/*

 * Copyright 1999-2003 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

/*

 *

 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved

 * (C) Copyright IBM Corp. 1996 - 2002 - All Rights Reserved

 *

 * The original version of this source code and documentation

 * is copyrighted and owned by Taligent, Inc., a wholly-owned

 * subsidiary of IBM. These materials are provided under terms

 * of a License Agreement between Taligent and Sun. This technology

 * is protected by multiple US and International patents.

 *

 * This notice and attribution to Taligent may not be removed.

 * Taligent is a registered trademark of Taligent, Inc.

 */

package java.text;

import java.util.Vector;

import java.util.Stack;

import java.util.Hashtable;

import java.text.CharacterIterator;

import java.io.InputStream;

import java.io.IOException;

/**

 * A subclass of RuleBasedBreakIterator that adds the ability to use a dictionary

 * to further subdivide ranges of text beyond what is possible using just the

 * state-table-based algorithm.  This is necessary, for example, to handle

 * word and line breaking in Thai, which doesn't use spaces between words.  The

 * state-table-based algorithm used by RuleBasedBreakIterator is used to divide

 * up text as far as possible, and then contiguous ranges of letters are

 * repeatedly compared against a list of known words (i.e., the dictionary)

 * to divide them up into words.

 *

 * DictionaryBasedBreakIterator uses the same rule language as RuleBasedBreakIterator,

 * but adds one more special substitution name: <dictionary>.  This substitution

 * name is used to identify characters in words in the dictionary.  The idea is that

 * if the iterator passes over a chunk of text that includes two or more characters

 * in a row that are included in <dictionary>, it goes back through that range and

 * derives additional break positions (if possible) using the dictionary.

 *

 * DictionaryBasedBreakIterator is also constructed with the filename of a dictionary

 * file.  It follows a prescribed search path to locate the dictionary (right now,

 * it looks for it in /com/ibm/text/resources in each directory in the classpath,

 * and won't find it in JAR files, but this location is likely to change).  The

 * dictionary file is in a serialized binary format.  We have a very primitive (and

 * slow) BuildDictionaryFile utility for creating dictionary files, but aren't

 * currently making it public.  Contact us for help.

 */

class DictionaryBasedBreakIterator extends RuleBasedBreakIterator {

    /**

     * a list of known words that is used to divide up contiguous ranges of letters,

     * stored in a compressed, indexed, format that offers fast access

     */

    private BreakDictionary dictionary;

    /**

     * a list of flags indicating which character categories are contained in

     * the dictionary file (this is used to determine which ranges of characters

     * to apply the dictionary to)

     */

    private boolean[] categoryFlags;

    /**

     * a temporary hiding place for the number of dictionary characters in the

     * last range passed over by next()

     */

    private int dictionaryCharCount;

    /**

     * when a range of characters is divided up using the dictionary, the break

     * positions that are discovered are stored here, preventing us from having

     * to use either the dictionary or the state table again until the iterator

     * leaves this range of text

     */

    private int[] cachedBreakPositions;

    /**

     * if cachedBreakPositions is not null, this indicates which item in the

     * cache the current iteration position refers to

     */

    private int positionInCache;

    /**

     * Constructs a DictionaryBasedBreakIterator.

     * @param description Same as the description parameter on RuleBasedBreakIterator,

     * except for the special meaning of "<dictionary>".  This parameter is just

     * passed through to RuleBasedBreakIterator's constructor.

     * @param dictionaryFilename The filename of the dictionary file to use

     */

    public DictionaryBasedBreakIterator(String dataFile, String dictionaryFile)

                                        throws IOException {

        super(dataFile);

        byte[] tmp = super.getAdditionalData();

        if (tmp != null) {

            prepareCategoryFlags(tmp);

            super.setAdditionalData(null);

        }

        dictionary = new BreakDictionary(dictionaryFile);

    }

    private void prepareCategoryFlags(byte[] data) {

        categoryFlags = new boolean[data.length];

        for (int i = 0; i < data.length; i++) {

            categoryFlags[i] = (data[i] == (byte)1) ? true : false;

        }

    }

    public void setText(CharacterIterator newText) {

        super.setText(newText);

        cachedBreakPositions = null;

        dictionaryCharCount = 0;

        positionInCache = 0;

    }

    /**

     * Sets the current iteration position to the beginning of the text.

     * (i.e., the CharacterIterator's starting offset).

     * @return The offset of the beginning of the text.

     */

    public int first() {

        cachedBreakPositions = null;

        dictionaryCharCount = 0;

        positionInCache = 0;

        return super.first();

    }

    /**

     * Sets the current iteration position to the end of the text.

     * (i.e., the CharacterIterator's ending offset).

     * @return The text's past-the-end offset.

     */

    public int last() {

        cachedBreakPositions = null;

        dictionaryCharCount = 0;

        positionInCache = 0;

        return super.last();

    }

    /**

     * Advances the iterator one step backwards.

     * @return The position of the last boundary position before the

     * current iteration position

     */

    public int previous() {

        CharacterIterator text = getText();

        // if we have cached break positions and we're still in the range

        // covered by them, just move one step backward in the cache

        if (cachedBreakPositions != null && positionInCache > 0) {

            --positionInCache;

            text.setIndex(cachedBreakPositions[positionInCache]);

            return cachedBreakPositions[positionInCache];

        }

        // otherwise, dump the cache and use the inherited previous() method to move

        // backward.  This may fill up the cache with new break positions, in which

        // case we have to mark our position in the cache

        else {

            cachedBreakPositions = null;

            int result = super.previous();

            if (cachedBreakPositions != null) {

                positionInCache = cachedBreakPositions.length - 2;

            }

            return result;

        }

    }

    /**

     * Sets the current iteration position to the last boundary position

     * before the specified position.

     * @param offset The position to begin searching from

     * @return The position of the last boundary before "offset"

     */

    public int preceding(int offset) {

        CharacterIterator text = getText();

        checkOffset(offset, text);

        // if we have no cached break positions, or "offset" is outside the

        // range covered by the cache, we can just call the inherited routine

        // (which will eventually call other routines in this class that may

        // refresh the cache)

        if (cachedBreakPositions == null || offset <= cachedBreakPositions[0] ||

                offset > cachedBreakPositions[cachedBreakPositions.length - 1]) {

            cachedBreakPositions = null;

            return super.preceding(offset);

        }

        // on the other hand, if "offset" is within the range covered by the cache,

        // then all we have to do is search the cache for the last break position

        // before "offset"

        else {

            positionInCache = 0;

            while (positionInCache < cachedBreakPositions.length

                   && offset > cachedBreakPositions[positionInCache]) {

                ++positionInCache;

            }

            --positionInCache;

            text.setIndex(cachedBreakPositions[positionInCache]);

            return text.getIndex();

        }

    }

    /**

     * Sets the current iteration position to the first boundary position after

     * the specified position.

     * @param offset The position to begin searching forward from

     * @return The position of the first boundary after "offset"

     */

    public int following(int offset) {

        CharacterIterator text = getText();

        checkOffset(offset, text);

        // if we have no cached break positions, or if "offset" is outside the

        // range covered by the cache, then dump the cache and call our

        // inherited following() method.  This will call other methods in this

        // class that may refresh the cache.

        if (cachedBreakPositions == null || offset < cachedBreakPositions[0] ||

                offset >= cachedBreakPositions[cachedBreakPositions.length - 1]) {

            cachedBreakPositions = null;

            return super.following(offset);

        }

        // on the other hand, if "offset" is within the range covered by the

        // cache, then just search the cache for the first break position

        // after "offset"

        else {

            positionInCache = 0;

            while (positionInCache < cachedBreakPositions.length

                   && offset >= cachedBreakPositions[positionInCache]) {

                ++positionInCache;

            }

            text.setIndex(cachedBreakPositions[positionInCache]);

            return text.getIndex();

        }

    }

    /**

     * This is the implementation function for next().

     */

    protected int handleNext() {

        CharacterIterator text = getText();

        // if there are no cached break positions, or if we've just moved

        // off the end of the range covered by the cache, we have to dump

        // and possibly regenerate the cache

        if (cachedBreakPositions == null ||

            positionInCache == cachedBreakPositions.length - 1) {

            // start by using the inherited handleNext() to find a tentative return

            // value.   dictionaryCharCount tells us how many dictionary characters

            // we passed over on our way to the tentative return value

            int startPos = text.getIndex();

            dictionaryCharCount = 0;

            int result = super.handleNext();

            // if we passed over more than one dictionary character, then we use

            // divideUpDictionaryRange() to regenerate the cached break positions

            // for the new range

            if (dictionaryCharCount > 1 && result - startPos > 1) {

                divideUpDictionaryRange(startPos, result);

            }

            // otherwise, the value we got back from the inherited fuction

            // is our return value, and we can dump the cache

            else {

                cachedBreakPositions = null;

                return result;

            }

        }

        // if the cache of break positions has been regenerated (or existed all

        // along), then just advance to the next break position in the cache

        // and return it

        if (cachedBreakPositions != null) {

            ++positionInCache;

            text.setIndex(cachedBreakPositions[positionInCache]);

            return cachedBreakPositions[positionInCache];

        }

        return -9999;   // SHOULD NEVER GET HERE!

    }

    /**

     * Looks up a character category for a character.

     */

    protected int lookupCategory(int c) {

        // this override of lookupCategory() exists only to keep track of whether we've

        // passed over any dictionary characters.  It calls the inherited lookupCategory()

        // to do the real work, and then checks whether its return value is one of the

        // categories represented in the dictionary.  If it is, bump the dictionary-

        // character count.

        int result = super.lookupCategory(c);

        if (result != RuleBasedBreakIterator.IGNORE && categoryFlags[result]) {

            ++dictionaryCharCount;

        }

        return result;

    }

    /**

     * This is the function that actually implements the dictionary-based

     * algorithm.  Given the endpoints of a range of text, it uses the

     * dictionary to determine the positions of any boundaries in this

     * range.  It stores all the boundary positions it discovers in

     * cachedBreakPositions so that we only have to do this work once

     * for each time we enter the range.

     */

    private void divideUpDictionaryRange(int startPos, int endPos) {

        CharacterIterator text = getText();

        // the range we're dividing may begin or end with non-dictionary characters

        // (i.e., for line breaking, we may have leading or trailing punctuation

        // that needs to be kept with the word).  Seek from the beginning of the

        // range to the first dictionary character

        text.setIndex(startPos);

        int c = getCurrent();

        int category = lookupCategory(c);

        while (category == IGNORE || !categoryFlags[category]) {

            c = getNext();

            category = lookupCategory(c);

        }

        // initialize.  We maintain two stacks: currentBreakPositions contains

        // the list of break positions that will be returned if we successfully

        // finish traversing the whole range now.  possibleBreakPositions lists

        // all other possible word ends we've passed along the way.  (Whenever

        // we reach an error [a sequence of characters that can't begin any word

        // in the dictionary], we back up, possibly delete some breaks from

        // currentBreakPositions, move a break from possibleBreakPositions

        // to currentBreakPositions, and start over from there.  This process

        // continues in this way until we either successfully make it all the way

        // across the range, or exhaust all of our combinations of break

        // positions.)

        Stack currentBreakPositions = new Stack();

        Stack possibleBreakPositions = new Stack();

        Vector wrongBreakPositions = new Vector();

        // the dictionary is implemented as a trie, which is treated as a state

        // machine.  -1 represents the end of a legal word.  Every word in the

        // dictionary is represented by a path from the root node to -1.  A path

        // that ends in state 0 is an illegal combination of characters.

        int state = 0;

        // these two variables are used for error handling.  We keep track of the

        // farthest we've gotten through the range being divided, and the combination

        // of breaks that got us that far.  If we use up all possible break

        // combinations, the text contains an error or a word that's not in the

        // dictionary.  In this case, we "bless" the break positions that got us the

        // farthest as real break positions, and then start over from scratch with

        // the character where the error occurred.

        int farthestEndPoint = text.getIndex();

        Stack bestBreakPositions = null;

        // initialize (we always exit the loop with a break statement)

        c = getCurrent();

        while (true) {

            // if we can transition to state "-1" from our current state, we're

            // on the last character of a legal word.  Push that position onto

            // the possible-break-positions stack

            if (dictionary.getNextState(state, 0) == -1) {

                possibleBreakPositions.push(new Integer(text.getIndex()));

            }

            // look up the new state to transition to in the dictionary

            state = dictionary.getNextStateFromCharacter(state, c);

            // if the character we're sitting on causes us to transition to

            // the "end of word" state, then it was a non-dictionary character

            // and we've successfully traversed the whole range.  Drop out

            // of the loop.

            if (state == -1) {

                currentBreakPositions.push(new Integer(text.getIndex()));

                break;

            }

            // if the character we're sitting on causes us to transition to

            // the error state, or if we've gone off the end of the range

            // without transitioning to the "end of word" state, we've hit

            // an error...

            else if (state == 0 || text.getIndex() >= endPos) {

                // if this is the farthest we've gotten, take note of it in

                // case there's an error in the text

                if (text.getIndex() > farthestEndPoint) {

                    farthestEndPoint = text.getIndex();

                    bestBreakPositions = (Stack)(currentBreakPositions.clone());

                }

                // wrongBreakPositions is a list of all break positions

                // we've tried starting that didn't allow us to traverse

                // all the way through the text.  Every time we pop a

                //break position off of currentBreakPositions, we put it

                // into wrongBreakPositions to avoid trying it again later.

                // If we make it to this spot, we're either going to back

                // up to a break in possibleBreakPositions and try starting

                // over from there, or we've exhausted all possible break

                // positions and are going to do the fallback procedure.

                // This loop prevents us from messing with anything in

                // possibleBreakPositions that didn't work as a starting

                // point the last time we tried it (this is to prevent a bunch of

                // repetitive checks from slowing down some extreme cases)

                Integer newStartingSpot = null;

                while (!possibleBreakPositions.isEmpty() && wrongBreakPositions.contains(

                            possibleBreakPositions.peek())) {

                    possibleBreakPositions.pop();

                }

                // if we've used up all possible break-position combinations, there's

                // an error or an unknown word in the text.  In this case, we start

                // over, treating the farthest character we've reached as the beginning

                // of the range, and "blessing" the break positions that got us that

                // far as real break positions

                if (possibleBreakPositions.isEmpty()) {

                    if (bestBreakPositions != null) {

                        currentBreakPositions = bestBreakPositions;

                        if (farthestEndPoint < endPos) {

                            text.setIndex(farthestEndPoint + 1);

                        }

                        else {

                            break;

                        }

                    }

                    else {

                        if ((currentBreakPositions.size() == 0 ||

                             ((Integer)(currentBreakPositions.peek())).intValue() != text.getIndex())

                            && text.getIndex() != startPos) {

                            currentBreakPositions.push(new Integer(text.getIndex()));

                        }

                        getNext();

                        currentBreakPositions.push(new Integer(text.getIndex()));

                    }

                }

                // if we still have more break positions we can try, then promote the

                // last break in possibleBreakPositions into currentBreakPositions,

                // and get rid of all entries in currentBreakPositions that come after

                // it.  Then back up to that position and start over from there (i.e.,

                // treat that position as the beginning of a new word)

                else {

                    Integer temp = (Integer)possibleBreakPositions.pop();

                    Object temp2 = null;

                    while (!currentBreakPositions.isEmpty() && temp.intValue() <

                           ((Integer)currentBreakPositions.peek()).intValue()) {

                        temp2 = currentBreakPositions.pop();

                        wrongBreakPositions.addElement(temp2);

                    }

                    currentBreakPositions.push(temp);

                    text.setIndex(((Integer)currentBreakPositions.peek()).intValue());

                }

                // re-sync "c" for the next go-round, and drop out of the loop if

                // we've made it off the end of the range

                c = getCurrent();

                if (text.getIndex() >= endPos) {

                    break;

                }

            }

            // if we didn't hit any exceptional conditions on this last iteration,

            // just advance to the next character and loop

            else {

                c = getNext();

            }

        }

        // dump the last break position in the list, and replace it with the actual

        // end of the range (which may be the same character, or may be further on

        // because the range actually ended with non-dictionary characters we want to

        // keep with the word)

        if (!currentBreakPositions.isEmpty()) {

            currentBreakPositions.pop();

        }

        currentBreakPositions.push(new Integer(endPos));

        // create a regular array to hold the break positions and copy

        // the break positions from the stack to the array (in addition,

        // our starting position goes into this array as a break position).

        // This array becomes the cache of break positions used by next()

        // and previous(), so this is where we actually refresh the cache.

        cachedBreakPositions = new int[currentBreakPositions.size() + 1];

        cachedBreakPositions[0] = startPos;

        for (int i = 0; i < currentBreakPositions.size(); i++) {

            cachedBreakPositions[i + 1] = ((Integer)currentBreakPositions.elementAt(i)).intValue();

        }

        positionInCache = 0;

    }

}