/*
 * Copyright 2002-2005 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.lang.builder;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

/**
 * <p>Assists in implementing {@link Object#hashCode()} methods.</p>
 *
 * <p> This class enables a good <code>hashCode</code> method to be built for any class. It
 * follows the rules laid out in the book
 * <a href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a>
 * by Joshua Bloch. Writing a good <code>hashCode</code> method is actually quite
 * difficult. This class aims to simplify the process.</p>
 *
 * <p>All relevant fields from the object should be included in the
 * <code>hashCode</code> method. Derived fields may be excluded. In general, any
 * field used in the <code>equals</code> method must be used in the <code>hashCode</code>
 * method.</p>
 *
 * <p>To use this class write code as follows:</p>
 * <pre>
 * public class Person {
 *   String name;
 *   int age;
 *   boolean isSmoker;
 *   ...
 *
 *   public int hashCode() {
 *     // you pick a hard-coded, randomly chosen, non-zero, odd number
 *     // ideally different for each class
 *     return new HashCodeBuilder(17, 37).
 *       append(name).
 *       append(age).
 *       append(smoker).
 *       toHashCode();
 *   }
 * }
 * </pre>
 *
 * <p>If required, the superclass <code>hashCode()</code> can be added
 * using {@link #appendSuper}.</p>
 *
 * <p>Alternatively, there is a method that uses reflection to determine
 * the fields to test. Because these fields are usually private, the method,
 * <code>reflectionHashCode</code>, uses <code>AccessibleObject.setAccessible</code> to
 * change the visibility of the fields. This will fail under a security manager,
 * unless the appropriate permissions are set up correctly. It is also slower
 * than testing explicitly.</p>
 *
 * <p>A typical invocation for this method would look like:</p>
 * <pre>
 * public int hashCode() {
 *   return HashCodeBuilder.reflectionHashCode(this);
 * }
 * </pre>
 *
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 1.0
 * @version $Id: HashCodeBuilder.java,v 1.1 2008/09/23 12:47:44 chm Exp $
 */
public class HashCodeBuilder {

    /**
     * Constant to use in building the hashCode.
     */
    private final int iConstant;
    /**
     * Running total of the hashCode.
     */
    private int iTotal = 0;

    /**
     * <p>Uses two hard coded choices for the constants
     * needed to build a <code>hashCode</code>.</p>
     */
    public HashCodeBuilder() {
        iConstant = 37;
        iTotal = 17;
    }

    /**
     * <p>Two randomly chosen, non-zero, odd numbers must be passed in.
     * Ideally these should be different for each class, however this is
     * not vital.</p>
     *
     * <p>Prime numbers are preferred, especially for the multiplier.</p>
     *
     * @param initialNonZeroOddNumber  a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber  a non-zero, odd number used as the multiplier
     * @throws IllegalArgumentException if the number is zero or even
     */
    public HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) {
        if (initialNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero initial value");
        }
        if (initialNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd initial value");
        }
        if (multiplierNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero multiplier");
        }
        if (multiplierNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd multiplier");
        }
        iConstant = multiplierNonZeroOddNumber;
        iTotal = initialNonZeroOddNumber;
    }

    //-------------------------------------------------------------------------

    /**
     * <p>This method uses reflection to build a valid hash code.</p>
     *
     * <p>This constructor uses two hard coded choices for the constants
     * needed to build a hash code.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.</p>
     *
     * <p>Transient members will be not be used, as they are likely derived
     * fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * @param object  the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object) {
        return reflectionHashCode(17, 37, object, false, null);
    }

    /**
     * <p>This method uses reflection to build a valid hash code.</p>
     *
     * <p>This constructor uses two hard coded choices for the constants needed
     * to build a hash code.</p>
     *
     * <p> It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.</p>
     *
     * <P>If the TestTransients parameter is set to <code>true</code>, transient
     * members will be tested, otherwise they are ignored, as they are likely
     * derived fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * @param object  the Object to create a <code>hashCode</code> for
     * @param testTransients  whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object, boolean testTransients) {
        return reflectionHashCode(17, 37, object, testTransients, null);
    }

    /**
     * <p>This method uses reflection to build a valid hash code.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.</p>
     *
     * <p>Transient members will be not be used, as they are likely derived
     * fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * <p>Two randomly chosen, non-zero, odd numbers must be passed in. Ideally
     * these should be different for each class, however this is not vital.
     * Prime numbers are preferred, especially for the multiplier.</p>
     *
     * @param initialNonZeroOddNumber  a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber  a non-zero, odd number used as the multiplier
     * @param object  the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException if the Object is <code>null</code>
     * @throws IllegalArgumentException if the number is zero or even
     */
    public static int reflectionHashCode(
            int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null);
    }

    /**
     * <p>This method uses reflection to build a valid hash code.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is also
     * not as efficient as testing explicitly.</p>
     *
     * <p>If the TestTransients parameter is set to <code>true</code>, transient
     * members will be tested, otherwise they are ignored, as they are likely
     * derived fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be tested. Superclass fields will be included.</p>
     *
     * <p>Two randomly chosen, non-zero, odd numbers must be passed in. Ideally
     * these should be different for each class, however this is not vital.
     * Prime numbers are preferred, especially for the multiplier.</p>
     *
     * @param initialNonZeroOddNumber  a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber  a non-zero, odd number used as the multiplier
     * @param object  the Object to create a <code>hashCode</code> for
     * @param testTransients  whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException if the Object is <code>null</code>
     * @throws IllegalArgumentException if the number is zero or even
     */
    public static int reflectionHashCode(
            int initialNonZeroOddNumber, int multiplierNonZeroOddNumber,
            Object object, boolean testTransients) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null);
    }
            
    /**
     * <p>This method uses reflection to build a valid hash code.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run under
     * a security manager, if the permissions are not set up correctly. It is also
     * not as efficient as testing explicitly.</p>
     *
     * <p>If the TestTransients parameter is set to <code>true</code>, transient
     * members will be tested, otherwise they are ignored, as they are likely
     * derived fields, and not part of the value of the <code>Object</code>.</p>
     *
     * <p>Static fields will not be included. Superclass fields will be included
     * up to and including the specified superclass. A null superclass is treated
     * as java.lang.Object.</p>
     *
     * <p>Two randomly chosen, non-zero, odd numbers must be passed in. Ideally
     * these should be different for each class, however this is not vital.
     * Prime numbers are preferred, especially for the multiplier.</p>
     *
     * @param initialNonZeroOddNumber  a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber  a non-zero, odd number used as the multiplier
     * @param object  the Object to create a <code>hashCode</code> for
     * @param testTransients  whether to include transient fields
     * @param reflectUpToClass  the superclass to reflect up to (inclusive),
     *  may be <code>null</code>
     * @return int hash code
     * @throws IllegalArgumentException if the Object is <code>null</code>
     * @throws IllegalArgumentException if the number is zero or even
     * @since 2.0
     */
    public static int reflectionHashCode(
        int initialNonZeroOddNumber,
        int multiplierNonZeroOddNumber,
        Object object,
        boolean testTransients,
        Class reflectUpToClass) {

        if (object == null) {
            throw new IllegalArgumentException("The object to build a hash code for must not be null");
        }
        HashCodeBuilder builder = new HashCodeBuilder(initialNonZeroOddNumber, multiplierNonZeroOddNumber);
        Class clazz = object.getClass();
        reflectionAppend(object, clazz, builder, testTransients);
        while (clazz.getSuperclass() != null && clazz != reflectUpToClass) {
            clazz = clazz.getSuperclass();
            reflectionAppend(object, clazz, builder, testTransients);
        }
        return builder.toHashCode();
    }

    /**
     * <p>Appends the fields and values defined by the given object of the
     * given <code>Class</code>.</p>
     * 
     * @param object  the object to append details of
     * @param clazz  the class to append details of
     * @param builder  the builder to append to
     * @param useTransients  whether to use transient fields
     */
    private static void reflectionAppend(Object object, Class clazz, HashCodeBuilder builder, boolean useTransients) {
        Field[] fields = clazz.getDeclaredFields();
        AccessibleObject.setAccessible(fields, true);
        for (int i = 0; i < fields.length; i++) {
            Field f = fields[i];
            if ((f.getName().indexOf('$') == -1)
                && (useTransients || !Modifier.isTransient(f.getModifiers()))
                && (!Modifier.isStatic(f.getModifiers()))) {
                try {
                    builder.append(f.get(object));
                } catch (IllegalAccessException e) {
                    //this can't happen. Would get a Security exception instead
                    //throw a runtime exception in case the impossible happens.
                    throw new InternalError("Unexpected IllegalAccessException");
                }
            }
        }
    }

    //-------------------------------------------------------------------------

    /**
     * <p>Adds the result of super.hashCode() to this builder.</p>
     *
     * @param superHashCode  the result of calling <code>super.hashCode()</code>
     * @return this HashCodeBuilder, used to chain calls.
     * @since 2.0
     */
    public HashCodeBuilder appendSuper(int superHashCode) {
        iTotal = iTotal * iConstant + superHashCode;
        return this;
    }

    //-------------------------------------------------------------------------

    /**
     * <p>Append a <code>hashCode</code> for an <code>Object</code>.</p>
     *
     * @param object  the Object to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(Object object) {
        if (object == null) {
            iTotal = iTotal * iConstant;

        } else {
            if (object.getClass().isArray() == false) {
                //the simple case, not an array, just the element
                iTotal = iTotal * iConstant + object.hashCode();

            } else {
                //'Switch' on type of array, to dispatch to the correct handler
                // This handles multi dimensional arrays
                if (object instanceof long[]) {
                    append((long[]) object);
                } else if (object instanceof int[]) {
                    append((int[]) object);
                } else if (object instanceof short[]) {
                    append((short[]) object);
                } else if (object instanceof char[]) {
                    append((char[]) object);
                } else if (object instanceof byte[]) {
                    append((byte[]) object);
                } else if (object instanceof double[]) {
                    append((double[]) object);
                } else if (object instanceof float[]) {
                    append((float[]) object);
                } else if (object instanceof boolean[]) {
                    append((boolean[]) object);
                } else {
                    // Not an array of primitives
                    append((Object[]) object);
                }
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>long</code>.</p>
     *
     * @param value  the long to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(long value) {
        iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for an <code>int</code>.</p>
     *
     * @param value  the int to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(int value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>short</code>.</p>
     *
     * @param value  the short to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(short value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>char</code>.</p>
     *
     * @param value  the char to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(char value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>byte</code>.</p>
     *
     * @param value  the byte to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(byte value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>double</code>.</p>
     *
     * @param value  the double to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(double value) {
        return append(Double.doubleToLongBits(value));
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>float</code>.</p>
     *
     * @param value  the float to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(float value) {
        iTotal = iTotal * iConstant + Float.floatToIntBits(value);
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>boolean</code>.</p>
     * <p>This adds <code>iConstant * 1</code> to the <code>hashCode</code>
     * and not a <code>1231</code> or <code>1237</code> as done in java.lang.Boolean. 
     * This is in accordance with the <quote>Effective Java</quote> design. </p>
     *
     * @param value  the boolean to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(boolean value) {
        iTotal = iTotal * iConstant + (value ? 0 : 1);
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for an <code>Object</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(Object[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>long</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(long[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for an <code>int</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(int[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>short</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(short[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>char</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(char[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>byte</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(byte[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>double</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(double[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>float</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(float[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Append a <code>hashCode</code> for a <code>boolean</code> array.</p>
     *
     * @param array  the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(boolean[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    /**
     * <p>Return the computed <code>hashCode</code>.</p>
     *
     * @return <code>hashCode</code> based on the fields appended
     */
    public int toHashCode() {
        return iTotal;
    }

}
