/*

 */

/*

 * Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.sun.org.apache.xml.internal.dtm.ref;

import com.sun.org.apache.xml.internal.utils.IntVector;

/** <p>DTMStringPool is an "interning" mechanism for strings. It will

 * create a stable 1:1 mapping between a set of string values and a set of

 * integer index values, so the integers can be used to reliably and

 * uniquely identify (and when necessary retrieve) the strings.</p>

 *

 * <p>Design Priorities:

 * <ul>

 * <li>String-to-index lookup speed is critical.</li>

 * <li>Index-to-String lookup speed is slightly less so.</li>

 * <li>Threadsafety is not guaranteed at this level.

 * Enforce that in the application if needed.</li>

 * <li>Storage efficiency is an issue but not a huge one.

 * It is expected that string pools won't exceed about 2000 entries.</li>

 * </ul>

 * </p>

 *

 * <p>Implementation detail: A standard Hashtable is relatively

 * inefficient when looking up primitive int values, especially when

 * we're already maintaining an int-to-string vector.  So I'm

 * maintaining a simple hash chain within this class.</p>

 *

 * <p>NOTE: There is nothing in the code that has a real dependency upon

 * String. It would work with any object type that implements reliable

 * .hashCode() and .equals() operations. The API enforces Strings because

 * it's safer that way, but this could trivially be turned into a general

 * ObjectPool if one was needed.</p>

 *

 * <p>Status: Passed basic test in main().</p>

 * */

public class DTMStringPool

{

  static final int HASHPRIME=101;

  int[] m_hashStart=new int[HASHPRIME];

  IntVector m_hashChain;

  public static final int NULL=-1;

  /**

   * Create a DTMStringPool using the given chain size

   *

   * @param chainSize The size of the hash chain vector

   */

  public DTMStringPool(int chainSize)

    {

      removeAllElements();

      // -sb Add this to force empty strings to be index 0.

      stringToIndex("");

    }

  public DTMStringPool()

    {

      this(512);

    }

  public void removeAllElements()

    {

      for(int i=0;i<HASHPRIME;++i)

        m_hashStart[i]=NULL;

      m_hashChain.removeAllElements();

    }

  /** @return string whose value is uniquely identified by this integer index.

   *  if index doesn't map to a string.

   * */

  public String indexToString(int i)

    {

      if(i==NULL) return null;

    }

  /** @return integer index uniquely identifying the value of this string. */

  public int stringToIndex(String s)

    {

      if(s==null) return NULL;

      int hashslot=s.hashCode()%HASHPRIME;

      if(hashslot<0) hashslot=-hashslot;

      // Is it one we already know?

      int hashlast=m_hashStart[hashslot];

      int hashcandidate=hashlast;

      while(hashcandidate!=NULL)

        {

            return hashcandidate;

          hashlast=hashcandidate;

          hashcandidate=m_hashChain.elementAt(hashcandidate);

        }

      // New value. Add to tables.

      int newIndex=m_intToString.size();

      m_hashChain.addElement(NULL);     // Initialize to no-following-same-hash

      if(hashlast==NULL)  // First for this hash

        m_hashStart[hashslot]=newIndex;

      else // Link from previous with same hash

        m_hashChain.setElementAt(newIndex,hashlast);

      return newIndex;

    }

  /** Command-line unit test driver. This test relies on the fact that

   * this version of the pool assigns indices consecutively, starting

   * from zero, as new unique strings are encountered.

   */

  public static void _main(String[] args)

  {

    String[] word={

      "Zero","One","Two","Three","Four","Five",

      "Six","Seven","Eight","Nine","Ten",

      "Eleven","Twelve","Thirteen","Fourteen","Fifteen",

      "Sixteen","Seventeen","Eighteen","Nineteen","Twenty",

      "Twenty-One","Twenty-Two","Twenty-Three","Twenty-Four",

      "Twenty-Five","Twenty-Six","Twenty-Seven","Twenty-Eight",

      "Twenty-Nine","Thirty","Thirty-One","Thirty-Two",

      "Thirty-Three","Thirty-Four","Thirty-Five","Thirty-Six",

      "Thirty-Seven","Thirty-Eight","Thirty-Nine"};

    DTMStringPool pool=new DTMStringPool();

    System.out.println("If no complaints are printed below, we passed initial test.");

    for(int pass=0;pass<=1;++pass)

      {

        int i;

        for(i=0;i<word.length;++i)

          {

            int j=pool.stringToIndex(word[i]);

            if(j!=i)

              System.out.println("\tMismatch populating pool: assigned "+

                                 j+" for create "+i);

          }

        for(i=0;i<word.length;++i)

          {

            int j=pool.stringToIndex(word[i]);

            if(j!=i)

              System.out.println("\tMismatch in stringToIndex: returned "+

                                 j+" for lookup "+i);

          }

        for(i=0;i<word.length;++i)

          {

            String w=pool.indexToString(i);

            if(!word[i].equals(w))

              System.out.println("\tMismatch in indexToString: returned"+

                                 w+" for lookup "+i);

          }

        pool.removeAllElements();

        System.out.println("\nPass "+pass+" complete\n");

      } // end pass loop

  }

}