Add: [AI] Get the number of vehicles in a given group (#9462)

src/script/api/ai_changelog.hpp

@@ -20,6 +20,7 @@
  * API additions:
  * \li AINewGRF
  * \li AINewGRFList
+ * \li AIGroup::GetNumVehicles
  *
  * \b 1.11.0
  *

src/script/api/script_group.cpp

@@ -106,6 +106,15 @@
 	return GetGroupNumEngines(ScriptObject::GetCompany(), group_id, engine_id);
 }
 
+/* static */ int32 ScriptGroup::GetNumVehicles(GroupID group_id, ScriptVehicle::VehicleType vehicle_type)
+{
+	bool valid_group = IsValidGroup(group_id);
+	if (!valid_group && group_id != GROUP_DEFAULT && group_id != GROUP_ALL) return -1;
+	if (!valid_group && (vehicle_type < ScriptVehicle::VT_RAIL || vehicle_type > ScriptVehicle::VT_AIR)) return -1;
+
+	return GetGroupNumVehicle(ScriptObject::GetCompany(), group_id, valid_group ? ::Group::Get(group_id)->vehicle_type : (::VehicleType)vehicle_type);
+}
+
 /* static */ bool ScriptGroup::MoveVehicle(GroupID group_id, VehicleID vehicle_id)
 {
 	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_DEFAULT);

src/script/api/script_group.hpp

@@ -128,6 +128,20 @@ public:
 	 */
 	static int32 GetNumEngines(GroupID group_id, EngineID engine_id);
 
+	/**
+	 * Get the total number of vehicles in a given group and its sub-groups.
+	 * @param group_id The group to get the number of vehicles in.
+	 * @param vehicle_type The type of vehicle of the group.
+	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL || group_id == GROUP_DEFAULT.
+	 * @pre IsValidGroup(group_id) || vehicle_type == ScriptVehicle::VT_ROAD || vehicle_type == ScriptVehicle::VT_RAIL ||
+	 *   vehicle_type == ScriptVehicle::VT_WATER || vehicle_type == ScriptVehicle::VT_AIR
+	 * @return The total number of vehicles in the group with id group_id and it's sub-groups.
+	 * @note If the group is valid (neither GROUP_ALL nor GROUP_DEFAULT), the value of
+	 *  vehicle_type is retrieved from the group itself and not from the input value.
+	 *  But if the group is GROUP_ALL or GROUP_DEFAULT, then vehicle_type must be valid.
+	 */
+	static int32 GetNumVehicles(GroupID group_id, ScriptVehicle::VehicleType vehicle_type);
+
 	/**
 	 * Move a vehicle to a group.
 	 * @param group_id The group to move the vehicle to.