-- Copyright (C) 2016-2020 Kim Alvefur

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

module:depends"csi"

local jid = require "util.jid";

local st = require "util.stanza";

local dt = require "util.datetime";

local filters = require "util.filters";

local queue_size = module:get_option_number("csi_queue_size", 256);

local important_payloads = module:get_option_set("csi_important_payloads", { });

function is_important(stanza) --> boolean, reason: string

	if stanza == " " then

		return true, "whitespace keepalive";

	elseif type(stanza) == "string" then

		return true, "raw data";

	elseif not st.is_stanza(stanza) then

	end

	if stanza.attr.xmlns ~= nil then

		-- stream errors, stream management etc

		return true, "nonza";

	end

	local st_name = stanza.name;

	if not st_name then return false; end

	local st_type = stanza.attr.type;

	if st_name == "presence" then

		if st_type == nil or st_type == "unavailable" or st_type == "error" then

			return false, "presence update";

		end

		-- TODO Some MUC awareness, e.g. check for the 'this relates to you' status code

		return true, "subscription request";

	elseif st_name == "message" then

		if st_type == "headline" then

			-- Headline messages are ephemeral by definition

			return false, "headline";

		end

		if st_type == "error" then

			return true, "delivery failure";

		end

		if stanza:get_child("sent", "urn:xmpp:carbons:2") then

			return true, "carbon";

		end

		local forwarded = stanza:find("{urn:xmpp:carbons:2}received/{urn:xmpp:forward:0}/{jabber:client}message");

		if forwarded then

			stanza = forwarded;

		end

		if stanza:get_child("body") then

			return true, "body";

		end

		if stanza:get_child("subject") then

			-- Last step of a MUC join

			return true, "subject";

		end

		if stanza:get_child("encryption", "urn:xmpp:eme:0") then

			-- Since we can't know what an encrypted message contains, we assume it's important

			-- XXX Experimental XEP

			return true, "encrypted";

		end

		if stanza:get_child("x", "jabber:x:conference") or stanza:find("{http://jabber.org/protocol/muc#user}x/invite") then

			return true, "invite";

		end

		if stanza:get_child(nil, "urn:xmpp:jingle-message:0") then

			-- XXX Experimental XEP stuck in Proposed for almost a year at the time of this comment

			return true, "jingle call";

		end

		for important in important_payloads do

			if stanza:find(important) then

				return true;

			end

		end

		return false;

	elseif st_name == "iq" then

		return true;

	end

end

module:hook("csi-is-stanza-important", function (event)

	local important, why = is_important(event.stanza);

	event.reason = why;

	return important;

end, -1);

local function should_flush(stanza, session, ctr) --> boolean, reason: string

	if ctr >= queue_size then

		return true, "queue size limit reached";

	end

	local event = { stanza = stanza, session = session };

	local ret = module:fire_event("csi-is-stanza-important", event)

	return ret, event.reason;

end

local function with_timestamp(stanza, from)

	if st.is_stanza(stanza) and stanza.attr.xmlns == nil and stanza.name ~= "iq" then

		stanza = st.clone(stanza);

		stanza:add_direct_child(st.stanza("delay", {xmlns = "urn:xmpp:delay", from = from, stamp = dt.datetime()}));

	end

	return stanza;

end

local measure_buffer_hold = module:measure("buffer_hold", "times");

local flush_reasons = setmetatable({}, {

		__index = function (t, reason)

			local m = module:measure("flush_reason."..reason:gsub("%W", "_"), "rate");

			t[reason] = m;

			return m;

		end;

	});

local function manage_buffer(stanza, session)

	local ctr = session.csi_counter or 0;

	local flush, why = should_flush(stanza, session, ctr);

	if flush then

		if session.csi_measure_buffer_hold then

			session.csi_measure_buffer_hold();

			session.csi_measure_buffer_hold = nil;

		end

		flush_reasons[why or "important"]();

		session.log("debug", "Flushing buffer (%s; queue size is %d)", why or "important", session.csi_counter);

		session.conn:resume_writes();

	else

		session.log("debug", "Holding buffer (%s; queue size is %d)", why or "unimportant", session.csi_counter);

		stanza = with_timestamp(stanza, jid.join(session.username, session.host))

	end

	session.csi_counter = ctr + 1;

	return stanza;

end

local function flush_buffer(data, session)

	session.log("debug", "Flushing buffer (%s; queue size is %d)", "client activity", session.csi_counter);

	flush_reasons["client activity"]();

	if session.csi_measure_buffer_hold then

		session.csi_measure_buffer_hold();

		session.csi_measure_buffer_hold = nil;

	end

	session.conn:resume_writes();

	return data;

end

function enable_optimizations(session)

	if session.conn and session.conn.pause_writes then

		session.conn:pause_writes();

		session.csi_measure_buffer_hold = measure_buffer_hold();

		session.csi_counter = 0;

		filters.add_filter(session, "stanzas/out", manage_buffer);

		filters.add_filter(session, "bytes/in", flush_buffer);

	else

		session.log("warn", "Session connection does not support write pausing");

	end

end

function disable_optimizations(session)

	filters.remove_filter(session, "stanzas/out", manage_buffer);

	filters.remove_filter(session, "bytes/in", flush_buffer);

	session.csi_counter = nil;

	if session.csi_measure_buffer_hold then

		session.csi_measure_buffer_hold();

		session.csi_measure_buffer_hold = nil;

	end

	if session.conn and session.conn.resume_writes then

		session.conn:resume_writes();

	end

end

module:hook("csi-client-inactive", function (event)

	local session = event.origin;

	enable_optimizations(session);

end);

module:hook("csi-client-active", function (event)

	local session = event.origin;

	disable_optimizations(session);

end);

module:hook("pre-resource-unbind", function (event)

	local session = event.session;

	disable_optimizations(session);

end, 1);

module:hook("c2s-ondrain", function (event)

	local session = event.session;

	if session.state == "inactive" and session.conn and session.conn.pause_writes then

		session.conn:pause_writes();

		session.csi_measure_buffer_hold = measure_buffer_hold();

		session.log("debug", "Buffer flushed, resuming inactive mode (queue size was %d)", session.csi_counter);

		session.csi_counter = 0;

	end

end);

function module.load()

	for _, user_session in pairs(prosody.hosts[module.host].sessions) do

		for _, session in pairs(user_session.sessions) do

			if session.state == "inactive" then

				enable_optimizations(session);

			end

		end

	end

end

function module.unload()

	for _, user_session in pairs(prosody.hosts[module.host].sessions) do

		for _, session in pairs(user_session.sessions) do

			if session.state == "inactive" then

				disable_optimizations(session);

			end

		end

	end

end