001// --------------------------------------------------------------------------------
002// Copyright 2002-2026 Echo Three, LLC
003//
004// Licensed under the Apache License, Version 2.0 (the "License");
005// you may not use this file except in compliance with the License.
006// You may obtain a copy of the License at
007//
008//     http://www.apache.org/licenses/LICENSE-2.0
009//
010// Unless required by applicable law or agreed to in writing, software
011// distributed under the License is distributed on an "AS IS" BASIS,
012// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013// See the License for the specific language governing permissions and
014// limitations under the License.
015// --------------------------------------------------------------------------------
016
017package com.echothree.model.control.item.server.logic.checksum;
018
019import com.echothree.util.common.message.ExecutionErrors;
020import com.echothree.util.server.message.ExecutionErrorAccumulator;
021import javax.enterprise.context.ApplicationScoped;
022
023@ApplicationScoped
024public class Gtin13ChecksumLogic
025        extends BaseChecksumLogic
026        implements ItemAliasChecksumInterface {
027
028    protected Gtin13ChecksumLogic() {
029        super();
030    }
031
032    @Override
033    public void checkChecksum(final ExecutionErrorAccumulator eea, final String alias) {
034        if(alias.length() == 13) {
035            var hasCharacterError = false;
036            var checksum = 0;
037
038            for(int i = 0; i < 12; i++) {
039                int d = getDigit(alias, i);
040
041                if(d == -1) {
042                    hasCharacterError = true;
043                    break;
044                }
045
046                // https://www.gs1.org/services/how-calculate-check-digit-manually
047                checksum += i % 2 == 0 ? d : (3 * d);
048            }
049
050            if(!hasCharacterError) {
051                var checkDigit = getDigit(alias, 12);
052
053                hasCharacterError = checkDigit == -1;
054
055                if(!hasCharacterError) {
056                    var intermediate = (10 - (checksum % 10)) % 10;
057
058                    if(intermediate != checkDigit) {
059                        eea.addExecutionError(ExecutionErrors.IncorrectGtin13Checksum.name(), alias);
060                    }
061                }
062            }
063
064            if(hasCharacterError) {
065                eea.addExecutionError(ExecutionErrors.IncorrectGtin13Character.name(), alias);
066            }
067        } else {
068            eea.addExecutionError(ExecutionErrors.IncorrectGtin13Length.name(), alias);
069        }
070    }
071
072}