001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.validator.routines.checkdigit;
018
019/**
020 * Modulus 10 <strong>ABA Number</strong> (or <strong>Routing Transit Number</strong> (RTN)) Check Digit
021 * calculation/validation.
022 *
023 * <p>
024 * ABA Numbers (or Routing Transit Numbers) are a nine digit numeric code used
025 * to identify American financial institutions for things such as checks or deposits
026 * (ABA stands for the American Bankers Association).
027 * </p>
028 *
029 * Check digit calculation is based on <em>modulus 10</em> with digits being weighted
030 * based on their position (from right to left) as follows:
031 *
032 * <ul>
033 *   <li>Digits 1, 4 and &amp; 7 are weighted 1</li>
034 *   <li>Digits 2, 5 and &amp; 8 are weighted 7</li>
035 *   <li>Digits 3, 6 and &amp; 9 are weighted 3</li>
036 * </ul>
037 *
038 * <p>
039 * For further information see
040 *  <a href="https://en.wikipedia.org/wiki/Routing_transit_number">Wikipedia -
041 *  Routing transit number</a>.
042 * </p>
043 *
044 * @since 1.4
045 */
046public final class ABANumberCheckDigit extends ModulusCheckDigit {
047
048    private static final long serialVersionUID = -8255937433810380145L;
049
050    /**
051     * Singleton Routing Transit Number Check Digit instance.
052     */
053    public static final CheckDigit ABAN_CHECK_DIGIT = new ABANumberCheckDigit();
054
055    /** Weighting given to digits depending on their right position */
056    private static final int[] POSITION_WEIGHT = {3, 1, 7};
057
058    /** An ABA number is exactly nine digits, the last being the check digit. */
059    private static final int ABAN_LEN = 9;
060
061    /**
062     * Constructs a modulus 10 Check Digit routine for ABA Numbers.
063     */
064    public ABANumberCheckDigit() {
065    }
066
067    /**
068     * {@inheritDoc}
069     *
070     * <p>
071     * The weight is taken from {@code rightPos}, which does not change when a character is prepended, so
072     * {@code ModulusCheckDigit} would accept an over-length code whose leading digit lands on a no-op weight (for
073     * example {@code 0123456780}). The nine-character length is checked here before the check digit test.
074     * </p>
075     */
076    @Override
077    public boolean isValid(final String code) {
078        return isLength(code, ABAN_LEN) && super.isValid(code);
079    }
080
081    /**
082     * Calculates the <em>weighted</em> value of a character in the
083     * code at a specified position.
084     * <p>
085     * ABA Routing numbers are weighted in the following manner:
086     * </p>
087     * <pre>{@code
088     *     left position: 1  2  3  4  5  6  7  8  9
089     *            weight: 3  7  1  3  7  1  3  7  1
090     * }</pre>
091     *
092     * @param charValue The numeric value of the character.
093     * @param leftPos The position of the character in the code, counting from left to right.
094     * @param rightPos The position of the character in the code, counting from right to left.
095     * @return The weighted value of the character.
096     */
097    @Override
098    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
099        final int weight = POSITION_WEIGHT[rightPos % 3]; // CHECKSTYLE IGNORE MagicNumber
100        return charValue * weight;
101    }
102
103}