package votorola.g.util; // Copyright 2001-2003, 2006, Michael Allan.  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Votorola Software"), to deal in the Votorola Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicence, and/or sell copies of the Votorola Software, and to permit persons to whom the Votorola Software is furnished to do so, subject to the following conditions: The preceding copyright notice and this permission notice shall be included in all copies or substantial portions of the Votorola Software. THE VOTOROLA SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE VOTOROLA SOFTWARE OR THE USE OR OTHER DEALINGS IN THE VOTOROLA SOFTWARE.

import votorola.g.lang.*;


/** Index offsetter for a sequence of fixed size.  It implements a logical index
  * whose start (logical zero) may be offset from actual zero, and whose increments
  * will wrap around the end of sequence.
  */
public @ThreadRestricted("touch") final class IndexOffsetter implements java.io.Serializable
{

    private static final long serialVersionUID = 0L;



    /** Constructs an IndexOffsetter.
      *
      *     @param s size per {@linkplain #size() size}()
      */
    public IndexOffsetter( int s ) { size = s; }



   // ------------------------------------------------------------------------------------


    /** Returns the actual index of a given logical index.
      *
      *     @param logicalIndex logical index in sequence (positive or negative)
      *     @return actual index, wrapped as necessary around the end of the sequence
      *
      *     @throws ArrayIndexOutOfBoundsException if |logicalIndex| >= size()
      */
    public int actualIndex( int logicalIndex )
    {
        if( Math.abs(logicalIndex) >= size ) throw new ArrayIndexOutOfBoundsException( logicalIndex );

        int actualIndex = actualIndexOfLogicalZero + logicalIndex;
        if( actualIndex >= size ) actualIndex -= size;
        else if( actualIndex < 0 ) actualIndex += size;
        return actualIndex;
    }



    /** Sets the actual index of logical index zero.  When this is zero (the default),
      * the logical index is identical to the actual index.
      *
      *     @throws ArrayIndexOutOfBoundsException if actualIndex &lt; 0
      *       or actualIndex &gt;= size()
      */
    public @ThreadRestricted void setActualIndexOfLogicalZero( int actualIndex )
    {
        if( actualIndex < 0 || actualIndex >= size ) throw new ArrayIndexOutOfBoundsException( actualIndex );

        actualIndexOfLogicalZero = actualIndex;
    }


        private int actualIndexOfLogicalZero = 0; // by default



    /** Returns the size of the sequence.
      */
    public int size() { return size; }


        private final int size;



}