/*
 * Copyright (c) 2003, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.util.sort;

import java.util.Vector;

/**
 * Quicksort utility class. 
 */
public class QSort
{
  /**
   * Use static methods, please 
   */
  protected QSort() { 
  }

  /**
   * Sort a vector with objects compareble using a comparison function.
   *
   * @param a Vector to sort
   * @param cf comparison function
   */
  static public void sort(Vector a, CompareFunc cf) {
     sort(a, 0, a.size() - 1, cf);
  }
  
  /**
   * Sort an array with objects compareble using a comparison function.
   *
   * @param a Array to sort
   * @param cf comparison function
   */
  static public void sort(Object a[], CompareFunc cf) {
     sort(a, 0, a.length - 1, cf);
  }

   /** 
    * This is a generic version of C.A.R Hoare's Quick Sort 
    * algorithm.  This will handle arrays that are already
    * sorted, and arrays with duplicate keys.
    *
    * @param a       an array with items compareble using a sort function 
    * @param lo0     left boundary of array partition
    * @param hi0     right boundary of array partition
    * @param cf comparison function
    */
  static void sort(Object a[], int lo0, int hi0, CompareFunc cf)
  {
    int lo = lo0;
    int hi = hi0;
    Object mid;
    
    if ( hi0 > lo0) {
	
      /* Arbitrarily establishing partition element as the midpoint of
       * the array.
       */
      mid = a[ ( lo0 + hi0 ) / 2 ];
      
      // loop through the array until indices cross
      while( lo <= hi )	{
	/* find the first element that is greater than or equal to 
	 * the partition element starting from the left Index.
	 */
	while( ( lo < hi0 ) && ( cf.compare(a[lo], mid) < 0 )) {
	  ++lo;
	}
	
	/* find an element that is smaller than or equal to 
	 * the partition element starting from the right Index.
	 */
	while( ( hi > lo0 ) && ( cf.compare(a[hi], mid ) > 0 )) {
	  --hi;
	}
	
	// if the indexes have not crossed, swap
	if( lo <= hi ) {
	  swap(a, lo, hi);
	  ++lo;
	  --hi;
	}
      }
      
      /* If the right index has not reached the left side of array
       * must now sort the left partition.
       */
      if( lo0 < hi ) {
	sort( a, lo0, hi, cf );
      }

      /* If the left index has not reached the right side of array
       * must now sort the right partition.
       */
      if( lo < hi0 ) {
	sort( a, lo, hi0, cf );
      }
    }
  }

  /**
   * Vector implementation...exactly as array version above
   */
  static void sort(Vector a, int lo0, int hi0, CompareFunc cf) {
    int lo = lo0;
    int hi = hi0;
    Object mid;
    
    if ( hi0 > lo0) {
      
      mid = a.elementAt( ( lo0 + hi0 ) / 2 );
      
      while( lo <= hi ) {
	while( ( lo < hi0 ) && ( cf.compare(a.elementAt(lo), mid) < 0 )) {
	  ++lo;
	}
	
	while( ( hi > lo0 ) && ( cf.compare(a.elementAt(hi), mid ) > 0 )) {
	  --hi;
	}
	
	if( lo <= hi ) {
	  swap(a, lo, hi);
	  ++lo;
	  --hi;
	}
      }
      
      if( lo0 < hi ) {
	sort( a, lo0, hi, cf );
      }

      if( lo < hi0 ) {
	sort( a, lo, hi0, cf );
      }
    }
  }
  
  private static void swap(Object a[], int i, int j) {
    Object tmp  = a[i]; 
    a[i] = a[j];
    a[j] = tmp;
  }

  private static void swap(Vector a, int i, int j) {
    Object tmp  = a.elementAt(i); 
    a.setElementAt(a.elementAt(j), i);
    a.setElementAt(tmp,            j);
  }
}