--[[
	diag_solveryaw.luau -- does the shell yaw solver actually fire for
	hatch_junk / hyper_x, and what does it produce?

	Hypothesis under test: the solver derives "nose" from the F/R wheel labels,
	so for a shell whose F wheels sit at +Z it should compute a 180-degree yaw
	and rotate the shell to face -Z. If that is happening, those two cars would
	look CORRECT -- but they look backwards. So either the solver is not being
	reached, or it computes something other than 180.

	CACHE GUARD FIRST. require() caches for the whole Studio session, so a
	build test can silently run OLD code. Before trusting anything below, the
	script re-reads Chassis.DRIVE_SIGN via require() and compares it to the
	.Source text. If they disagree, the cache is stale and the script ABORTS
	rather than reporting a number that means nothing.
]]

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

-- ---- cache guard -------------------------------------------------------
local chMod = find("Chassis")
if not chMod then
	return "FATAL: Chassis not found"
end
local srcHasNeg1 = chMod.Source:find("DRIVE_SIGN = -1", 1, true) ~= nil
local okReq, Chassis = pcall(require, chMod)
if not okReq then
	return "FATAL: require(Chassis) failed: " .. tostring(Chassis)
end
local liveNeg1 = (Chassis.DRIVE_SIGN == -1)

log(
	string.format(
		"cache guard: source DRIVE_SIGN=-1? %s   require() DRIVE_SIGN=%s",
		tostring(srcHasNeg1),
		tostring(Chassis.DRIVE_SIGN)
	)
)
if srcHasNeg1 ~= liveNeg1 then
	log("")
	log(">>> ABORT: require() cache disagrees with source. Any build measured now")
	log("    would use STALE code. Restart Studio (or reopen the place) and re-run.")
	return table.concat(out, "\n")
end
log("cache guard: PASS (require matches source)")
log("")

-- ---- what does the solver compute? -------------------------------------
-- Recompute the solver's own input the same way the source does: nose is the
-- F-centroid minus R-centroid, in shell-local space; yaw = -atan2(nose.X, -nose.Z).
local TARGETS = { "rx7_fc", "silv_s15", "gtr_r34", "hatch_junk", "hyper_x" }
local shells = {}
for _, root in ipairs({ RS, SSS, game:GetService("ServerStorage"), workspace }) do
	for _, d in ipairs(root:GetDescendants()) do
		if d:IsA("Model") and d:FindFirstChild("Wheels") and not shells[d.Name] then
			for _, t in ipairs(TARGETS) do
				if d.Name == t then
					shells[d.Name] = d
				end
			end
		end
	end
end

log(string.format("%-11s %-12s %-14s %s", "shell", "nose.Z", "solver yaw", "meaning"))
log(string.rep("-", 74))

for _, name in ipairs(TARGETS) do
	local shell = shells[name]
	if not shell then
		log(string.format("%-11s NOT FOUND", name))
		continue
	end
	local pivotInv = shell:GetPivot():Inverse()
	local wheels = shell:FindFirstChild("Wheels")
	local fSum, fN, rSum, rN = Vector3.zero, 0, Vector3.zero, 0
	for _, w in ipairs(wheels: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 lp = pivotInv * (sum / n)
			local head = w.Name:sub(1, 1):upper()
			if head == "F" then
				fSum, fN = fSum + lp, fN + 1
			elseif head == "R" then
				rSum, rN = rSum + lp, rN + 1
			end
		end
	end
	if fN == 0 or rN == 0 then
		log(string.format("%-11s no F/R labels", name))
		continue
	end
	local nose = (fSum / fN) - (rSum / rN)
	local yaw = -math.atan2(nose.X, -nose.Z)
	local deg = math.deg(yaw)
	local meaning
	if math.abs(deg) < 15 then
		meaning = "no rotation applied"
	elseif math.abs(math.abs(deg) - 180) < 15 then
		meaning = "180 flip -> solver DOES correct this shell"
	else
		meaning = "partial rotation"
	end
	log(
		string.format(
			"%-11s %-12s %-14s %s",
			name,
			string.format("%+.1f", nose.Z),
			string.format("%+.1f deg", deg),
			meaning
		)
	)
end

log("")
log("If the two reported-backwards shells show a 180 flip here, the solver is")
log("already correcting them in theory -- so the fault is that this code path")
log("is not reached at build time, NOT the maths. That distinction decides the fix.")

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