Operator.java

/*
 * Copyright (C) 2009 eXo Platform SAS.
 * 
 * This is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 * 
 * This software is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this software; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA, or see the FSF
 * site: http://www.fsf.org.
 */
package org.xcmis.search.model.constraint;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Comparison operator.
 */
public enum Operator {
      EQUAL_TO("="),
      GREATER_THAN(">"),
      GREATER_THAN_OR_EQUAL_TO(">="),
      LESS_THAN("<"),
      LESS_THAN_OR_EQUAL_TO("<="),
      LIKE("LIKE"),
      NOT_EQUAL_TO("!=");

   private static final Map<String, Operator> OPERATORS_BY_SYMBOL;
   
   public static final Operator[] ALL =
      new Operator[]{
         EQUAL_TO,
         GREATER_THAN,
         GREATER_THAN_OR_EQUAL_TO,
         LESS_THAN,
         LESS_THAN_OR_EQUAL_TO,
         LIKE,
         NOT_EQUAL_TO};
   
   static
   {
      Map<String, Operator> opsBySymbol = new HashMap<String, Operator>();
      for (Operator operator : Operator.values())
      {
         opsBySymbol.put(operator.getSymbol().toUpperCase(), operator);
      }
      opsBySymbol.put("<>", NOT_EQUAL_TO);
      OPERATORS_BY_SYMBOL = Collections.unmodifiableMap(opsBySymbol);
   }

   private final String symbol;

   private Operator(String symbol)
   {
      this.symbol = symbol;
   }

   /**
    * Get the equivalent operator if the operands are to be reversed.
    * 
    * @return the reverse operator; never null
    */
   public Operator getReverse()
   {
      switch (this)
      {
         case GREATER_THAN :
            return LESS_THAN;
         case GREATER_THAN_OR_EQUAL_TO :
            return LESS_THAN_OR_EQUAL_TO;
         case LESS_THAN :
            return GREATER_THAN;
         case LESS_THAN_OR_EQUAL_TO :
            return GREATER_THAN_OR_EQUAL_TO;
         case EQUAL_TO :
         case LIKE :
         case NOT_EQUAL_TO :
         default :
            return this;
      }
   }

   /**
    * Get the symbol for this operator.
    * 
    * @return the symbolic representation; never null
    */
   public String getSymbol()
   {
      return symbol;
   }

   /**
    * Determine whether this operator is one that is used to define a range of
    * values: {@link #LESS_THAN <}, {@link #GREATER_THAN >},
    * {@link #LESS_THAN_OR_EQUAL_TO <=}, or {@link #GREATER_THAN_OR_EQUAL_TO >=}
    * .
    * 
    * @return true if this operator is a range operator, or false otherwise
    */
   public boolean isRangeOperator()
   {
      switch (this)
      {
         case GREATER_THAN :
         case GREATER_THAN_OR_EQUAL_TO :
         case LESS_THAN :
         case LESS_THAN_OR_EQUAL_TO :
            return true;
         case EQUAL_TO :
         case LIKE :
         case NOT_EQUAL_TO :
         default :
            return false;
      }
   }

   /**
    * {@inheritDoc}
    * 
    * @see java.lang.Enum#toString()
    */
   @Override
   public String toString()
   {
      return symbol;
   }

   /**
    * Attempt to find the Operator given a symbol. The matching is done
    * independent of case.
    * 
    * @param symbol
    *           the symbol
    * @return the Operator having the supplied symbol, or null if there is no
    *         Operator with the supplied symbol
    */
   public static Operator forSymbol(String symbol)
   {
      return OPERATORS_BY_SYMBOL.get(symbol.toUpperCase());
   }
}