colddb = {}

function colddb.Colddb(dir)
	if not minetest.mkdir(dir) then
		error(string.format("%s is not a directory.", dir))
	end
	
	local self = {}
	
	local directory = dir
	local mem_pool = {}
	local mem_pool_del = {}
	local add_to_mem_pool = true
	local async = async.Async()
	local use_async = true
	
	async.priority(150, 250)
	
	-- make tables weak so the garbage-collector will remove unused data
	setmetatable(mem_pool, {__mode = "kv"})
	setmetatable(mem_pool_del, {__mode = "kv"})
	
	self.get_directory = function()
		return directory
	end
	
	self.set_directory = function(new_directory)
		directory = new_directory
		if not minetest.mkdir(directory) then
			error(string.format("%s is not a directory.", dir))
		end
	end
	
	self.get_memory_pool = function()
		return mem_pool
	end
	
	self.set_memory_pool = function(pool)
		mem_pool = pool
	end
	
	self.get_async = function()
		return async
	end
	
	self.set_async = function(new_async)
		async = new_async
	end
	
	self.add_to_memory_pool = function(value)
		if value then
			add_to_mem_pool = value
		end
		return add_to_mem_pool
	end

	self.use_async = function(value)
		use_async = value
	end
	
	local function file_exists(name)
		local f = io.open(string.format("%s/%s.cold", directory, name), "r")
		if f ~= nil then 
			io.close(f)
			return true
		else 
			return false 
		end
		return false 
	end

	local function load_into_mem(name, _table)
		if add_to_mem_pool then
			mem_pool[name] = {mem = _table}
		end
	end
	
	self.exists = function(name)
		return file_exists(name)
	end
	
	local function delete_file(name)
		local text = string.format("%s/%s.cold", directory, name)
		
		local err, msg = os.remove(text) 
		if err == nil then 
			minetest.log(string.format("error removing db data %s error message: %s", text, msg))
		end
	end
	
	local function load_table(name)
		local f = io.open(string.format("%s/%s.cold", directory, name), "r")
		if f then
			local data = minetest.deserialize(f:read("*a"))
			f:close()
			return data
		end
		return nil
	end
	
	local function save_table(name, _table)
		minetest.log(string.format("%s/%s.cold", directory, name))
		if save_table == nil or name == nil then
			return false
		end
		return minetest.safe_file_write(string.format("%s/%s.cold", directory, name), minetest.serialize(_table))
	end

	local function save_key(name)
		return minetest.safe_file_write(string.format("%s/%s.cold", directory, name), "")
	end

	local function load_key(name)
		local f = io.open(string.format("%s/%s.cold", directory, name), "r")
		if f then
			f:close()
			return true
		end
		return false
	end
	
	self.set_mem = function(name, _table)
		load_into_mem(name, _table)
		mem_pool_del[name] = nil
	end
	
	self.save_mem = function(name)
		if use_async then
			async.queue_task(function() 
				if mem_pool[name] ~= nil then
					save_table(name, mem_pool[name].mem)
				end
			end)
		else
			if mem_pool[name] ~= nil then
				save_table(name, mem_pool[name].mem)
			end
		end
		
		mem_pool_del[name] = nil
	end
	
	self.clear_mem = function(name)
		mem_pool[name] = nil
		mem_pool_del[name] = nil
	end

	self.set = function(name, _table)
		if use_async then
			async.queue_task(function() 
				save_table(name, _table)
			end)
		else
			save_table(name, _table)
		end

		if add_to_mem_pool then
			load_into_mem(name, _table)
		end
		
		mem_pool_del[name] = nil
	end

	self.set_key = function(name)
		if use_async then
			async.queue_task(function() 
				save_key(name)
			end)
		else
			save_key(name)
		end

		if add_to_mem_pool then
			load_into_mem(name, "")
		end
		mem_pool_del[name] = nil
	end

	self.get = function(name, callback)
		if mem_pool_del[name] then
			if callback then
				callback(nil)
			end
			return nil
		end
		if callback then
			async.queue_task(function() 
				local pm = mem_pool[name]
				if pm then
					return pm.mem
				else
					local _table = load_table(name)
					if _table then
						load_into_mem(name, _table)
						return _table
					end
				end
				mem_pool_del[name] = true
				return nil
			end,callback)
		else
			local pm = mem_pool[name]
			if pm then
				return pm.mem
			else
				local _table = load_table(name)
				if _table then
					load_into_mem(name, _table)
					return _table
				end
			end
			mem_pool_del[name] = true
			return nil
		end
	end

	self.get_key = function(name, callback)
		if mem_pool_del[name] then
			if callback then
				callback(false)
			end
			return false
		end
		if callback then
			async.queue_task(function() 
				local pm = mem_pool[name]
				if pm then
					return true
				else
					local bool = load_key(name)
					if bool then
						load_into_mem(name, bool)
						return bool
					end
				end
				mem_pool_del[name] = true
				return nil
			end,callback)
		else
			local pm = mem_pool[name]
			if pm then
				return true
			else
				local bool = load_key(name)
				if bool then
					load_into_mem(name, bool)
					return bool
				end
			end
			mem_pool_del[name] = true
			return nil
		end
	end

	self.remove = function(name)
		mem_pool[name] = nil
		mem_pool_del[name] = true
		
		if use_async then
			async.queue_task(function()
				delete_file(name)
			end)
		else
			delete_file(name)
		end
	end

	self.sub_database = function(path)
		local db = colddb.Colddb(dir .. "/" .. path)
		db.set_async(async)
		return db
	end

	self.to_array = function()
		local entries = {}

		for k, v in pairs(minetest.get_dir_list(directory, false)) do
			entries[#entries + 1] = v:sub(0, v:len() - 5)
		end

		return entries
	end

	self.to_table = function()
		local entries = {}

		for k, v in pairs(minetest.get_dir_list(directory, false)) do
			entries[v:sub(0, v:len() - 5)] = true
		end

		return entries
	end

	self.iterate = function()
		local entries = {}

		for k, v in pairs(minetest.get_dir_list(directory, false)) do
			entries[v:sub(0, v:len() - 5)] = true
		end

		return pairs(entries)
	end
	
	return self
end