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 *      http://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
019import java.io.Serializable;
020
021/**
022 * Abstract <b>Modulus</b> Check digit calculation/validation.
023 * <p>
024 * Provides a <i>base</i> class for building <i>modulus</i> Check
025 * Digit routines.
026 * <p>
027 * This implementation only handles <i>numeric</i> codes, such as
028 * <b>EAN-13</b>. For <i>alphanumeric</i> codes such as <b>EAN-128</b> you
029 * will need to implement/override the <code>toInt()</code> and
030 * <code>toChar()</code> methods.
031 * <p>
032 *
033 * @version $Revision: 1227719 $ $Date: 2012-01-05 12:45:51 -0500 (Thu, 05 Jan 2012) $
034 * @since Validator 1.4
035 */
036public abstract class ModulusCheckDigit implements CheckDigit, Serializable {
037
038    private static final long serialVersionUID = 2948962251251528941L;
039
040    private final int modulus;
041
042    /**
043     * Construct a {@link CheckDigit} routine for a specified modulus.
044     *
045     * @param modulus The modulus value to use for the check digit calculation
046     */
047    public ModulusCheckDigit(int modulus) {
048        this.modulus = modulus;
049    }
050
051    /**
052     * Return the modulus value this check digit routine is based on.
053     *
054     * @return The modulus value this check digit routine is based on
055     */
056    public int getModulus() {
057        return modulus;
058    }
059
060    /**
061     * Validate a modulus check digit for a code.
062     *
063     * @param code The code to validate
064     * @return <code>true</code> if the check digit is valid, otherwise
065     * <code>false</code>
066     */
067    public boolean isValid(String code) {
068        if (code == null || code.length() == 0) {
069            return false;
070        }
071        try {
072            int modulusResult = calculateModulus(code, true);
073            return (modulusResult == 0);
074        } catch (CheckDigitException  ex) {
075            return false;
076        }
077    }
078
079    /**
080     * Calculate a modulus <i>Check Digit</i> for a code.
081     *
082     * @param code The code to calculate the Check Digit for
083     * @return The calculated Check Digit
084     * @throws CheckDigitException if an error occurs calculating
085     * the check digit for the specified code
086     */
087    public String calculate(String code) throws CheckDigitException {
088        if (code == null || code.length() == 0) {
089            throw new CheckDigitException("Code is missing");
090        }
091        int modulusResult = calculateModulus(code, false);
092        int charValue = (modulus - modulusResult) % modulus;
093        return toCheckDigit(charValue);
094    }
095
096    /**
097     * Calculate the modulus for a code.
098     *
099     * @param code The code to calculate the modulus for.
100     * @param includesCheckDigit Whether the code includes the Check Digit or not.
101     * @return The modulus value
102     * @throws CheckDigitException if an error occurs calculating the modulus
103     * for the specified code
104     */
105    protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
106        int total = 0;
107        for (int i = 0; i < code.length(); i++) {
108            int lth = code.length() + (includesCheckDigit ? 0 : 1);
109            int leftPos  = i + 1;
110            int rightPos = lth - i;
111            int charValue = toInt(code.charAt(i), leftPos, rightPos);
112            total += weightedValue(charValue, leftPos, rightPos);
113        }
114        if (total == 0) {
115            throw new CheckDigitException("Invalid code, sum is zero");
116        }
117        return (total % modulus);
118    }
119
120    /**
121     * Calculates the <i>weighted</i> value of a character in the
122     * code at a specified position.
123     * <p>
124     * Some modulus routines weight the value of a character
125     * depending on its position in the code (e.g. ISBN-10), while
126     * others use different weighting factors for odd/even positions
127     * (e.g. EAN or Luhn). Implement the appropriate mechanism
128     * required by overriding this method.
129     *
130     * @param charValue The numeric value of the character
131     * @param leftPos The position of the character in the code, counting from left to right
132     * @param rightPos The positionof the character in the code, counting from right to left
133     * @return The weighted value of the character
134     * @throws CheckDigitException if an error occurs calculating
135     * the weighted value
136     */
137    protected abstract int weightedValue(int charValue, int leftPos, int rightPos)
138            throws CheckDigitException;
139
140
141    /**
142     * Convert a character at a specified position to an integer value.
143     * <p>
144     * <b>Note:</b> this implementation only handlers numeric values
145     * For non-numeric characters, override this method to provide
146     * character-->integer conversion.
147     *
148     * @param character The character to convert
149     * @param leftPos The position of the character in the code, counting from left to right
150     * @param rightPos The positionof the character in the code, counting from right to left
151     * @return The integer value of the character
152     * @throws CheckDigitException if character is non-numeric
153     */
154    protected int toInt(char character, int leftPos, int rightPos)
155            throws CheckDigitException {
156        if (Character.isDigit(character)) {
157            return Character.getNumericValue(character);
158        } else {
159            throw new CheckDigitException("Invalid Character[" +
160                    leftPos + "] = '" + character + "'");
161        }
162    }
163
164    /**
165     * Convert an integer value to a check digit.
166     * <p>
167     * <b>Note:</b> this implementation only handles numeric values
168     * For non-numeric characters, override this method to provide
169     * integer-->character conversion.
170     *
171     * @param charValue The integer value of the character
172     * @return The converted character
173     * @throws CheckDigitException if integer character value
174     * doesn't represent a numeric character
175     */
176    protected String toCheckDigit(int charValue)
177            throws CheckDigitException {
178        if (charValue >= 0 && charValue <= 9) {
179            return Integer.toString(charValue);
180        } else {
181            throw new CheckDigitException("Invalid Check Digit Value =" +
182                    + charValue);
183        }
184    }
185
186    /**
187     * Add together the individual digits in a number.
188     *
189     * @param number The number whose digits are to be added
190     * @return The sum of the digits
191     */
192    public static int sumDigits(int number) {
193        int total = 0;
194        int todo = number;
195        while (todo > 0) {
196            total += todo % 10;
197            todo  = todo / 10;
198        }
199        return total;
200    }
201
202}