local st = require "util.stanza";

local t_insert, t_remove = table.insert, table.remove;

local math_min = math.min;

local tonumber, tostring = tonumber, tostring;

local add_filter = require "util.filters".add_filter;

local timer = require "util.timer";

local xmlns_sm = "urn:xmpp:sm:2";

local sm_attr = { xmlns = xmlns_sm };

local resume_timeout = 300;

local max_unacked_stanzas = 0;

module:add_event_hook("stream-features",

		function (session, features)

			features:tag("sm", sm_attr):tag("optional"):up():up();

		end);

module:hook("s2s-stream-features",

		function (data)

			data.features:tag("sm", sm_attr):tag("optional"):up():up();

		end);

module:hook_stanza(xmlns_sm, "enable",

		function (session, stanza)

			module:log("debug", "Enabling stream management");

			session.smacks = true;

			-- Overwrite process_stanza() and send()

			local queue = {};

			session.outgoing_stanza_queue = queue;

			session.last_acknowledged_stanza = 0;

			local _send = session.sends2s or session.send;

			local function new_send(stanza)

				local attr = stanza.attr;

				if attr and not attr.xmlns then -- Stanza in default stream namespace

					queue[#queue+1] = st.clone(stanza);

				end

				local ok, err = _send(stanza);

				if ok and #queue > max_unacked_stanzas and not session.awaiting_ack then

					session.awaiting_ack = true;

					return _send(st.stanza("r", { xmlns = xmlns_sm }));

				end

				return ok, err;

			end

			if session.sends2s then

				session.sends2s = new_send;

			else

				session.send = new_send;

			end

			session.handled_stanza_count = 0;

			add_filter(session, "stanzas/in", function (stanza)

				if not stanza.attr.xmlns then

					session.handled_stanza_count = session.handled_stanza_count + 1;

					session.log("debug", "Handled %d incoming stanzas", session.handled_stanza_count);

				end

				return stanza;

			end);

			if not stanza.attr.resume then -- FIXME: Resumption should be a different spec :/

				_send(st.stanza("enabled", sm_attr));

				return true;

			end

		end, 100);

module:hook_stanza(xmlns_sm, "r", function (origin, stanza)

	if not origin.smacks then

		module:log("debug", "Received ack request from non-smack-enabled session");

		return;

	end

	module:log("debug", "Received ack request, acking for %d", origin.handled_stanza_count);

	-- Reply with <a>

	(origin.sends2s or origin.send)(st.stanza("a", { xmlns = xmlns_sm, h = tostring(origin.handled_stanza_count) }));

	return true;

end);

module:hook_stanza(xmlns_sm, "a", function (origin, stanza)

	if not origin.smacks then return; end

	origin.awaiting_ack = nil;

	-- Remove handled stanzas from outgoing_stanza_queue

	local handled_stanza_count = tonumber(stanza.attr.h)-origin.last_acknowledged_stanza;

	local queue = origin.outgoing_stanza_queue;

	if handled_stanza_count > #queue then

		module:log("warn", "The client says it handled %d new stanzas, but we only sent %d :)",

			handled_stanza_count, #queue);

		for i=1,#queue do

			module:log("debug", "Q item %d: %s", i, tostring(queue[i]));

		end

	end

	for i=1,math_min(handled_stanza_count,#queue) do

		t_remove(origin.outgoing_stanza_queue, 1);

	end

	origin.last_acknowledged_stanza = origin.last_acknowledged_stanza + handled_stanza_count;

	return true;

end);

--TODO: Optimise... incoming stanzas should be handled by a per-session

-- function that has a counter as an upvalue (no table indexing for increments,

-- and won't slow non-198 sessions). We can also then remove the .handled flag

-- on stanzas

function handle_unacked_stanzas(session)

	local queue = session.outgoing_stanza_queue;

	local error_attr = { type = "cancel" };

	if #queue > 0 then

		session.outgoing_stanza_queue = {};

		for i=1,#queue do

			local reply = st.reply(queue[i]);

			if reply.attr.to ~= session.full_jid then

				reply.attr.type = "error";

				reply:tag("error", error_attr)

					:tag("recipient-unavailable", {xmlns = "urn:ietf:params:xml:ns:xmpp-stanzas"});

				core_process_stanza(session, reply);

			end

		end

	end

end

local _destroy_session = sessionmanager.destroy_session;

function sessionmanager.destroy_session(session, err)

	if session.smacks then

		if not session.resumption_token then

			local queue = session.outgoing_stanza_queue;

			if #queue > 0 then

				module:log("warn", "Destroying session with %d unacked stanzas:", #queue);

				for i=1,#queue do

					module:log("warn", "::%s", tostring(queue[i]));

				end

				handle_unacked_stanzas(session);

			end

		else

			session.hibernating = true;

			timer.add_task(resume_timeout, function ()

				if session.hibernating then

					session.resumption_token = nil;

					sessionmanager.destroy_session(session); -- Re-destroy

				end

			end);

			return; -- Postpone destruction for now

		end

	end

	return _destroy_session(session, err);

end