperty(`--delay-${p}`,`${delay}s`);
		});

		// aria label
		const faces = [
			"Sad face",
			"Slightly sad face",
			"Straight face",
			"Slightly happy face",
			"Happy face"
		];
		let faceIndex = Math.floor(faces.length * percent / 100);
		if (faceIndex === faces.length) --faceIndex;

		this.face?.setAttribute("aria-label",faces[faceIndex]);
	}
}