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

local ciphers = require "openssl.cipher";

local jid = require "util.jid";

local json = require "util.json";

local random = require "util.random";

local st = require "util.stanza";

local xmlns_jmi = "urn:xmpp:jingle-message:0";

local xmlns_push = "urn:xmpp:push:0";

local xmlns_push_encrypt = "tigase:push:encrypt:0";

local xmlns_push_encrypt_aes_128_gcm = "tigase:push:encrypt:aes-128-gcm";

-- https://xeps.tigase.net//docs/push-notifications/encrypt/#41-discovering-support

local function account_disco_info(event)

	event.reply:tag("feature", {var=xmlns_push_encrypt}):up();

	event.reply:tag("feature", {var=xmlns_push_encrypt_aes_128_gcm}):up();

end

module:hook("account-disco-info", account_disco_info);

function handle_register(event)

	local encrypt = event.stanza:get_child("enable", xmlns_push):get_child("encrypt", xmlns_push_encrypt);

	if not encrypt then return; end

	local algorithm = encrypt.attr.alg;

	if algorithm ~= "aes-128-gcm" then

		event.origin.send(st.error_reply(

			event.stanza, "modify", "feature-not-implemented", "Unknown encryption algorithm"

		));

		return false;

	end

	local key_base64 = encrypt:get_text();

	local key_binary = base64.decode(key_base64);

	if not key_binary or #key_binary ~= 16 then

		event.origin.send(st.error_reply(

			event.stanza, "modify", "bad-request", "Invalid encryption key"

		));

		return false;

	end

	event.push_info.encryption = {

		algorithm = algorithm;

		key_base64 = key_base64;

	};

end

function handle_push(event)

	local encryption = event.push_info.encryption;

	if not encryption then return; end

	if encryption.algorithm ~= "aes-128-gcm" then

		event.reason = "Unsupported encryption algorithm: "..tostring(encryption.algorithm);

		return true;

	end

	local push_summary = event.push_summary;

	local original_stanza = event.original_stanza;

	local body = original_stanza:get_child_text("body");

	if #body > 255 then

		body = body:sub(1, 255);

	end

	local push_payload = {

		unread = tonumber(push_summary["message-count"]) or 1;

		sender = jid.bare(original_stanza.attr.from);

		message = body;

	};

	if original_stanza.name == "message" then

		if original_stanza.attr.type == "groupchat" then

			push_payload.type = "groupchat";

			push_payload.nickname = jid.resource(original_stanza.attr.from);

		elseif original_stanza.attr.type ~= "error" then

			local jmi_propose = original_stanza:get_child("propose", xmlns_jmi);

			if jmi_propose then

				push_payload.type = "call";

				push_payload.sid = jmi_propose.attr.id;

			else

				push_payload.type = "chat";

			end

		end

	elseif original_stanza.name == "presence"

	and original_stanza.attr.type == "subscribe" then

		push_payload.type = "subscribe";

	end

	local iv = random.bytes(12);

	local key_binary = base64.decode(encryption.key_base64);

	local push_json = json.encode(push_payload);

	-- FIXME: luaossl does not expose the EVP_CTRL_GCM_GET_TAG API, so we append 16 NUL bytes

	-- Siskin does not validate the tag anyway.

	local encrypted_payload = base64.encode(ciphers.new("AES-128-GCM"):encrypt(key_binary, iv):final(push_json)..string.rep("\0", 16));

	local encrypted_element = st.stanza("encrypted", { xmlns = xmlns_push_encrypt, iv = base64.encode(iv) })

		:text(encrypted_payload);

end

module:hook("cloud_notify/registration", handle_register);

module:hook("cloud_notify/push", handle_push);