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>single-digit 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: 1739357 $
034 * @since Validator 1.4
035 */
036public abstract class ModulusCheckDigit implements CheckDigit, Serializable {
037
038    private static final long serialVersionUID = 2948962251251528941L;
039
040    // N.B. The modulus can be > 10 provided that the implementing class overrides toCheckDigit and toInt
041    // (for example as in ISBN10CheckDigit)
042    private final int modulus;
043
044    /**
045     * Construct a {@link CheckDigit} routine for a specified modulus.
046     *
047     * @param modulus The modulus value to use for the check digit calculation
048     */
049    public ModulusCheckDigit(int modulus) {
050        this.modulus = modulus;
051    }
052
053    /**
054     * Return the modulus value this check digit routine is based on.
055     *
056     * @return The modulus value this check digit routine is based on
057     */
058    public int getModulus() {
059        return modulus;
060    }
061
062    /**
063     * Validate a modulus check digit for a code.
064     *
065     * @param code The code to validate
066     * @return <code>true</code> if the check digit is valid, otherwise
067     * <code>false</code>
068     */
069    @Override
070    public boolean isValid(String code) {
071        if (code == null || code.length() == 0) {
072            return false;
073        }
074        try {
075            int modulusResult = calculateModulus(code, true);
076            return (modulusResult == 0);
077        } catch (CheckDigitException  ex) {
078            return false;
079        }
080    }
081
082    /**
083     * Calculate a modulus <i>Check Digit</i> for a code which does not yet have one.
084     *
085     * @param code The code for which to calculate the Check Digit; 
086     * the check digit should not be included
087     * @return The calculated Check Digit
088     * @throws CheckDigitException if an error occurs calculating the check digit
089     */
090    @Override
091    public String calculate(String code) throws CheckDigitException {
092        if (code == null || code.length() == 0) {
093            throw new CheckDigitException("Code is missing");
094        }
095        int modulusResult = calculateModulus(code, false);
096        int charValue = (modulus - modulusResult) % modulus;
097        return toCheckDigit(charValue);
098    }
099
100    /**
101     * Calculate the modulus for a code.
102     *
103     * @param code The code to calculate the modulus for.
104     * @param includesCheckDigit Whether the code includes the Check Digit or not.
105     * @return The modulus value
106     * @throws CheckDigitException if an error occurs calculating the modulus
107     * for the specified code
108     */
109    protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
110        int total = 0;
111        for (int i = 0; i < code.length(); i++) {
112            int lth = code.length() + (includesCheckDigit ? 0 : 1);
113            int leftPos  = i + 1;
114            int rightPos = lth - i;
115            int charValue = toInt(code.charAt(i), leftPos, rightPos);
116            total += weightedValue(charValue, leftPos, rightPos);
117        }
118        if (total == 0) {
119            throw new CheckDigitException("Invalid code, sum is zero");
120        }
121        return total % modulus;
122    }
123
124    /**
125     * Calculates the <i>weighted</i> value of a character in the
126     * code at a specified position.
127     * <p>
128     * Some modulus routines weight the value of a character
129     * depending on its position in the code (e.g. ISBN-10), while
130     * others use different weighting factors for odd/even positions
131     * (e.g. EAN or Luhn). Implement the appropriate mechanism
132     * required by overriding this method.
133     *
134     * @param charValue The numeric value of the character
135     * @param leftPos The position of the character in the code, counting from left to right
136     * @param rightPos The positionof the character in the code, counting from right to left
137     * @return The weighted value of the character
138     * @throws CheckDigitException if an error occurs calculating
139     * the weighted value
140     */
141    protected abstract int weightedValue(int charValue, int leftPos, int rightPos)
142            throws CheckDigitException;
143
144
145    /**
146     * Convert a character at a specified position to an integer value.
147     * <p>
148     * <b>Note:</b> this implementation only handlers numeric values
149     * For non-numeric characters, override this method to provide
150     * character--&gt;integer conversion.
151     *
152     * @param character The character to convert
153     * @param leftPos The position of the character in the code, counting from left to right (for identifiying the position in the string)
154     * @param rightPos The position of the character in the code, counting from right to left (not used here)
155     * @return The integer value of the character
156     * @throws CheckDigitException if character is non-numeric
157     */
158    protected int toInt(char character, int leftPos, int rightPos)
159            throws CheckDigitException {
160        if (Character.isDigit(character)) {
161            return Character.getNumericValue(character);
162        }
163        throw new CheckDigitException("Invalid Character[" +
164                leftPos + "] = '" + character + "'");
165    }
166
167    /**
168     * Convert an integer value to a check digit.
169     * <p>
170     * <b>Note:</b> this implementation only handles single-digit numeric values
171     * For non-numeric characters, override this method to provide
172     * integer--&gt;character conversion.
173     *
174     * @param charValue The integer value of the character
175     * @return The converted character
176     * @throws CheckDigitException if integer character value
177     * doesn't represent a numeric character
178     */
179    protected String toCheckDigit(int charValue)
180            throws CheckDigitException {
181        if (charValue >= 0 && charValue <= 9) { // CHECKSTYLE IGNORE MagicNumber
182            return Integer.toString(charValue);
183        }
184        throw new CheckDigitException("Invalid Check Digit Value =" +
185                + charValue);
186    }
187
188    /**
189     * Add together the individual digits in a number.
190     *
191     * @param number The number whose digits are to be added
192     * @return The sum of the digits
193     */
194    public static int sumDigits(int number) {
195        int total = 0;
196        int todo = number;
197        while (todo > 0) {
198            total += todo % 10; // CHECKSTYLE IGNORE MagicNumber
199            todo  = todo / 10; // CHECKSTYLE IGNORE MagicNumber
200        }
201        return total;
202    }
203
204}