-- READ-ONLY REGRESSION CHECK. Does NOT build. Inspects whatever is currently
-- in Studio and compares against every property we had verified as good, so we
-- can tell whether the last edits preserved the good version or damaged it.
--
-- Known-good baseline (measured earlier this session):
--   ramp PAEastSlip total bend 30.7deg, worst 1.3, over5=0, level run 20
--   ramp PAWestSlip total bend 34.4deg, worst 1.4, over5=0, level run 20
--   AuxLane parts = 30   (user's hand-edited count, NOT the source's 52)
--   unguarded deck edges = 0 across all 823 samples
--   parts ~= 16788
local out = {}
local function say(s) table.insert(out, s) end

local map = workspace:FindFirstChild("Map")
if not map then return "Map MISSING -- nothing built" end

local UP = Vector3.new(0, 1, 0)
local function flat(v) return Vector3.new(v.X, 0, v.Z) end

local parts = 0
local deck, aux, bars, slipParts = {}, {}, {}, {}
for _, d in ipairs(map:GetDescendants()) do
	if d:IsA("BasePart") then
		parts += 1
		local k = d.Name:match("^Road_(%d+)$") or d.Name:match("^Deck_(%d+)$")
		if k then deck[tonumber(k)] = d end
		local a = d.Name:match("^AuxLane_(%d+)$")
		if a then aux[tonumber(a)] = d end
		if d.Name == "Barrier" or d.Name == "EdgeRail" then table.insert(bars, d) end
		if d.Name:match("Slip") then table.insert(slipParts, d) end
	end
end
say(("parts = %d          (baseline ~16788)"):format(parts))

-- 1. RAMP SMOOTHNESS -- the thing the user cares most about right now
local rampOK = true
for _, s in ipairs({ "PAWestSlip", "PAEastSlip" }) do
	local segs = {}
	for _, d in ipairs(map:GetDescendants()) do
		if d:IsA("BasePart") then
			local k = d.Name:match("^" .. s .. "_Deck_(%d+)$")
			if k then table.insert(segs, { i = tonumber(k), p = d.Position, cf = d.CFrame }) end
		end
	end
	table.sort(segs, function(a, b) return a.i < b.i end)
	if #segs == 0 then
		say(s .. ": ABSENT  <<< RAMP GONE")
		rampOK = false
	else
		local total, worst, worstAt, over = 0, 0, -1, 0
		for j = 2, #segs do
			local a, b = segs[j - 1].cf.LookVector, segs[j].cf.LookVector
			local dth = math.deg(math.acos(math.clamp(a:Dot(b), -1, 1)))
			total += dth
			if dth > worst then worst = dth; worstAt = segs[j].i end
			if dth > 5 then over += 1 end
		end
		local topY, level = segs[1].p.Y, 0
		for _, sg in ipairs(segs) do
			if math.abs(sg.p.Y - topY) < 0.5 then level += 1 else break end
		end
		if over > 0 then rampOK = false end
		say(("%s: segs=%d total=%.1fdeg worst=%.1f@%d over5=%d level=%d %s"):format(
			s, #segs, total, worst, worstAt, over, level,
			over == 0 and "OK" or "<<< KINKED"))
	end
end
say(rampOK and ">> RAMPS STILL SMOOTH" or ">> RAMP REGRESSION")

-- 2. USER'S DELETED LANE -- must stay deleted
local auxN, inRange = 0, 0
for i in pairs(aux) do
	auxN += 1
	if i >= 525 and i <= 550 then inRange += 1 end
end
say(("AuxLane = %d (baseline 30) | inside deleted run 525..550 = %d (want 0) %s"):format(
	auxN, inRange, (auxN == 30 and inRange == 0) and "OK" or "<<< REGRESSION"))

-- 3. BARRIER COVERAGE -- full loop
local holes = {}
local swept = 0
for i, d in pairs(deck) do
	swept += 1
	local right = d.CFrame.LookVector:Cross(UP).Unit
	for _, sgn in ipairs({ -1, 1 }) do
		local edge = d.Position + right * sgn * (d.Size.X / 2 + 2)
		local bd = math.huge
		for _, b in ipairs(bars) do
			if math.abs(b.Position.Y - edge.Y) < 14 then
				local dd = (flat(b.Position) - flat(edge)).Magnitude
				if dd < bd then bd = dd end
			end
		end
		if bd >= 12 then
			local okb = false
			local a = aux[i]
			if a then
				local outer = a.Position + right * sgn * (a.Size.X / 2 + 2)
				local bd2 = math.huge
				for _, b in ipairs(bars) do
					if math.abs(b.Position.Y - outer.Y) < 14 then
						local dd = (flat(b.Position) - flat(outer)).Magnitude
						if dd < bd2 then bd2 = dd end
					end
				end
				if bd2 < 14 then okb = true end
			end
			if not okb then
				local sd = math.huge
				for _, p in ipairs(slipParts) do
					local dd = (flat(p.Position) - flat(edge)).Magnitude
					if dd < sd then sd = dd end
				end
				if sd > 30 then table.insert(holes, i .. (sgn < 0 and "L" or "R")) end
			end
		end
	end
end
say(("barrier sweep: %d samples, unguarded=%d %s"):format(swept, #holes,
	#holes == 0 and "OK" or ("<<< " .. table.concat(holes, ","))))

-- 4. FENCE JOG at the suppression boundary
local prevLat, jogs = nil, {}
for i = 505, 570 do
	local d = deck[i]
	if d then
		local right = d.CFrame.LookVector:Cross(UP).Unit
		local best, bestLat = math.huge, nil
		for _, b in ipairs(bars) do
			if b.Name == "Barrier" and math.abs(b.Position.Y - d.Position.Y) < 14 then
				local rel = b.Position - d.Position
				local along = math.abs(rel:Dot(d.CFrame.LookVector))
				local lat = rel:Dot(right)
				if along < 22 and lat < 0 and along < best then best = along; bestLat = lat end
			end
		end
		if bestLat then
			if prevLat then
				local step = math.abs(math.abs(bestLat) - math.abs(prevLat))
				if step > 10 then table.insert(jogs, ("%d(%.1f)"):format(i, step)) end
			end
			prevLat = bestLat
		else
			prevLat = nil
		end
	end
end
say(("fence jogs >10 studs: %d %s"):format(#jogs,
	#jogs == 0 and "OK" or ("<<< " .. table.concat(jogs, " "))))

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