Lexer.java

/*
 * (c) Copyright 2010-2011 AgileBirds
 *
 * This file is part of OpenFlexo.
 *
 * OpenFlexo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * OpenFlexo 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with OpenFlexo. If not, see <http://www.gnu.org/licenses/>.
 *
 */
package cb.parser;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.PushbackReader;
import java.io.Reader;
import java.util.Stack;

public class Lexer {
	private PushbackReader _reader;
	private int _line = 1;

	public static final int LPAREN = 0;
	public static final int RPAREN = 1;
	public static final int IDENT = 2;
	public static final int INTEGER = 3;
	public static final int FLOAT = 4;
	public static final int BOOLEAN = 5;
	public static final int TAG = 6;
	public static final int STRING = 7;
	public static final int MULTI_STRING = 8;
	public static final int COMMA = 9;
	public static final int EOF = -1;

	public Lexer(Reader r) {
		_reader = new PushbackReader(new BufferedReader(r, 8192));
	}

	private void skipWS() throws IOException {
		int ch;

		while (Character.isWhitespace((char) (ch = _reader.read()))) {
			if (ch == '\n') {
				_line++;
			}
		}

		_reader.unread(ch);
	}

	private StringBuffer buf = new StringBuffer();

	public Token parseNumber() throws IOException {
		int kind = INTEGER;
		int ch = _reader.read();

		buf.setLength(0);

		if (ch == '+' || ch == '-') {
			buf.append((char) ch);
			ch = _reader.read();
		}

		while (Character.isDigit((char) ch) || ch == '.') {
			if (ch == '.') {
				if (kind == FLOAT) {
					throw new RuntimeException("Lexer Error: Found second . in float");
				}
				kind = FLOAT;
			}

			buf.append((char) ch);
			ch = _reader.read();
		}

		_reader.unread(ch);

		return Token.createToken(kind, buf.toString(), _line);
	}

	public Token parseString() throws IOException {
		int ch = _reader.read();

		buf.setLength(0);

		buf.append('"');

		ch = _reader.read();
		while (ch != '"') {
			if (ch == '\\') {
				buf.append('\\');
				ch = _reader.read();
				buf.append((char) ch);
			} else {
				buf.append((char) ch);
			}
			ch = _reader.read();
		}

		buf.append('"');

		return Token.createToken(STRING, buf.toString(), _line);
	}

	public Token parseMultiString() throws IOException {
		int ch = _reader.read();

		buf.setLength(0);

		while (ch == '|') {
			buf.append('|');

			while ((ch = _reader.read()) != '\n') {
				buf.append((char) ch);
			}

			buf.append('\n');
			_line++;
			ch = _reader.read();
		}

		_reader.unread(ch);

		return Token.createToken(MULTI_STRING, buf.toString(), _line);
	}

	public Token parseIdent() throws IOException {
		int ch = _reader.read();

		buf.setLength(0);

		while (Character.isJavaIdentifierPart((char) ch)) {
			buf.append((char) ch);
			ch = _reader.read();
		}

		_reader.unread(ch);

		String img = buf.toString();

		if (img.equals("TRUE")) {
			return Token.TRUE;
		} else if (img.equals("FALSE")) {
			return Token.FALSE;
		} else {
			return Token.createToken(IDENT, img, _line);
		}
	}

	private Stack stack = new Stack();

	public void ungetToken(Token t) {
		stack.push(t);
	}

	public Token getToken() {
		if (!stack.empty()) {
			return (Token) stack.pop();
		}

		int kind;
		String image;

		try {
			skipWS();
			int ch = _reader.read();

			switch (ch) {
			case '(':
				return Token.LPAREN;

			case ')':
				return Token.RPAREN;

			case ',':
				return Token.COMMA;

			case '@':
				Token t = parseNumber();
				t.image = "@" + t.image;
				t.kind = TAG;

				return t;

			case '0':
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
			case '8':
			case '9':
			case '-':
			case '+':
			case '.':
				_reader.unread(ch);
				return parseNumber();

			case '"':
				_reader.unread(ch);
				return parseString();

			case '|':
				_reader.unread(ch);
				return parseMultiString();

			case 65535: // -1
				return Token.EOF;

			default:
				if (Character.isJavaIdentifierStart((char) ch)) {
					_reader.unread(ch);
					return parseIdent();
				} else {
					throw new RuntimeException("Lexer error: Unknown token: " + (char) ch + "(" + ch + ")" + (ch < 0));
				}
			}
		} catch (IOException e) {
			throw new RuntimeException("Lexer error: " + e);
		}
	}

	public int getLine() {
		return _line;
	}
}