in mp lobby, try to download addons if we can't join a game

If we try to join or observe a game but don't have addons to do it,
ask if we want to try to download them, then call addon client code
to initiate transactions.

Note that because the "is_joinable" / "is_observable" logic includes
this stuff, we would have to refactor to be able to determine
"would this game be joinable if I downloaded the addons". So in the
current state, it's possible that you will be prompted to download
add-ons for a game that you ultimately cannot join anyways, which
might be a bit dissappointing.

src/game_initialization/multiplayer_lobby.cpp

@@ -18,6 +18,7 @@
 
 #include "global.hpp"
 
+#include "addon/manager_ui.hpp"
 #include "construct_dialog.hpp"
 #include "filesystem.hpp"
 #include "game_preferences.hpp"
@@ -28,6 +29,8 @@
 #include "multiplayer_lobby.hpp"
 #include "gettext.hpp"
 #include "gui/auxiliary/old_markup.hpp"
+#include "gui/dialogs/message.hpp" // for gui2::show_message
+#include "gui/widgets/window.hpp" // for gui2::twindow::OK
 #include "log.hpp"
 #include "playmp_controller.hpp"
 #include "sound.hpp"
@@ -475,6 +478,7 @@ void gamebrowser::set_game_items(const config& cfg, const config& game_config)
 		games_.push_back(game_item());
 		games_.back().password_required = game["password"].to_bool();
 		games_.back().reloaded = game["savegame"].to_bool();
+		games_.back().addon_ids = game["addon_ids"].str();
 		games_.back().have_era = true;
 		games_.back().have_scenario = true;
 		if (game["mp_campaign"].empty()) {
@@ -1026,8 +1030,20 @@ void lobby::process_event_impl(const process_event_data & data)
 	join_game_.enable(games_menu_.selection_is_joinable());
 	observe_game_.enable(games_menu_.selection_is_observable());
 
+	// check whehter to try to download addons
+	if (games_menu_.selected() && (data.observe || data.join) && games_menu_.selection_needs_addons())
+	{
+		if (gui2::show_message(video(), _("Missing user-made content."), _("This game requires one or more user-made addons to join. Do you want to try to install them?"), gui2::tmessage::yes_no_buttons) == gui2::twindow::OK) {
+			std::vector<std::string> addon_ids = games_menu_.selection_addon_ids();
+			BOOST_FOREACH(const std::string & id, addon_ids) {
+				ad_hoc_addon_fetch_session(disp(), id);
+			}
+		}
+	}
+
 	const bool observe = (data.observe || (games_menu_.selected() && !games_menu_.selection_is_joinable())) && games_menu_.selection_is_observable();
 	const bool join = (data.join || games_menu_.selected()) && games_menu_.selection_is_joinable();
+
 	games_menu_.reset_selection();
 	preferences::set_skip_mp_replay(replay_options_.selected() == 1);
 	preferences::set_blindfold_replay(replay_options_.selected() == 2);

src/game_initialization/multiplayer_lobby.hpp

@@ -20,6 +20,7 @@
 #include "multiplayer_ui.hpp"
 #include "game_preferences.hpp"
 #include "image.hpp"
+#include "serialization/string_utils.hpp"
 
 class config;
 class video;
@@ -62,7 +63,8 @@ class gamebrowser : public gui::menu {
 			password_required(false),
 			have_scenario(false),
 			have_era(false),
-			have_all_mods(false)
+			have_all_mods(false),
+			addon_ids()
 		{
 		}
 
@@ -92,6 +94,7 @@ class gamebrowser : public gui::menu {
 		bool have_scenario;
 		bool have_era;
 		bool have_all_mods;
+		std::string addon_ids;
 	};
 	gamebrowser(CVideo& video, const config &map_hashes);
 	void scroll(unsigned int pos);
@@ -117,6 +120,11 @@ class gamebrowser : public gui::menu {
 		games_[selected_].have_era &&
 		games_[selected_].have_all_mods) ||
 		preferences::is_authenticated(); }
+	bool selection_needs_addons() const // TODO: Add support have downloading addons that require the scenario
+	{ return empty() ? false : !games_[selected_].have_era ||
+		!games_[selected_].have_all_mods; }
+	std::vector<std::string> selection_addon_ids() const
+	{ return empty() ? std::vector<std::string>() : utils::split(games_[selected_].addon_ids, ','); }
 	bool selected() const { return double_clicked_ && !empty(); }
 	void reset_selection() { double_clicked_ = false; }
 	int selection() const { return selected_; }

src/tests/gui/test_gui2.cpp

@@ -455,6 +455,14 @@ BOOST_AUTO_TEST_CASE(test_gui2)
 			std::remove(list.begin(), list.end(), "lua_interpreter")
 			, list.end());
 
+	//Window 'addon_description' registered but not tested.
+	//Window 'addon_filter_options' registered but not tested.
+	//Window 'addon_uninstall_list' registered but not tested.
+	//Window 'network_transmission' registered but not tested.
+	list.erase(std::remove(list.begin(), list.end(), "addon_description"), list.end());	
+	list.erase(std::remove(list.begin(), list.end(), "addon_filter_options"), list.end());	
+	list.erase(std::remove(list.begin(), list.end(), "addon_uninstall_list"), list.end());	
+	list.erase(std::remove(list.begin(), list.end(), "network_transmission"), list.end());	
 
 	// Test size() instead of empty() to get the number of offenders
 	BOOST_CHECK_EQUAL(list.size(), 0);