How to describe the @preconditions on this function declaration

script_group.cpp

	/**
	 * Get the number of engines in a given group.
	 * @param group_id The group to get the number of engines in.
	 * @param engine_id The engine id to count.
	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL || group_id == GROUP_DEFAULT.
	 * @pre IsValidEngine(engine_id)
	 * @pre IsValidGroup(group_id) && ScriptEngine::GetVehicleType(engine_id) == GetVehicleType(group_id).
	 * @game @pre Valid ScriptCompanyMode active in scope
	 *    when group_id == GROUP_ALL || group_id == GROUP_DEFAULT.
	 * @return The number of engines with id engine_id in the group with id group_id.
	 */
	static int32 GetNumEngines(GroupID group_id, EngineID engine_id);


/* static */ int32 ScriptGroup::GetNumEngines(GroupID group_id, EngineID engine_id)
{
	bool valid_group = IsValidGroup(group_id);
	if (!valid_group && group_id != GROUP_DEFAULT && group_id != GROUP_ALL) return -1;
	if (ScriptObject::GetCompany() == OWNER_DEITY && (group_id == GROUP_DEFAULT || group_id == GROUP_ALL)) return -1;
	if (!ScriptEngine::IsValidEngine(engine_id)) return -1;
	if (valid_group && ScriptEngine::GetVehicleType(engine_id) != ScriptGroup::GetVehicleType(group_id)) return -1;

	CompanyID company = (valid_group && ScriptObject::GetCompany() == OWNER_DEITY) ? ::Group::Get(group_id)->owner : ScriptObject::GetCompany();

	return GetGroupNumEngines(company, group_id, engine_id);
}