-- Implementation of https://xmpp.org/extensions/inbox/occupant-id.html

-- XEP-0421: Anonymous unique occupant identifiers for MUCs

module:depends("muc");

local uuid = require "util.uuid";

local hmac_sha256 = require "util.hashes".hmac_sha256;

local b64encode = require "util.encodings".base64.encode;

local xmlns_occupant_id = "urn:xmpp:occupant-id:0";

local function edit_occupant(event)

	local occupant, room = event.occupant, event.room;

	local bare = occupant.bare_jid;

	-- TODO: Move the salt on the MUC component. Setting the salt on the room

	-- can be problematic when the room is destroyed. Next time it's recreated

	-- the salt will be different and so will be the unique_id. Or maybe we want

	-- this anyway?

	if room._data.occupant_id_salt == nil then

		local salt = uuid.generate();

		room._data.occupant_id_salt = salt;

	end

	local unique_id = b64encode(hmac_sha256(bare, room._data.occupant_id_salt));

	-- TODO: Store this only once per bare jid and not once per occupant?

	local stanza = event.stanza;

	stanza:tag("occupant-id", { xmlns = xmlns_occupant_id })

		:text(unique_id)

		:up();

end

local function handle_stanza(event)

	local stanza, occupant = event.stanza, event.occupant;

	if stanza.name == "presence" and stanza.attr.type == "unavailable" then -- not required here

		return;

	end

	-- strip any existing <occupant-id/> tags to avoid forgery

	stanza:remove_children("occupant-id", xmlns_occupant_id);

	local unique_id = occupant.sessions[stanza.attr.from]

		:get_child("occupant-id", xmlns_occupant_id)

		:get_text();

	stanza:tag("occupant-id", { xmlns = xmlns_occupant_id })

		:text(unique_id)

		:up();

end

module:add_feature(xmlns_occupant_id);

module:hook("muc-disco#info", function (event)

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

end);

module:hook("muc-occupant-pre-join", edit_occupant);

module:hook("muc-occupant-groupchat", handle_stanza);