local socket = require("socket")

local network = {}

local client

-- Packet IDs
network.MSG_KEY_PRESS = 1
network.MSG_GAMESTATE = 2

--------------------------------------------------
-- Packing
--------------------------------------------------

local function packU16(n)
	return string.char(math.floor(n / 256) % 256, n % 256)
end

local function packU32(n)
	return string.char(math.floor(n / 16777216) % 256, math.floor(n / 65536) % 256, math.floor(n / 256) % 256, n % 256)
end

local function unpackU16(s)
	local b1, b2 = s:byte(1, 2)
	return b1 * 256 + b2
end

local function unpackU32(s)
	local b1, b2, b3, b4 = s:byte(1, 4)

	return b1 * 16777216 + b2 * 65536 + b3 * 256 + b4
end

--------------------------------------------------
-- Connection
--------------------------------------------------

function network.connect(ip, port)
	client = assert(socket.tcp())

	client:settimeout(0)

	local ok, err = client:connect(ip, port)

	-- Non-blocking connect is expected
	if not ok and err ~= "timeout" then
		error(err)
	end

	print("Connecting...")
end

--------------------------------------------------
-- Sending
--------------------------------------------------

function network.sendPacket(id, payload)
	if not client then
		return
	end

	payload = payload or ""

	local length = 2 + #payload

	local packet = packU32(length) .. packU16(id) .. payload

	client:send(packet)
end

function network.sendKey(key)
	network.sendPacket(network.MSG_KEY_PRESS, key)
end

--------------------------------------------------
-- Packet handlers
--------------------------------------------------

network.handlers = {}

function network.on(id, callback)
	network.handlers[id] = callback
end

--------------------------------------------------
-- Receiving
--------------------------------------------------

local function receivePacket()
	local lenData, err = client:receive(4)

	if not lenData then
		return nil
	end

	local length = unpackU32(lenData)

	local idData = client:receive(2)
	if not idData then
		return nil
	end

	local msgID = unpackU16(idData)

	local payload = ""

	if length > 2 then
		payload = client:receive(length - 2)

		if not payload then
			return nil
		end
	end

	return msgID, payload
end

--------------------------------------------------
-- Poll every frame
--------------------------------------------------

function network.update()
	if not client then
		return
	end

	while true do
		local id, payload = receivePacket()

		if not id then
			break
		end

		local handler = network.handlers[id]

		if handler then
			handler(payload)
		end
	end
end

return network