--[[
	verify_convention.luau -- prove the forward convention is now consistent.

	Deliberately NOT measuring anything derived from a constant. The previous
	harness read Wheel_* positions, which come straight from
	Chassis.WHEELBASE_HALF (5.9) -- identical for every car whether or not any
	fix applied, so it passed vacuously. Here every assertion is a RELATIONSHIP
	that genuinely differs between the broken and fixed builds:

	  1. The steering servo must sit on the axle that LEADS under throttle.
	     Broken build: servos on the trailing axle (shopping-cart caster).
	  2. The shell nose must point the same way the seat drives.
	     Broken build: 180 degrees opposed.
	  3. DRIVE_SIGN must spin the wheels toward the direction of travel.

	Builds each car via the real path (Chassis.tuningFor + _buildForDiag) in
	the Edit datamodel, where require() is fresh.
]]

local SSS = game:GetService("ServerScriptService")
local RS = game:GetService("ReplicatedStorage")

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 function findModule(name: string): ModuleScript?
	for _, root in ipairs({ SSS, RS }) do
		local hit = root:FindFirstChild(name, true)
		if hit and hit:IsA("ModuleScript") then
			return hit
		end
	end
	return nil
end

local cmMod = findModule("CarManager")
local carsMod = findModule("Cars")
local chassisMod = findModule("Chassis")
if not (cmMod and carsMod and chassisMod) then
	return "FATAL: missing module(s)"
end

local CarManager = require(cmMod)
local Cars = require(carsMod)
local Chassis = require(chassisMod)

if typeof(CarManager._buildForDiag) ~= "function" then
	return "FATAL: _buildForDiag absent -- stale CarManager, refusing to report"
end

log(string.format("Chassis.DRIVE_SIGN = %s", tostring(Chassis.DRIVE_SIGN)))
log("")

local carList = Cars.List or Cars.All
if typeof(carList) ~= "table" or #carList == 0 then
	return "FATAL: empty car list"
end

log(string.format("%-11s %-22s %-24s %s", "car", "steered axle", "shell nose vs drive", "verdict"))
log(string.rep("-", 78))

local tested, failed = 0, 0

for _, car in ipairs(carList) do
	if typeof(car) ~= "table" or not car.Id then
		continue
	end

	local tuning = Chassis.tuningFor(car)
	local ok, model = pcall(CarManager._buildForDiag, car, tuning)
	if not ok or typeof(model) ~= "Instance" then
		log(string.format("%-11s BUILD FAILED: %s", car.Id, tostring(model)))
		failed += 1
		continue
	end

	local body = model:FindFirstChild("Body")
	local seat
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("VehicleSeat") then
			seat = d
			break
		end
	end

	if not (body and body:IsA("BasePart") and seat) then
		log(string.format("%-11s NO BODY/SEAT", car.Id))
		failed += 1
		model:Destroy()
		continue
	end

	tested += 1
	local inv = body.CFrame:Inverse()
	-- Direction of travel under positive throttle, in body-local space.
	local driveZ = inv:VectorToObjectSpace(seat.CFrame.LookVector).Z
	local drivePos = driveZ > 0

	-- (1) Which axle carries the steering servos?
	local servoZ, servoN = 0, 0
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("HingeConstraint") and d.ActuatorType == Enum.ActuatorType.Servo then
			local host = d.Parent
			if host and host:IsA("BasePart") then
				servoZ += (inv * host.CFrame).Z
				servoN += 1
			end
		end
	end
	local steerLeads, steerTxt = false, "no servos"
	if servoN > 0 then
		local sm = servoZ / servoN
		steerLeads = (drivePos and sm > 0) or (not drivePos and sm < 0)
		steerTxt = string.format("z=%+.2f %s", sm, steerLeads and "LEADS" or "TRAILS")
	end

	-- (2) Shell nose vs direction of travel.
	local shell
	for _, c in ipairs(model:GetChildren()) do
		if c:IsA("Model") then
			shell = c
			break
		end
	end
	local shellOk, shellTxt = true, "no shell"
	if shell then
		local shellLook = shell:GetPivot().LookVector
		local seatLook = seat.CFrame.LookVector
		local a = Vector3.new(shellLook.X, 0, shellLook.Z)
		local b = Vector3.new(seatLook.X, 0, seatLook.Z)
		if a.Magnitude > 1e-4 and b.Magnitude > 1e-4 then
			local deg = math.deg(math.acos(math.clamp(a.Unit:Dot(b.Unit), -1, 1)))
			shellOk = deg < 30
			shellTxt = string.format("%.1f deg %s", deg, shellOk and "OK" or "FLIPPED")
		end
	end

	local pass = (servoN == 0 or steerLeads) and shellOk
	if not pass then
		failed += 1
	end
	log(string.format("%-11s %-22s %-24s %s", car.Id, steerTxt, shellTxt, pass and "PASS" or "FAIL"))
	model:Destroy()
end

log("")
if tested == 0 then
	log(">>> NOTHING TESTED -- this is a FAILURE, not a pass.")
elseif failed > 0 then
	log(string.format(">>> %d/%d FAILED", failed, tested))
else
	log(string.format(">>> ALL %d CARS PASS: steered axle leads, shell faces travel", tested))
end

return table.concat(out, "\n")