local st = require "util.stanza";

local uuid_generate = require "util.uuid".generate;

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

local math_min = math.min;

local os_time = os.time;

local tonumber, tostring = tonumber, tostring;

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

local timer = require "util.timer";

local datetime = require "util.datetime";

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

local xmlns_errors = "urn:ietf:params:xml:ns:xmpp-stanzas";

local xmlns_delay = "urn:xmpp:delay";

local sm_attr = { xmlns = xmlns_sm };

local resume_timeout = module:get_option_number("smacks_hibernation_time", 300);

local s2s_smacks = module:get_option_boolean("smacks_enabled_s2s", false);

local max_unacked_stanzas = module:get_option_number("smacks_max_unacked_stanzas", 0);

local core_process_stanza = prosody.core_process_stanza;

local c2s_sessions = module:shared("/*/c2s/sessions");

local session_registry = {};

local function can_do_smacks(session, advertise_only)

	if session.smacks then return false, "unexpected-request", "Stream management is already enabled"; end

	local session_type = session.type;

	if session_type == "c2s" then

		if not(advertise_only) and not(session.resource) then -- Fail unless we're only advertising sm

			return false, "unexpected-request", "Client must bind a resource before enabling stream management";

		end

		return true;

	elseif s2s_smacks and (session_type == "s2sin" or session_type == "s2sout") then

		return true;

	end

	return false, "service-unavailable", "Stream management is not available for this stream";

end

module:hook("stream-features",

		function (event)

			if can_do_smacks(event.origin, true) then

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

			end

		end);

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

		function (event)

			if can_do_smacks(event.origin, true) then

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

			end

		end);

module:hook_stanza("http://etherx.jabber.org/streams", "features",

		function (session, stanza)

			if can_do_smacks(session) and stanza:get_child("sm", xmlns_sm) then

				session.sends2s(st.stanza("enable", sm_attr));

			end

end);

local function wrap_session(session, resume)

	-- Overwrite process_stanza() and send()

	local queue;

	if not resume then

		queue = {};

		session.outgoing_stanza_queue = queue;

		session.last_acknowledged_stanza = 0;

	else

		queue = session.outgoing_stanza_queue;

	end

	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

			local cached_stanza = st.clone(stanza);

			if cached_stanza and cached_stanza:get_child("delay", xmlns_delay) == nil then

				cached_stanza = cached_stanza:tag("delay", { xmlns = xmlns_delay, from = session.host, stamp = datetime.datetime()});

			end

			queue[#queue+1] = cached_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", sm_attr));

		end

		return ok, err;

	end

	if session.sends2s then

		session.sends2s = new_send;

	else

		session.send = new_send;

	end

	if not resume then

		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);

	end

	return session;

end

module:hook_stanza(xmlns_sm, "enable", function (session, stanza)

	local ok, err, err_text = can_do_smacks(session);

	if not ok then

		session.log("warn", "Failed to enable smacks: %s", err_text); -- TODO: XEP doesn't say we can send error text, should it?

		session.send(st.stanza("failed", { xmlns = xmlns_sm }):tag(err, { xmlns = xmlns_errors}));

		return true;

	end

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

	session.smacks = true;

	wrap_session(session);

	local resume_token;

	local resume = stanza.attr.resume;

	if resume == "true" or resume == "1" then

		resume_token = uuid_generate();

		session_registry[resume_token] = session;

		session.resumption_token = resume_token;

	end

	(session.sends2s or session.send)(st.stanza("enabled", { xmlns = xmlns_sm, id = resume_token, resume = resume }));

	return true;

end, 100);

module:hook_stanza(xmlns_sm, "enabled", function (session, stanza)

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

	session.smacks = true;

	wrap_session(session);

	-- FIXME Resume?

	return true;

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

	--log("debug", "ACK: h=%s, last=%s", stanza.attr.h or "", origin.last_acknowledged_stanza or "");

	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);

		module:log("debug", "Client h: %d, our h: %d", tonumber(stanza.attr.h), origin.last_acknowledged_stanza);

		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

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

	local session, err = event.session, event.error;

	if session.smacks and err ~= "session closed" 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.log("debug", "mod_smacks hibernating session for up to %d seconds", resume_timeout);

			local hibernate_time = os_time(); -- Track the time we went into hibernation

			session.hibernating = hibernate_time;

			local resumption_token = session.resumption_token;

			timer.add_task(resume_timeout, function ()

				session.log("debug", "mod_smacks hibernation timeout reached...");

				-- We need to check the current resumption token for this resource

				-- matches the smacks session this timer is for in case it changed

				-- (for example, the client may have bound a new resource and

				-- started a new smacks session, or not be using smacks)

				local curr_session = hosts[session.host].sessions[session.username].sessions[session.resource];

				if curr_session.resumption_token == resumption_token

				-- Check the hibernate time still matches what we think it is,

				-- otherwise the session resumed and re-hibernated.

				and session.hibernating == hibernate_time then

					session.log("debug", "Destroying session for hibernating too long");

					session_registry[session.resumption_token] = nil;

					session.resumption_token = nil;

					sessionmanager.destroy_session(session);

				else

					session.log("debug", "Session resumed before hibernation timeout, all is well")

				end

			end);

			return true; -- Postpone destruction for now

		end

	end

end);

module:hook_stanza(xmlns_sm, "resume", function (session, stanza)

	local id = stanza.attr.previd;

	local original_session = session_registry[id];

	if not original_session then

		session.log("debug", "Tried to resume non-existent session with id %s", id);

		session.send(st.stanza("failed", sm_attr)

			:tag("item-not-found", { xmlns = xmlns_errors })

		);

	elseif session.username == original_session.username

	and session.host == original_session.host then

		session.log("debug", "mod_smacks resuming existing session...");

		-- TODO: All this should move to sessionmanager (e.g. session:replace(new_session))

		if original_session.conn then

			session.log("debug", "mod_smacks closing an old connection for this session");

			local conn = original_session.conn;

			c2s_sessions[conn] = nil;

			conn:close();

		end

		original_session.ip = session.ip;

		original_session.conn = session.conn;

		original_session.send = session.send;

		original_session.stream = session.stream;

		original_session.secure = session.secure;

		original_session.hibernating = nil;

		local filter = original_session.filter;

		local stream = session.stream;

		local log = session.log;

		function original_session.data(data)

			data = filter("bytes/in", data);

			if data then

				local ok, err = stream:feed(data);

				if ok then return; end

				log("debug", "Received invalid XML (%s) %d bytes: %s", tostring(err), #data, data:sub(1, 300):gsub("[\r\n]+", " "):gsub("[%z\1-\31]", "_"));

				original_session:close("xml-not-well-formed");

			end

		end

		wrap_session(original_session, true);

		-- Inform xmppstream of the new session (passed to its callbacks)

		stream:set_session(original_session);

		-- Similar for connlisteners

		c2s_sessions[session.conn] = original_session;

		session.send(st.stanza("resumed", { xmlns = xmlns_sm,

			h = original_session.handled_stanza_count, previd = id }));

		-- Fake an <a> with the h of the <resume/> from the client

		original_session:dispatch_stanza(st.stanza("a", { xmlns = xmlns_sm,

			h = stanza.attr.h }));

		-- Ok, we need to re-send any stanzas that the client didn't see

		-- ...they are what is now left in the outgoing stanza queue

		local queue = original_session.outgoing_stanza_queue;

		for i=1,#queue do

			session.send(queue[i]);

		end

	else

		module:log("warn", "Client %s@%s[%s] tried to resume stream for %s@%s[%s]",

			session.username or "?", session.host or "?", session.type,

			original_session.username or "?", original_session.host or "?", original_session.type);

		session.send(st.stanza("failed", sm_attr)

			:tag("not-authorized", { xmlns = xmlns_errors }));

	end

	return true;

end);