package gnu.crypto.util;  // -*- mode: java; c-basic-offset: 3 -*-

// ---------------------------------------------------------------------------
// $Id: Sequence.java,v 1.2 2005/10/06 04:24:19 rsdio Exp $
//
// Copyright (C) 2004 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// GNU Crypto 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
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; see the file COPYING.  If not, write to the
//
//    Free Software Foundation Inc.,
//    51 Franklin Street, Fifth Floor,
//    Boston, MA 02110-1301
//    USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give
// you permission to link this library with independent modules to
// produce an executable, regardless of the license terms of these
// independent modules, and to copy and distribute the resulting
// executable under terms of your choice, provided that you also meet,
// for each linked independent module, the terms and conditions of the
// license of that module.  An independent module is a module which is
// not derived from or based on this library.  If you modify this
// library, you may extend this exception to your version of the
// library, but you are not obligated to do so.  If you do not wish to
// do so, delete this exception statement from your version.
//
// ---------------------------------------------------------------------------

import java.util.AbstractList;
import java.util.LinkedList;

/**
 * A monotonic sequence of integers in the finite field 2<sup>32</sup>.
 */
public final class Sequence extends AbstractList {

   // Field.
   // ------------------------------------------------------------------------

   private final Integer[] sequence;

   // Constructor.
   // ------------------------------------------------------------------------

   /**
    * Create a sequence of integers from 0 to <i>end</i>, with an increment
    * of 1. If <i>end</i> is less than 0, then the sequence will wrap around
    * through all positive integers then negative integers until the end
    * value is reached. Naturally, this will result in an enormous object,
    * so don't do this.
    *
    * @param end The ending value.
    */
   public Sequence(int end) {
      this(0, end, 1);
   }

   /**
    * Create a sequence of integers from <i>start</i> to <i>end</i>, with an
    * increment of 1. If <i>end</i> is less than <i>start</i>, then the sequence
    * will wrap around until the end value is reached. Naturally, this will
    * result in an enormous object, so don't do this.
    *
    * @param start The starting value.
    * @param end The ending value.
    */
   public Sequence(int start, int end) {
      this(start, end, 1);
   }

   /**
    * Create a sequence of integers from <i>start</i> to <i>end</i>, with an
    * increment of <i>span</i>. If <i>end</i> is less than <i>start</i>, then
    * the sequence will wrap around until the end value is reached. Naturally,
    * this will result in an enormous object, so don't do this.
    *
    * <p><i>span</i> can be negative, resulting in a decresing sequence.
    *
    * <p>If <i>span</i> is 0, then the sequence will contain {<i>start</i>,
    * <i>end</i>} if <i>start</i> != <i>end</i>, or just the singleton
    * <i>start</i> if <i>start</i> == <i>end</i>.
    *
    * @param start The starting value.
    * @param end The ending value.
    * @param span The increment value.
    */
   public Sequence(int start, int end, int span) {
      if (span == 0) {
         if (start != end) {
            sequence = new Integer[] { new Integer(start), new Integer(end) };
         } else {
            sequence = new Integer[] { new Integer(start) };
         }
      } else {
         LinkedList l = new LinkedList();
         for (int i = start; i != end; i += span) {
            l.add(new Integer(i));
         }
         l.add(new Integer(end));
         sequence = (Integer[]) l.toArray(new Integer[l.size()]);
      }
   }

   // Instance methods.
   // ------------------------------------------------------------------------

   public Object get(int index) {
      if (index < 0 || index >= size()) {
         throw new IndexOutOfBoundsException("index="+index+", size="+size());
      }
      return sequence[index];
   }

   public int size() {
      return sequence.length;
   }

   public Object[] toArray() {
      return (Object[]) sequence.clone();
   }
}
