-- Storage and saving
local mod_storage = minetest.get_mod_storage();
local map_data = {
    generated = minetest.deserialize(mod_storage:get_string("map")) or {},

    maps = minetest.deserialize(mod_storage:get_string("maps")) or {},
    next_map_id = mod_storage:get_int("next_map_id"),
};

if map_data.next_map_id == 0 then
    map_data.next_map_id = 1;
end

local function save()
    mod_storage:set_string("maps", minetest.serialize(map_data.maps));
    mod_storage:set_int("next_map_id", map_data.next_map_id);
    mod_storage:set_string("map", minetest.serialize(map_data.generated));
end
minetest.register_on_shutdown(save);
minetest.register_on_leaveplayer(save);

local function periodic_save()
    save();
    minetest.after(60, periodic_save);
end
minetest.after(60, periodic_save);

return map_data;