const PI = Math.PI;
const PI_TIMES_TWO = Math.PI * 2;

export const lerp = (start: number, end: number, t: number) => {
	return start + (end - start) * t;
};

// https://gist.github.com/itsmrpeck/be41d72e9d4c72d2236de687f6f53974
export const degreeLerp = (start: number, end: number, t: number) => {
	let result: number;
	const diff = end - start;
	if (diff < -180) {
		// lerp upwards past 360
		end += 360;
		result = lerp(start, end, t);
		if (result >= 360) {
			result -= 360;
		}
	} else if (diff > 180) {
		// lerp downwards past 0
		end -= 360;
		result = lerp(start, end, t);
		if (result < 0) {
			result += 360;
		}
	} else {
		// straight lerp
		result = lerp(start, end, t);
	}

	return result;
};

// https://gist.github.com/itsmrpeck/be41d72e9d4c72d2236de687f6f53974
export const radianLerp = (start: number, end: number, t: number) => {
	let result: number;
	const diff = end - start;
	if (diff < -PI) {
		// lerp upwards past PI_TIMES_TWO
		end += PI_TIMES_TWO;
		result = lerp(start, end, t);
		if (result >= PI_TIMES_TWO) {
			result -= PI_TIMES_TWO;
		}
	} else if (diff > PI) {
		// lerp downwards past 0
		end -= PI_TIMES_TWO;
		result = lerp(start, end, t);
		if (result < 0) {
			result += PI_TIMES_TWO;
		}
	} else {
		// straight lerp
		result = lerp(start, end, t);
	}

	return result;
};