-- FLYOVER PROBE. Two things the connectivity check cannot tell you:
--
--   1. Does the crossing actually pass OVER the mainline deck, with real
--      vertical clearance? A "flyover" that intersects the deck is just a
--      wall. Measured as: for every Cross part, find mainline Road parts
--      directly beneath it in plan, and report the worst (smallest) gap
--      between the ramp underside and the road topside.
--
--   2. Does the descent land tangent and flush on the FAR carriageway?
--      Reported as the dY at the last descent part vs the road beneath it.
--
-- Every metric carries a CONTROL that must come back non-zero, because a
-- silent 0 from a mis-scoped query is indistinguishable from a genuine pass
-- -- that exact trap produced two phantom "defects" earlier in this build.

local ws = game:GetService("Workspace")
local map = ws:FindFirstChild("Map")
if not map then
	return "NO MAP"
end

local cross, descent, roads = {}, {}, {}
for _, d in ipairs(map:GetDescendants()) do
	if d:IsA("BasePart") then
		local nm = d.Name
		if nm:find("RampCross_") then
			table.insert(cross, d)
		elseif nm:find("RampNear_") then
			table.insert(descent, d)
		elseif nm:sub(1, 5) == "Road_" then
			table.insert(roads, d)
		end
	end
end

-- plan-view overlap (ignores Y entirely)
local function planOverlap(a, b)
	return math.abs(a.Position.X - b.Position.X) < (a.Size.X + b.Size.X) / 2
		and math.abs(a.Position.Z - b.Position.Z) < (a.Size.Z + b.Size.Z) / 2
end

local out = {}

-- CONTROL 1: a road part must plan-overlap itself.
local ctlSelf = (#roads > 0 and planOverlap(roads[1], roads[1])) and 1 or 0
table.insert(out, ("CONTROL planOverlap-self=%d (want 1)"):format(ctlSelf))

-- CLEARANCE over the deck.
local worst, worstAt, nOver = 1e9, "none", 0
for _, cp in ipairs(cross) do
	for _, rd in ipairs(roads) do
		if planOverlap(cp, rd) then
			nOver += 1
			-- ramp underside minus road topside
			local gap = (cp.Position.Y - cp.Size.Y / 2) - (rd.Position.Y + rd.Size.Y / 2)
			if gap < worst then
				worst, worstAt = gap, cp.Name .. " over " .. rd.Name
			end
		end
	end
end
if nOver == 0 then
	table.insert(out, "CROSSING: 0 road parts under any Cross part -- ramp does NOT span the deck")
else
	table.insert(out, ("CROSSING: %d overlaps | worst vertical gap=%.1f at %s"):format(nOver, worst, worstAt))
end

-- LANDING: last descent part of each ramp vs the road under it.
local function tailOf(prefix)
	local best, bestIdx = nil, -1
	for _, p in ipairs(descent) do
		if p.Name:sub(1, #prefix) == prefix then
			local i = tonumber(p.Name:match("_(%d+)$")) or 0
			if i > bestIdx then
				best, bestIdx = p, i
			end
		end
	end
	return best
end
for _, pre in ipairs({ "PAEntryRampNear", "PAExitRampNear" }) do
	local t = tailOf(pre)
	if not t then
		table.insert(out, pre .. ": no tail part")
	else
		local bestGap, bestNm = 1e9, "none"
		for _, rd in ipairs(roads) do
			if planOverlap(t, rd) then
				local dy = (t.Position.Y - t.Size.Y / 2) - (rd.Position.Y + rd.Size.Y / 2)
				if math.abs(dy) < math.abs(bestGap) then
					bestGap, bestNm = dy, rd.Name
				end
			end
		end
		if bestNm == "none" then
			table.insert(out, ("%s LANDING: tail is over NO road -- lands off the carriageway"):format(pre))
		else
			table.insert(out, ("%s LANDING: dY=%.1f onto %s"):format(pre, bestGap, bestNm))
		end
	end
end

table.insert(out, ("counts cross=%d descent=%d roads=%d"):format(#cross, #descent, #roads))
return table.concat(out, "\n")