-- Verification v3: seam lip measured against the KNOWN shared sample point.
--
-- v2 still had a sign bug: Roblox CFrame.LookVector is the -Z axis, so a deck
-- built with CFrame.lookAt(mid, mid+dir) has its FORWARD end at local
-- z = -(Size.Z-2)/2 and its REAR end at +(Size.Z-2)/2. v2 had these swapped,
-- comparing deck i's rear to deck i+1's rear -- a systematic error that
-- reported a near-constant 5.2 on every sloped segment regardless of zone.
--
-- This version avoids guessing signs: for each deck it takes BOTH end faces,
-- picks whichever is nearer the shared sample point b.pos in XZ, and reports
-- the surface-height difference there. Sanity-checked against the flat-ground
-- expectation and cross-checked with a downward raycast.
local sss = game:GetService("ServerScriptService")
local orig = sss:FindFirstChild("MapBuilder", true)
local clone = orig:Clone()
clone.Name = "MapBuilder_Verify3"
clone.Parent = orig.Parent
local okM, MB = pcall(require, clone)
if not okM then
	clone:Destroy()
	return "FAIL require: " .. tostring(MB)
end
local okB, map = pcall(MB.build)
if not okB then
	clone:Destroy()
	return "FAIL build: " .. tostring(map)
end

local Circuit = require(game:GetService("ReplicatedStorage"):FindFirstChild("Circuit", true))
local samples = Circuit.samples
local n = #samples

local decks = {}
for _, d in ipairs(map:GetDescendants()) do
	if d:IsA("BasePart") then
		local idx = d.Name:match("^Road_(%d+)$")
		if idx then
			decks[tonumber(idx)] = d
		end
	end
end

local out = {}
local function line(s)
	out[#out + 1] = s
end

-- Top-surface height of deck `d` at the end nearest world point `p` (XZ).
local function topAtNearestEnd(d, p)
	local half = (d.Size.Z - 2) / 2
	local best, bestD = nil, math.huge
	for _, z in ipairs({ -half, half }) do
		local w = d.CFrame * CFrame.new(0, d.Size.Y / 2, z)
		local dd = (Vector3.new(w.X, 0, w.Z) - Vector3.new(p.X, 0, p.Z)).Magnitude
		if dd < bestD then
			best, bestD = w.Y, dd
		end
	end
	return best, bestD
end

local worst, worstAt, worstGap = 0, -1, 0
local lips = {}
for i = 1, n do
	local j = (i % n) + 1
	local a, b = decks[i], decks[j]
	if a and b then
		local shared = samples[j].pos -- the sample both decks meet at
		local ya, da = topAtNearestEnd(a, shared)
		local yb, db = topAtNearestEnd(b, shared)
		local lip = math.abs(ya - yb)
		lips[#lips + 1] = { lip, i, math.max(da, db) }
		if lip > worst then
			worst, worstAt, worstGap = lip, i, math.max(da, db)
		end
	end
end
table.sort(lips, function(p, q)
	return p[1] > q[1]
end)
local top = {}
for k = 1, math.min(5, #lips) do
	top[#top + 1] = ("i=%d:%.4f(%s)"):format(lips[k][2], lips[k][1], samples[lips[k][2]].piece)
end
line(
	("SEAM max lip=%.4f at i=%d (endpoint XZ err %.3f) -> %s"):format(
		worst,
		worstAt,
		worstGap,
		worst <= 0.30 and "PASS" or "FAIL"
	)
)
line("SEAM top5: " .. table.concat(top, " "))

-- Independent cross-check: raycast down onto the driving surface just before
-- and just after each seam. A real step would show up here too.
-- MUST filter to the Expressway folder only. Filtering on the whole map lets
-- the ray hit TunnelCeiling / MedianFence / overpass decks on the way down and
-- reports a bogus ~19-stud "step" that has nothing to do with the road surface.
local rp = RaycastParams.new()
rp.FilterType = Enum.RaycastFilterType.Include
rp.FilterDescendantsInstances = { map:FindFirstChild("Expressway") }
local rWorst, rAt = 0, -1
for i = 1, n do
	local j = (i % n) + 1
	local p = samples[j].pos
	local fwd = (samples[(j % n) + 1].pos - samples[i].pos)
	fwd = Vector3.new(fwd.X, 0, fwd.Z)
	if fwd.Magnitude > 0.01 then
		fwd = fwd.Unit
		local h1 = workspace:Raycast(p - fwd * 3 + Vector3.new(0, 40, 0), Vector3.new(0, -120, 0), rp)
		local h2 = workspace:Raycast(p + fwd * 3 + Vector3.new(0, 40, 0), Vector3.new(0, -120, 0), rp)
		if h1 and h2 then
			local d = math.abs(h1.Position.Y - h2.Position.Y)
			if d > rWorst then
				rWorst, rAt = d, i
			end
		end
	end
end
line(
	("RAYCAST surface step across seams (+-3 studs): max=%.4f at i=%d -> %s"):format(
		rWorst,
		rAt,
		rWorst <= 0.60 and "PASS" or "FAIL"
	)
)

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