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The ANTLR 4 grammar compiler.
There is a newer version: 4.13.2
/*
 * [The "BSD license"]
 *  Copyright (c) 2012 Terence Parr
 *  Copyright (c) 2012 Sam Harwell
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.antlr.v4.tool.interp;

import org.antlr.v4.Tool;
import org.antlr.v4.runtime.ANTLRInputStream;
import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.CommonTokenFactory;
import org.antlr.v4.runtime.Lexer;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.TokenFactory;
import org.antlr.v4.runtime.TokenSource;
import org.antlr.v4.runtime.atn.LexerATNSimulator;
import org.antlr.v4.runtime.atn.PredictionContextCache;
import org.antlr.v4.runtime.dfa.DFA;
import org.antlr.v4.runtime.misc.Pair;
import org.antlr.v4.tool.LexerGrammar;

public class LexerInterpreter implements TokenSource {
	protected LexerGrammar g;
	protected LexerATNSimulator interp;
	protected CharStream input;
	protected Pair tokenFactorySourcePair;

	/** How to create token objects */
	protected TokenFactory _factory = CommonTokenFactory.DEFAULT;

	protected final DFA[] _decisionToDFA = new DFA[1];
	protected final PredictionContextCache _sharedContextCache =
		new PredictionContextCache();

	public LexerInterpreter(LexerGrammar g, String inputString) {
		this(g);
		setInput(inputString);
	}

	public LexerInterpreter(LexerGrammar g) {
		Tool antlr = new Tool();
		antlr.process(g,false);
		interp = new LexerATNSimulator(g.atn,_decisionToDFA,_sharedContextCache);
	}

	public void setInput(String inputString) {
		setInput(new ANTLRInputStream(inputString));
	}

	public void setInput(CharStream input) {
		this.input = input;
		this.tokenFactorySourcePair = new Pair(this, input);
	}

	@Override
	public String getSourceName() {	return g.name; }

	@Override
	public void setTokenFactory(TokenFactory factory) {
		this._factory = factory;
	}

	@Override
	public TokenFactory getTokenFactory() {
		return _factory;
	}

	@Override
	public int getCharPositionInLine() {
		return 0;
	}

	@Override
	public int getLine() {
		return 0;
	}

	@Override
	public CharStream getInputStream() {
		return input;
	}

	@Override
	public Token nextToken() {
		// TODO: Deal with off channel tokens
		int start = input.index();
		int tokenStartCharPositionInLine = interp.getCharPositionInLine();
		int tokenStartLine = interp.getLine();
		int mark = input.mark(); // make sure unuffered stream holds chars long enough to get text
		try {
			int ttype = interp.match(input, Lexer.DEFAULT_MODE);
			int stop = input.index()-1;

			return _factory.create(tokenFactorySourcePair, ttype, null, Token.DEFAULT_CHANNEL, start, stop,
								   tokenStartLine, tokenStartCharPositionInLine);
		}
		finally {
			input.release(mark);
		}
	}
}