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	/*
	* Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
	*/
	/*
	* 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;
	import java.util.ArrayList;
	import java.util.List;

	/** <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>
	*
	* @LastModified: Oct 2017
	*/
	public class DTMStringPool
	{
	List<String> m_intToString;
	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)
	{
	m_intToString = new ArrayList<>();
	m_hashChain= new IntVector(chainSize);
	removeAllElements();

	// -sb Add this to force empty strings to be index 0.
	stringToIndex("");
	}

	public DTMStringPool()
	{
	this(512);
	}

	public void removeAllElements()
	{
	m_intToString.clear();
	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.
	* @throws java.lang.IndexOutOfBoundsException
	* if index doesn't map to a string.
	* */
	public String indexToString(int i)
	throws java.lang.IndexOutOfBoundsException
	{
	if(i==NULL) return null;
	return m_intToString.get(i);
	}

	/** @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)
	{
	if(m_intToString.get(hashcandidate).equals(s))
	return hashcandidate;

	hashlast=hashcandidate;
	hashcandidate=m_hashChain.elementAt(hashcandidate);
	}

	// New value. Add to tables.
	int newIndex=m_intToString.size();
	m_intToString.add(s);

	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
	}
	}

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