/*
    *  Copyright 2001-2009 Stephen Colebourne
    *
    *  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.joda.time.field;
  
  import java.io.Serializable;
  import java.util.HashMap;
  
  import org.joda.time.DurationField;
  import org.joda.time.DurationFieldType;
  
  /**
   * A placeholder implementation to use when a duration field is not supported.
   * <p>
   * UnsupportedDurationField is thread-safe and immutable.
   *
   * @author Brian S O'Neill
   * @since 1.0
   */
  public final class UnsupportedDurationField extends DurationField implements Serializable {
  
      /** Serialization lock. */
      private static final long serialVersionUID = -6390301302770925357L;
  
      /** The cache of unsupported duration field instances */
      private static HashMap<DurationFieldType, UnsupportedDurationField> cCache;
  
      /**
       * Gets an instance of UnsupportedDurationField for a specific named field.
       * The returned instance is cached.
       * 
       * @param type  the type to obtain
       * @return the instance
       */
      public static synchronized UnsupportedDurationField getInstance(DurationFieldType type) {
          UnsupportedDurationField field;
          if (cCache == null) {
              cCache = new HashMap<DurationFieldType, UnsupportedDurationField>(7);
              field = null;
          } else {
              field = cCache.get(type);
          }
          if (field == null) {
              field = new UnsupportedDurationField(type);
              cCache.put(type, field);
          }
          return field;
      }
  
      /** The name of the field */
      private final DurationFieldType iType;
  
      /**
       * Constructor.
       * 
       * @param type  the type to use
       */
      private UnsupportedDurationField(DurationFieldType type) {
          iType = type;
      }
  
      //-----------------------------------------------------------------------
      // Design note: Simple Accessors return a suitable value, but methods
      // intended to perform calculations throw an UnsupportedOperationException.
  
      public final DurationFieldType getType() {
          return iType;
      }
  
      public String getName() {
          return iType.getName();
      }
  
      /**
       * This field is not supported.
       *
       * @return false always
       */
      public boolean isSupported() {
          return false;
      }
  
      /**
       * This field is precise.
       * 
       * @return true always
       */
     public boolean isPrecise() {
         return true;
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public int getValue(long duration) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getValueAsLong(long duration) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public int getValue(long duration, long instant) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getValueAsLong(long duration, long instant) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getMillis(int value) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getMillis(long value) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getMillis(int value, long instant) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getMillis(long value, long instant) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long add(long instant, int value) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long add(long instant, long value) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public int getDifference(long minuendInstant, long subtrahendInstant) {
         throw unsupported();
     }
 
     /**
      * Always throws UnsupportedOperationException
      *
      * @throws UnsupportedOperationException
      */
     public long getDifferenceAsLong(long minuendInstant, long subtrahendInstant) {
         throw unsupported();
     }
 
     /**
      * Always returns zero.
      *
      * @return zero always
      */
     public long getUnitMillis() {
         return 0;
     }
 
     /**
      * Always returns zero, indicating that sort order is not relevent.
      *
      * @return zero always
      */
     public int compareTo(DurationField durationField) {
         return 0;
     }
 
     //------------------------------------------------------------------------
     /**
      * Compares this duration field to another.
      * 
      * @param obj  the object to compare to
      * @return true if equal
      */
     public boolean equals(Object obj) {
         if (this == obj) {
             return true;
         } else if (obj instanceof UnsupportedDurationField) {
             UnsupportedDurationField other = (UnsupportedDurationField) obj;
             if (other.getName() == null) {
                 return (getName() == null);
             }
             return (other.getName().equals(getName()));
         }
         return false;
     }
 
     /**
      * Gets a suitable hashcode.
      * 
      * @return the hashcode
      */
     public int hashCode() {
         return getName().hashCode();
     }
 
     /**
      * Get a suitable debug string.
      * 
      * @return debug string
      */
     public String toString() {
         return "UnsupportedDurationField[" + getName() + ']';
     }
 
     /**
      * Ensure proper singleton serialization
      */
     private Object readResolve() {
         return getInstance(iType);
     }
 
     private UnsupportedOperationException unsupported() {
         return new UnsupportedOperationException(iType + " field is unsupported");
     }
 
 }