mapgen_rivers = {}

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

dofile(modpath .. 'settings.lua')

local blocksize = mapgen_rivers.blocksize
local sea_level = mapgen_rivers.sea_level
local riverbed_slope = mapgen_rivers.riverbed_slope

local make_polygons = dofile(modpath .. 'polygons.lua')

local transform_quadri = dofile(modpath .. 'geometry.lua')

local heightmaps = dofile(modpath .. 'heightmap.lua')

-- Linear interpolation
local function interp(v00, v01, v11, v10, xf, zf)
	local v0 = v01*xf + v00*(1-xf)
	local v1 = v11*xf + v10*(1-xf)
	return v1*zf + v0*(1-zf)
end

local data = {}

local noise_x_params = {
	offset = 0,
	scale = 1,
	seed = -4574,
	spread = {x=64, y=32, z=64},
	octaves = 3,
	persistence = 0.75,
	lacunarity = 2,
}

local noise_z_params = {
	offset = 0,
	scale = 1,
	seed = -7940,
	spread = {x=64, y=32, z=64},
	octaves = 3,
	persistence = 0.75,
	lacunarity = 2,
}

local noise_distort_params = {
	offset = 0,
	scale = 10,
	seed = 676,
	spread = {x=1024, y=1024, z=1024},
	octaves = 5,
	persistence = 0.5,
	lacunarity = 2,
	flags = "absvalue",
}

local noise_x_obj, noise_z_obj, noise_distort_obj
local noise_x_map = {}
local noise_z_map = {}
local noise_distort_map = {}
local mapsize
local init = false

local function generate(minp, maxp, seed)
	local chulens = {
		x = maxp.x-minp.x+1,
		y = maxp.y-minp.y+1,
		z = maxp.z-minp.z+1,
	}

	if not init then
		mapsize = {
			x = chulens.x,
			y = chulens.y+1,
			z = chulens.z,
		}
		noise_x_obj = minetest.get_perlin_map(noise_x_params, mapsize)
		noise_z_obj = minetest.get_perlin_map(noise_z_params, mapsize)
		noise_distort_obj = minetest.get_perlin_map(noise_distort_params, chulens)
		init = true
	end

	noise_x_obj:get_3d_map_flat(minp, noise_x_map)
	noise_z_obj:get_3d_map_flat(minp, noise_z_map)
	noise_distort_obj:get_2d_map_flat(minp, noise_distort_map)

	local xmin, xmax, zmin, zmax = minp.x, maxp.x, minp.z, maxp.z
	local i = 0
	local i2d = 0
	for z=minp.z, maxp.z do
		for y=minp.y, maxp.y+1 do
			for x=minp.x, maxp.x do
				i = i+1
				i2d = i2d+1
				local distort = noise_distort_map[i2d]
				local xv = noise_x_map[i]*distort + x
				if xv < xmin then xmin = xv end
				if xv > xmax then xmax = xv end
				noise_x_map[i] = xv
				local zv = noise_z_map[i]*distort + z
				if zv < zmin then zmin = zv end
				if zv > zmax then zmax = zv end
				noise_z_map[i] = zv
			end
			i2d = i2d-chulens.x
		end
	end

	local pminp = {x=math.floor(xmin), z=math.floor(zmin)}
	local pmaxp = {x=math.floor(xmax)+1, z=math.floor(zmax)+1}
	local incr = pmaxp.z-pminp.z+1
	local i_origin = 1 - pminp.x*incr - pminp.z
	local terrain_map, lake_map = heightmaps(pminp, pmaxp)

	local c_stone = minetest.get_content_id("default:stone")
	local c_dirt = minetest.get_content_id("default:dirt")
	local c_lawn = minetest.get_content_id("default:dirt_with_grass")
	local c_sand = minetest.get_content_id("default:sand")
	local c_water = minetest.get_content_id("default:water_source")
	local c_rwater = minetest.get_content_id("default:river_water_source")

	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	vm:get_data(data)

	local a = VoxelArea:new({MinEdge = emin, MaxEdge = emax})
	local ystride = a.ystride -- Tip : the ystride of a VoxelArea is the number to add to the array index to get the index of the position above. It's faster because it avoids to completely recalculate the index.

	local nid = mapsize.x*(mapsize.y-1) + 1
	local incrY = -mapsize.x
	local incrX = 1 - mapsize.y*incrY
	local incrZ = mapsize.x*mapsize.y - mapsize.x*incrX - mapsize.x*mapsize.y*incrY
	
	for z = minp.z, maxp.z do
		for x = minp.x, maxp.x do
			local ivm = a:index(x, minp.y, z)
			local ground_above = false
			for y = maxp.y+1, minp.y, -1 do
				local xn = noise_x_map[nid]
				local zn = noise_z_map[nid]
				local x0 = math.floor(xn)
				local z0 = math.floor(zn)

				local i0 = i_origin + x0*incr + z0
				local i1 = i0+incr
				local i2 = i1+1
				local i3 = i0+1

				local terrain = interp(terrain_map[i0], terrain_map[i1], terrain_map[i2], terrain_map[i3], xn-x0, zn-z0)
				if y <= maxp.y then
					local lake = math.min(lake_map[i0], lake_map[i1], lake_map[i2], lake_map[i3])

					local is_lake = lake > terrain
					local ivm = a:index(x, y, z)
					if y <= terrain then
						if y <= terrain-1 or ground_above then
							data[ivm] = c_stone
						elseif is_lake then
							data[ivm] = c_sand
						else
							data[ivm] = c_lawn
						end
					elseif y <= lake and lake > sea_level then
						data[ivm] = c_rwater
					elseif y <= sea_level then
						data[ivm] = c_water
					end
				end

				ground_above = y <= terrain

				ivm = ivm + ystride
				nid = nid + incrY
			end
			nid = nid + incrX
		end
		nid = nid + incrZ
	end

	vm:set_data(data)
	minetest.generate_ores(vm, minp, maxp)
	vm:set_lighting({day = 0, night = 0})
	vm:calc_lighting()
	vm:update_liquids()
	vm:write_to_map()
end

minetest.register_on_generated(generate)