-- transforms Roblox types into intermediate types, converting
-- between spaces as necessary to preserve perceptual linearity
local typeMetadata = {
	number = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			return {value}
		end,

		fromIntermediate = function(value)
			return value[1]
		end,
	},

	NumberRange = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			return {value.Min, value.Max}
		end,

		fromIntermediate = function(value)
			return NumberRange.new(value[1], value[2])
		end,
	},

	UDim = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			return {value.Scale, value.Offset}
		end,

		fromIntermediate = function(value)
			return UDim.new(value[1], value[2])
		end,
	},

	UDim2 = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			local x = value.X
			local y = value.Y
			return {x.Scale, x.Offset, y.Scale, y.Offset}
		end,

		fromIntermediate = function(value)
			return UDim2.new(value[1], value[2], value[3], value[4])
		end,
	},

	Vector2 = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			return {value.X, value.Y}
		end,

		fromIntermediate = function(value)
			return Vector2.new(value[1], value[2])
		end,
	},

	Vector3 = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			return {value.X, value.Y, value.Z}
		end,

		fromIntermediate = function(value)
			return Vector3.new(value[1], value[2], value[3])
		end,
	},

	Color3 = {
		springType = LinearSpring.new,

		toIntermediate = function(value)
			-- convert RGB to a variant of cieluv space
			local r, g, b = value.R, value.G, value.B

			-- D65 sRGB 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
			local x = 0.9257063972951867*r - 0.8333736323779866*g - 0.09209820666085898*b
			local y = 0.2125862307855956*r + 0.71517030370341085*g + 0.0722004986433362*b
			local z = 3.6590806972265883*r + 11.4426895800574232*g + 4.1149915024264843*b

			-- xyz -> modified cieluv
			local l = y > 0.008856451679035631 and 116*y^(1/3) - 16 or 903.296296296296*y

			local u, v
			if z > 1e-14 then
				u = l*x/z
				v = l*(9*y/z - 0.46832)
			else
				u = -0.19783*l
				v = -0.46832*l
			end

			return {l, u, v}
		end,

		fromIntermediate = function(value)
			-- convert back from modified cieluv to rgb space

			local l = value[1]
			if l < 0.0197955 then
				return Color3.new(0, 0, 0)
			end
			local u = value[2]/l + 0.19783
			local v = value[3]/l + 0.46832

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

			-- xyz -> D65 sRGB
			local r =  7.2914074*x - 1.5372080*y - 0.4986286*z
			local g = -2.1800940*x + 1.8757561*y + 0.0415175*z
			local b =  0.1253477*x - 0.2040211*y + 1.0569959*z

			-- clamp minimum sRGB 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

			-- gamma correction from D65
			-- clamp to avoid undesirable overflow wrapping behavior on certain properties (e.g. BasePart.Color)
			return Color3.new(
				min(r < 3.1306684425e-3 and 12.92*r or 1.055*r^(1/2.4) - 0.055, 1),
				min(g < 3.1306684425e-3 and 12.92*g or 1.055*g^(1/2.4) - 0.055, 1),
				min(b < 3.1306684425e-3 and 12.92*b or 1.055*b^(1/2.4) - 0.055, 1)
			)
		end,
	},
}

local springStates = {} -- {[instance] = {[property] = spring}

RunService.Stepped:Connect(function(_, dt)
	for instance, state in pairs(springStates) do
		for propName, spring in pairs(state) do
			if spring:canSleep() then
				state[propName] = nil
				instance[propName] = spring.rawTarget
			else
				instance[propName] = spring:step(dt)
			end
		end

		if not next(state) then
			springStates[instance] = nil
		end
	end
end)

local function assertType(argNum, fnName, expectedType, value)
	if not STRICT_TYPES then
		return
	end

	if not expectedType:find(typeof(value)) then
		error(
			("bad argument #%d to %s (%s expected, got %s)"):format(
				argNum,
				fnName,
				expectedType,
				typeof(value)
			),
			3
		)
	end
end

local spr = {}

function spr.target(instance, dampingRatio, frequency, properties)
	assertType(1, "spr.target", "Instance", instance)
	assertType(2, "spr.target", "number", dampingRatio)
	assertType(3, "spr.target", "number", frequency)
	assertType(4, "spr.target", "table", properties)

	if dampingRatio ~= dampingRatio or dampingRatio < 0 then
		error(("expected damping ratio >= 0; got %.2f"):format(dampingRatio), 2)
	end

	if frequency ~= frequency or frequency < 0 then
		error(("expected undamped frequency >= 0; got %.2f"):format(frequency), 2)
	end

	local state = springStates[instance]

	if not state then
		state = {}
		springStates[instance] = state
	end

	for propName, propTarget in pairs(properties) do
		local propValue = instance[propName]

		if STRICT_TYPES and typeof(propTarget) ~= typeof(propValue) then
			error(
				("bad property %s to spr.target (%s expected, got %s)"):format(
					propName,
					typeof(propValue),
					typeof(propTarget)
				),
				2
			)
		end

		local spring = state[propName]
		if not spring then
			local md = typeMetadata[typeof(propTarget)]

			if not md then
				error("unsupported type: " .. typeof(propTarget), 2)
			end

			spring = md.springType(dampingRatio, frequency, propValue, md, propTarget)
			state[propName] = spring
		end

		spring.d = dampingRatio
		spring.f = frequency
		spring:setGoal(propTarget)
	end
end

function spr.stop(instance, property)
	assertType(1, "spr.stop", "Instance", instance)
	assertType(2, "spr.stop", "string|nil", property)

	if property then
		local state = springStates[instance]
		if state then
			state[property] = nil
		end
	else
		springStates[instance] = nil
	end
end

if STRICT_API_ACCESS then
	return tableLock(spr)
else
	return spr
end