/* gnu/regexp/RETokenWordBoundary.java
   Copyright (C) 2001, 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.

GNU Classpath is distributed in the hope that it will be useful, but
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package gnu.regexp;

/**
 * Represents a combination lookahead/lookbehind for POSIX [:alnum:].
 */
final class RETokenWordBoundary extends REToken {
    private boolean negated;
    private int where;
    static final int BEGIN = 1;
    static final int END = 2;

    RETokenWordBoundary(int subIndex, int where, boolean negated) {
	super(subIndex);
	this.where = where;
	this.negated = negated;
    }
    
    boolean match(CharIndexed input, REMatch mymatch) {
	// Word boundary means input[index-1] was a word character
	// and input[index] is not, or input[index] is a word character
	// and input[index-1] was not
	//  In the string "one two three", these positions match:
	//  |o|n|e| |t|w|o| |t|h|r|e|e|
	//  ^     ^ ^     ^ ^         ^
	boolean after = false;  // is current character a letter or digit?
	boolean before = false; // is previous character a letter or digit?
	char ch;

	// TODO: Also check REG_ANCHORINDEX vs. anchor
	if (((mymatch.eflags & RE.REG_ANCHORINDEX) != RE.REG_ANCHORINDEX) 
	    || (mymatch.offset + mymatch.index > mymatch.anchor)) {
	    if ((ch = input.charAt(mymatch.index - 1)) != CharIndexed.OUT_OF_BOUNDS) {
		before = Character.isLetterOrDigit(ch) || (ch == '_');
	    }
	}

	if ((ch = input.charAt(mymatch.index)) != CharIndexed.OUT_OF_BOUNDS) {
	    after = Character.isLetterOrDigit(ch) || (ch == '_');
	}

	// if (before) and (!after), we're at end (\>)
	// if (after) and (!before), we're at beginning (\<)
	boolean doNext = false;

	if ((where & BEGIN) == BEGIN) {
	    doNext = after && !before;
	}
	if ((where & END) == END) {
	    doNext ^= before && !after;
	}

	if (negated) doNext = !doNext;

	return (doNext ? next(input, mymatch) : false);
    }
    
    void dump(StringBuffer os) {
	if (where == (BEGIN | END)) {
	    os.append( negated ? "\\B" : "\\b" );
	} else if (where == BEGIN) {
	    os.append("\\<");
	} else {
	    os.append("\\>");
	}
    }
}