/*

  * Copyright 2006-2011 The Kuali Foundation

  * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php

  *

  * 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.kuali.rice.core.api.util;

 import org.apache.commons.lang.ArrayUtils;

 import org.apache.commons.lang.builder.HashCodeBuilder;

 import java.lang.reflect.Field;

 import java.util.Calendar;

 /**

  * Class of static utility methods used to aid in the generation of hashcode values and equals comparisons of objects

  * for corner cases that EqualsBuilder and HashCodeBuilder of commons-lang cannot cover.

  */

 public final class EqualsAndHashCodeUtils {

     private EqualsAndHashCodeUtils(){

         throw new UnsupportedOperationException("do not call");

     }

     /**

      * This method provides an equals comparison of two objects by evaluating the results of compareTo across specified

      * internal fields of the class of the two objects being compared.

      * <p/>

      * This method should be used where evaluating equality on fields of two instances of type T using .equals() yields

      * false, but for the purposes of determining equality of the two instances of type T, should be true.  An example

      * is where a class has internal fields of type Calendar that need equality determined using only its time value

      * and not other internal fields of Calendar.

      *

      * @param o1         The first object used in an equality operation using compareTo

      * @param o2         The second object used in an equality operation using compareTo

      * @param fieldNames All field names within type T that should be determined equal or not using compareTo

      * @param <T>        Type of both o1 and o2 parameters.  Guarantees both o1 and o2 are the same reference type.

      * @return true if (o1.field.compareTo(o2.field) == 0) is true for all passed in fieldNames.  Otherwise false

      *         is returned.  False is also returned if any fields specified in fieldNames are not of type Comparable or if one

      *         (but not both) of the passed in objects are null references.

      */

     public static <T> boolean equalsUsingCompareToOnFields(T o1, T o2, String... fieldNames) {

         if (o1 == o2) {

             return true;

         }

         if (o1 == null || o2 == null) {

             return false;

         }

         boolean isEqual = true;

         Class<?> targetClass = o1.getClass();

         try {

             for (String fieldName : fieldNames) {

                 Field field = targetClass.getDeclaredField(fieldName);

                 field.setAccessible(true);

                 Class<?> fieldClass = field.getType();

                 if (ArrayUtils.contains(fieldClass.getInterfaces(), Comparable.class)) {

                     @SuppressWarnings("unchecked") Comparable<Object> c1 = (Comparable<Object>) field.get(o1);

                     @SuppressWarnings("unchecked") Comparable<Object> c2 = (Comparable<Object>) field.get(o2);

                     if (c1 == c2) {

                         continue;

                     }

                     if (c1 == null || c2 == null) {

                         isEqual = false;

                     } else {

                         isEqual = (c1.compareTo(c2) == 0);

                     }

                 } else {

                     isEqual = false;

                 }

                 if (!isEqual) {

                     break;

                 }

             }

             return isEqual;

         } catch (Exception e) {

             throw new RuntimeException(e);

         }

     }

     /**

      * Generates an int hashcode from all calendars passed in.  This is a convenience method for hashcode methods

      * to call if they have to generate hashcodes from fields of type Calendar when those Calendar fields

      * have equality evaluated using compareTo and not equals within the equals method of the container class.

      *

      * @param calendars

      * @return int hashcode value generated by using the long value returned from each Calendar.getTimeInMillis()

      */

     public static int hashCodeForCalendars(Calendar... calendars) {

         HashCodeBuilder hcb = new HashCodeBuilder();

         for (Calendar calendar : calendars) {

             if (calendar != null) {

                 hcb.append(calendar.getTimeInMillis());

             }

         }

         return hcb.toHashCode();

     }

 }