-- Combines two colors in CIELUV space.
-- Color3 LerpCIELUV(Color3 fromColor, Color3 toColor, float t)
-- @author Fraktality

-- https://www.w3.org/Graphics/Color/srgb

local Black = Color3.fromRGB(0, 0, 0)

return function(c0, c1, t)
	local u0, v0, u1, v1

	-- Convert from linear RGB to scaled CIELUV (RgbToLuv13)
	local r, g, b = c0.r, c0.g, c0.b
	-- Apply inverse gamma correction
	r = r < 0.0404482362771076 and r/12.92 or 0.87941546140213*(r + 0.055)^2.4
	g = g < 0.0404482362771076 and g/12.92 or 0.87941546140213*(g + 0.055)^2.4
	b = b < 0.0404482362771076 and b/12.92 or 0.87941546140213*(b + 0.055)^2.4
	-- sRGB->XYZ->CIELUV
	local y = 0.2125862307855956*r + 0.71517030370341085*g + 0.0722004986433362*b
	local z = 3.6590806972265883*r + 11.4426895800574232*g + 4.1149915024264843*b
	local l0 = y > 0.008856451679035631 and 116*y^(1/3) - 16 or 903.296296296296*y
	if z > 1e-15 then
		u0, v0 = l0*(0.9257063972951867*r - 0.8333736323779866*g - 0.09209820666085898*b)/z, l0*(9*y/z - 0.46832)
	else
		u0, v0 = -0.19783*l0, -0.46832*l0
	end

	-- Convert from linear RGB to scaled CIELUV (RgbToLuv13)
	r, g, b = c1.r, c1.g, c1.b
	-- Apply inverse gamma correction
	r = r < 0.0404482362771076 and r/12.92 or 0.87941546140213*(r + 0.055)^2.4
	g = g < 0.0404482362771076 and g/12.92 or 0.87941546140213*(g + 0.055)^2.4
	b = b < 0.0404482362771076 and b/12.92 or 0.87941546140213*(b + 0.055)^2.4
	-- sRGB->XYZ->CIELUV
	y = 0.2125862307855956*r + 0.71517030370341085*g + 0.0722004986433362*b
	z = 3.6590806972265883*r + 11.4426895800574232*g + 4.1149915024264843*b
	local l1 = y > 0.008856451679035631 and 116*y^(1/3) - 16 or 903.296296296296*y
	if z > 1e-15 then
		u1, v1 = l1*(0.9257063972951867*r - 0.8333736323779866*g - 0.09209820666085898*b)/z, l1*(9*y/z - 0.46832)
	else
		u1, v1 = -0.19783*l1, -0.46832*l1
	end

	-- The inputs aren't needed anymore, so don't drag out their lifetimes
	-- c0, c1 = nil, nil

	-- return function(t)
	-- Interpolate
	local l = (1 - t)*l0 + t*l1
	if l < 0.0197955 then
		return Black
	end
	local u = ((1 - t)*u0 + t*u1)/l + 0.19783
	local v = ((1 - t)*v0 + t*v1)/l + 0.46832

	-- CIELUV->XYZ
	y = (l + 16)/116
	y = y > 0.206896551724137931 and y*y*y or 0.12841854934601665*y - 0.01771290335807126
	local x = y*u/v
	z = y*((3 - 0.75*u)/v - 5)

	-- XYZ->linear sRGB
	r =  7.2914074*x - 1.5372080*y - 0.4986286*z
	g = -2.1800940*x + 1.8757561*y + 0.0415175*z
	b =  0.1253477*x - 0.2040211*y + 1.0569959*z

	-- Adjust for the lowest out-of-bounds component
	if r < 0 and r < g and r < b then
		r, g, b = 0, g - r, b - r
	elseif g < 0 and g < b then
		r, g, b = r - g, 0, b - g
	elseif b < 0 then
		r, g, b = r - b, g - b, 0
	end

	-- Apply gamma correction
	r = r < 3.1306684425e-3 and 12.92*r or 1.055*r^(1/2.4) - 0.055
	g = g < 3.1306684425e-3 and 12.92*g or 1.055*g^(1/2.4) - 0.055
	b = b < 3.1306684425e-3 and 12.92*b or 1.055*b^(1/2.4) - 0.055

	return Color3.new(
		-- Clamp the result
		r > 1 and 1 or r < 0 and 0 or r,
		g > 1 and 1 or g < 0 and 0 or g,
		b > 1 and 1 or b < 0 and 0 or b
	)
	-- end
end