/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 
 *******************************************************************************/
package org.eclipse.dltk.core.search.index;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;

import org.eclipse.dltk.compiler.CharOperation;
import org.eclipse.dltk.compiler.util.HashtableOfIntValues;
import org.eclipse.dltk.compiler.util.HashtableOfObject;
import org.eclipse.dltk.compiler.util.SimpleLookupTable;
import org.eclipse.dltk.compiler.util.SimpleSet;
import org.eclipse.dltk.core.search.SearchPattern;
import org.eclipse.dltk.internal.core.util.Messages;
import org.eclipse.dltk.internal.core.util.SimpleWordSet;
import org.eclipse.dltk.internal.core.util.Util;

public class DiskIndex {

	String fileName;

	private int headerInfoOffset;

	private int numberOfChunks;

	private int sizeOfLastChunk;

	private int[] chunkOffsets;

	private int documentReferenceSize; // 1, 2 or more bytes... depends on # of
	// document names

	private int startOfCategoryTables;

	private HashtableOfIntValues categoryOffsets;

	private int cacheUserCount;

	private String[][] cachedChunks; // decompressed chunks of document names

	private HashtableOfObject categoryTables; // category name ->
	// HashtableOfObject(words ->
	// int[] of document #'s) or
	// offset if not read yet

	private char[] cachedCategoryName;

	public static final String SIGNATURE = "DLTK INDEX VERSION 1.009"; //$NON-NLS-1$

	public final static boolean DEBUG = false;

	private static final int RE_INDEXED = -1;

	private static final int DELETED = -2;

	private static final int CHUNK_SIZE = 100;

	static class IntList {

		int size;

		int[] elements;

		IntList(int[] elements) {
			this.elements = elements;
			this.size = elements.length;
		}

		void add(int newElement) {
			if (this.size == this.elements.length) {
				int newSize = this.size * 3;
				if (newSize < 7)
					newSize = 7;
				System.arraycopy(this.elements, 0,
						this.elements = new int[newSize], 0, this.size);
			}
			this.elements[this.size++] = newElement;
		}

		int[] asArray() {
			int[] result = new int[this.size];
			System.arraycopy(this.elements, 0, result, 0, this.size);
			return result;
		}
	}

	DiskIndex(String fileName) {
		this.fileName = fileName;

		// clear cached items
		this.headerInfoOffset = -1;
		this.numberOfChunks = -1;
		this.sizeOfLastChunk = -1;
		this.chunkOffsets = null;
		this.documentReferenceSize = -1;
		this.cacheUserCount = -1;
		this.cachedChunks = null;
		this.categoryTables = null;
		this.cachedCategoryName = null;
		this.categoryOffsets = null;
	}

	SimpleSet addDocumentNames(String substring, MemoryIndex memoryIndex)
			throws IOException {
		// must skip over documents which have been added/changed/deleted in the
		// memory index
		String[] docNames = readAllDocumentNames();
		SimpleSet results = new SimpleSet(docNames.length);
		if (substring == null) {
			if (memoryIndex == null) {
				for (int i = 0, l = docNames.length; i < l; i++)
					results.add(docNames[i]);
			} else {
				SimpleLookupTable docsToRefs = memoryIndex.docsToReferences;
				for (int i = 0, l = docNames.length; i < l; i++) {
					String docName = docNames[i];
					if (!docsToRefs.containsKey(docName))
						results.add(docName);
				}
			}
		} else {
			if (memoryIndex == null) {
				for (int i = 0, l = docNames.length; i < l; i++)
					if (docNames[i].startsWith(substring, 0))
						results.add(docNames[i]);
			} else {
				SimpleLookupTable docsToRefs = memoryIndex.docsToReferences;
				for (int i = 0, l = docNames.length; i < l; i++) {
					String docName = docNames[i];
					if (docName.startsWith(substring, 0)
							&& !docsToRefs.containsKey(docName))
						results.add(docName);
				}
			}
		}
		return results;
	}

	private HashtableOfObject addQueryResult(HashtableOfObject results,
			char[] word, HashtableOfObject wordsToDocNumbers,
			MemoryIndex memoryIndex) throws IOException {
		// must skip over documents which have been added/changed/deleted in the
		// memory index
		if (results == null)
			results = new HashtableOfObject(13);
		EntryResult result = (EntryResult) results.get(word);
		if (memoryIndex == null) {
			if (result == null)
				results.put(word, new EntryResult(word, wordsToDocNumbers));
			else
				result.addDocumentTable(wordsToDocNumbers);
		} else {
			SimpleLookupTable docsToRefs = memoryIndex.docsToReferences;
			if (result == null)
				result = new EntryResult(word, null);
			int[] docNumbers = readDocumentNumbers(wordsToDocNumbers.get(word));
			for (int i = 0, l = docNumbers.length; i < l; i++) {
				String docName = readDocumentName(docNumbers[i]);
				if (!docsToRefs.containsKey(docName))
					result.addDocumentName(docName);
			}
			if (!result.isEmpty())
				results.put(word, result);
		}
		return results;
	}

	HashtableOfObject addQueryResults(char[][] categories, char[] key,
			int matchRule, MemoryIndex memoryIndex) throws IOException {
		// assumes sender has called startQuery() & will call stopQuery() when
		// finished
		if (this.categoryOffsets == null)
			return null; // file is empty

		HashtableOfObject results = null; // initialized if needed
		if (key == null) {
			for (int i = 0, l = categories.length; i < l; i++) {
				HashtableOfObject wordsToDocNumbers = readCategoryTable(
						categories[i], true); // cache if key is null since
				// its a definite match
				if (wordsToDocNumbers != null) {
					char[][] words = wordsToDocNumbers.keyTable;
					if (results == null)
						results = new HashtableOfObject(
								wordsToDocNumbers.elementSize);
					for (int j = 0, m = words.length; j < m; j++)
						if (words[j] != null)
							results = addQueryResult(results, words[j],
									wordsToDocNumbers, memoryIndex);
				}
			}
			if (results != null && this.cachedChunks == null)
				cacheDocumentNames();
		} else {
			switch (matchRule) {
			case SearchPattern.R_EXACT_MATCH | SearchPattern.R_CASE_SENSITIVE:
				for (int i = 0, l = categories.length; i < l; i++) {
					HashtableOfObject wordsToDocNumbers = readCategoryTable(
							categories[i], false);
					if (wordsToDocNumbers != null
							&& wordsToDocNumbers.containsKey(key))
						results = addQueryResult(results, key,
								wordsToDocNumbers, memoryIndex);
				}
				break;
			case SearchPattern.R_PREFIX_MATCH | SearchPattern.R_CASE_SENSITIVE:
				for (int i = 0, l = categories.length; i < l; i++) {
					HashtableOfObject wordsToDocNumbers = readCategoryTable(
							categories[i], false);
					if (wordsToDocNumbers != null) {
						char[][] words = wordsToDocNumbers.keyTable;
						for (int j = 0, m = words.length; j < m; j++) {
							char[] word = words[j];
							if (word != null && key[0] == word[0]
									&& CharOperation.prefixEquals(key, word))
								results = addQueryResult(results, word,
										wordsToDocNumbers, memoryIndex);
						}
					}
				}
				break;
			default:
				for (int i = 0, l = categories.length; i < l; i++) {
					HashtableOfObject wordsToDocNumbers = readCategoryTable(
							categories[i], false);
					if (wordsToDocNumbers != null) {
						char[][] words = wordsToDocNumbers.keyTable;
						for (int j = 0, m = words.length; j < m; j++) {
							char[] word = words[j];
							if (word != null
									&& Index.isMatch(key, word, matchRule))
								results = addQueryResult(results, word,
										wordsToDocNumbers, memoryIndex);
						}
					}
				}
			}
		}

		if (results == null)
			return null;
		return results;
	}

	private void cacheDocumentNames() throws IOException {
		// will need all document names so get them now
		this.cachedChunks = new String[this.numberOfChunks][];
		DataInputStream stream = new DataInputStream(new BufferedInputStream(
				new FileInputStream(getIndexFile()),
				this.numberOfChunks > 5 ? 4096 : 2048));
		try {
			stream.skip(this.chunkOffsets[0]);
			for (int i = 0; i < this.numberOfChunks; i++) {
				int size = i == this.numberOfChunks - 1 ? this.sizeOfLastChunk
						: CHUNK_SIZE;
				readChunk(this.cachedChunks[i] = new String[size], stream, 0,
						size);
			}
		} finally {
			stream.close();
		}
	}

	private String[] computeDocumentNames(String[] onDiskNames,
			int[] positions, SimpleLookupTable indexedDocuments,
			MemoryIndex memoryIndex) {
		int onDiskLength = onDiskNames.length;
		Object[] docNames = memoryIndex.docsToReferences.keyTable;
		Object[] referenceTables = memoryIndex.docsToReferences.valueTable;
		if (onDiskLength == 0) {
			// disk index was empty, so add every indexed document
			for (int i = 0, l = referenceTables.length; i < l; i++)
				if (referenceTables[i] != null)
					indexedDocuments.put(docNames[i], null); // remember each
			// new document

			String[] newDocNames = new String[indexedDocuments.elementSize];
			int count = 0;
			Object[] added = indexedDocuments.keyTable;
			for (int i = 0, l = added.length; i < l; i++)
				if (added[i] != null)
					newDocNames[count++] = (String) added[i];
			Util.sort(newDocNames);
			for (int i = 0, l = newDocNames.length; i < l; i++)
				indexedDocuments.put(newDocNames[i], new Integer(i));
			return newDocNames;
		}

		// initialize positions as if each document will remain in the same
		// position
		for (int i = 0; i < onDiskLength; i++)
			positions[i] = i;

		// find out if the memory index has any new or deleted documents, if not
		// then the names & positions are the same
		int numDeletedDocNames = 0;
		int numReindexedDocNames = 0;
		nextPath: for (int i = 0, l = docNames.length; i < l; i++) {
			String docName = (String) docNames[i];
			if (docName != null) {
				for (int j = 0; j < onDiskLength; j++) {
					if (docName.equals(onDiskNames[j])) {
						if (referenceTables[i] == null) {
							positions[j] = DELETED;
							numDeletedDocNames++;
						} else {
							positions[j] = RE_INDEXED;
							numReindexedDocNames++;
						}
						continue nextPath;
					}
				}
				if (referenceTables[i] != null)
					indexedDocuments.put(docName, null); // remember each new
				// document, skip
				// deleted documents
				// which were never
				// saved
			}
		}

		String[] newDocNames = onDiskNames;
		if (numDeletedDocNames > 0 || indexedDocuments.elementSize > 0) {
			// some new documents have been added or some old ones deleted
			newDocNames = new String[onDiskLength
					+ indexedDocuments.elementSize - numDeletedDocNames];
			int count = 0;
			for (int i = 0; i < onDiskLength; i++)
				if (positions[i] >= RE_INDEXED)
					newDocNames[count++] = onDiskNames[i]; // keep each
			// unchanged
			// document
			Object[] added = indexedDocuments.keyTable;
			for (int i = 0, l = added.length; i < l; i++)
				if (added[i] != null)
					newDocNames[count++] = (String) added[i]; // add each new
			// document
			Util.sort(newDocNames);
			for (int i = 0, l = newDocNames.length; i < l; i++)
				if (indexedDocuments.containsKey(newDocNames[i]))
					indexedDocuments.put(newDocNames[i], new Integer(i)); // remember
			// the
			// position
			// for
			// each
			// new
			// document
		}

		// need to be able to look up an old position (ref# from a ref[]) and
		// map it to its new position
		// if its old position == DELETED then its forgotton
		// if its old position == ReINDEXED then its also forgotten but its new
		// position is needed to map references
		int count = -1;
		for (int i = 0; i < onDiskLength;) {
			switch (positions[i]) {
			case DELETED:
				i++; // skip over deleted... references are forgotten
				break;
			case RE_INDEXED:
				String newName = newDocNames[++count];
				if (newName.equals(onDiskNames[i])) {
					indexedDocuments.put(newName, new Integer(count)); // the
					// reindexed
					// docName
					// that
					// was
					// at
					// position
					// i is
					// now
					// at
					// position
					// count
					i++;
				}
				break;
			default:
				if (newDocNames[++count].equals(onDiskNames[i]))
					positions[i++] = count; // the unchanged docName that was at
				// position i is now at position
				// count
			}
		}
		return newDocNames;
	}

	private void copyQueryResults(HashtableOfObject categoryToWords,
			int newPosition) {
		char[][] categoryNames = categoryToWords.keyTable;
		Object[] wordSets = categoryToWords.valueTable;
		for (int i = 0, l = categoryNames.length; i < l; i++) {
			char[] categoryName = categoryNames[i];
			if (categoryName != null) {
				SimpleWordSet wordSet = (SimpleWordSet) wordSets[i];
				HashtableOfObject wordsToDocs = (HashtableOfObject) this.categoryTables
						.get(categoryName);
				if (wordsToDocs == null)
					this.categoryTables.put(categoryName,
							wordsToDocs = new HashtableOfObject(
									wordSet.elementSize));

				char[][] words = wordSet.words;
				for (int j = 0, m = words.length; j < m; j++) {
					char[] word = words[j];
					if (word != null) {
						Object o = wordsToDocs.get(word);
						if (o == null) {
							wordsToDocs.put(word, new int[] { newPosition });
						} else if (o instanceof IntList) {
							((IntList) o).add(newPosition);
						} else {
							IntList list = new IntList((int[]) o);
							list.add(newPosition);
							wordsToDocs.put(word, list);
						}
					}
				}
			}
		}
	}

	File getIndexFile() {
		if (this.fileName == null)
			return null;

		return new File(this.fileName);
	}

	void initialize(boolean reuseExistingFile) throws IOException {
		File indexFile = getIndexFile();
		if (indexFile.exists()) {
			if (reuseExistingFile) {
				RandomAccessFile file = new RandomAccessFile(this.fileName, "r"); //$NON-NLS-1$
				try {
					String signature = file.readUTF();
					if (!signature.equals(SIGNATURE))
						throw new IOException(Messages.exception_wrongFormat);

					this.headerInfoOffset = file.readInt();
					if (this.headerInfoOffset > 0) // file is empty if its not
						// set
						readHeaderInfo(file);
				} finally {
					file.close();
				}
				return;
			}
			if (!indexFile.delete()) {
				if (DEBUG)
					System.out
							.println("initialize - Failed to delete index " + this.fileName); //$NON-NLS-1$
				throw new IOException("Failed to delete index " + this.fileName); //$NON-NLS-1$
			}
		}
		if (indexFile.createNewFile()) {
			RandomAccessFile file = new RandomAccessFile(this.fileName, "rw"); //$NON-NLS-1$
			try {
				file.writeUTF(SIGNATURE);
				file.writeInt(-1); // file is empty
			} finally {
				file.close();
			}
		} else {
			if (DEBUG)
				System.out
						.println("initialize - Failed to create new index " + this.fileName); //$NON-NLS-1$
			throw new IOException("Failed to create new index " + this.fileName); //$NON-NLS-1$
		}
	}

	private void initializeFrom(DiskIndex diskIndex, File newIndexFile)
			throws IOException {
		if (newIndexFile.exists() && !newIndexFile.delete()) { // delete the
			// temporary
			// index file
			if (DEBUG)
				System.out
						.println("initializeFrom - Failed to delete temp index " + this.fileName); //$NON-NLS-1$
		} else if (!newIndexFile.createNewFile()) {
			if (DEBUG)
				System.out
						.println("initializeFrom - Failed to create temp index " + this.fileName); //$NON-NLS-1$
			throw new IOException(
					"Failed to create temp index " + this.fileName); //$NON-NLS-1$
		}

		int size = diskIndex.categoryOffsets == null ? 8
				: diskIndex.categoryOffsets.elementSize;
		this.categoryOffsets = new HashtableOfIntValues(size);
		this.categoryTables = new HashtableOfObject(size);
	}

	private void mergeCategories(DiskIndex onDisk, int[] positions,
			DataOutputStream stream) throws IOException {
		// at this point, this.categoryTables contains the names -> wordsToDocs
		// added in copyQueryResults()
		char[][] oldNames = onDisk.categoryOffsets.keyTable;
		for (int i = 0, l = oldNames.length; i < l; i++) {
			char[] oldName = oldNames[i];
			if (oldName != null && !this.categoryTables.containsKey(oldName))
				this.categoryTables.put(oldName, null);
		}

		char[][] categoryNames = this.categoryTables.keyTable;
		for (int i = 0, l = categoryNames.length; i < l; i++)
			if (categoryNames[i] != null)
				mergeCategory(categoryNames[i], onDisk, positions, stream);
		this.categoryTables = null;
	}

	private void mergeCategory(char[] categoryName, DiskIndex onDisk,
			int[] positions, DataOutputStream stream) throws IOException {
		HashtableOfObject wordsToDocs = (HashtableOfObject) this.categoryTables
				.get(categoryName);
		if (wordsToDocs == null)
			wordsToDocs = new HashtableOfObject(3);

		HashtableOfObject oldWordsToDocs = onDisk.readCategoryTable(
				categoryName, true);
		if (oldWordsToDocs != null) {
			char[][] oldWords = oldWordsToDocs.keyTable;
			Object[] oldArrayOffsets = oldWordsToDocs.valueTable;
			nextWord: for (int i = 0, l = oldWords.length; i < l; i++) {
				char[] oldWord = oldWords[i];
				if (oldWord != null) {
					int[] oldDocNumbers = (int[]) oldArrayOffsets[i];
					int length = oldDocNumbers.length;
					int[] mappedNumbers = new int[length];
					int count = 0;
					for (int j = 0; j < length; j++) {
						int pos = positions[oldDocNumbers[j]];
						if (pos > RE_INDEXED) // forget any reference to a
							// document which was deleted or
							// re_indexed
							mappedNumbers[count++] = pos;
					}
					if (count < length) {
						if (count == 0)
							continue nextWord; // skip words which no longer
						// have any references
						System.arraycopy(mappedNumbers, 0,
								mappedNumbers = new int[count], 0, count);
					}

					Object o = wordsToDocs.get(oldWord);
					if (o == null) {
						wordsToDocs.put(oldWord, mappedNumbers);
					} else {
						IntList list = null;
						if (o instanceof IntList) {
							list = (IntList) o;
						} else {
							list = new IntList((int[]) o);
							wordsToDocs.put(oldWord, list);
						}
						for (int j = 0; j < count; j++)
							list.add(mappedNumbers[j]);
					}
				}
			}
			onDisk.categoryTables.put(categoryName, null); // flush cached
			// table
		}
		writeCategoryTable(categoryName, wordsToDocs, stream);
	}

	DiskIndex mergeWith(MemoryIndex memoryIndex) throws IOException {
		// assume write lock is held
		// compute & write out new docNames
		String[] docNames = readAllDocumentNames();
		int previousLength = docNames.length;
		int[] positions = new int[previousLength]; // keeps track of the
		// position of each document
		// in the new sorted
		// docNames
		SimpleLookupTable indexedDocuments = new SimpleLookupTable(3); // for
		// each
		// new/changed
		// document
		// in
		// the
		// memoryIndex
		docNames = computeDocumentNames(docNames, positions, indexedDocuments,
				memoryIndex);
		if (docNames.length == 0) {
			if (previousLength == 0)
				return this; // nothing to do... memory index contained
			// deleted documents that had never been saved

			// index is now empty since all the saved documents were removed
			DiskIndex newDiskIndex = new DiskIndex(this.fileName);
			newDiskIndex.initialize(false);
			return newDiskIndex;
		}

		DiskIndex newDiskIndex = new DiskIndex(this.fileName + ".tmp"); //$NON-NLS-1$
		File newIndexFile = newDiskIndex.getIndexFile();
		try {
			newDiskIndex.initializeFrom(this, newIndexFile);
			DataOutputStream stream = new DataOutputStream(
					new BufferedOutputStream(new FileOutputStream(newIndexFile,
							false), 2048));
			int offsetToHeader = -1;
			try {
				newDiskIndex.writeAllDocumentNames(docNames, stream);
				docNames = null; // free up the space

				// add each new/changed doc to empty category tables using its
				// new position #
				if (indexedDocuments.elementSize > 0) {
					Object[] names = indexedDocuments.keyTable;
					Object[] integerPositions = indexedDocuments.valueTable;
					for (int i = 0, l = names.length; i < l; i++)
						if (names[i] != null)
							newDiskIndex
									.copyQueryResults(
											(HashtableOfObject) memoryIndex.docsToReferences
													.get(names[i]),
											((Integer) integerPositions[i])
													.intValue());
				}
				indexedDocuments = null; // free up the space

				// merge each category table with the new ones & write them out
				if (previousLength == 0)
					newDiskIndex.writeCategories(stream);
				else
					newDiskIndex.mergeCategories(this, positions, stream);
				offsetToHeader = stream.size();
				newDiskIndex.writeHeaderInfo(stream);
				positions = null; // free up the space
			} finally {
				stream.close();
			}
			newDiskIndex.writeOffsetToHeader(offsetToHeader);

			// rename file by deleting previous index file & renaming temp one
			File old = getIndexFile();
			if (old.exists() && !old.delete()) {
				if (DEBUG)
					System.out
							.println("mergeWith - Failed to delete " + this.fileName); //$NON-NLS-1$
				throw new IOException(
						"Failed to delete index file " + this.fileName); //$NON-NLS-1$
			}
			if (!newIndexFile.renameTo(old)) {
				if (DEBUG)
					System.out
							.println("mergeWith - Failed to rename " + this.fileName); //$NON-NLS-1$
				throw new IOException(
						"Failed to rename index file " + this.fileName); //$NON-NLS-1$
			}
		} catch (IOException e) {
			if (newIndexFile.exists() && !newIndexFile.delete())
				if (DEBUG)
					System.out
							.println("mergeWith - Failed to delete temp index " + newDiskIndex.fileName); //$NON-NLS-1$
			throw e;
		}

		newDiskIndex.fileName = this.fileName;
		return newDiskIndex;
	}

	private synchronized String[] readAllDocumentNames() throws IOException {
		if (this.numberOfChunks <= 0)
			return new String[0];

		DataInputStream stream = new DataInputStream(new BufferedInputStream(
				new FileInputStream(getIndexFile()),
				this.numberOfChunks > 5 ? 4096 : 2048));
		try {
			stream.skip(this.chunkOffsets[0]);
			int lastIndex = this.numberOfChunks - 1;
			String[] docNames = new String[lastIndex * CHUNK_SIZE
					+ sizeOfLastChunk];
			for (int i = 0; i < this.numberOfChunks; i++)
				readChunk(docNames, stream, i * CHUNK_SIZE,
						i < lastIndex ? CHUNK_SIZE : sizeOfLastChunk);
			return docNames;
		} finally {
			stream.close();
		}
	}

	private synchronized HashtableOfObject readCategoryTable(
			char[] categoryName, boolean readDocNumbers) throws IOException {
		// result will be null if categoryName is unknown
		int offset = this.categoryOffsets.get(categoryName);
		if (offset == HashtableOfIntValues.NO_VALUE)
			return null;

		if (this.categoryTables == null) {
			this.categoryTables = new HashtableOfObject(3);
		} else {
			HashtableOfObject cachedTable = (HashtableOfObject) this.categoryTables
					.get(categoryName);
			if (cachedTable != null) {
				if (readDocNumbers) { // must cache remaining document number
					// arrays
					Object[] arrayOffsets = cachedTable.valueTable;
					for (int i = 0, l = arrayOffsets.length; i < l; i++)
						if (arrayOffsets[i] instanceof Integer)
							arrayOffsets[i] = readDocumentNumbers(arrayOffsets[i]);
				}
				return cachedTable;
			}
		}

		DataInputStream stream = new DataInputStream(new BufferedInputStream(
				new FileInputStream(getIndexFile()), 2048));
		HashtableOfObject categoryTable = null;
		char[][] matchingWords = null;
		int count = 0;
		int firstOffset = -1;
		try {
			stream.skip(offset);
			int size = stream.readInt();
			try {
				if (size < 0) { // DEBUG
					System.err
							.println("-------------------- DEBUG --------------------"); //$NON-NLS-1$
					System.err.println("file = " + getIndexFile()); //$NON-NLS-1$
					System.err.println("offset = " + offset); //$NON-NLS-1$
					System.err.println("size = " + size); //$NON-NLS-1$
					System.err
							.println("--------------------   END   --------------------"); //$NON-NLS-1$
				}
				categoryTable = new HashtableOfObject(size);
			} catch (OutOfMemoryError oom) {
				// DEBUG
				oom.printStackTrace();
				System.err
						.println("-------------------- DEBUG --------------------"); //$NON-NLS-1$
				System.err.println("file = " + getIndexFile()); //$NON-NLS-1$
				System.err.println("offset = " + offset); //$NON-NLS-1$
				System.err.println("size = " + size); //$NON-NLS-1$
				System.err
						.println("--------------------   END   --------------------"); //$NON-NLS-1$
				throw oom;
			}
			int largeArraySize = 256;
			for (int i = 0; i < size; i++) {
				char[] word = Util.readUTF(stream);
				int arrayOffset = stream.readInt();
				// if arrayOffset is:
				// <= 0 then the array size == 1 with the value -> -arrayOffset
				// > 1 & < 256 then the size of the array is > 1 & < 256, the
				// document array follows immediately
				// 256 if the array size >= 256 followed by another int which is
				// the offset to the array (written prior to the table)
				if (arrayOffset <= 0) {
					categoryTable.put(word, new int[] { -arrayOffset }); // store
					// 1
					// element
					// array
					// by
					// negating
					// documentNumber
				} else if (arrayOffset < largeArraySize) {
					categoryTable.put(word, readDocumentArray(stream,
							arrayOffset)); // read in-lined array providing
					// size
				} else {
					arrayOffset = stream.readInt(); // read actual offset
					if (readDocNumbers) {
						if (matchingWords == null)
							matchingWords = new char[size][];
						if (count == 0)
							firstOffset = arrayOffset;
						matchingWords[count++] = word;
					}
					categoryTable.put(word, new Integer(arrayOffset)); // offset
					// to
					// array
					// in
					// the
					// file
				}
			}
			this.categoryTables.put(categoryName, categoryTable);
			// cache the table as long as its not too big
			// in practise, some tables can be greater than 500K when the
			// contain more than 10K elements
			this.cachedCategoryName = categoryTable.elementSize < 10000 ? categoryName
					: null;
		} finally {
			stream.close();
		}

		if (matchingWords != null && count > 0) {
			stream = new DataInputStream(new BufferedInputStream(
					new FileInputStream(getIndexFile()), 2048));
			try {
				stream.skip(firstOffset);
				for (int i = 0; i < count; i++)
					// each array follows the previous one
					categoryTable.put(matchingWords[i], readDocumentArray(
							stream, stream.readInt()));
			} finally {
				stream.close();
			}
		}
		return categoryTable;
	}

	private void readChunk(String[] docNames, DataInputStream stream,
			int index, int size) throws IOException {
		String current = stream.readUTF();
		docNames[index++] = current;
		for (int i = 1; i < size; i++) {
			int start = stream.readUnsignedByte(); // number of identical
			// characters at the
			// beginning
			int end = stream.readUnsignedByte(); // number of identical
			// characters at the end
			String next = stream.readUTF();
			if (start > 0) {
				if (end > 0) {
					int length = current.length();
					next = current.substring(0, start) + next
							+ current.substring(length - end, length);
				} else {
					next = current.substring(0, start) + next;
				}
			} else if (end > 0) {
				int length = current.length();
				next = next + current.substring(length - end, length);
			}
			docNames[index++] = next;
			current = next;
		}
	}

	private int[] readDocumentArray(DataInputStream stream, int arraySize)
			throws IOException {
		int[] result = new int[arraySize];
		switch (this.documentReferenceSize) {
		case 1:
			for (int i = 0; i < arraySize; i++)
				result[i] = stream.readUnsignedByte();
			break;
		case 2:
			for (int i = 0; i < arraySize; i++)
				result[i] = stream.readUnsignedShort();
			break;
		default:
			for (int i = 0; i < arraySize; i++)
				result[i] = stream.readInt();
			break;
		}
		return result;
	}

	synchronized String readDocumentName(int docNumber) throws IOException {
		if (this.cachedChunks == null)
			this.cachedChunks = new String[this.numberOfChunks][];

		int chunkNumber = docNumber / CHUNK_SIZE;
		String[] chunk = this.cachedChunks[chunkNumber];
		if (chunk == null) {
			boolean isLastChunk = chunkNumber == this.numberOfChunks - 1;
			int start = this.chunkOffsets[chunkNumber];
			int numberOfBytes = (isLastChunk ? this.startOfCategoryTables
					: this.chunkOffsets[chunkNumber + 1])
					- start;
			if (numberOfBytes < 0)
				throw new IllegalArgumentException();
			byte[] bytes = new byte[numberOfBytes];
			FileInputStream file = new FileInputStream(getIndexFile());
			try {
				file.skip(start);
				if (file.read(bytes, 0, numberOfBytes) != numberOfBytes)
					throw new IOException();
			} finally {
				file.close();
			}
			DataInputStream stream = new DataInputStream(
					new ByteArrayInputStream(bytes));
			int numberOfNames = isLastChunk ? this.sizeOfLastChunk : CHUNK_SIZE;
			chunk = this.cachedChunks[chunkNumber] = new String[numberOfNames];
			readChunk(chunk, stream, 0, numberOfNames);
		}
		return chunk[docNumber - (chunkNumber * CHUNK_SIZE)];
	}

	synchronized int[] readDocumentNumbers(Object arrayOffset)
			throws IOException {
		// arrayOffset is either a cached array of docNumbers or an Integer
		// offset in the file
		if (arrayOffset instanceof int[])
			return (int[]) arrayOffset;

		DataInputStream stream = new DataInputStream(new BufferedInputStream(
				new FileInputStream(getIndexFile()), 2048));
		try {
			stream.skip(((Integer) arrayOffset).intValue());
			return readDocumentArray(stream, stream.readInt());
		} finally {
			stream.close();
		}
	}

	private void readHeaderInfo(RandomAccessFile file) throws IOException {
		file.seek(this.headerInfoOffset);

		// must be same order as writeHeaderInfo()
		this.numberOfChunks = file.readInt();
		this.sizeOfLastChunk = file.readUnsignedByte();
		this.documentReferenceSize = file.readUnsignedByte();

		this.chunkOffsets = new int[this.numberOfChunks];
		for (int i = 0; i < this.numberOfChunks; i++)
			this.chunkOffsets[i] = file.readInt();

		this.startOfCategoryTables = file.readInt();

		int size = file.readInt();
		this.categoryOffsets = new HashtableOfIntValues(size);
		for (int i = 0; i < size; i++)
			this.categoryOffsets.put(Util.readUTF(file), file.readInt()); // cache
		// offset
		// to
		// category
		// table
		this.categoryTables = new HashtableOfObject(3);
	}

	synchronized void startQuery() {
		this.cacheUserCount++;
	}

	synchronized void stopQuery() {
		if (--this.cacheUserCount < 0) {
			// clear cached items
			this.cacheUserCount = -1;
			this.cachedChunks = null;
			if (this.categoryTables != null) {
				if (this.cachedCategoryName == null) {
					this.categoryTables = null;
				} else if (this.categoryTables.elementSize > 1) {
					HashtableOfObject newTables = new HashtableOfObject(3);
					newTables.put(this.cachedCategoryName, this.categoryTables
							.get(this.cachedCategoryName));
					this.categoryTables = newTables;
				}
			}
		}
	}

	private void writeAllDocumentNames(String[] sortedDocNames,
			DataOutputStream stream) throws IOException {
		if (sortedDocNames.length == 0)
			throw new IllegalArgumentException();

		// assume the file was just created by initializeFrom()
		// in order, write: SIGNATURE & headerInfoOffset place holder, then each
		// compressed chunk of document names
		stream.writeUTF(SIGNATURE);
		this.headerInfoOffset = stream.size();
		stream.writeInt(-1); // will overwrite with correct value later

		int size = sortedDocNames.length;
		this.numberOfChunks = (size / CHUNK_SIZE) + 1;
		this.sizeOfLastChunk = size % CHUNK_SIZE;
		if (this.sizeOfLastChunk == 0) {
			this.numberOfChunks--;
			this.sizeOfLastChunk = CHUNK_SIZE;
		}
		this.documentReferenceSize = size <= 0x7F ? 1
				: (size <= 0x7FFF ? 2 : 4); // number of bytes used to encode a
		// reference

		this.chunkOffsets = new int[this.numberOfChunks];
		int lastIndex = this.numberOfChunks - 1;
		for (int i = 0; i < this.numberOfChunks; i++) {
			this.chunkOffsets[i] = stream.size();

			int chunkSize = i == lastIndex ? this.sizeOfLastChunk : CHUNK_SIZE;
			int chunkIndex = i * CHUNK_SIZE;
			String current = sortedDocNames[chunkIndex];
			stream.writeUTF(current);
			for (int j = 1; j < chunkSize; j++) {
				String next = sortedDocNames[chunkIndex + j];
				int len1 = current.length();
				int len2 = next.length();
				int max = len1 < len2 ? len1 : len2;
				int start = 0; // number of identical characters at the
				// beginning (also the index of first character
				// that is different)
				while (current.charAt(start) == next.charAt(start)) {
					start++;
					if (max == start)
						break; // current is 'abba', next is 'abbab'
				}
				if (start > 255)
					start = 255;

				int end = 0; // number of identical characters at the end
				while (current.charAt(--len1) == next.charAt(--len2)) {
					end++;
					if (len2 == start)
						break; // current is 'abbba', next is 'abba'
					if (len1 == 0)
						break; // current is 'xabc', next is 'xyabc'
				}
				if (end > 255)
					end = 255;
				stream.writeByte(start);
				stream.writeByte(end);

				int last = next.length() - end;
				stream
						.writeUTF(start < last ? next.substring(start, last)
								: ""); //$NON-NLS-1$
				current = next;
			}
		}
		this.startOfCategoryTables = stream.size() + 1;
	}

	private void writeCategories(DataOutputStream stream) throws IOException {
		char[][] categoryNames = this.categoryTables.keyTable;
		Object[] tables = this.categoryTables.valueTable;
		for (int i = 0, l = categoryNames.length; i < l; i++)
			if (categoryNames[i] != null)
				writeCategoryTable(categoryNames[i],
						(HashtableOfObject) tables[i], stream);
		this.categoryTables = null;
	}

	private void writeCategoryTable(char[] categoryName,
			HashtableOfObject wordsToDocs, DataOutputStream stream)
			throws IOException {
		// the format of a category table is as follows:
		// any document number arrays with >= 256 elements are written before
		// the table (the offset to each array is remembered)
		// then the number of word->int[] pairs in the table is written
		// for each word -> int[] pair, the word is written followed by:
		// an int <= 0 if the array size == 1
		// an int > 1 & < 256 for the size of the array if its > 1 & < 256, the
		// document array follows immediately
		// 256 if the array size >= 256 followed by another int which is the
		// offset to the array (written prior to the table)

		int largeArraySize = 256;
		Object[] values = wordsToDocs.valueTable;
		for (int i = 0, l = values.length; i < l; i++) {
			Object o = values[i];
			if (o != null) {
				if (o instanceof IntList)
					o = values[i] = ((IntList) values[i]).asArray();
				int[] documentNumbers = (int[]) o;
				if (documentNumbers.length >= largeArraySize) {
					values[i] = new Integer(stream.size());
					writeDocumentNumbers(documentNumbers, stream);
				}
			}
		}

		this.categoryOffsets.put(categoryName, stream.size()); // remember the
		// offset to the
		// start of the
		// table
		this.categoryTables.put(categoryName, null); // flush cached table
		stream.writeInt(wordsToDocs.elementSize);
		char[][] words = wordsToDocs.keyTable;
		for (int i = 0, l = words.length; i < l; i++) {
			Object o = values[i];
			if (o != null) {
				Util.writeUTF(stream, words[i]);
				if (o instanceof int[]) {
					int[] documentNumbers = (int[]) o;
					if (documentNumbers.length == 1)
						stream.writeInt(-documentNumbers[0]); // store an
					// array of 1
					// element by
					// negating the
					// documentNumber
					// (can be zero)
					else
						writeDocumentNumbers(documentNumbers, stream);
				} else {
					stream.writeInt(largeArraySize); // mark to identify that
					// an offset follows
					stream.writeInt(((Integer) o).intValue()); // offset in the
					// file of the
					// array of
					// document
					// numbers
				}
			}
		}
	}

	private void writeDocumentNumbers(int[] documentNumbers,
			DataOutputStream stream) throws IOException {
		// must store length as a positive int to detect in-lined array of 1
		// element
		int length = documentNumbers.length;
		stream.writeInt(length);
		Util.sort(documentNumbers);
		switch (this.documentReferenceSize) {
		case 1:
			for (int i = 0; i < length; i++)
				stream.writeByte(documentNumbers[i]);
			break;
		case 2:
			for (int i = 0; i < length; i++)
				stream.writeShort(documentNumbers[i]);
			break;
		default:
			for (int i = 0; i < length; i++)
				stream.writeInt(documentNumbers[i]);
			break;
		}
	}

	private void writeHeaderInfo(DataOutputStream stream) throws IOException {
		stream.writeInt(this.numberOfChunks);
		stream.writeByte(this.sizeOfLastChunk);
		stream.writeByte(this.documentReferenceSize);

		// apend the file with chunk offsets
		for (int i = 0; i < this.numberOfChunks; i++)
			stream.writeInt(this.chunkOffsets[i]);

		stream.writeInt(this.startOfCategoryTables);

		// append the file with the category offsets... # of name -> offset
		// pairs, followed by each name & an offset to its word->doc# table
		stream.writeInt(this.categoryOffsets.elementSize);
		char[][] categoryNames = this.categoryOffsets.keyTable;
		int[] offsets = this.categoryOffsets.valueTable;
		for (int i = 0, l = categoryNames.length; i < l; i++) {
			if (categoryNames[i] != null) {
				Util.writeUTF(stream, categoryNames[i]);
				stream.writeInt(offsets[i]);
			}
		}
	}

	private void writeOffsetToHeader(int offsetToHeader) throws IOException {
		if (offsetToHeader > 0) {
			RandomAccessFile file = new RandomAccessFile(this.fileName, "rw"); //$NON-NLS-1$
			try {
				file.seek(this.headerInfoOffset); // offset to position in
				// header
				file.writeInt(offsetToHeader);
				this.headerInfoOffset = offsetToHeader; // update to reflect the
				// correct offset
			} finally {
				file.close();
			}
		}
	}
}
