local boost = 4
local sprint = 8

local players = game:GetService("Players")
local runservice = game:GetService("RunService")
local uis = game:GetService("UserInputService")
local player = players.LocalPlayer

local hb_conn
local lv
local att
local sprinting = false

local function teardown()
	if hb_conn then hb_conn:Disconnect() hb_conn = nil end
	if lv then lv:Destroy() lv = nil end
	if att and att:GetAttribute("_lv_created") then att:Destroy() end
	att = nil
end

local function setup(char)
	teardown()
	local hrp = char:WaitForChild("HumanoidRootPart")
	local hum = char:WaitForChild("Humanoid")

	att = hrp:FindFirstChildOfClass("Attachment")
	if not att then
		att = Instance.new("Attachment")
		att.Name = "lv_att"
		att:SetAttribute("_lv_created", true)
		att.Parent = hrp
	end

	lv = Instance.new("LinearVelocity")
	lv.Attachment0 = att
	lv.RelativeTo = Enum.ActuatorRelativeTo.World
	lv.VelocityConstraintMode = Enum.VelocityConstraintMode.Plane
	lv.ForceLimitMode = Enum.ForceLimitMode.Magnitude
	lv.PrimaryTangentAxis = Vector3.new(1,0,0)
	lv.SecondaryTangentAxis = Vector3.new(0,0,1)
	lv.PlaneVelocity = Vector2.zero
	lv.MaxForce = hrp.AssemblyMass * 4000
	lv.Enabled = false
	lv.Parent = hrp

	hb_conn = runservice.Heartbeat:Connect(function()
		if not hum or hum.Health <= 0 then if lv.Enabled then lv.Enabled = false end return end

		local dir = hum.MoveDirection
		dir = Vector3.new(dir.X, 0, dir.Z)
		if dir.Magnitude < 1e-3 then
			if lv.Enabled then lv.Enabled = false end
			return
		end

		local target_speed = (hum.WalkSpeed or 16) + (sprinting and sprint or boost)
		local desired = dir.Unit * target_speed

		lv.PlaneVelocity = Vector2.new(desired.X, desired.Z)
		lv.MaxForce = hrp.AssemblyMass * 4000
		if not lv.Enabled then lv.Enabled = true end
	end)
end

if player.Character then setup(player.Character) end
player.CharacterAdded:Connect(setup)

uis.InputBegan:Connect(function(input, gp)
	if gp then return end
	if input.KeyCode == Enum.KeyCode.LeftShift then sprinting = true end
end)

uis.InputEnded:Connect(function(input, gp)
	if gp then return end
	if input.KeyCode == Enum.KeyCode.LeftShift then sprinting = false end
end)