--[[
	diag_contact.luau -- the front wheels now steer correctly (0.01 deg error)
	but the car still will not change heading (1.4 deg over 5 s, understeer
	3465x). Steering geometry is therefore no longer the problem: the tyres
	are producing no lateral force.

	Most likely cause: the hub is welded RIGIDLY to the body with no
	suspension travel, and the Body part is CanCollide=true. If the body
	is resting on the pad, the car slides on a big low-friction box and the
	wheels are carrying little or no load.

	This measures actual ground contact and per-wheel load.
]]

local ServerScriptService = game:GetService("ServerScriptService")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RunService = game:GetService("RunService")

local out = {}
local function log(...)
	local parts = {}
	for i = 1, select("#", ...) do
		parts[#parts + 1] = tostring((select(i, ...)))
	end
	table.insert(out, table.concat(parts, " "))
end

local Shared = ReplicatedStorage:FindFirstChild("Shared")
local Cars = require(Shared.Cars)
local Chassis = require(Shared.Chassis)

local orig = ServerScriptService:FindFirstChild("Server", true):FindFirstChild("CarManager")
local clone = orig:Clone()
clone.Parent = orig.Parent
local CarManager = require(clone)

local pad = Instance.new("Part")
pad.Size = Vector3.new(6000, 8, 6000)
pad.Position = Vector3.new(0, 5000, 0)
pad.Anchored = true
pad.Material = Enum.Material.Concrete
pad.Parent = workspace
local padTop = pad.Position.Y + 4
log(string.format("pad top surface Y = %.2f", padTop))

local car = Cars.Get("gtr_r34")
local tuning = Chassis.tuningFor(car)
local model = CarManager._buildForDiag(car, tuning)
model.Parent = workspace
model:PivotTo(CFrame.new(0, padTop + 3, 0))

local body = model.PrimaryPart
local wheels, servos, motors = {}, {}, {}
for _, d in ipairs(model:GetDescendants()) do
	if d:IsA("BasePart") and d.Name:sub(1, 6) == "Wheel_" then
		table.insert(wheels, d)
	elseif d:IsA("HingeConstraint") then
		if d.Name == Chassis.STEER_SERVO_NAME then
			table.insert(servos, d)
		elseif d.Name == Chassis.WHEEL_MOTOR_NAME then
			table.insert(motors, d)
		end
	end
end
table.sort(wheels, function(a, b)
	return a.Name < b.Name
end)

for _ = 1, 120 do
	RunService.Heartbeat:Wait()
end

log("")
log("--- AT REST ---")
log(
	string.format(
		"body: centre Y %.2f, size %s, CanCollide %s",
		body.Position.Y,
		tostring(body.Size),
		tostring(body.CanCollide)
	)
)
log(
	string.format(
		"body underside Y = %.2f  (pad top %.2f) -> gap %.2f %s",
		body.Position.Y - body.Size.Y / 2,
		padTop,
		(body.Position.Y - body.Size.Y / 2) - padTop,
		((body.Position.Y - body.Size.Y / 2) - padTop) < 0.05 and "*** BODY ON THE GROUND ***" or "(clear)"
	)
)
log(string.format("WHEEL_RADIUS %.2f", Chassis.WHEEL_RADIUS))

for _, w in ipairs(wheels) do
	local bottom = w.Position.Y - Chassis.WHEEL_RADIUS
	log(
		string.format(
			"  %-10s centre Y %7.2f  bottom %7.2f  gap to pad %6.2f  %s",
			w.Name,
			w.Position.Y,
			bottom,
			bottom - padTop,
			math.abs(bottom - padTop) < 0.1 and "CONTACT" or ((bottom - padTop) > 0.1 and "FLOATING" or "SUNK")
		)
	)
end

-- Who is actually touching the pad?
log("")
log("--- PARTS TOUCHING THE PAD ---")
local touching = pad:GetTouchingParts()
local names = {}
for _, p in ipairs(touching) do
	if p:IsDescendantOf(model) then
		names[#names + 1] = p.Name
	end
end
log(#names > 0 and ("  " .. table.concat(names, ", ")) or "  <nothing from the car>")

-- Rolling, steered: is the body dragging?
log("")
log("--- ROLLING @ ~200, STEERED -14 ---")
local topW = tuning.MaxWheelAngularVelocity
for step = 1, 240 do
	for _, mo in ipairs(motors) do
		mo.MotorMaxTorque = tuning.MotorMaxTorque
		mo.AngularVelocity = -topW
	end
	for _, s in ipairs(servos) do
		s.TargetAngle = -14
	end
	if step % 60 == 0 then
		local contactNames = {}
		for _, p in ipairs(pad:GetTouchingParts()) do
			if p:IsDescendantOf(model) then
				contactNames[#contactNames + 1] = p.Name
			end
		end
		local slip = body.AssemblyLinearVelocity
		local fwd = body.CFrame.LookVector
		local right = body.CFrame.RightVector
		log(
			string.format(
				"t %.1f  speed %6.1f  fwd %6.1f  lateral %6.1f  yaw %6.3f  bodyGap %5.2f  touching: %s",
				step / 60,
				slip.Magnitude,
				slip:Dot(fwd),
				slip:Dot(right),
				body.AssemblyAngularVelocity.Y,
				(body.Position.Y - body.Size.Y / 2) - padTop,
				#contactNames > 0 and table.concat(contactNames, ",") or "none"
			)
		)
	end
	RunService.Heartbeat:Wait()
end

model:Destroy()
pad:Destroy()
clone:Destroy()
return table.concat(out, "\n")