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package org.antlr.runtime;

A lexer is recognizer that draws input symbols from a character stream.
 lexer grammars result in a subclass of this object. A Lexer object
 uses simplified match() and error recovery mechanisms in the interest
 of speed.
/** A lexer is recognizer that draws input symbols from a character stream.
 *  lexer grammars result in a subclass of this object. A Lexer object
 *  uses simplified match() and error recovery mechanisms in the interest
 *  of speed.
 */
public abstract class Lexer extends BaseRecognizer implements TokenSource {
	
Where is the lexer drawing characters from? /** Where is the lexer drawing characters from? */
	protected CharStream input;

	public Lexer() {
	}

	public Lexer(CharStream input) {
		this.input = input;
	}

	public Lexer(CharStream input, RecognizerSharedState state) {
		super(state);
		this.input = input;
	}

	@Override
	public void reset() {
		super.reset(); // reset all recognizer state variables
		// wack Lexer state variables
		if ( input!=null ) {
			input.seek(0); // rewind the input
		}
		if ( state==null ) {
			return; // no shared state work to do
		}
		state.token = null;
		state.type = Token.INVALID_TOKEN_TYPE;
		state.channel = Token.DEFAULT_CHANNEL;
		state.tokenStartCharIndex = -1;
		state.tokenStartCharPositionInLine = -1;
		state.tokenStartLine = -1;
		state.text = null;
	}

	
Return a token from this source; i.e., match a token on the char
 stream.
/** Return a token from this source; i.e., match a token on the char
	 *  stream.
	 */
	public Token nextToken() {
		while (true) {
			state.token = null;
			state.channel = Token.DEFAULT_CHANNEL;
			state.tokenStartCharIndex = input.index();
			state.tokenStartCharPositionInLine = input.getCharPositionInLine();
			state.tokenStartLine = input.getLine();
			state.text = null;
			if ( input.LA(1)==CharStream.EOF ) {
				return getEOFToken();
			}
			try {
				mTokens();
				if ( state.token==null ) {
					emit();
				}
				else if ( state.token==Token.SKIP_TOKEN ) {
					continue;
				}
				return state.token;
			}
			catch (MismatchedRangeException re) {
				reportError(re);
				// matchRange() routine has already called recover()
			}
			catch (MismatchedTokenException re) {
				reportError(re);
				// match() routine has already called recover()
			}
			catch (RecognitionException re) {
				reportError(re);
				recover(re); // throw out current char and try again
			}
		}
	}

	
Returns the EOF token (default), if you need
 to return a custom token instead override this method.
/** Returns the EOF token (default), if you need
	 *  to return a custom token instead override this method.
	 */
	public Token getEOFToken() {
		Token eof = new CommonToken(input,Token.EOF,
									Token.DEFAULT_CHANNEL,
									input.index(),input.index());
		eof.setLine(getLine());
		eof.setCharPositionInLine(getCharPositionInLine());
		return eof;
	}

	
Instruct the lexer to skip creating a token for current lexer rule
 and look for another token.  nextToken() knows to keep looking when
 a lexer rule finishes with token set to SKIP_TOKEN.  Recall that
 if token==null at end of any token rule, it creates one for you
 and emits it.
/** Instruct the lexer to skip creating a token for current lexer rule
	 *  and look for another token.  nextToken() knows to keep looking when
	 *  a lexer rule finishes with token set to SKIP_TOKEN.  Recall that
	 *  if token==null at end of any token rule, it creates one for you
	 *  and emits it.
	 */
	public void skip() {
		state.token = Token.SKIP_TOKEN;
	}

	
This is the lexer entry point that sets instance var 'token' /** This is the lexer entry point that sets instance var 'token' */
	public abstract void mTokens() throws RecognitionException;

	
Set the char stream and reset the lexer /** Set the char stream and reset the lexer */
	public void setCharStream(CharStream input) {
		this.input = null;
		reset();
		this.input = input;
	}

	public CharStream getCharStream() {
		return this.input;
	}

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

	
Currently does not support multiple emits per nextToken invocation
 for efficiency reasons.  Subclass and override this method and
 nextToken (to push tokens into a list and pull from that list rather
 than a single variable as this implementation does).
/** Currently does not support multiple emits per nextToken invocation
	 *  for efficiency reasons.  Subclass and override this method and
	 *  nextToken (to push tokens into a list and pull from that list rather
	 *  than a single variable as this implementation does).
	 */
	public void emit(Token token) {
		state.token = token;
	}

	
The standard method called to automatically emit a token at the
 outermost lexical rule.  The token object should point into the
 char buffer start..stop.  If there is a text override in 'text',
 use that to set the token's text.  Override this method to emit
 custom Token objects.
 If you are building trees, then you should also override
 Parser or TreeParser.getMissingSymbol().
/** The standard method called to automatically emit a token at the
	 *  outermost lexical rule.  The token object should point into the
	 *  char buffer start..stop.  If there is a text override in 'text',
	 *  use that to set the token's text.  Override this method to emit
	 *  custom Token objects.
	 *
	 *  If you are building trees, then you should also override
	 *  Parser or TreeParser.getMissingSymbol().
	 */
	public Token emit() {
		Token t = new CommonToken(input, state.type, state.channel, state.tokenStartCharIndex, getCharIndex()-1);
		t.setLine(state.tokenStartLine);
		t.setText(state.text);
		t.setCharPositionInLine(state.tokenStartCharPositionInLine);
		emit(t);
		return t;
	}

	public void match(String s) throws MismatchedTokenException {
		int i = 0;
		while ( i<s.length() ) {
			if ( input.LA(1)!=s.charAt(i) ) {
				if ( state.backtracking>0 ) {
					state.failed = true;
					return;
				}
				MismatchedTokenException mte =
					new MismatchedTokenException(s.charAt(i), input);
				recover(mte);
				throw mte;
			}
			i++;
			input.consume();
			state.failed = false;
		}
	}

	public void matchAny() {
		input.consume();
	}

	public void match(int c) throws MismatchedTokenException {
		if ( input.LA(1)!=c ) {
			if ( state.backtracking>0 ) {
				state.failed = true;
				return;
			}
			MismatchedTokenException mte =
				new MismatchedTokenException(c, input);
			recover(mte);  // don't really recover; just consume in lexer
			throw mte;
		}
		input.consume();
		state.failed = false;
	}

	public void matchRange(int a, int b)
		throws MismatchedRangeException
	{
		if ( input.LA(1)<a || input.LA(1)>b ) {
			if ( state.backtracking>0 ) {
				state.failed = true;
				return;
			}
			MismatchedRangeException mre =
				new MismatchedRangeException(a,b,input);
			recover(mre);
			throw mre;
		}
		input.consume();
		state.failed = false;
	}

	public int getLine() {
		return input.getLine();
	}

	public int getCharPositionInLine() {
		return input.getCharPositionInLine();
	}

	
What is the index of the current character of lookahead? /** What is the index of the current character of lookahead? */
	public int getCharIndex() {
		return input.index();
	}

	
Return the text matched so far for the current token or any
 text override.
/** Return the text matched so far for the current token or any
	 *  text override.
	 */
	public String getText() {
		if ( state.text!=null ) {
			return state.text;
		}
		return input.substring(state.tokenStartCharIndex,getCharIndex()-1);
	}

	
Set the complete text of this token; it wipes any previous
 changes to the text.
/** Set the complete text of this token; it wipes any previous
	 *  changes to the text.
	 */
	public void setText(String text) {
		state.text = text;
	}

	@Override
	public void reportError(RecognitionException e) {
		/** TODO: not thought about recovery in lexer yet.
		 *
		// if we've already reported an error and have not matched a token
		// yet successfully, don't report any errors.
		if ( errorRecovery ) {
			//System.err.print("[SPURIOUS] ");
			return;
		}
		errorRecovery = true;
		 */

		displayRecognitionError(this.getTokenNames(), e);
	}

	@Override
	public String getErrorMessage(RecognitionException e, String[] tokenNames) {
		String msg;
		if ( e instanceof MismatchedTokenException ) {
			MismatchedTokenException mte = (MismatchedTokenException)e;
			msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting "+getCharErrorDisplay(mte.expecting);
		}
		else if ( e instanceof NoViableAltException ) {
			NoViableAltException nvae = (NoViableAltException)e;
			// for development, can add "decision=<<"+nvae.grammarDecisionDescription+">>"
			// and "(decision="+nvae.decisionNumber+") and
			// "state "+nvae.stateNumber
			msg = "no viable alternative at character "+getCharErrorDisplay(e.c);
		}
		else if ( e instanceof EarlyExitException ) {
			EarlyExitException eee = (EarlyExitException)e;
			// for development, can add "(decision="+eee.decisionNumber+")"
			msg = "required (...)+ loop did not match anything at character "+getCharErrorDisplay(e.c);
		}
		else if ( e instanceof MismatchedNotSetException ) {
			MismatchedNotSetException mse = (MismatchedNotSetException)e;
			msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+mse.expecting;
		}
		else if ( e instanceof MismatchedSetException ) {
			MismatchedSetException mse = (MismatchedSetException)e;
			msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+mse.expecting;
		}
		else if ( e instanceof MismatchedRangeException ) {
			MismatchedRangeException mre = (MismatchedRangeException)e;
			msg = "mismatched character "+getCharErrorDisplay(e.c)+" expecting set "+
				  getCharErrorDisplay(mre.a)+".."+getCharErrorDisplay(mre.b);
		}
		else {
			msg = super.getErrorMessage(e, tokenNames);
		}
		return msg;
	}

	public String getCharErrorDisplay(int c) {
		String s = String.valueOf((char)c);
		switch ( c ) {
			case Token.EOF :
				s = "<EOF>";
				break;
			case '\n' :
				s = "\\n";
				break;
			case '\t' :
				s = "\\t";
				break;
			case '\r' :
				s = "\\r";
				break;
		}
		return "'"+s+"'";
	}

	
Lexers can normally match any char in it's vocabulary after matching
 a token, so do the easy thing and just kill a character and hope
 it all works out.  You can instead use the rule invocation stack
 to do sophisticated error recovery if you are in a fragment rule.
/** Lexers can normally match any char in it's vocabulary after matching
	 *  a token, so do the easy thing and just kill a character and hope
	 *  it all works out.  You can instead use the rule invocation stack
	 *  to do sophisticated error recovery if you are in a fragment rule.
	 */
	public void recover(RecognitionException re) {
		//System.out.println("consuming char "+(char)input.LA(1)+" during recovery");
		//re.printStackTrace();
		input.consume();
	}

	public void traceIn(String ruleName, int ruleIndex)  {
		String inputSymbol = ((char)input.LT(1))+" line="+getLine()+":"+getCharPositionInLine();
		super.traceIn(ruleName, ruleIndex, inputSymbol);
	}

	public void traceOut(String ruleName, int ruleIndex)  {
		String inputSymbol = ((char)input.LT(1))+" line="+getLine()+":"+getCharPositionInLine();
		super.traceOut(ruleName, ruleIndex, inputSymbol);
	}
}