--[[
	diag_builtnose.luau -- END-TO-END measurement. Build each car for real via
	CarManager._buildForDiag, then measure where the finished shell's nose
	actually points relative to the chassis forward axis.

	Why this and not more code reading: the solver computes the right 180-degree
	yaw (diag_solveryaw) and applies it without centring error (diag_centrefix),
	yet two cars still look backwards. So something AFTER the PivotTo must be
	undoing it. Rather than guess which line, measure the finished article.

	noseDot = (shell nose direction) dot (body LookVector)
	    +1  -> shell nose points where the car drives  (CORRECT)
	    -1  -> shell nose points backwards             (REVERSED)

	Cache guard first: require() caches per Studio session, so a stale
	CarManager would silently build old code and make this whole test a lie.
]]

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

local out = {}
local function log(s)
	table.insert(out, s)
end

local function find(name)
	for _, root in ipairs({ SSS, RS, game:GetService("ServerStorage"), workspace }) do
		local m = root:FindFirstChild(name, true)
		if m and m:IsA("ModuleScript") then
			return m
		end
	end
	return nil
end

local cmMod = find("CarManager")
if not cmMod then
	return "FATAL: CarManager not found"
end
-- Guard: the reverted source must be what require() hands back.
local srcOK = cmMod.Source:find("isFront = zSign < 0", 1, true) ~= nil
if not srcOK then
	return "FATAL: CarManager source is not the reverted version -- aborting"
end
local ok, CM = pcall(require, cmMod)
if not ok then
	return "FATAL: require(CarManager) failed: " .. tostring(CM)
end
if type(CM._buildForDiag) ~= "function" then
	return "FATAL: CarManager._buildForDiag missing (stale require cache?) -- restart Studio"
end

local Cars = require(RS:WaitForChild("Shared"):WaitForChild("Cars"))
local ChassisMod = require(RS:WaitForChild("Shared"):WaitForChild("Chassis"))

local TARGETS = { "rx7_fc", "silv_s15", "gtr_r34", "hatch_junk", "hyper_x" }

log(string.format("%-11s %-10s %-12s %s", "shell", "noseDot", "yaw err", "verdict"))
log(string.rep("-", 62))

local built = 0
for _, name in ipairs(TARGETS) do
	-- buildCarModel(car: Car, tuning: Tuning) -- NOT a string id. Passing a
	-- string was the harness bug that produced the CarManager:277 nil error.
	local carDef = Cars.Get(name)
	if not carDef then
		log(string.format("%-11s NOT IN Cars.List", name))
		continue
	end
	local tuning = ChassisMod.tuningFor(carDef)
	local okB, car = pcall(CM._buildForDiag, carDef, tuning)
	if not okB or not car then
		log(string.format("%-11s BUILD FAILED: %s", name, tostring(car)))
		continue
	end
	built += 1

	local body = car:FindFirstChild("Body") or car.PrimaryPart
	local shell = nil
	for _, d in ipairs(car:GetChildren()) do
		if d:IsA("Model") and d:FindFirstChild("Wheels") then
			shell = d
			break
		end
	end

	if not body or not shell then
		log(string.format("%-11s no body/shell on built car", name))
		car:Destroy()
		continue
	end

	-- Shell nose in WORLD space, from the shell's own wheel labels.
	local wf = shell:FindFirstChild("Wheels")
	local fSum, fN, rSum, rN = Vector3.zero, 0, Vector3.zero, 0
	for _, w in ipairs(wf:GetChildren()) do
		local sum, n = Vector3.zero, 0
		if w:IsA("BasePart") then
			sum, n = w.Position, 1
		end
		for _, d in ipairs(w:GetDescendants()) do
			if d:IsA("BasePart") then
				sum, n = sum + d.Position, n + 1
			end
		end
		if n > 0 then
			local h = w.Name:sub(1, 1):upper()
			if h == "F" then
				fSum, fN = fSum + (sum / n), fN + 1
			elseif h == "R" then
				rSum, rN = rSum + (sum / n), rN + 1
			end
		end
	end

	if fN == 0 or rN == 0 then
		log(string.format("%-11s no F/R labels on built shell", name))
		car:Destroy()
		continue
	end

	local nose = (fSum / fN) - (rSum / rN)
	nose = Vector3.new(nose.X, 0, nose.Z)
	if nose.Magnitude < 0.01 then
		log(string.format("%-11s degenerate nose vector", name))
		car:Destroy()
		continue
	end
	nose = nose.Unit

	local fwd = body.CFrame.LookVector
	fwd = Vector3.new(fwd.X, 0, fwd.Z).Unit

	local dot = nose:Dot(fwd)
	local yawErr = math.deg(math.acos(math.clamp(dot, -1, 1)))

	local verdict
	if dot > 0.85 then
		verdict = "CORRECT (nose = drive dir)"
	elseif dot < -0.85 then
		verdict = "*** REVERSED ***"
	else
		verdict = "skewed"
	end

	log(
		string.format(
			"%-11s %-10s %-12s %s",
			name,
			string.format("%+.3f", dot),
			string.format("%.1f deg", yawErr),
			verdict
		)
	)
	car:Destroy()
end

log("")
if built == 0 then
	log(">>> NOTHING BUILT -- this is a FAILURE, not a pass.")
else
	log(string.format(">>> built and measured %d/5 cars, then destroyed them (no scene changes)", built))
	log("    This is the finished article, after every stage of the build pipeline.")
end

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