local EvolutionModel = dofile(mapgen_rivers.modpath .. '/terrainlib_lua/erosion.lua')
local twist = dofile(mapgen_rivers.modpath .. '/terrainlib_lua/twist.lua')

local blocksize = 12
local variation_speed = 70

local np_base = {
	offset = 0,
	scale = 200,
	seed = 2469,
	octaves = 8,
	spread = {x=4000/blocksize, y=4000/blocksize, z=4000/blocksize},
	persist = 0.6,
	lacunarity = 2,
}

local time = 10
local time_step = 1
local niter = math.ceil(time/time_step)
time_step = time / niter

local function generate()
	local grid = mapgen_rivers.grid
	local size = grid.size

	local seed = tonumber(minetest.get_mapgen_setting("seed"))
	np_base.seed = (np_base.seed or 0) + seed

	local nobj_base = PerlinNoiseMap(np_base, {x=size.x, y=1, z=size.y})
	--nobj_base:calc_3d_map({x=0, y=0, z=0})

	--local dem = nobj_base:get_map_slice({z=1}, {z=1})
	local dem = nobj_base:get_3d_map_flat({x=0, y=0, z=0})
	dem.X = size.x
	dem.Y = size.y

	local model = EvolutionModel()
	model.dem = dem
	local ref_dem = model:define_isostasy(dem)

	local variation_step = variation_speed * time_step
	for i=1, niter do
		--nobj_base:get_map_slice({z=i+1}, {z=1}, ref_dem)
		nobj_base:get_3d_map_flat({x=0, y=variation_step*i, z=0}, ref_dem)

		model:diffuse(time_step)
		model:flow()
		model:erode(time_step)
		model:isostasy()
	end
	model:flow()

	local mfloor = math.floor
	local mmin, mmax = math.min, math.max
	local offset_x, offset_y = twist(model.dirs, model.rivers, 5)
	for i=1, size.x*size.y do
		offset_x[i] = mmin(mmax(offset_x[i]*256, -128), 127)
		offset_y[i] = mmin(mmax(offset_y[i]*256, -128), 127)
	end

	mapgen_rivers.write_map('dem', model.dem, 2)
	mapgen_rivers.write_map('lakes', model.lakes, 2)
	mapgen_rivers.write_map('dirs', model.dirs, 1)
	mapgen_rivers.write_map('rivers', model.rivers, 4)
	mapgen_rivers.write_map('offset_x', offset_x, 1)
	mapgen_rivers.write_map('offset_y', offset_y, 1)
	local sfile = io.open(mapgen_rivers.world_data_path .. 'size', "w")
	sfile:write(size.x..'\n'..size.y)
	sfile:close()

    grid.dem = model.dem
    grid.lakes = model.lakes
    grid.dirs = model.dirs
    grid.rivers = model.rivers
    grid.offset_x = offset_x
    grid.offset_y = offset_y
end

return generate