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

		toIntermediate = function(value)
			return {value and 1 or 0}
		end,

		fromIntermediate = function(value)
			return value[1] >= 0.5
		end,
	},

	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], round(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], round(value[2]), value[3], round(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 = rgbToLuv,
		fromIntermediate = luvToRgb,
	},
	
	-- Only takes start and end keypoints
	ColorSequence = {
		springType = LinearSpring.new,
		toIntermediate = function(value)
			local keypoints = value.Keypoints
			
			local luv0 = rgbToLuv(keypoints[1].Value)
			local luv1 = rgbToLuv(keypoints[#keypoints].Value)
			
			return {
				luv0[1], luv0[2], luv0[3],
				luv1[1], luv1[2], luv1[3],
			}
		end,

		fromIntermediate = function(value)
			return ColorSequence.new(
				luvToRgb{value[1], value[2], value[3]},
				luvToRgb{value[4], value[5], value[6]}
			)
		end,
	},
}

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

RunService.Heartbeat:Connect(function(dt)
	for instance, state in springStates do
		for propName, spring in 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 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)
	if STRICT_TYPES then
		assertType(1, "spr.target", "Instance", instance)
		assertType(2, "spr.target", "number", dampingRatio)
		assertType(3, "spr.target", "number", frequency)
		assertType(4, "spr.target", "table", properties)
	end

	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 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)
	if STRICT_TYPES then
		assertType(1, "spr.stop", "Instance", instance)
		assertType(2, "spr.stop", "string|nil", property)
	end

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

return table.freeze(spr)