tokyo-wangan-racing/tools/diag_shellgeom.luau

--[[
	diag_shellgeom.luau -- measure the SHELL BODYWORK directly.

	Two prior attempts both returned dZ = -11.80 for every car, which is the
	chassis wheelbase: the "shell wheels" being matched are in fact the
	chassis Wheel_* parts, so those runs proved nothing about shell facing.

	Stop relying on wheel names. Instead:
	  1. Dump the real child structure of one shell so we can see what is
	     actually in there after the build.
	  2. Measure asymmetric BODYWORK mass: a car's cabin/rear sits behind its
	     nose, so the shell's own parts are not symmetric front-to-back.
	     Compare the shell part centroid against the shell AABB centre along
	     body-local Z -- the sign flips when the shell is rotated 180.
	  3. Cross-check against the same measurement on the raw TEMPLATE, where
	     diag_shellyaw2 already established ground truth (hatch_junk and
	     hyper_x authored nose-toward +Z, the other three nose-toward -Z).
	If the built car's sign matches the template's, the flip never happened.
]]

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 cloneMod = orig:Clone()
cloneMod.Parent = orig.Parent
local CarManager = require(cloneMod)

-- 1. What is actually inside a built shell?
local car0 = Cars.Get("hyper_x")
local m0 = CarManager._buildForDiag(car0, Chassis.tuningFor(car0))
m0.Parent = workspace
m0:PivotTo(CFrame.new(0, 5010, 0))
local shell0 = m0:FindFirstChild("Shell")
log("=== STRUCTURE of built hyper_x Shell ===")
if shell0 then
	for _, c in ipairs(shell0:GetChildren()) do
		local extra = ""
		if c:IsA("Folder") or c:IsA("Model") then
			local kids = {}
			for _, k in ipairs(c:GetChildren()) do
				kids[#kids + 1] = k.Name
			end
			extra = " {" .. table.concat(kids, ",") .. "}"
		end
		log(string.format("   %-16s %s%s", c.Name, c.ClassName, extra))
	end
else
	log("   <no Shell>")
end
m0:Destroy()
log("")

-- 2/3. Bodywork asymmetry, template vs built.
local function asymmetry(root: Instance, frame: CFrame): number?
	-- Volume-weighted centroid of bodywork, minus AABB centre, along local Z.
	local inv = frame:Inverse()
	local sum, wsum = 0, 0
	local lo, hi = math.huge, -math.huge
	for _, p in ipairs(root:GetDescendants()) do
		if p:IsA("BasePart") then
			local n = p.Name:lower()
			-- exclude wheels/tyres of any naming convention
			if not (n:find("wheel") or n:find("tyre") or n:find("tire") or n:find("rim")) then
				local z = (inv * p.Position).Z
				local vol = p.Size.X * p.Size.Y * p.Size.Z
				sum += z * vol
				wsum += vol
				lo = math.min(lo, z)
				hi = math.max(hi, z)
			end
		end
	end
	if wsum <= 0 then
		return nil
	end
	local centroid = sum / wsum
	local aabbCentre = (lo + hi) / 2
	return centroid - aabbCentre
end

log("=== BODYWORK ASYMMETRY along local Z (centroid - aabb centre) ===")
log("A car has more mass toward the REAR (cabin/boot), so on a correctly")
log("faced shell this should be POSITIVE (mass behind centre, nose at -Z).")
log("")
log(string.format("%-14s %14s %14s   %s", "car", "template", "built", "verdict"))

for _, template in ipairs(ReplicatedStorage.CarModels:GetChildren()) do
	local id = template.Name
	local tA = asymmetry(template, template:GetPivot())
	local car = Cars.Get(id)
	local bA = nil
	if car then
		local m = CarManager._buildForDiag(car, Chassis.tuningFor(car))
		m.Parent = workspace
		m:PivotTo(CFrame.new(0, 5010, 0))
		for _ = 1, 3 do
			RunService.Heartbeat:Wait()
		end
		local sh = m:FindFirstChild("Shell")
		if sh then
			bA = asymmetry(sh, m.PrimaryPart.CFrame)
		end
		m:Destroy()
	end
	local verdict = "?"
	if tA and bA then
		local flipped = (tA > 0) ~= (bA > 0)
		verdict = flipped and "rotated by build" or "NOT rotated"
	end
	log(
		string.format(
			"%-14s %14s %14s   %s",
			id,
			tA and string.format("%+.3f", tA) or "n/a",
			bA and string.format("%+.3f", bA) or "n/a",
			verdict
		)
	)
end

cloneMod:Destroy()
return table.concat(out, "\n")