-- LUALOCALS < ---------------------------------------------------------
local error, ipairs, math, minetest, nodecore, pairs
    = error, ipairs, math, minetest, nodecore, pairs
local math_floor
    = math.floor
-- LUALOCALS > ---------------------------------------------------------

local thickness = 128

nodecore.stratadata = nodecore.memoize(function()
		local data = {}
		data.stratbyid = {}
		for i = 1, 65535 do data.stratbyid[i] = false end
		data.altsbyid = {}
		for i = 1, 65535 do data.altsbyid[i] = false end
		for k, v in pairs(minetest.registered_nodes) do
			if v.strata then
				local sn
				for s, n in ipairs(v.strata) do
					if n == k then sn = s end
				end
				if not sn then error(k .. " not found in own strata") end
				local cid = minetest.get_content_id(k)
				data.stratbyid[cid] = sn
				data.altsbyid[cid] = {}
				for s, n in ipairs(v.strata) do
					data.altsbyid[cid][s] = minetest.get_content_id(n)
				end
			end
		end
		return data
	end)

nodecore.register_mapgen_shared({
		label = "stone strata",
		func = function(minp, maxp, area, data, _, _, _, rng)
			if minp.y > -64 then return end

			local ai = area.index
			local t = nodecore.hard_stone_strata
			local sd = nodecore.stratadata()
			local byid = sd.stratbyid
			local alts = sd.altsbyid

			for z = minp.z, maxp.z do
				for y = minp.y, maxp.y do
					local raw = y / -thickness
					local strat = math_floor(raw)
					local dither = raw - strat
					if strat > t then
						strat = t
						dither = nil
					elseif dither > (4 / thickness) then
						dither = nil
					else
						dither = (dither * thickness + 1) / 5
					end
					local offs = ai(area, 0, y, z)
					for x = minp.x, maxp.x do
						local i = offs + x
						if byid[data[i]] then
							if dither and rng() >= dither then
								data[i] = alts[data[i]][strat]
							else
								data[i] = alts[data[i]][strat + 1]
							end
						end
					end
				end
			end
		end,
		priority = -100
	})