/*
 * @(#)RuleBasedBreakIterator.java	1.13 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 * @(#)RuleBasedBreakIterator.java	1.3 99/04/07
 *
 * (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.util.Enumeration;
import java.text.CharacterIterator;
import java.text.StringCharacterIterator;
import sun.text.CompactByteArray;

/**
 * <p>A subclass of BreakIterator whose behavior is specified using a list of rules.</p>
 *
 * <p>There are two kinds of rules, which are separated by semicolons: <i>substitutions</i>
 * and <i>regular expressions.</i></p>
 *
 * <p>A substitution rule defines a name that can be used in place of an expression. It
 * consists of a name, which is a string of characters contained in angle brackets, an equals
 * sign, and an expression. (There can be no whitespace on either side of the equals sign.)
 * To keep its syntactic meaning intact, the expression must be enclosed in parentheses or
 * square brackets. A substitution is visible after its definition, and is filled in using
 * simple textual substitution. Substitution definitions can contain other substitutions, as
 * long as those substitutions have been defined first. Substitutions are generally used to
 * make the regular expressions (which can get quite complex) shorted and easier to read.
 * They typically define either character categories or commonly-used subexpressions.</p>
 *
 * <p>There is one special substitution.  If the description defines a substitution
 * called "<ignore>", the expression must be a [] expression, and the
 * expression defines a set of characters (the "<em>ignore characters</em>") that
 * will be transparent to the BreakIterator.  A sequence of characters will break the
 * same way it would if any ignore characters it contains are taken out.  Break
 * positions never occur befoer ignore characters.</p>
 *
 * <p>A regular expression uses a subset of the normal Unix regular-expression syntax, and
 * defines a sequence of characters to be kept together. With one significant exception, the
 * iterator uses a longest-possible-match algorithm when matching text to regular
 * expressions. The iterator also treats descriptions containing multiple regular expressions
 * as if they were ORed together (i.e., as if they were separated by |).</p>
 *
 * <p>The special characters recognized by the regular-expression parser are as follows:</p>
 *
 * <blockquote>
 *   <table border="1" width="100%">
 *     <tr>
 *       <td width="6%">*</td>
 *       <td width="94%">Specifies that the expression preceding the asterisk may occur any number
 *       of times (including not at all).</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">{}</td>
 *       <td width="94%">Encloses a sequence of characters that is optional.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">()</td>
 *       <td width="94%">Encloses a sequence of characters.  If followed by *, the sequence
 *       repeats.  Otherwise, the parentheses are just a grouping device and a way to delimit
 *       the ends of expressions containing |.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">|</td>
 *       <td width="94%">Separates two alternative sequences of characters.  Either one
 *       sequence or the other, but not both, matches this expression.  The | character can
 *       only occur inside ().</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">.</td>
 *       <td width="94%">Matches any character.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">*?</td>
 *       <td width="94%">Specifies a non-greedy asterisk.  *? works the same way as *, except
 *       when there is overlap between the last group of characters in the expression preceding the
 *       * and the first group of characters following the *.  When there is this kind of
 *       overlap, * will match the longest sequence of characters that match the expression before
 *       the *, and *? will match the shortest sequence of characters matching the expression
 *       before the *?.  For example, if you have "xxyxyyyxyxyxxyxyxyy" in the text,
 *       "x[xy]*x" will match through to the last x (i.e., "<strong>xxyxyyyxyxyxxyxyx</strong>yy",
 *       but "x[xy]*?x" will only match the first two xes ("<strong>xx</strong>yxyyyxyxyxxyxyxyy").</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">[]</td>
 *       <td width="94%">Specifies a group of alternative characters.  A [] expression will
 *       match any single character that is specified in the [] expression.  For more on the
 *       syntax of [] expressions, see below.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">/</td>
 *       <td width="94%">Specifies where the break position should go if text matches this
 *       expression.  (e.g., "[a-z]*/[:Zs:]*[1-0]" will match if the iterator sees a run
 *       of letters, followed by a run of whitespace, followed by a digit, but the break position
 *       will actually go before the whitespace).  Expressions that don't contain / put the
 *       break position at the end of the matching text.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">\</td>
 *       <td width="94%">Escape character.  The \ itself is ignored, but causes the next
 *       character to be treated as literal character.  This has no effect for many
 *       characters, but for the characters listed above, this deprives them of their special
 *       meaning.  (There are no special escape sequences for Unicode characters, or tabs and
 *       newlines; these are all handled by a higher-level protocol.  In a Java string,
 *       "\n" will be converted to a literal newline character by the time the
 *       regular-expression parser sees it.  Of course, this means that \ sequences that are
 *       visible to the regexp parser must be written as \\ when inside a Java string.)  All
 *       characters in the ASCII range except for letters, digits, and control characters are
 *       reserved characters to the parser and must be preceded by \ even if they currently don't
 *       mean anything.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">!</td>
 *       <td width="94%">If ! appears at the beginning of a regular expression, it tells the regexp
 *       parser that this expression specifies the backwards-iteration behavior of the iterator,
 *       and not its normal iteration behavior.  This is generally only used in situations
 *       where the automatically-generated backwards-iteration brhavior doesn't produce
 *       satisfactory results and must be supplemented with extra client-specified rules.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%"><em>(all others)</em></td>
 *       <td width="94%">All other characters are treated as literal characters, which must match
 *       the corresponding character(s) in the text exactly.</td>
 *     </tr>
 *   </table>
 * </blockquote>
 *
 * <p>Within a [] expression, a number of other special characters can be used to specify
 * groups of characters:</p>
 *
 * <blockquote>
 *   <table border="1" width="100%">
 *     <tr>
 *       <td width="6%">-</td>
 *       <td width="94%">Specifies a range of matching characters.  For example
 *       "[a-p]" matches all lowercase Latin letters from a to p (inclusive).  The -
 *       sign specifies ranges of continuous Unicode numeric values, not ranges of characters in a
 *       language's alphabetical order: "[a-z]" doesn't include capital letters, nor does
 *       it include accented letters such as a-umlaut.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">::</td>
 *       <td width="94%">A pair of colons containing a one- or two-letter code matches all
 *       characters in the corresponding Unicode category.  The two-letter codes are the same
 *       as the two-letter codes in the Unicode database (for example, "[:Sc::Sm:]"
 *       matches all currency symbols and all math symbols).  Specifying a one-letter code is
 *       the same as specifying all two-letter codes that begin with that letter (for example,
 *       "[:L:]" matches all letters, and is equivalent to
 *       "[:Lu::Ll::Lo::Lm::Lt:]").  Anything other than a valid two-letter Unicode
 *       category code or a single letter that begins a Unicode category code is illegal within
 *       colons.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">[]</td>
 *       <td width="94%">[] expressions can nest.  This has no effect, except when used in
 *       conjunction with the ^ token.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%">^</td>
 *       <td width="94%">Excludes the character (or the characters in the [] expression) following
 *       it from the group of characters.  For example, "[a-z^p]" matches all Latin
 *       lowercase letters except p.  "[:L:^[\u4e00-\u9fff]]" matches all letters
 *       except the Han ideographs.</td>
 *     </tr>
 *     <tr>
 *       <td width="6%"><em>(all others)</em></td>
 *       <td width="94%">All other characters are treated as literal characters.  (For
 *       example, "[aeiou]" specifies just the letters a, e, i, o, and u.)</td>
 *     </tr>
 *   </table>
 * </blockquote>
 *
 * <p>For a more complete explanation, see <a
 * href="http://www.ibm.com/java/education/boundaries/boundaries.html">http://www.ibm.com/java/education/boundaries/boundaries.html</a>.
 *   For examples, see the resource data (which is annotated).</p>
 *
 * @author Richard Gillam
 * @version $RCSFile$ $Revision: 1.1 $ $Date: 1998/11/05 19:32:04 $
 */
class RuleBasedBreakIterator extends BreakIterator {

    /**
     * A token used as a character-category value to identify ignore characters
     */
    protected static final byte IGNORE = -1;

    /**
     * The state number of the starting state
     */
    private static final short START_STATE = 1;

    /**
     * The state-transition value indicating "stop"
     */
    private static final short STOP_STATE = 0;

    /**
     * The textual description this iterator was created from
     */
    private String description;

    /**
     * A table that indexes from character values to character category numbers
     */
    private CompactByteArray charCategoryTable = null;

    /**
     * The table of state transitions used for forward iteration
     */
    private short[] stateTable = null;

    /**
     * The table of state transitions used to sync up the iterator with the
     * text in backwards and random-access iteration
     */
    private short[] backwardsStateTable = null;

    /**
     * A list of flags indicating which states in the state table are accepting
     * ("end") states
     */
    private boolean[] endStates = null;

    /**
     * A list of flags indicating which states in the state table are
     * lookahead states (states which turn lookahead on and off)
     */
    private boolean[] lookaheadStates = null;

    /**
     * The number of character categories (and, thus, the number of columns in
     * the state tables)
     */
    private int numCategories;

    /**
     * The character iterator through which this BreakIterator accesses the text
     */
    private CharacterIterator text = null;

    //=======================================================================
    // constructors
    //=======================================================================

    /**
     * Constructs a RuleBasedBreakIterator according to the description
     * provided.  If the description is malformed, throws an
     * IllegalArgumentException.  Normally, instead of constructing a
     * RuleBasedBreakIterator directory, you'll use the factory methods
     * on BreakIterator to create one indirectly from a description
     * in the framework's resource files.  You'd use this when you want
     * special behavior not provided by the built-in iterators.
     */
    public RuleBasedBreakIterator(String description) {
        this.description = description;

        // the actual work is done by the Builder class
        Builder builder = makeBuilder();
        builder.buildBreakIterator();
    }

    /**
     * Creates a Builder.
     */
    protected Builder makeBuilder() {
        return new Builder();
    }

    //=======================================================================
    // boilerplate
    //=======================================================================
    /**
     * Clones this iterator.
     * @return A newly-constructed RuleBasedBreakIterator with the same
     * behavior as this one.
     */
    public Object clone()
    {
        RuleBasedBreakIterator result = (RuleBasedBreakIterator) super.clone();
        if (text != null) {
            result.text = (CharacterIterator) text.clone();
        }
        return result;
    }

    /**
     * Returns true if both BreakIterators are of the same class, have the same
     * rules, and iterate over the same text.
     */
    public boolean equals(Object that) {
        try {
            RuleBasedBreakIterator other = (RuleBasedBreakIterator) that;
            if (!description.equals(other.description)) {
                return false;
            }
            if (text == null) {
                return other.text == null;
            }
            else {
                return text.equals(other.text);
            }
        }
        catch(ClassCastException e) {
            return false;
        }
    }

    /**
     * Returns the description used to create this iterator
     */
    public String toString() {
        return description;
    }

    /**
     * Compute a hashcode for this BreakIterator
     * @return A hash code
     */
    public int hashCode()
    {
        return description.hashCode();
    }

    //=======================================================================
    // BreakIterator overrides
    //=======================================================================

    /**
     * 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() {
        CharacterIterator t = getText();

        t.first();
        return t.getIndex();
    }

    /**
     * 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() {
        CharacterIterator t = getText();

        // I'm not sure why, but t.last() returns the offset of the last character,
        // rather than the past-the-end offset
        t.setIndex(t.getEndIndex());
        return t.getIndex();
    }

    /**
     * Advances the iterator either forward or backward the specified number of steps.
     * Negative values move backward, and positive values move forward.  This is
     * equivalent to repeatedly calling next() or previous().
     * @param n The number of steps to move.  The sign indicates the direction
     * (negative is backwards, and positive is forwards).
     * @return The character offset of the boundary position n boundaries away from
     * the current one.
     */
    public int next(int n) {
        int result = current();
        while (n > 0) {
            result = handleNext();
            --n;
        }
        while (n < 0) {
            result = previous();
            ++n;
        }
        return result;
    }

    /**
     * Advances the iterator to the next boundary position.
     * @return The position of the first boundary after this one.
     */
    public int next() {
        return handleNext();
    }

    /**
     * Advances the iterator backwards, to the last boundary preceding this one.
     * @return The position of the last boundary position preceding this one.
     */
    public int previous() {
        // if we're already sitting at the beginning of the text, return DONE
        CharacterIterator text = getText();
        if (current() == text.getBeginIndex()) {
            return BreakIterator.DONE;
        }

        // set things up.  handlePrevious() will back us up to some valid
        // break position before the current position (we back our internal
        // iterator up one step to prevent handlePrevious() from returning
        // the current position), but not necessarily the last one before
        // where we started
        int start = current();
        text.previous();
        int lastResult = handlePrevious();
        int result = lastResult;

        // iterate forward from the known break position until we pass our
        // starting point.  The last break position before the starting
        // point is our return value
        while (result != BreakIterator.DONE && result < start) {
            lastResult = result;
            result = handleNext();
        }

        // set the current iteration position to be the last break position
        // before where we started, and then return that value
        text.setIndex(lastResult);
        return lastResult;
    }

    /**
     * Throw IllegalArgumentException unless begin <= offset < end.
     */
    protected static final void checkOffset(int offset, CharacterIterator text) {
        if (offset < text.getBeginIndex() || offset >= text.getEndIndex()) {
            throw new IllegalArgumentException("offset out of bounds");
        }
    }

    /**
     * Sets the iterator to refer to the first boundary position following
     * the specified position.
     * @offset The position from which to begin searching for a break position.
     * @return The position of the first break after the current position.
     */
    public int following(int offset) {

        CharacterIterator text = getText();
        checkOffset(offset, text);

        // Set our internal iteration position (temporarily)
        // to the position passed in.  If this is the _beginning_ position,
        // then we can just use next() to get our return value
        text.setIndex(offset);
        if (offset == text.getBeginIndex()) {
            return handleNext();
        }

        // otherwise, we have to sync up first.  Use handlePrevious() to back
        // us up to a known break position before the specified position (if
        // we can determine that the specified position is a break position,
        // we don't back up at all).  This may or may not be the last break
        // position at or before our starting position.  Advance forward
        // from here until we've passed the starting position.  The position
        // we stop on will be the first break position after the specified one.
        int result = handlePrevious();
        while (result != BreakIterator.DONE && result <= offset) {
            result = handleNext();
        }
        return result;
    }

    /**
     * Sets the iterator to refer to the last boundary position before the
     * specified position.
     * @offset The position to begin searching for a break from.
     * @return The position of the last boundary before the starting position.
     */
    public int preceding(int offset) {
        // if we start by updating the current iteration position to the
        // position specified by the caller, we can just use previous()
        // to carry out this operation
        CharacterIterator text = getText();
        checkOffset(offset, text);
        text.setIndex(offset);
        return previous();
    }

    /**
     * Returns true if the specfied position is a boundary position.  As a side
     * effect, leaves the iterator pointing to the first boundary position at
     * or after "offset".
     * @param offset the offset to check.
     * @return True if "offset" is a boundary position.
     */
    public boolean isBoundary(int offset) {
        CharacterIterator text = getText();
        checkOffset(offset, text);
        if (offset == text.getBeginIndex()) {
            return true;
        }

        // to check whether this is a boundary, we can use following() on the
        // position before the specified one and return true if the position we
        // get back is the one the user specified
        else {
            return following(offset - 1) == offset;
        }
    }

    /**
     * Returns the current iteration position.
     * @return The current iteration position.
     */
    public int current() {
        return getText().getIndex();
    }

    /**
     * Return a CharacterIterator over the text being analyzed.  This version
     * of this method returns the actual CharacterIterator we're using internally.
     * Changing the state of this iterator can have undefined consequences.  If
     * you need to change it, clone it first.
     * @return An iterator over the text being analyzed.
     */
    public CharacterIterator getText() {
        // The iterator is initialized pointing to no text at all, so if this
        // function is called while we're in that state, we have to fudge an
        // an iterator to return.
        if (text == null) {
            text = new StringCharacterIterator("");
        }
        return text;
    }

    /**
     * Set the iterator to analyze a new piece of text.  This function resets
     * the current iteration position to the beginning of the text.
     * @param newText An iterator over the text to analyze.
     */
    public void setText(CharacterIterator newText) {
        // Test iterator to see if we need to wrap it in a SafeCharIterator.
        // The correct behavior for CharacterIterators is to allow the
        // position to be set to the endpoint of the iterator.  Many
        // CharacterIterators do not uphold this, so this is a workaround
        // to permit them to use this class.
        int end = newText.getEndIndex();
        boolean goodIterator;
        try {
            newText.setIndex(end);  // some buggy iterators throw an exception here
            goodIterator = newText.getIndex() == end;
        }
        catch(IllegalArgumentException e) {
            goodIterator = false;
        }

        if (goodIterator) {
            text = newText;
        }
        else {
            text = new SafeCharIterator(newText);
        }
        text.first();
    }


    //=======================================================================
    // implementation
    //=======================================================================

    /**
     * This method is the actual implementation of the next() method.  All iteration
     * vectors through here.  This method initializes the state machine to state 1
     * and advances through the text character by character until we reach the end
     * of the text or the state machine transitions to state 0.  We update our return
     * value every time the state machine passes through a possible end state.
     */
    protected int handleNext() {
        // if we're already at the end of the text, return DONE.
        CharacterIterator text = getText();
        if (text.getIndex() == text.getEndIndex()) {
            return BreakIterator.DONE;
        }

        // no matter what, we always advance at least one character forward
        int result = text.getIndex() + 1;
        int lookaheadResult = 0;

        // begin in state 1
        int state = START_STATE;
        int category;
        char c = text.current();

        // loop until we reach the end of the text or transition to state 0
        while (c != CharacterIterator.DONE && state != STOP_STATE) {

            // look up the current character's character category (which tells us
            // which column in the state table to look at)
            category = lookupCategory(c);

            // if the character isn't an ignore character, look up a state
            // transition in the state table
            if (category != IGNORE) {
                state = lookupState(state, category);
            }

            // if the state we've just transitioned to is a lookahead state,
            // (but not also an end state), save its position.  If it's
            // both a lookahead state and an end state, update the break position
            // to the last saved lookup-state position
            if (lookaheadStates[state]) {
                if (endStates[state]) {
                    result = lookaheadResult;
                }
                else {
                    lookaheadResult = text.getIndex() + 1;
                }
            }

            // otherwise, if the state we've just transitioned to is an accepting
            // state, update the break position to be the current iteration position
            else {
                if (endStates[state]) {
                    result = text.getIndex() + 1;
                }
            }

            c = text.next();
        }

        // if we've run off the end of the text, and the very last character took us into
        // a lookahead state, advance the break position to the lookahead position
        // (the theory here is that if there are no characters at all after the lookahead
        // position, that always matches the lookahead criteria)
        if (c == CharacterIterator.DONE && lookaheadResult == text.getEndIndex()) {
            result = lookaheadResult;
        }

        text.setIndex(result);
        return result;
    }

    /**
     * This method backs the iterator back up to a "safe position" in the text.
     * This is a position that we know, without any context, must be a break position.
     * The various calling methods then iterate forward from this safe position to
     * the appropriate position to return.  (For more information, see the description
     * of buildBackwardsStateTable() in RuleBasedBreakIterator.Builder.)
     */
    protected int handlePrevious() {
        CharacterIterator text = getText();
        int state = START_STATE;
        int category = 0;
        int lastCategory = 0;
        char c = text.current();

        // loop until we reach the beginning of the text or transition to state 0
        while (c != CharacterIterator.DONE && state != STOP_STATE) {

            // save the last character's category and look up the current
            // character's category
            lastCategory = category;
            category = lookupCategory(c);

            // if the current character isn't an ignore character, look up a
            // state transition in the backwards state table
            if (category != IGNORE) {
                state = lookupBackwardState(state, category);
            }

            // then advance one character backwards
            c = text.previous();
        }

        // if we didn't march off the beginning of the text, we're either one or two
        // positions away from the real break position.  (One because of the call to
        // previous() at the end of the loop above, and another because the character
        // that takes us into the stop state will always be the character BEFORE
        // the break position.)
        if (c != CharacterIterator.DONE) {
            if (lastCategory != IGNORE) {
                text.setIndex(text.getIndex() + 2);
            }
            else {
                text.next();
            }
        }
        return text.getIndex();
    }

    /**
     * Looks up a character's category (i.e., its category for breaking purposes,
     * not its Unicode category)
     */
    protected int lookupCategory(char c) {
        return charCategoryTable.elementAt(c);
    }

    /**
     * Given a current state and a character category, looks up the
     * next state to transition to in the state table.
     */
    protected int lookupState(int state, int category) {
        return stateTable[state * numCategories + category];
    }

    /**
     * Given a current state and a character category, looks up the
     * next state to transition to in the backwards state table.
     */
    protected int lookupBackwardState(int state, int category) {
        return backwardsStateTable[state * numCategories + category];
    }

    //=======================================================================
    // RuleBasedBreakIterator.Builder
    //=======================================================================
    /**
     * The Builder class has the job of constructing a RuleBasedBreakIterator from a
     * textual description.  A Builder is constructed by RuleBasedBreakIterator's
     * constructor, which uses it to construct the iterator itself and then throws it
     * away.
     * <p>The construction logic is separated out into its own class for two primary
     * reasons:
     * <ul><li>The construction logic is quite sophisticated and large.  Separating it
     * out into its own class means the code must only be loaded into memory while a
     * RuleBasedBreakIterator is being constructed, and can be purged after that.
     * <li>There is a fair amount of state that must be maintained throughout the
     * construction process that is not needed by the iterator after construction.
     * Separating this state out into another class prevents all of the functions that
     * construct the iterator from having to have really long parameter lists,
     * (hopefully) contributing to readability and maintainability.</ul>
     * <p>It'd be really nice if this could be an independent class rather than an
     * inner class, because that would shorten the source file considerably, but
     * making Builder an inner class of RuleBasedBreakIterator allows it direct access
     * to RuleBasedBreakIterator's private members, which saves us from having to
     * provide some kind of "back door" to the Builder class that could then also be
     * used by other classes.
     */
    protected class Builder {
        /**
         * A temporary holding place used for calculating the character categories.
         * This object contains CharSet objects.
         */
        protected Vector categories = null;

        /**
         * A table used to map parts of regexp text to lists of character categories,
         * rather than having to figure them out from scratch each time
         */
        protected Hashtable expressions = null;

        /**
         * A temporary holding place for the list of ignore characters
         */
        protected CharSet ignoreChars = null;

        /**
         * A temporary holding place where the forward state table is built
         */
        protected Vector tempStateTable = null;

        /**
         * A list of all the states that have to be filled in with transitions to the
         * next state that is created.  Used when building the state table from the
         * regular expressions.
         */
        protected Vector decisionPointList = null;

        /**
         * A stack for holding decision point lists.  This is used to handle nested
         * parentheses and braces in regexps.
         */
        protected Stack decisionPointStack = null;

        /**
         * A list of states that loop back on themselves.  Used to handle .*?
         */
        protected Vector loopingStates = null;

        /**
         * Looping states actually have to be backfilled later in the process
         * than everything else.  This is where a the list of states to backfill
         * is accumulated.  This is also used to handle .*?
         */
        protected Vector statesToBackfill = null;

        /**
         * A list mapping pairs of state numbers for states that are to be combined
         * to the state number of the state representing their combination.  Used
         * in the process of making the state table deterministic to prevent
         * infinite recursion.
         */
        protected Vector mergeList = null;

        /**
         * A flag that is used to indicate when the list of looping states can
         * be reset.
         */
        protected boolean clearLoopingStates = false;

        /**
         * A bit mask used to indicate a bit in the table's flags column that marks a
         * state as an accepting state.
         */
        protected static final int END_STATE_FLAG = 0x8000;

        /**
         * A bit mask used to indicate a bit in the table's flags column that marks a
         * state as one the builder shouldn't loop to any looping states
         */
        protected static final int DONT_LOOP_FLAG = 0x4000;

        /**
         * A bit mask used to indicate a bit in the table's flags column that marks a
         * state as a lookahead state.
         */
        protected static final int LOOKAHEAD_STATE_FLAG = 0x2000;

        /**
         * A bit mask representing the union of the mask values listed above.
         * Used for clearing or masking off the flag bits.
         */
        protected static final int ALL_FLAGS = END_STATE_FLAG | LOOKAHEAD_STATE_FLAG
                | DONT_LOOP_FLAG;

        /**
         * No special construction is required for the Builder.
         */
        public Builder() {
        }

        /**
         * This is the main function for setting up the BreakIterator's tables.  It
         * just vectors different parts of the job off to other functions.
         */
        public void buildBreakIterator() {
            Vector tempRuleList = buildRuleList(description);
            buildCharCategories(tempRuleList);
            buildStateTable(tempRuleList);
            buildBackwardsStateTable(tempRuleList);
        }

        /**
         * Thus function has three main purposes:
         * <ul><li>Perform general syntax checking on the description, so the rest of the
         * build code can assume that it's parsing a legal description.
         * <li>Split the description into separate rules
         * <li>Perform variable-name substitutions (so that no one else sees variable names)
         * </ul>
         */
        private Vector buildRuleList(String description) {
            // invariants:
            // - parentheses must be balanced: ()[]{}<>
            // - nothing can be nested inside <>
            // - nothing can be nested inside [] except more []s
            // - pairs of ()[]{}<> must not be empty
            // - ; can only occur at the outer level
            // - | can only appear inside ()
            // - only one = or / can occur in a single rule
            // - = and / cannot both occur in the same rule
            // - <> can only occur on the left side of a = expression
            //   (because we'll perform substitutions to eliminate them other places)
            // - the left-hand side of a = expression can only be a single character
            //   (possibly with \) or text inside <>
            // - the right-hand side of a = expression must be enclosed in [] or ()
            // - * may not occur at the beginning of a rule, nor may it follow
            //   =, /, (, (, |, }, ;, or *
            // - ? may only follow *
            // - the rule list must contain at least one / rule
            // - no rule may be empty
            // - all printing characters in the ASCII range except letters and digits
            //   are reserved and must be preceded by \
            // - ! may only occur at the beginning of a rule

            // set up a vector to contain the broken-up description (each entry in the
            // vector is a separate rule) and a stack for keeping track of opening
            // punctuation
            Vector tempRuleList = new Vector();
            Stack parenStack = new Stack();

            int p = 0;
            int ruleStart = 0;
            char c = '\u0000';
            char lastC = '\u0000';
            char lastOpen = '\u0000';
            boolean haveEquals = false;
            boolean havePipe = false;
            boolean sawVarName = false;
            final String charsThatCantPrecedeAsterisk = "=/{(|}*;\u0000";

            // if the description doesn't end with a semicolon, tack a semicolon onto the end
            if (description.length() != 0 && description.charAt(description.length() - 1) != ';') {
                description = description + ";";
            }

            // for each character, do...
            while (p < description.length()) {
                c = description.charAt(p);
                switch (c) {
                    // if the character is a backslash, skip the character that follows it
                    // (it'll get treated as a literal character)
                    case '\\':
                        ++p;
                        break;

                    // if the character is opening punctuation, verify that no nesting
                    // rules are broken, and push the character onto the stack
                    case '{':
                    case '<':
                    case '[':
                    case '(':
                        if (lastOpen == '<') {
                            error("Can't nest brackets inside <>", p, description);
                        }
                        if (lastOpen == '[' && c != '[') {
                            error("Can't nest anything in [] but []", p, description);
                        }

                        // if we see < anywhere except on the left-hand side of =,
                        // we must be seeing a variable name that was never defined
                        if (c == '<' && (haveEquals || havePipe)) {
                            error("Unknown variable name", p, description);
                        }

                        lastOpen = c;
                        parenStack.push(new Character(c));
                        if (c == '<') {
                            sawVarName = true;
                        }
                        break;

                    // if the character is closing punctuation, verify that it matches the
                    // last opening punctuation we saw, and that the brackets contain
                    // something, then pop the stack
                    case '}':
                    case '>':
                    case ']':
                    case ')':
                        char expectedClose = '\u0000';
                        switch (lastOpen) {
                            case '{':
                                expectedClose = '}';
                                break;
                            case '[':
                                expectedClose = ']';
                                break;
                            case '(':
                                expectedClose = ')';
                                break;
                            case '<':
                                expectedClose = '>';
                                break;
                        }
                        if (c != expectedClose) {
                            error("Unbalanced parentheses", p, description);
                        }
                        if (lastC == lastOpen) {
                            error("Parens don't contain anything", p, description);
                        }
                        parenStack.pop();
                        if (!parenStack.empty()) {
                            lastOpen = ((Character)(parenStack.peek())).charValue();
                        }
                        else {
                            lastOpen = '\u0000';
                        }

                        break;

                    // if the character is an asterisk, make sure it occurs in a place
                    // where an asterisk can legally go
                    case '*':
                        if (charsThatCantPrecedeAsterisk.indexOf(lastC) != -1) {
                            error("Misplaced asterisk", p, description);
                        }
                        break;

                    // if the character is a question mark, make sure it follows an asterisk
                    case '?':
                        if (lastC != '*') {
                            error("Misplaced ?", p, description);
                        }
                        break;

                    // if the character is an equals sign, make sure we haven't seen another
                    // equals sign or a slash yet
                    case '=':
                        if (haveEquals || havePipe) {
                            error("More than one = or / in rule", p, description);
                        }
                        haveEquals = true;
                        break;

                    // if the character is a slash, make sure we haven't seen another slash
                    // or an equals sign yet
                    case '/':
                        if (haveEquals || havePipe) {
                            error("More than one = or / in rule", p, description);
                        }
                        if (sawVarName) {
                            error("Unknown variable name", p, description);
                        }
                        havePipe = true;
                        break;

                    // if the character is an exclamation point, make sure it occurs only
                    // at the beginning of a rule
                    case '!':
                        if (lastC != ';' && lastC != '\u0000') {
                            error("! can only occur at the beginning of a rule", p, description);
                        }
                        break;

                    // we don't have to do anything special on a period
                    case '.':
                        break;

                    // if the character is a syntax character that can only occur
                    // inside [], make sure that it does in fact only occur inside [].
                    case '^':
                    case '-':
                    case ':':
                        if (lastOpen != '[' && lastOpen != '<') {
                            error("Illegal character", p, description);
                        }
                        break;

                    // if the character is a semicolon, do the following...
                    case ';':
                        // make sure the rule contains something and that there are no
                        // unbalanced parentheses or brackets
                        if (lastC == ';' || lastC == '\u0000') {
                            error("Empty rule", p, description);
                        }
                        if (!parenStack.empty()) {
                            error("Unbalanced parenheses", p, description);
                        }

                        if (parenStack.empty()) {
                            // if the rule contained an = sign, call processSubstitution()
                            // to replace the substitution name with the substitution text
                            // wherever it appears in the description
                            if (haveEquals) {
                                description = processSubstitution(description.substring(ruleStart,
                                                p), description, p + 1);
                            }
                            else {
                                // otherwise, check to make sure the rule doesn't reference
                                // any undefined substitutions
                                if (sawVarName) {
                                    error("Unknown variable name", p, description);
                                }

                                // then add it to tempRuleList
                                tempRuleList.addElement(description.substring(ruleStart, p));
                            }

                            // and reset everything to process the next rule
                            ruleStart = p + 1;
                            haveEquals = havePipe = sawVarName = false;
                        }
                        break;

                    // if the character is a vertical bar, check to make sure that it
                    // occurs inside a () expression and that the character that precedes
                    // it isn't also a vertical bar
                    case '|':
                        if (lastC == '|') {
                            error("Empty alternative", p, description);
                        }
                        if (parenStack.empty() || lastOpen != '(') {
                            error("Misplaced |", p, description);
                        }
                        break;

                    // if the character is anything else (escaped characters are
                    // skipped and don't make it here), it's an error
                    default:
                        if (c >= ' ' && c < '\u007f' && !Character.isLetter(c)
                            && !Character.isDigit(c)) {
                            error("Illegal character", p, description);
                        }
                        break;
                }
                lastC = c;
                ++p;
            }
            if (tempRuleList.size() == 0) {
                error("No valid rules in description", p, description);
            }
            return tempRuleList;
        }

        /**
         * This function performs variable-name substitutions.  First it does syntax
         * checking on the variable-name definition.  If it's syntactically valid, it
         * then goes through the remainder of the description and does a simple
         * find-and-replace of the variable name with its text.  (The variable text
         * must be enclosed in either [] or () for this to work.)
         */
        protected String processSubstitution(String substitutionRule, String description,
                        int startPos) {
            // isolate out the text on either side of the equals sign
            String replace;
            String replaceWith;
            int equalPos = substitutionRule.indexOf('=');
            replace = substitutionRule.substring(0, equalPos);
            replaceWith = substitutionRule.substring(equalPos + 1);

            // check to see whether the substitution name is something we've declared
            // to be "special".  For RuleBasedBreakIterator itself, this is "<ignore>".
            // This function takes care of any extra processing that has to be done
            // with "special" substitution names.
            handleSpecialSubstitution(replace, replaceWith, startPos, description);

            // perform various other syntax checks on the rule
            if (replaceWith.length() == 0) {
                error("Nothing on right-hand side of =", startPos, description);
            }
            if (replace.length() == 0) {
                error("Nothing on left-hand side of =", startPos, description);
            }
            if (replace.length() == 2 && replace.charAt(0) != '\\') {
                error("Illegal left-hand side for =", startPos, description);
            }
            if (replace.length() >= 3 && replace.charAt(0) != '<' && replace.charAt(equalPos - 1)
                            != '>') {
                error("Illegal left-hand side for =", startPos, description);
            }
            if (!(replaceWith.charAt(0) == '[' && replaceWith.charAt(replaceWith.length() - 1)
                    == ']') && !(replaceWith.charAt(0) == '(' && replaceWith.charAt(
                    replaceWith.length() - 1) == ')')) {
                error("Illegal right-hand side for =", startPos, description);
            }

            // now go through the rest of the description (which hasn't been broken up
            // into separate rules yet) and replace every occurrence of the
            // substitution name with the substitution body
            StringBuffer result = new StringBuffer();
            result.append(description.substring(0, startPos));
            int lastPos = startPos;
            int pos = description.indexOf(replace, startPos);
            while (pos != -1) {
                result.append(description.substring(lastPos, pos));
                result.append(replaceWith);
                lastPos = pos + replace.length();
                pos = description.indexOf(replace, lastPos);
            }
            result.append(description.substring(lastPos));
            return result.toString();
        }

        /**
         * This function defines a protocol for handling substitution names that
         * are "special," i.e., that have some property beyond just being
         * substitutions.  At the RuleBasedBreakIterator level, we have one
         * special substitution name, "<ignore>".  Subclasses can override this
         * function to add more.  Any special processing that has to go on beyond
         * that which is done by the normal substitution-processing code is done
         * here.
         */
        protected void handleSpecialSubstitution(String replace, String replaceWith,
                    int startPos, String description) {
            // if we get a definition for a substitution called "ignore", it defines
            // the ignore characters for the iterator.  Check to make sure the expression
            // is a [] expression, and if it is, parse it and store the characters off
            // to the side.
            if (replace.equals("<ignore>")) {
                if (replaceWith.charAt(0) == '(') {
                    error("Ignore group can't be enclosed in (", startPos, description);
                }
                ignoreChars = CharSet.parseString(replaceWith);
            }
        }

        /**
         * This function builds the character category table.  On entry,
         * tempRuleList is a vector of break rules that has had variable names substituted.
         * On exit, the charCategoryTable data member has been initialized to hold the
         * character category table, and tempRuleList's rules have been munged to contain
         * character category numbers everywhere a literal character or a [] expression
         * originally occurred.
         */
        protected void buildCharCategories(Vector tempRuleList) {
            int bracketLevel = 0;
            int p = 0;
            int lineNum = 0;

            // build hash table of every literal character or [] expression in the rule list
            // and use CharSet.parseString() to derive a CharSet object representing the
            // characters each refers to
            expressions = new Hashtable();
            while (lineNum < tempRuleList.size()) {
                String line = (String)(tempRuleList.elementAt(lineNum));
                p = 0;
                while (p < line.length()) {
                    char c = line.charAt(p);
                    switch (c) {
                        // skip over all syntax characters except [
                        case '{': case '}': case '(': case ')': case '*': case '.':
                        case '/': case '|': case ';': case '?': case '!':
                            break;

                        // for [, find the matching ] (taking nested [] pairs into account)
                        // and add the whole expression to the expression list
                        case '[':
                            int q = p + 1;
                            ++bracketLevel;
                            while (q < line.length() && bracketLevel != 0) {
                                c = line.charAt(q);
				switch (c) {
				case '\\':
				    q++;
				    break;
                                case '[':
                                    ++bracketLevel;
				    break;
				case ']':
				    --bracketLevel;
				    break;
				}
                                ++q;
                            }
                            if (expressions.get(line.substring(p, q)) == null) {
                                expressions.put(line.substring(p, q), CharSet.parseString(line.
                                                substring(p, q)));
                            }
                            p = q - 1;
                            break;

                        // for \ sequences, just move to the next character and treat
                        // it as a single character
                        case '\\':
                            ++p;
                            c = line.charAt(p);
                            // DON'T break; fall through into "default" clause

                        // for an isolated single character, add it to the expression list
                        default:
                            expressions.put(line.substring(p, p + 1), CharSet.parseString(line.
                                            substring(p, p + 1)));
                            break;
                    }
                    ++p;
                }
                ++lineNum;
            }
            // dump CharSet's internal expression cache
            CharSet.releaseExpressionCache();

            // create the temporary category table (which is a vector of CharSet objects)
            categories = new Vector();
            if (ignoreChars != null) {
                categories.addElement(ignoreChars);
            }
            else {
                categories.addElement(new CharSet());
            }
            ignoreChars = null;

            // this is a hook to allow subclasses to add categories on their own
            mungeExpressionList(expressions);

            // Derive the character categories.  Go through the existing character categories
            // looking for overlap.  Any time there's overlap, we create a new character
            // category for the characters that overlapped and remove them from their original
            // category.  At the end, any characters that are left in the expression haven't
            // been mentioned in any category, so another new category is created for them.
            // For example, if the first expression is [abc], then a, b, and c will be placed
            // into a single character category.  If the next expression is [bcd], we will first
            // remove b and c from their existing category (leaving a behind), create a new
            // category for b and c, and then create another new category for d (which hadn't
            // been mentioned in the previous expression).
            // At no time should a character ever occur in more than one character category.

            // for each expression in the expressions list, do...
            Enumeration iter = expressions.elements();
            while (iter.hasMoreElements()) {
                // initialize the working char set to the chars in the current expression
                CharSet e = (CharSet)iter.nextElement();

                // for each category in the category list, do...
                for (int j = categories.size() - 1; !e.empty() && j > 0; j--) {

                    // if there's overlap between the current working set of chars
                    // and the current category...
                    CharSet that = (CharSet)(categories.elementAt(j));
                    if (!that.intersection(e).empty()) {

                        // add a new category for the characters that were in the
                        // current category but not in the working char set
                        CharSet temp = that.difference(e);
                        if (!temp.empty()) {
                            categories.addElement(temp);
                        }

                        // remove those characters from the working char set and replace
                        // the current category with the characters that it did
                        // have in common with the current working char set
                        temp = e.intersection(that);
                        e = e.difference(that);
                        if (!temp.equals(that)) {
                            categories.setElementAt(temp, j);
                        }
                    }
                }

                // if there are still characters left in the working char set,
                // add a new category containing them
                if (!e.empty()) {
                    categories.addElement(e);
                }
            }

            // we have the ignore characters stored in position 0.  Make an extra pass through
            // the character category list and remove anything from the ignore list that shows
            // up in some other category
            CharSet allChars = new CharSet();
            for (int i = 1; i < categories.size(); i++)
                allChars = allChars.union((CharSet)(categories.elementAt(i)));
            CharSet ignoreChars = (CharSet)(categories.elementAt(0));
            ignoreChars = ignoreChars.difference(allChars);
            categories.setElementAt(ignoreChars, 0);

            // now that we've derived the character categories, go back through the expression
            // list and replace each CharSet object with a String that represents the
            // character categories that expression refers to.  The String is encoded: each
            // character is a character category number (plus 0x100 to avoid confusing them
            // with syntax characters in the rule grammar)
            iter = expressions.keys();
            while (iter.hasMoreElements()) {
                String key = (String)iter.nextElement();
                CharSet cs = (CharSet)expressions.get(key);
                StringBuffer cats = new StringBuffer();

                // for each category...
                for (int j = 0; j < categories.size(); j++) {

                    // if the current expression contains characters in that category...
                    CharSet temp = cs.intersection((CharSet)(categories.elementAt(j)));
                    if (!temp.empty()) {

                        // then add the encoded category number to the String for this
                        // expression
                        cats.append((char)(0x100 + j));
                        if (temp.equals(cs)) {
                            break;
                        }
                    }
                }

                // once we've finished building the encoded String for this expression,
                // replace the CharSet object with it
                expressions.put(key, cats.toString());
            }

            // and finally, we turn the temporary category table into a permanent category
            // table, which is a CompactByteArray. (we skip category 0, which by definition
            // refers to all characters not mentioned specifically in the rules)
            charCategoryTable = new CompactByteArray((byte)0);

            // for each category...
            for (int i = 0; i < categories.size(); i++) {
                CharSet chars = (CharSet)(categories.elementAt(i));

                // go through the character ranges in the category one by one...
                Enumeration enum = chars.getChars();
                while (enum.hasMoreElements()) {
                    char[] range = (char[])(enum.nextElement());

                    // and set the corresponding elements in the CompactArray accordingly
                    if (i != 0) {
                        charCategoryTable.setElementAt(range[0], range[1], (byte)i);
                    }

                    // (category 0 is special-- it's the hiding place for the ignore
                    // characters, whose real category number in the CompactArray is
                    // -1 [this is because category 0 contains all characters not
                    // specifically mentioned anywhere in the rules] )
                    else {
                        charCategoryTable.setElementAt(range[0], range[1], IGNORE);
                    }
                }
            }

            // once we've populated the CompactArray, compact it
            charCategoryTable.compact();

            // initialize numCategories
            numCategories = categories.size();
        }

        protected void mungeExpressionList(Hashtable expressions) {
            // empty in the parent class.  This function provides a hook for subclasses
            // to mess with the character category table.
        }

        /**
         * This is the function that builds the forward state table.  Most of the real
         * work is done in parseRule(), which is called once for each rule in the
         * description.
         */
        private void buildStateTable(Vector tempRuleList) {
            // initialize our temporary state table, and fill it with two states:
            // state 0 is a dummy state that allows state 1 to be the starting state
            // and 0 to represent "stop".  State 1 is added here to seed things
            // before we start parsing
            tempStateTable = new Vector();
            tempStateTable.addElement(new short[numCategories + 1]);
            tempStateTable.addElement(new short[numCategories + 1]);

            // call parseRule() for every rule in the rule list (except those which
            // start with !, which are actually backwards-iteration rules)
            for (int i = 0; i < tempRuleList.size(); i++) {
                String rule = (String)tempRuleList.elementAt(i);
                if (rule.charAt(0) != '!') {
                    parseRule(rule, true);
                }
            }

            // finally, use finishBuildingStateTable() to minimize the number of
            // states in the table and perform some other cleanup work
            finishBuildingStateTable(true);
	}

        /**
         * This is where most of the work really happens.  This routine parses a single
         * rule in the rule description, adding and modifying states in the state
         * table according to the new expression.  The state table is kept deterministic
         * throughout the whole operation, although some ugly postprocessing is needed
         * to handle the *? token.
         */
        private void parseRule(String rule, boolean forward) {
            // algorithm notes:
            //   - The basic idea here is to read successive character-category groups
            //   from the input string.  For each group, you create a state and point
            //   the appropriate entries in the previous state to it.  This produces a
            //   straight line from the start state to the end state.  The {}, *, and (|)
            //   idioms produce branches in this straight line.  These branches (states
            //   that can transition to more than one other state) are called "decision
            //   points."  A list of decision points is kept.  This contains a list of
            //   all states that can transition to the next state to be created.  For a
            //   straight line progression, the only thing in the decision-point list is
            //   the current state.  But if there's a branch, the decision-point list
            //   will contain all of the beginning points of the branch when the next
            //   state to be created represents the end point of the branch.  A stack is
            //   used to save decision point lists in the presence of nested parentheses
            //   and the like.  For example, when a { is encountered, the current decision
            //   point list is saved on the stack and restored when the corresponding }
            //   is encountered.  This way, after the } is read, the decision point list
            //   will contain both the state right before the } _and_ the state before
            //   the whole {} expression.  Both of these states can transition to the next
            //   state after the {} expression.
            //   - one complication arises when we have to stamp a transition value into
            //   an array cell that already contains one.  The updateStateTable() and
            //   mergeStates() functions handle this case.  Their basic approach is to
            //   create a new state that combines the two states that conflict and point
            //   at it when necessary.  This happens recursively, so if the merged states
            //   also conflict, they're resolved in the same way, and so on.  There are
            //   a number of tests aimed at preventing infinite recursion.
            //   - another complication arises with repeating characters.  It's somewhat
            //   ambiguous whether the user wants a greedy or non-greedy match in these cases.
            //   (e.g., whether "[a-z]*abc" means the SHORTEST sequence of letters ending in
            //   "abc" or the LONGEST sequence of letters ending in "abc".  We've adopted
            //   the *? to mean "shortest" and * by itself to mean "longest".  (You get the
            //   same result with both if there's no overlap between the repeating character
            //   group and the group immediately following it.)  Handling the *? token is
            //   rather complicated and involves keeping track of whether a state needs to
            //   be merged (as described above) or merely overwritten when you update one of
            //   its cells, and copying the contents of a state that loops with a *? token
            //   into some of the states that follow it after the rest of the table-building
            //   process is complete ("backfilling").
            // implementation notes:
            //   - This function assumes syntax checking has been performed on the input string
            //   prior to its being passed in here.  It assumes that parentheses are
            //   balanced, all literal characters are enclosed in [] and turned into category
            //   numbers, that there are no illegal characters or character sequences, and so
            //   on.  Violation of these invariants will lead to undefined behavior.
            //   - It'd probably be better to use linked lists rather than Vector and Stack
            //   to maintain the decision point list and stack.  I went for simplicity in
            //   this initial implementation.  If performance is critical enough, we can go
            //   back and fix this later.
            //   -There are a number of important limitations on the *? token.  It does not work
            //   right when followed by a repeating character sequence (e.g., ".*?(abc)*")
            //   (although it does work right when followed by a single repeating character).
            //   It will not always work right when nested in parentheses or braces (although
            //   sometimes it will).  It also will not work right if the group of repeating