Rock.Model.RegistrationService.GetTotalPayments C# (CSharp) Method

        public decimal GetTotalPayments( int registrationId )
        {
            return GetPayments( registrationId )
                .Select( p => p.Amount ).DefaultIfEmpty()
                .Sum();
        }

        /// <summary>
        /// Sets the registration state
        /// </summary>
        private void SetRegistrationState()
        {
            string registrationSlug = PageParameter( REGISTRATION_SLUG_PARAM_NAME );
            int? registrationInstanceId = PageParameter( REGISTRATION_INSTANCE_ID_PARAM_NAME ).AsIntegerOrNull();
            int? registrationId = PageParameter( REGISTRATION_ID_PARAM_NAME ).AsIntegerOrNull();
            int? groupId = PageParameter( REGISTRATION_GROUP_ID_PARAM_NAME ).AsIntegerOrNull();
            int? campusId = PageParameter( REGISTRATION_CAMPUS_ID_PARAM_NAME ).AsIntegerOrNull();

            // Not inside a "using" due to serialization needing context to still be active
            var rockContext = new RockContext();

            // An existing registration id was specified
            if ( registrationId.HasValue )
            {
                var registrationService = new RegistrationService( rockContext );
                var registration = registrationService
                    .Queryable( "Registrants.PersonAlias.Person,Registrants.GroupMember,RegistrationInstance.Account,RegistrationInstance.RegistrationTemplate.Fees,RegistrationInstance.RegistrationTemplate.Discounts,RegistrationInstance.RegistrationTemplate.Forms.Fields.Attribute,RegistrationInstance.RegistrationTemplate.FinancialGateway" )
                    .Where( r => r.Id == registrationId.Value )
                    .FirstOrDefault();
                if ( registration != null )
                {
                    RegistrationInstanceState = registration.RegistrationInstance;
                    RegistrationState = new RegistrationInfo( registration, rockContext );
                    RegistrationState.PreviousPaymentTotal = registrationService.GetTotalPayments( registration.Id );
                }
            }

            // A registration slug was specified
            if ( RegistrationState == null && !string.IsNullOrWhiteSpace( registrationSlug ) )
            {
                var dateTime = RockDateTime.Now;
                var linkage = new EventItemOccurrenceGroupMapService( rockContext )
                    .Queryable( "RegistrationInstance.Account,RegistrationInstance.RegistrationTemplate.Fees,RegistrationInstance.RegistrationTemplate.Discounts,RegistrationInstance.RegistrationTemplate.Forms.Fields.Attribute,RegistrationInstance.RegistrationTemplate.FinancialGateway" )
                    .Where( l =>
                        l.UrlSlug == registrationSlug &&
                        l.RegistrationInstance != null &&
                        l.RegistrationInstance.IsActive &&
                        l.RegistrationInstance.RegistrationTemplate != null &&
                        l.RegistrationInstance.RegistrationTemplate.IsActive &&
                        (!l.RegistrationInstance.StartDateTime.HasValue || l.RegistrationInstance.StartDateTime <= dateTime ) &&
                        (!l.RegistrationInstance.EndDateTime.HasValue || l.RegistrationInstance.EndDateTime > dateTime )  )
                    .FirstOrDefault();

                if ( linkage != null )
                {
                    RegistrationInstanceState = linkage.RegistrationInstance;
                    GroupId = linkage.GroupId;
                    RegistrationState = new RegistrationInfo( CurrentPerson );
                }
            }

            // A group id and campus id were specified
            if ( RegistrationState == null && groupId.HasValue && campusId.HasValue )
            {
                var dateTime = RockDateTime.Now;
                var linkage = new EventItemOccurrenceGroupMapService( rockContext )
                    .Queryable( "RegistrationInstance.Account,RegistrationInstance.RegistrationTemplate.Fees,RegistrationInstance.RegistrationTemplate.Discounts,RegistrationInstance.RegistrationTemplate.Forms.Fields.Attribute,RegistrationInstance.RegistrationTemplate.FinancialGateway" )
                    .Where( l =>
                        l.GroupId == groupId &&
                        l.EventItemOccurrence != null &&
                        l.EventItemOccurrence.CampusId == campusId &&
                        l.RegistrationInstance != null &&
                        l.RegistrationInstance.IsActive &&
                        l.RegistrationInstance.RegistrationTemplate != null &&
                        l.RegistrationInstance.RegistrationTemplate.IsActive &&
                        ( !l.RegistrationInstance.StartDateTime.HasValue || l.RegistrationInstance.StartDateTime <= dateTime ) &&
                        ( !l.RegistrationInstance.EndDateTime.HasValue || l.RegistrationInstance.EndDateTime > dateTime ) )
                    .FirstOrDefault();

                if ( linkage != null )
                {
                    RegistrationInstanceState = linkage.RegistrationInstance;
                    GroupId = linkage.GroupId;
                    RegistrationState = new RegistrationInfo( CurrentPerson );
                }
            }

            // A registratio instance id was specified
            if ( RegistrationState == null && registrationInstanceId.HasValue )
            {
                var dateTime = RockDateTime.Now;
                RegistrationInstanceState = new RegistrationInstanceService( rockContext )
                    .Queryable( "Account,RegistrationTemplate.Fees,RegistrationTemplate.Discounts,RegistrationTemplate.Forms.Fields.Attribute,RegistrationTemplate.FinancialGateway" )
                    .Where( r =>
                        r.Id == registrationInstanceId.Value &&
                        r.IsActive &&
                        r.RegistrationTemplate != null &&
                        r.RegistrationTemplate.IsActive &&
                        ( !r.StartDateTime.HasValue || r.StartDateTime <= dateTime ) &&
                        ( !r.EndDateTime.HasValue || r.EndDateTime > dateTime ) )
                    .FirstOrDefault();

                if ( RegistrationInstanceState != null )
                {
                    RegistrationState = new RegistrationInfo( CurrentPerson );
                }
            }

            if ( RegistrationState != null && !RegistrationState.Registrants.Any() )
            {
                SetRegistrantState( 1 );
            }
        }