Campaign Lua functions for branching

code/mission/missioncampaign.cpp

@@ -1792,7 +1792,7 @@ void mission_campaign_exit_loop()
  * all previous missions marked skipped
  * this relies on correct mission ordering in the campaign file
  */
-bool mission_campaign_jump_to_mission(const char* filename, bool no_skip)
+bool mission_campaign_jump_to_mission(const char* filename, bool no_skip, bool preserve_loadout)
 {
 	int i = 0, mission_num = -1;
 	constexpr size_t dest_filename_size = 64;
@@ -1825,12 +1825,14 @@ bool mission_campaign_jump_to_mission(const char* filename, bool no_skip)
 		// based on player feedback, let's NOT restart the campaign but rather fail gracefully
 		return false;
 	} else {
-		for (SCP_vector<ship_info>::iterator it = Ship_info.begin(); it != Ship_info.end(); it++) {
-			i = static_cast<int>(std::distance(Ship_info.begin(), it));
-			Campaign.ships_allowed[i] = 1;
-		}
-		for (i = 0; i < weapon_info_size(); i++) {
-			Campaign.weapons_allowed[i] = 1;
+		if (!preserve_loadout) {
+			for (auto it = Ship_info.begin(); it != Ship_info.end(); it++) {
+				i = static_cast<int>(std::distance(Ship_info.begin(), it));
+				Campaign.ships_allowed[i] = 1;
+			}
+			for (i = 0; i < weapon_info_size(); i++) {
+				Campaign.weapons_allowed[i] = 1;
+			}
 		}
 
 		Campaign.next_mission = mission_num;
@@ -1843,6 +1845,87 @@ bool mission_campaign_jump_to_mission(const char* filename, bool no_skip)
 	}
 }
 
+SCP_vector<SCP_string> mission_campaign_get_valid_next_missions()
+{
+	SCP_vector<SCP_string> valid_missions;
+
+	// This can be queried from UI states outside active mission gameplay
+	// where GM_CAMPAIGN_MODE may not be set even though a campaign is loaded.
+	if (Campaign.name[0] == '\0' || Campaign.num_missions <= 0) {
+		return valid_missions;
+	}
+
+	// During normal campaign flow, current_mission is set to -1 after accepting a mission
+	// and before the next mission actually starts. In that window, prev_mission is the
+	// mission whose branching formula produced the current next_mission.
+	// Prefer prev_mission when available since branch selection outside missions is
+	// generally based on the mission just completed.
+	int branch_source_mission = Campaign.prev_mission;
+	if (branch_source_mission < 0) {
+		branch_source_mission = Campaign.current_mission;
+	}
+
+	if (branch_source_mission < 0 || branch_source_mission >= Campaign.num_missions) {
+		// Campaigns that haven't started yet can have both current_mission and prev_mission
+		// unset. In that case, next_mission is the only available entry point.
+		if (Campaign.next_mission >= 0 && Campaign.next_mission < Campaign.num_missions) {
+			valid_missions.emplace_back(Campaign.missions[Campaign.next_mission].name);
+		}
+		return valid_missions;
+	}
+
+	auto& current = Campaign.missions[branch_source_mission];
+	if (current.formula < 0) {
+		return valid_missions;
+	}
+
+	// This helper is intended to enumerate all valid branches from a cond formula.
+	// If the formula is not cond, return an empty list.
+	if (get_operator_const(CTEXT(current.formula)) != OP_COND) {
+		return valid_missions;
+	}
+
+	const int saved_next = Campaign.next_mission;
+	int clauses = CDR(current.formula);
+
+	while (clauses >= 0) {
+		const int clause = CAR(clauses);
+		if (clause < 0) {
+			clauses = CDR(clauses);
+			continue;
+		}
+
+		flush_sexp_tree(current.formula);
+
+		const int condition = CAR(clause);
+		const int condition_result = eval_sexp(condition);
+		if (condition_result == SEXP_TRUE) {
+			Campaign.next_mission = -1;
+			int actions = CDR(clause);
+
+			while (actions >= 0) {
+				const int exp = CAR(actions);
+				if (exp >= -1) {
+					eval_sexp(exp);
+				}
+				actions = CDR(actions);
+			}
+
+			if (Campaign.next_mission >= 0 && Campaign.next_mission < Campaign.num_missions && Campaign.next_mission != branch_source_mission) {
+				const auto& mission_name = Campaign.missions[Campaign.next_mission].name;
+				if (std::find(valid_missions.begin(), valid_missions.end(), mission_name) == valid_missions.end()) {
+					valid_missions.emplace_back(mission_name);
+				}
+			}
+		}
+
+		clauses = CDR(clauses);
+	}
+
+	Campaign.next_mission = saved_next;
+	return valid_missions;
+}
+
 void mission_campaign_load_failure_popup()
 {
 	if (Campaign_load_failure == 0) {

code/mission/missioncampaign.h

@@ -247,7 +247,10 @@ void mission_campaign_skip_to_next();
 void mission_campaign_exit_loop();
 
 // jump to specified mission
-bool mission_campaign_jump_to_mission(const char* filename, bool no_skip = false);
+bool mission_campaign_jump_to_mission(const char* filename, bool no_skip = false, bool preserve_loadout = false);
+
+// get a list of all valid next missions in the campaign
+SCP_vector<SCP_string> mission_campaign_get_valid_next_missions();
 
 // stuff for the end of the campaign of the single player game
 void mission_campaign_end_init();

code/scripting/api/libs/mission.cpp

@@ -3207,17 +3207,29 @@ ADE_FUNC(getPrevMissionFilename, l_Campaign, NULL, "Gets previous mission filena
 }
 
 // DahBlount - This jumps to a mission, the reason it accepts a boolean value is so that players can return to campaign maps
-ADE_FUNC(jumpToMission, l_Campaign, "string filename, [boolean hub]", "Jumps to a mission based on the filename. Optionally, the player can be sent to a hub mission without setting missions to skipped.", "boolean", "Jumps to a mission, returning true if successful, false if unsuccessful (e.g. the mission could not be found in the campaign), or nil if no mission was specified.")
+ADE_FUNC(jumpToMission, l_Campaign, "string filename, [boolean hub, boolean preserve]", "Jumps to a mission based on the filename. Optionally, the player can be sent to a hub mission without setting missions to skipped or preserve loadout.", "boolean", "Jumps to a mission, returning true if successful, false if unsuccessful (e.g. the mission could not be found in the campaign), or nil if no mission was specified.")
 {
 	const char* filename = nullptr;
 	bool hub = false;
-	if (!ade_get_args(L, "s|b", &filename, &hub))
+	bool preserve = false;
+	if (!ade_get_args(L, "s|b", &filename, &hub, &preserve))
 		return ADE_RETURN_NIL;
 
-	bool success = mission_campaign_jump_to_mission(filename, hub);
+	bool success = mission_campaign_jump_to_mission(filename, hub, preserve);
 	return ade_set_args(L, "b", success);
 }
 
+ADE_FUNC(getValidNextMissions, l_Campaign, nullptr, "Gets all valid next mission filenames for the current campaign.", "table", "A list of mission filenames, or an empty table if none are valid.")
+{
+	auto table = luacpp::LuaTable::create(L);
+	auto valid_missions = mission_campaign_get_valid_next_missions();
+	for (size_t i = 0; i < valid_missions.size(); ++i) {
+		table.addValue(static_cast<int>(i + 1), valid_missions[i]);
+	}
+
+	return ade_set_args(L, "t", &table);
+}
+
 ADE_VIRTVAR(CustomData, l_Campaign, nullptr, "Gets the custom data table for this campaign", "table", "The campaign's custom data table") 
 {
 	if (ADE_SETTING_VAR) {