-- Ctor
function ActiveCastStatic.new(caster: Caster, origin: Vector3, direction: Vector3, velocity: Vector3 | number, castDataPacket: FastCastBehavior): ActiveCast
	if typeof(velocity) == "number" then
		velocity = direction.Unit * velocity
	end	
	
	if (castDataPacket.HighFidelitySegmentSize <= 0) then
		error("Cannot set FastCastBehavior.HighFidelitySegmentSize <= 0!", 0)
	end
	
	-- Basic setup
	local cast = {
		Caster = caster,
		
		-- Data that keeps track of what's going on as well as edits we might make during runtime.
		StateInfo = {
			UpdateConnection = nil,
			Paused = false,
			TotalRuntime = 0,
			DistanceCovered = 0,
			HighFidelitySegmentSize = castDataPacket.HighFidelitySegmentSize,
			HighFidelityBehavior = castDataPacket.HighFidelityBehavior,
			IsActivelySimulatingPierce = false,
			IsActivelyResimulating = false,
			CancelHighResCast = false,
			Trajectories = {
				{
					StartTime = 0,
					EndTime = -1,
					Origin = origin,
					InitialVelocity = velocity,
					Acceleration = castDataPacket.Acceleration
				}
			}
		},
		
		-- Information pertaining to actual raycasting.
		RayInfo = {
			Parameters = castDataPacket.RaycastParams,
			WorldRoot = workspace,
			MaxDistance = castDataPacket.MaxDistance or 1000,
			CosmeticBulletObject = castDataPacket.CosmeticBulletTemplate, -- This is intended. We clone it a smidge of the way down.
			CanPierceCallback = castDataPacket.CanPierceFunction
		},
		
		UserData = {}
	}
	
	if cast.StateInfo.HighFidelityBehavior == 2 then
		cast.StateInfo.HighFidelityBehavior = 3
	end
	
	
	if cast.RayInfo.Parameters ~= nil then
		cast.RayInfo.Parameters = CloneCastParams(cast.RayInfo.Parameters)
	else
		cast.RayInfo.Parameters = RaycastParams.new()
	end

	local usingProvider = false
	if castDataPacket.CosmeticBulletProvider == nil then
		-- The provider is nil. Use a cosmetic object clone.
		if cast.RayInfo.CosmeticBulletObject ~= nil then
			cast.RayInfo.CosmeticBulletObject = cast.RayInfo.CosmeticBulletObject:Clone()
			cast.RayInfo.CosmeticBulletObject.CFrame = CFrame.new(origin, origin + direction)
			cast.RayInfo.CosmeticBulletObject.Parent = castDataPacket.CosmeticBulletContainer
		end
	else
		-- The provider is not nil.
		-- Is it what we want?
		if typeof(castDataPacket.CosmeticBulletProvider) == "PartCache" then
			-- this modded version of typeof is implemented up top.
			-- Aside from that, yes, it's a part cache. Good to go!
			
			if cast.RayInfo.CosmeticBulletObject ~= nil then
				-- They also set the template. Not good. Warn + clear this up.
				warn("Do not define FastCastBehavior.CosmeticBulletTemplate and FastCastBehavior.CosmeticBulletProvider at the same time! The provider will be used, and CosmeticBulletTemplate will be set to nil.")
				cast.RayInfo.CosmeticBulletObject = nil
				castDataPacket.CosmeticBulletTemplate = nil
			end

			cast.RayInfo.CosmeticBulletObject = castDataPacket.CosmeticBulletProvider:GetPart()
			cast.RayInfo.CosmeticBulletObject.CFrame = CFrame.new(origin, origin + direction)
			usingProvider = true
		else
			warn("FastCastBehavior.CosmeticBulletProvider was not an instance of the PartCache module (an external/separate model)! Are you inputting an instance created via PartCache.new? If so, are you on the latest version of PartCache? Setting FastCastBehavior.CosmeticBulletProvider to nil.")
			castDataPacket.CosmeticBulletProvider = nil
		end
	end

	local targetContainer: Instance;
	if usingProvider then
		targetContainer = castDataPacket.CosmeticBulletProvider.CurrentCacheParent
	else
		targetContainer = castDataPacket.CosmeticBulletContainer
	end
	
	if castDataPacket.AutoIgnoreContainer == true and targetContainer ~= nil then
		local ignoreList = cast.RayInfo.Parameters.FilterDescendantsInstances
		if table.find(ignoreList, targetContainer) == nil then
			table.insert(ignoreList, targetContainer)
			cast.RayInfo.Parameters.FilterDescendantsInstances = ignoreList
		end
	end
	
	local event
	if RunService:IsClient() then
		event = RunService.RenderStepped
	else
		event = RunService.Heartbeat
	end
	
	setmetatable(cast, ActiveCastStatic)
	
	cast.StateInfo.UpdateConnection = event:Connect(function (delta)
		if cast.StateInfo.Paused then return end
		
		PrintDebug("Casting for frame.")
		local latestTrajectory = cast.StateInfo.Trajectories[#cast.StateInfo.Trajectories]
		if (cast.StateInfo.HighFidelityBehavior == 3 and latestTrajectory.Acceleration ~= Vector3.new() and cast.StateInfo.HighFidelitySegmentSize > 0) then
			
			local timeAtStart = tick()
			
			if cast.StateInfo.IsActivelyResimulating then
				cast:Terminate()
				error("Cascading cast lag encountered! The caster attempted to perform a high fidelity cast before the previous one completed, resulting in exponential cast lag. Consider increasing HighFidelitySegmentSize.")
			end
			
			cast.StateInfo.IsActivelyResimulating = true
			
			-- Actually want to calculate this early to find displacement
			local origin = latestTrajectory.Origin
			local totalDelta = cast.StateInfo.TotalRuntime - latestTrajectory.StartTime
			local initialVelocity = latestTrajectory.InitialVelocity
			local acceleration = latestTrajectory.Acceleration
			
			local lastPoint = GetPositionAtTime(totalDelta, origin, initialVelocity, acceleration)
			local lastVelocity = GetVelocityAtTime(totalDelta, initialVelocity, acceleration)
			local lastDelta = cast.StateInfo.TotalRuntime - latestTrajectory.StartTime
			
			cast.StateInfo.TotalRuntime += delta
			
			-- Recalculate this.
			totalDelta = cast.StateInfo.TotalRuntime - latestTrajectory.StartTime
			
			local currentPoint = GetPositionAtTime(totalDelta, origin, initialVelocity, acceleration)
			local currentVelocity = GetVelocityAtTime(totalDelta, initialVelocity, acceleration) 
			local totalDisplacement = currentPoint - lastPoint -- This is the displacement from where the ray was on the last from to where the ray is now.
			
			local rayDir = totalDisplacement.Unit * currentVelocity.Magnitude * delta
			local targetWorldRoot = cast.RayInfo.WorldRoot
			
			local function castFunction(lastPoint, rayDir, params)
				local resultOfCast = targetWorldRoot:Raycast(lastPoint, rayDir, params)

				if resultOfCast then
					local hitInstance = resultOfCast.Instance

					if hitInstance.Parent:IsA("Accoutrement") then
						table.insert(params.FilterDescendantsInstances, hitInstance)
						resultOfCast = nil
					end

					if hitInstance.CanCollide == false then
						table.insert(params.FilterDescendantsInstances, hitInstance)
						resultOfCast = nil
					end

					if hitInstance.CanCollide == false and hitInstance.Transparency > 0.2 then
						table.insert(params.FilterDescendantsInstances, hitInstance)
						resultOfCast = nil
					end
				end

				return resultOfCast
			end
			
			local resultOfCast = castFunction(lastPoint, rayDir, cast.RayInfo.Parameters)
			
			local point = currentPoint
			
			if (resultOfCast ~= nil) then
				point = resultOfCast.Position
			end
			
			local rayDisplacement = (point - lastPoint).Magnitude
			
			-- Now undo this. The line below in the for loop will add this time back gradually.
			cast.StateInfo.TotalRuntime -= delta
			
			-- And now that we have displacement, we can calculate segment size.
			local numSegmentsDecimal = rayDisplacement / cast.StateInfo.HighFidelitySegmentSize -- say rayDisplacement is 5.1, segment size is 0.5 -- 10.2 segments
			local numSegmentsReal = math.floor(numSegmentsDecimal) -- 10 segments + 0.2 extra segments
			if (numSegmentsReal == 0) then
				numSegmentsReal = 1
			end
			
			local timeIncrement = delta / numSegmentsReal
			
			for segmentIndex = 1, numSegmentsReal do
				if getmetatable(cast) == nil then return end -- Could have been disposed.
				if cast.StateInfo.CancelHighResCast then
					cast.StateInfo.CancelHighResCast = false
					break
				end
				PrintDebug("[" .. segmentIndex .. "] Subcast of time increment " .. timeIncrement)
				SimulateCast(cast, timeIncrement, true)
			end
			
			if getmetatable(cast) == nil then return end -- Could have been disposed.
			cast.StateInfo.IsActivelyResimulating = false
			
			if (tick() - timeAtStart) > 0.016 * 5 then
				warn("Extreme cast lag encountered! Consider increasing HighFidelitySegmentSize.")
			end
			
		else
			SimulateCast(cast, delta, false)
		end
	end)
	
	return cast
end

function ActiveCastStatic.SetStaticFastCastReference(ref)
	FastCast = ref
end