local base64 = require "util.encodings".base64;

local hashes = require "util.hashes";

local net = require "util.net";

local random = require "util.random";

local struct = require "util.struct";

--- Private helpers

-- XORs a string with another string

local function sxor(x, y)

	local r = {};

	for i = 1, #x do

		r[i] = string.char(bit32.bxor(x:byte(i), y:byte(i)));

	end

	return table.concat(r);

end

--- Public helpers

-- Following draft-uberti-behave-turn-rest-00, convert a 'secret' string

-- into a username/password pair that can be used to auth to a TURN server

local function get_user_pass_from_secret(secret, ttl, opt_username)

	ttl = ttl or 86400;

	local username;

	if opt_username then

		username = ("%d:%s"):format(os.time() + ttl, opt_username);

	else

		username = ("%d"):format(os.time() + ttl);

	end

	local password = base64.encode(hashes.hmac_sha1(secret, username));

	return username, password, ttl;

end

-- Following RFC 8489 9.2, convert credentials to a HMAC key for signing

local function get_long_term_auth_key(realm, username, password)

	return hashes.md5(username..":"..realm..":"..password);

end

--- Packet building/parsing

local packet_methods = {};

local packet_mt = { __index = packet_methods };

local magic_cookie = string.char(0x21, 0x12, 0xA4, 0x42);

local methods = {

	binding = 0x001;

	-- TURN

	allocate = 0x003;

	refresh = 0x004;

	send = 0x006;

	data = 0x007;

	create_permission = 0x008;

	channel_bind = 0x009;

};

local method_lookup = {};

for name, value in pairs(methods) do

	method_lookup[name] = value;

	method_lookup[value] = name;

end

local classes = {

	request = 0;

	indication = 1;

	success = 2;

	error = 3;

};

local class_lookup = {};

for name, value in pairs(classes) do

	class_lookup[name] = value;

	class_lookup[value] = name;

end

local attributes = {

	["mapped-address"] = 0x0001;

	["username"] = 0x0006;

	["message-integrity"] = 0x0008;

	["error-code"] = 0x0009;

	["unknown-attributes"] = 0x000A;

	["realm"] = 0x0014;

	["nonce"] = 0x0015;

	["xor-mapped-address"] = 0x0020;

	["software"] = 0x8022;

	["alternate-server"] = 0x8023;

	["fingerprint"] = 0x8028;

	["message-integrity-sha256"] = 0x001C;

	["password-algorithm"] = 0x001D;

	["userhash"] = 0x001E;

	["password-algorithms"] = 0x8002;

	["alternate-domains"] = 0x8003;

	-- TURN

	["requested-transport"] = 0x0019;

};

local attribute_lookup = {};

for name, value in pairs(attributes) do

	attribute_lookup[name] = value;

	attribute_lookup[value] = name;

end

function packet_methods:serialize_header(length)

	assert(#self.transaction_id == 12, "invalid transaction id length");

	local header = struct.pack(">I2I2",

		self.type,

		length

	)..magic_cookie..self.transaction_id;

	return header;

end

function packet_methods:serialize()

	local payload = table.concat(self.attributes);

	return self:serialize_header(#payload)..payload;

end

function packet_methods:is_request()

	return bit32.band(self.type, 0x0110) == 0x0000;

end

function packet_methods:is_indication()

	return bit32.band(self.type, 0x0110) == 0x0010;

end

function packet_methods:is_success_resp()

	return bit32.band(self.type, 0x0110) == 0x0100;

end

function packet_methods:is_err_resp()

	return bit32.band(self.type, 0x0110) == 0x0110;

end

function packet_methods:get_method()

	local method = bit32.bor(

		bit32.rshift(bit32.band(self.type, 0x3E00), 2),

		bit32.rshift(bit32.band(self.type, 0x00E0), 1),

		bit32.band(self.type, 0x000F)

	);

	return method, method_lookup[method];

end

function packet_methods:get_class()

	local class = bit32.bor(

		bit32.rshift(bit32.band(self.type, 0x0100), 7),

		bit32.rshift(bit32.band(self.type, 0x0010), 4)

	);

	return class, class_lookup[class];

end

function packet_methods:set_type(method, class)

	if type(method) == "string" then

		method = assert(method_lookup[method:lower()], "unknown method: "..method);

	end

	if type(class) == "string" then

		class = assert(classes[class], "unknown class: "..class);

	end

	self.type = bit32.bor(

		bit32.lshift(bit32.band(method, 0x1F80), 2),

		bit32.lshift(bit32.band(method, 0x0070), 1),

		bit32.band(method, 0x000F),

		bit32.lshift(bit32.band(class, 0x0002), 7),

		bit32.lshift(bit32.band(class, 0x0001), 4)

	);

end

local function _serialize_attribute(attr_type, value)

	local len = #value;

	local padding = string.rep("\0", (4 - len)%4);

	return struct.pack(">I2I2",

		attr_type, len

	)..value..padding;

end

function packet_methods:add_attribute(attr_type, value)

	if type(attr_type) == "string" then

		attr_type = assert(attributes[attr_type], "unknown attribute: "..attr_type);

	end

	table.insert(self.attributes, _serialize_attribute(attr_type, value));

end

function packet_methods:deserialize(bytes)

	local type, len, cookie = struct.unpack(">I2I2I4", bytes);

	assert(#bytes == (len + 20), "incorrect packet length");

	assert(cookie == 0x2112A442, "invalid magic cookie");

	self.type = type;

	self.transaction_id = bytes:sub(9, 20);

	self.attributes = {};

	local pos = 21;

	while pos < #bytes do

		local attr_hdr = bytes:sub(pos, pos+3);

		assert(#attr_hdr == 4, "packet truncated in attribute header");

		local attr_type, attr_len = struct.unpack(">I2I2", attr_hdr); --luacheck: ignore 211/attr_type

		if attr_len == 0 then

			table.insert(self.attributes, attr_hdr);

			pos = pos + 20;

		else

			local data = bytes:sub(pos + 4, pos + 3 + attr_len);

			assert(#data == attr_len, "packet truncated in attribute value");

			table.insert(self.attributes, attr_hdr..data);

			local n_padding = (4 - attr_len)%4;

			pos = pos + 4 + attr_len + n_padding;

		end

	end

	return self;

end

function packet_methods:get_attribute(attr_type)

	if type(attr_type) == "string" then

		attr_type = assert(attribute_lookup[attr_type:lower()], "unknown attribute: "..attr_type);

	end

	for _, attribute in ipairs(self.attributes) do

		if struct.unpack(">I2", attribute) == attr_type then

			return attribute:sub(5);

		end

	end

end

local addr_families = { "IPv4", "IPv6" };

function packet_methods:get_mapped_address()

	local data = self:get_attribute("mapped-address");

	if not data then return; end

	local family, port = struct.unpack("x>BI2", data);

	local addr = data:sub(5);

	return {

		family = addr_families[family] or "unknown";

		port = port;

		address = net.ntop(addr);

	};

end

function packet_methods:get_xor_mapped_address()

	local data = self:get_attribute("xor-mapped-address");

	if not data then return; end

	local family, port = struct.unpack("x>BI2", data);

	local addr = sxor(data:sub(5), magic_cookie..self.transaction_id);

	return {

		family = addr_families[family] or "unknown";

		port = bit32.bxor(port, 0x2112);

		address = net.ntop(addr);

		address_raw = data:sub(5);

	};

end

function packet_methods:add_message_integrity(key)

	-- Add attribute with a dummy value so we can artificially increase

	-- the packet 'length'

	self:add_attribute("message-integrity", string.rep("\0", 20));

	-- Get the packet data, minus the message-integrity attribute itself

	local pkt = self:serialize():sub(1, -25);

	local hash = hashes.hmac_sha1(key, pkt, false);

	self.attributes[#self.attributes] = nil;

	assert(#hash == 20, "invalid hash length");

	self:add_attribute("message-integrity", hash);

end

do

	local transports = {

		udp = 0x11;

	};

	function packet_methods:add_requested_transport(transport)

		local transport_code = transports[transport];

		assert(transport_code, "unsupported transport: "..tostring(transport));

		self:add_attribute("requested-transport", string.char(

			transport_code, 0x00, 0x00, 0x00

		));

	end

end

function packet_methods:get_error()

	local err_attr = self:get_attribute("error-code");

	if not err_attr then

		return nil;

	end

	local number = err_attr:byte(4);

	local class = bit32.band(0x07, err_attr:byte(3));

	local msg = err_attr:sub(5);

	return (class*100)+number, msg;

end

local function new_packet(method, class)

	local p = setmetatable({

		transaction_id = random.bytes(12);

		length = 0;

		attributes = {};

	}, packet_mt);

	p:set_type(method or "binding", class or "request");

	return p;

end

return {

	new_packet = new_packet;

	get_user_pass_from_secret = get_user_pass_from_secret;

	get_long_term_auth_key = get_long_term_auth_key;

};