local modpath = minetest.get_modpath(minetest.get_current_modname())

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

local blocksize = tonumber(mapgen_rivers.settings:get("blocksize"))
local tectonic_speed = tonumber(mapgen_rivers.settings:get("tectonic_speed"))

local np_base = mapgen_rivers.settings:get_np_group("np_base")
np_base.spread.x = np_base.spread.x / blocksize
np_base.spread.y = np_base.spread.y / blocksize
np_base.spread.z = np_base.spread.z / blocksize

local evol_params = {
	K = tonumber(mapgen_rivers.settings:get("river_erosion_coef")),
	m = tonumber(mapgen_rivers.settings:get("river_erosion_power")),
	d = tonumber(mapgen_rivers.settings:get("difusive_erosion")),
}

local time = tonumber(mapgen_rivers.settings:get("evol_time"))
local time_step = tonumber(mapgen_rivers.settings:get("evol_time_step"))
local niter = math.ceil(time/time_step)
time_step = time / niter

-- Setup the model
local size = {
	x = tonumber(mapgen_rivers.settings:get("grid_x_size")),
	y = tonumber(mapgen_rivers.settings:get("grid_z_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})

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

local tectonic_step = tectonic_speed * time_step
collectgarbage()

-- Run the model
for i=1, niter do
	minetest.log("info", "[mapgen_rivers] Iteration " .. i .. " of " .. niter)

	model:diffuse(time_step)
	model:flow()
	model:erode(time_step)
	if i < niter then
		if tectonic_step ~= 0 then
			nobj_base:get_3d_map_flat({x=0, y=tectonic_step*i, z=0}, ref_dem)
		end
		model:isostasy()
	end

	collectgarbage()
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

-- Write the results in the world directory
local datapath = minetest.get_worldpath() .. "/river_data/"
minetest.mkdir(datapath)

local function write_map(filename, data, bytes)
	local size = #data
	local file = io.open(datapath .. filename, 'wb')

	local bytelist = {}
	for j=1, bytes do
		bytelist[j] = 0
	end

    local unpk = unpack
    local schar = string.char
    local floor = math.floor
	for i=1, size do
		local n = floor(data[i])
		data[i] = n
		for j=bytes, 2, -1 do
			bytelist[j] = n % 256
			n = floor(n / 256)
		end
		bytelist[1] = n % 256

		file:write(schar(unpk(bytelist)))
	end

	file:close()
end

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

local use_interactive_loader
if minetest.settings:has("mapgen_rivers_use_interactive_loader") then
	use_interactive_loader = minetest.settings:get_bool("mapgen_rivers_use_interactive_loader")
else
	use_interactive_loader = not minetest.settings:get_bool("mapgen_rivers_load_all")
end

if not use_interactive_loader then
    mapgen_rivers.grid = {
        size = size,
	    dem = model.dem,
	    lakes = model.lakes,
	    dirs = model.dirs,
	    rivers = model.rivers,
	    offset_x = offset_x,
	    offset_y = offset_y,
    }
end