1 files changed, 370 insertions, 0 deletions
diff --git a/apps/web/src/lib/animation/interpolation.ts b/apps/web/src/lib/animation/interpolation.ts
new file mode 100644
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+++ b/apps/web/src/lib/animation/interpolation.ts
@@ -0,0 +1,370 @@
+import type {
+	AnimationChannel,
+	AnimationValue,
+	ColorAnimationChannel,
+	DiscreteValue,
+	DiscreteAnimationChannel,
+	NumberAnimationChannel,
+} from "@/types/animation";
+import { TIME_EPSILON_SECONDS } from "@/constants/animation-constants";
+
+function byTimeAscending({
+	leftTime,
+	rightTime,
+}: {
+	leftTime: number;
+	rightTime: number;
+}): number {
+	return leftTime - rightTime;
+}
+
+function isWithinTimePair({
+	time,
+	leftTime,
+	rightTime,
+}: {
+	time: number;
+	leftTime: number;
+	rightTime: number;
+}): boolean {
+	return (
+		time >= leftTime - TIME_EPSILON_SECONDS &&
+		time <= rightTime + TIME_EPSILON_SECONDS
+	);
+}
+
+function clamp01({ value }: { value: number }): number {
+	return Math.max(0, Math.min(1, value));
+}
+
+function parseHexChannel({ hex }: { hex: string }): number | null {
+	const value = Number.parseInt(hex, 16);
+	return Number.isNaN(value) ? null : value;
+}
+
+function parseHexColor({
+	color,
+}: {
+	color: string;
+}): { red: number; green: number; blue: number; alpha: number } | null {
+	const trimmed = color.trim();
+	if (!trimmed.startsWith("#")) {
+		return null;
+	}
+
+	const rawHex = trimmed.slice(1);
+	if (rawHex.length === 3 || rawHex.length === 4) {
+		const [redHex, greenHex, blueHex, alphaHex = "f"] = rawHex.split("");
+		const red = parseHexChannel({ hex: `${redHex}${redHex}` });
+		const green = parseHexChannel({ hex: `${greenHex}${greenHex}` });
+		const blue = parseHexChannel({ hex: `${blueHex}${blueHex}` });
+		const alpha = parseHexChannel({ hex: `${alphaHex}${alphaHex}` });
+		if (
+			red === null ||
+			green === null ||
+			blue === null ||
+			alpha === null
+		) {
+			return null;
+		}
+
+		return { red, green, blue, alpha: alpha / 255 };
+	}
+
+	if (rawHex.length === 6 || rawHex.length === 8) {
+		const red = parseHexChannel({ hex: rawHex.slice(0, 2) });
+		const green = parseHexChannel({ hex: rawHex.slice(2, 4) });
+		const blue = parseHexChannel({ hex: rawHex.slice(4, 6) });
+		const alphaHex = rawHex.length === 8 ? rawHex.slice(6, 8) : "ff";
+		const alpha = parseHexChannel({ hex: alphaHex });
+		if (
+			red === null ||
+			green === null ||
+			blue === null ||
+			alpha === null
+		) {
+			return null;
+		}
+
+		return { red, green, blue, alpha: alpha / 255 };
+	}
+
+	return null;
+}
+
+function formatRgbaColor({
+	red,
+	green,
+	blue,
+	alpha,
+}: {
+	red: number;
+	green: number;
+	blue: number;
+	alpha: number;
+}): string {
+	const roundedRed = Math.round(red);
+	const roundedGreen = Math.round(green);
+	const roundedBlue = Math.round(blue);
+	const roundedAlpha = Math.round(clamp01({ value: alpha }) * 1000) / 1000;
+	return `rgba(${roundedRed}, ${roundedGreen}, ${roundedBlue}, ${roundedAlpha})`;
+}
+
+function lerpNumber({
+	leftValue,
+	rightValue,
+	progress,
+}: {
+	leftValue: number;
+	rightValue: number;
+	progress: number;
+}): number {
+	return leftValue + (rightValue - leftValue) * progress;
+}
+
+function interpolateColor({
+	leftColor,
+	rightColor,
+	progress,
+}: {
+	leftColor: string;
+	rightColor: string;
+	progress: number;
+}): string {
+	const leftParsed = parseHexColor({ color: leftColor });
+	const rightParsed = parseHexColor({ color: rightColor });
+	if (!leftParsed || !rightParsed) {
+		return progress >= 1 ? rightColor : leftColor;
+	}
+
+	return formatRgbaColor({
+		red: lerpNumber({
+			leftValue: leftParsed.red,
+			rightValue: rightParsed.red,
+			progress,
+		}),
+		green: lerpNumber({
+			leftValue: leftParsed.green,
+			rightValue: rightParsed.green,
+			progress,
+		}),
+		blue: lerpNumber({
+			leftValue: leftParsed.blue,
+			rightValue: rightParsed.blue,
+			progress,
+		}),
+		alpha: lerpNumber({
+			leftValue: leftParsed.alpha,
+			rightValue: rightParsed.alpha,
+			progress,
+		}),
+	});
+}
+
+export function normalizeChannel<TChannel extends AnimationChannel>({
+	channel,
+}: {
+	channel: TChannel;
+}): TChannel {
+	return {
+		...channel,
+		keyframes: [...channel.keyframes].sort((leftKeyframe, rightKeyframe) =>
+			byTimeAscending({
+				leftTime: leftKeyframe.time,
+				rightTime: rightKeyframe.time,
+			}),
+		),
+	} as TChannel;
+}
+
+function evaluateChannelValueAtTime<TKeyframe extends { time: number; value: TValue }, TValue>({
+	keyframes,
+	time,
+	fallbackValue,
+	getInterpolatedValue,
+}: {
+	keyframes: TKeyframe[] | undefined;
+	time: number;
+	fallbackValue: TValue;
+	getInterpolatedValue: ({
+		leftKeyframe,
+		rightKeyframe,
+		progress,
+	}: {
+		leftKeyframe: TKeyframe;
+		rightKeyframe: TKeyframe;
+		progress: number;
+	}) => TValue;
+}): TValue {
+	if (!keyframes || keyframes.length === 0) {
+		return fallbackValue;
+	}
+
+	const firstKeyframe = keyframes[0];
+	const lastKeyframe = keyframes[keyframes.length - 1];
+	if (!firstKeyframe || !lastKeyframe) {
+		return fallbackValue;
+	}
+
+	if (time <= firstKeyframe.time + TIME_EPSILON_SECONDS) {
+		return firstKeyframe.value;
+	}
+
+	if (time >= lastKeyframe.time - TIME_EPSILON_SECONDS) {
+		return lastKeyframe.value;
+	}
+
+	for (let keyframeIndex = 0; keyframeIndex < keyframes.length - 1; keyframeIndex++) {
+		const leftKeyframe = keyframes[keyframeIndex];
+		const rightKeyframe = keyframes[keyframeIndex + 1];
+
+		if (Math.abs(time - rightKeyframe.time) <= TIME_EPSILON_SECONDS) {
+			return rightKeyframe.value;
+		}
+
+		const isBetweenPair = isWithinTimePair({
+			time,
+			leftTime: leftKeyframe.time,
+			rightTime: rightKeyframe.time,
+		});
+		if (!isBetweenPair) {
+			continue;
+		}
+
+		const span = rightKeyframe.time - leftKeyframe.time;
+		if (Math.abs(span) <= TIME_EPSILON_SECONDS) {
+			return rightKeyframe.value;
+		}
+
+		const progress = clamp01({
+			value: (time - leftKeyframe.time) / span,
+		});
+
+		return getInterpolatedValue({
+			leftKeyframe,
+			rightKeyframe,
+			progress,
+		});
+	}
+
+	return lastKeyframe.value;
+}
+
+export function getNumberChannelValueAtTime({
+	channel,
+	time,
+	fallbackValue,
+}: {
+	channel: NumberAnimationChannel | undefined;
+	time: number;
+	fallbackValue: number;
+}): number {
+	return evaluateChannelValueAtTime({
+		keyframes: channel?.keyframes,
+		time,
+		fallbackValue,
+		getInterpolatedValue: ({ leftKeyframe, rightKeyframe, progress }) => {
+			if (leftKeyframe.interpolation === "hold") {
+				return leftKeyframe.value;
+			}
+
+			return lerpNumber({
+				leftValue: leftKeyframe.value,
+				rightValue: rightKeyframe.value,
+				progress,
+			});
+		},
+	});
+}
+
+function getColorValueAtTime({
+	channel,
+	time,
+	fallbackValue,
+}: {
+	channel: ColorAnimationChannel | undefined;
+	time: number;
+	fallbackValue: string;
+}): string {
+	return evaluateChannelValueAtTime({
+		keyframes: channel?.keyframes,
+		time,
+		fallbackValue,
+		getInterpolatedValue: ({ leftKeyframe, rightKeyframe, progress }) => {
+			if (leftKeyframe.interpolation === "hold") {
+				return leftKeyframe.value;
+			}
+
+			return interpolateColor({
+				leftColor: leftKeyframe.value,
+				rightColor: rightKeyframe.value,
+				progress,
+			});
+		},
+	});
+}
+
+function getDiscreteValueAtTime({
+	channel,
+	time,
+	fallbackValue,
+}: {
+	channel: DiscreteAnimationChannel | undefined;
+	time: number;
+	fallbackValue: DiscreteValue;
+}): DiscreteValue {
+	return evaluateChannelValueAtTime({
+		keyframes: channel?.keyframes,
+		time,
+		fallbackValue,
+		getInterpolatedValue: ({ leftKeyframe }) => leftKeyframe.value,
+	});
+}
+
+export function getChannelValueAtTime({
+	channel,
+	time,
+	fallbackValue,
+}: {
+	channel: AnimationChannel | undefined;
+	time: number;
+	fallbackValue: AnimationValue;
+}): AnimationValue {
+	if (!channel || channel.keyframes.length === 0) {
+		return fallbackValue;
+	}
+
+	if (channel.valueKind === "number") {
+		if (typeof fallbackValue !== "number") {
+			return fallbackValue;
+		}
+
+		return getNumberChannelValueAtTime({
+			channel,
+			time,
+			fallbackValue,
+		});
+	}
+
+	if (channel.valueKind === "color") {
+		if (typeof fallbackValue !== "string") {
+			return fallbackValue;
+		}
+
+		return getColorValueAtTime({
+			channel,
+			time,
+			fallbackValue,
+		});
+	}
+
+	if (typeof fallbackValue !== "string" && typeof fallbackValue !== "boolean") {
+		return fallbackValue;
+	}
+
+	return getDiscreteValueAtTime({
+		channel,
+		time,
+		fallbackValue,
+	});
+}