local st = require "prosody.util.stanza";
local jid_bare = require "prosody.util.jid".bare;

local xmlns_privilege = "urn:xmpp:privilege:2";
local xmlns_forward = "urn:xmpp:forward:0";
local xmlns_carbons = "urn:xmpp:carbons:2";
local bare_sessions = prosody.bare_sessions;

local allowed_component_jid = module:get_option_string("privileged_entity_jid");

module:log("info", "mod_privilege loaded for host=%s privileged_entity_jid=%s", module.host or "?", allowed_component_jid or "");

local function iter_sessions(user_sessions)
	if not user_sessions or not user_sessions.sessions then
		return function() return nil end;
	end
	return pairs(user_sessions.sessions);
end

local function send_privilege_advertisement(session)
	if not allowed_component_jid or allowed_component_jid == "" then
		module:log("debug", "Privilege advertisement skipped: no privileged_entity_jid configured");
		return;
	end
	if session.host ~= allowed_component_jid then
		module:log("debug", "Privilege advertisement skipped: session host %s != %s", session.host or "?", allowed_component_jid);
		return;
	end
	local msg = st.message({
		from = module.host;
		to = session.host;
		type = "normal";
	});
	msg:tag("privilege", { xmlns = xmlns_privilege })
		:tag("perm", { access = "message", type = "outgoing" }):up()
	:up();
	session.send(msg);
	module:log("info", "Advertised outgoing message privilege to %s", session.host);
end

local function unwrap_forwarded_message(stanza)
	local privilege = stanza:get_child("privilege", xmlns_privilege);
	if not privilege then
		return nil;
	end
	local forwarded = privilege:get_child("forwarded", xmlns_forward);
	if not forwarded then
		return nil;
	end
	for _, tag in ipairs(forwarded.tags or {}) do
		if tag.name == "message" then
			return tag;
		end
	end
	return nil;
end

local function is_carbon_delivery(inner)
	if not inner then
		return false;
	end
	return inner:get_child("sent", xmlns_carbons) ~= nil
		or inner:get_child("received", xmlns_carbons) ~= nil;
end

local function deliver_carbon_to_user_sessions(bare_jid, inner)
	local user_sessions = bare_sessions[bare_jid];
	if not user_sessions then
		module:log("debug", "Privilege carbon skipped for offline user %s", bare_jid);
		return true;
	end
	local delivered = false;
	for _, session in iter_sessions(user_sessions) do
		if session.full_jid and session.send then
			local copy = st.clone(inner);
			copy.attr.to = session.full_jid;
			session.send(copy);
			delivered = true;
		end
	end
	module:log("debug", "Privilege carbon delivered user=%s delivered=%s", bare_jid, tostring(delivered));
	return true;
end

local function handle_privileged_carbon(event)
	local origin, stanza = event.origin, event.stanza;
	if not origin or origin.type ~= "component" then
		return nil;
	end
	if allowed_component_jid and allowed_component_jid ~= "" and origin.host ~= allowed_component_jid then
		module:log("debug", "Ignoring privileged message from unexpected component %s", origin.host or "?");
		return nil;
	end

	local inner = unwrap_forwarded_message(stanza);
	if not is_carbon_delivery(inner) then
		module:log("debug", "Ignoring privileged message without carbon payload from %s", origin.host or "?");
		return nil;
	end

	local bare_to = jid_bare(inner.attr.to);
	local bare_from = jid_bare(inner.attr.from);
	if not bare_to or bare_to == "" or bare_to ~= bare_from then
		module:log("warn", "Rejected malformed privileged carbon from %s", origin.host or "?");
		return true;
	end
	if bare_to:match("@(.+)$") ~= module.host then
		module:log("debug", "Ignoring privileged carbon for remote host %s", bare_to);
		return nil;
	end

	return deliver_carbon_to_user_sessions(bare_to, inner);
end

module:hook_global("component-authenticated", function(event)
	module:log("info", "component-authenticated for %s", event.session and event.session.host or "?");
	send_privilege_advertisement(event.session);
end);

module:hook("pre-message/host", handle_privileged_carbon, 10);
module:hook("message/host", handle_privileged_carbon, 10);