-- Parameters

local YWATER = 1 -- y of water level
local YSURF = 4 -- y of surface centre and top of beach
local TERSCA = 128 -- Terrain vertical scale in nodes
local TSTONE = 0.04 -- Stone density threshold, depth of sand or biome nodes

-- Noise parameters

-- 3D noise

local np_terrain = {
	offset = 0,
	scale = 1,
	spread = {x=384, y=256, z=384},
	seed = 5900033,
	octaves = 5,
	persist = 0.63,
	lacunarity = 2.0,
	--flags = ""
}

-- 2D noise

local np_biome = {
	offset = 0,
	scale = 1,
	spread = {x=512, y=512, z=512},
	seed = -188900,
	octaves = 3,
	persist = 0.4,
	lacunarity = 2.0,
	--flags = ""
}

-- Nodes

minetest.register_node("stability:grass", {
	description = "Grass",
	tiles = {"default_grass.png", "default_dirt.png", "default_grass.png"},
	groups = {crumbly=3},
	sounds = default.node_sound_dirt_defaults({
		footstep = {name="default_grass_footstep", gain=0.25},
	}),
})

minetest.register_node("stability:dirt", {
	description = "Dirt",
	tiles = {"default_dirt.png"},
	groups = {crumbly=3},
	sounds = default.node_sound_dirt_defaults(),
})

-- Set mapgen parameters

minetest.register_on_mapgen_init(function(mgparams)
	minetest.set_mapgen_params({mgname="singlenode", flags="nolight"})
end)

-- Initialize noise objects to nil

local nobj_terrain = nil
local nobj_biome = nil

-- On generated function

minetest.register_on_generated(function(minp, maxp, seed)
	local t0 = os.clock()
	local x1 = maxp.x
	local y1 = maxp.y
	local z1 = maxp.z
	local x0 = minp.x
	local y0 = minp.y
	local z0 = minp.z
	
	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
	local data = vm:get_data()
	
	local c_air = minetest.get_content_id("air")
	local c_ignore = minetest.get_content_id("ignore")

	local c_stone = minetest.get_content_id("default:stone")
	local c_destone = minetest.get_content_id("default:desert_stone")
	local c_sand  = minetest.get_content_id("default:sand")
	local c_desand  = minetest.get_content_id("default:desert_sand")
	local c_water = minetest.get_content_id("default:water_source")
	local c_dirtsnow = minetest.get_content_id("default:dirt_with_snow")
	local c_snowblock = minetest.get_content_id("default:snowblock")
	
	local c_grass  = minetest.get_content_id("stability:grass")
	local c_dirt   = minetest.get_content_id("stability:dirt")

	local sidelen = x1 - x0 + 1
	local overlen = sidelen + 2
	local ystridevm = sidelen + 32 -- strides for voxelmanip
	local zstridevm = ystridevm ^ 2
	local ystridepm = overlen -- strides for perlinmaps, densitymap, stability map
	local zstridepm = ystridepm ^ 2

	local chulens3d = {x=overlen, y=overlen, z=overlen}
	local chulens2d = {x=overlen, y=overlen, z=1}
	local minpos3d = {x=x0-1, y=y0-1, z=z0-1}
	local minpos2d = {x=x0-1, y=z0-1}
	
	nobj_terrain = nobj_terrain or minetest.get_perlin_map(np_terrain, chulens3d)
	nobj_biome = nobj_biome or minetest.get_perlin_map(np_biome, chulens2d)
	
	local nvals_terrain = nobj_terrain:get3dMap_flat(minpos3d)
	local nvals_biome = nobj_biome:get2dMap_flat(minpos2d)
	local dvals = {} -- 3D densitymap

	local ni3d = 1
	local ni2d = 1
	for z = z0 - 1, z1 + 1 do
		for y = y0 - 1, y1 + 1 do
			local vi = area:index(x0 - 1, y, z)
			for x = x0 - 1, x1 + 1 do
				local n_terrain = nvals_terrain[ni3d]
				local n_biome = nvals_biome[ni2d]

				local grad = (YSURF - y) / TERSCA
				local tstone = TSTONE
				if y <= YSURF then -- make shore and seabed shallower
					grad = grad * 4
					tstone = TSTONE * 4
				end
				local density = n_terrain + grad
				dvals[ni3d] = density

				if density >= tstone then
					if n_biome > 0.4 then
						data[vi] = c_destone
					else
						data[vi] = c_stone
					end
				end

				ni3d = ni3d + 1
				ni2d = ni2d + 1
				vi = vi + 1
			end
			ni2d = ni2d - overlen
		end
		ni2d = ni2d + overlen
	end
	
	local stable = {} -- stability map
	local under = {} -- node under map
	for y = y0, y1 + 1 do
		local tstone = TSTONE
		if y <= YSURF then
			tstone = TSTONE * 4
		end
		for z = z0, z1 do
			local vi = area:index(x0, y, z)
			local di = (z - z0 + 1) * zstridepm
			+ (y - y0 + 1) * ystridepm
			+ 2 -- +2 because starting at x = x0
			local ni2d = (z - z0 + 1) * ystridepm
			+ 2 -- also used for stability map

			for x = x0, x1 do
				local density = dvals[di]
				local n_biome = nvals_biome[ni2d]

				if density >= tstone then -- existing stone
					stable[ni2d] = true
					under[ni2d] = 0
				elseif density > 0 and (stable[ni2d] or y == y0) then -- biome layer
					local nodu  = data[(vi - ystridevm)]
					local node  = data[(vi - ystridevm + 1)]
					local nodw  = data[(vi - ystridevm - 1)]
					local nodn  = data[(vi - ystridevm + zstridevm)]
					local nods  = data[(vi - ystridevm - zstridevm)]
					local nodne = data[(vi - ystridevm + zstridevm + 1)]
					local nodnw = data[(vi - ystridevm + zstridevm - 1)]
					local nodse = data[(vi - ystridevm - zstridevm + 1)]
					local nodsw = data[(vi - ystridevm - zstridevm - 1)]

					if y == y0 then
						if nodu == c_air or nodu == c_ignore
						or node == c_air or node == c_ignore
						or nodw == c_air or nodw == c_ignore
						or nodn == c_air or nodn == c_ignore
						or nods == c_air or nods == c_ignore
						or nodne == c_air or nodne == c_ignore
						or nodnw == c_air or nodnw == c_ignore
						or nodse == c_air or nodse == c_ignore
						or nodsw == c_air or nodsw == c_ignore then
							stable[ni2d] = false
						else
							stable[ni2d] = true
						end
					else
						if node == c_air
						or nodw == c_air
						or nodn == c_air
						or nods == c_air
						or nodne == c_air
						or nodnw == c_air
						or nodse == c_air
						or nodsw == c_air then
							stable[ni2d] = false
						end
					end

					if stable[ni2d] and y <= y1 then
						if y <= YSURF then
							data[vi] = c_sand
						elseif n_biome > 0.4 then
							data[vi] = c_desand
							under[ni2d] = 3
						elseif n_biome < -0.4 then
							data[vi] = c_dirt
							under[ni2d] = 1
						else
							data[vi] = c_dirt
							under[ni2d] = 2
						end
					elseif under[ni2d] ~= 0 then
						if under[ni2d] == 1 then
							data[(vi - ystridevm)] = c_dirtsnow
						elseif under[ni2d] == 2 then
							data[(vi - ystridevm)] = c_grass
						end
						under[ni2d] = 0
					end
				elseif under[ni2d] ~= 0 then
					if under[ni2d] == 1 then
						data[(vi - ystridevm)] = c_dirtsnow
					elseif under[ni2d] == 2 then
						data[(vi - ystridevm)] = c_grass
					end
					under[ni2d] = 0
					stable[ni2d] = false
				else
					stable[ni2d] = false
				end

				vi = vi + 1
				di = di + 1
				ni2d = ni2d + 1
			end
		end
	end

	for z = z0, z1 do
		for y = y0, y1 do
			local vi = area:index(x0, y, z)
			for x = x0, x1 do
				if data[vi] == c_air and y <= YWATER then
					data[vi] = c_water
				end

				vi = vi + 1
			end
		end
	end
	
	vm:set_data(data)
	vm:calc_lighting()
	vm:write_to_map(data)
	vm:update_liquids()

	local chugent = math.ceil((os.clock() - t0) * 1000)
	print ("[stability] "..chugent.." ms  minpos ("..x0.." "..y0.." "..z0..")")
end)