/* Sequence.java -- a sequence of integers.
   Copyright (C) 2004, 2006, 2014, 2015 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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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.

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Foundation, Inc., 51 Franklin St, 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
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permission to link this library with independent modules to produce an
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package gnu.java.security.util;

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<Integer>
{
  private final Integer[] sequence;

  /**
   * 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[] { Integer.valueOf(start),
                                     Integer.valueOf(end) };
        else
          sequence = new Integer[] { Integer.valueOf(start) };
      }
    else
      {
        LinkedList<Integer> l = new LinkedList<Integer>();
        for (int i = start; i != end; i += span)
          l.add(Integer.valueOf(i));

        l.add(Integer.valueOf(end));
        sequence = l.toArray(new Integer[l.size()]);
      }
  }

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

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

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