/*
 [The "BSD license"]
 Copyright (c) 2005-2009 Terence Parr
 All rights reserved.

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 modification, are permitted provided that the following conditions
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 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
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 IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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package org.antlr.runtime;

The most common stream of tokens where every token is buffered up
 and tokens are filtered for a certain channel (the parser will only
 see these tokens).
 Even though it buffers all of the tokens, this token stream pulls tokens
 from the tokens source on demand. In other words, until you ask for a
 token using consume(), LT(), etc. the stream does not pull from the lexer.
 The only difference between this stream and BufferedTokenStream superclass
 is that this stream knows how to ignore off channel tokens. There may be
 a performance advantage to using the superclass if you don't pass
 whitespace and comments etc. to the parser on a hidden channel (i.e.,
 you set $channel instead of calling skip() in lexer rules.)
 @see org.antlr.runtime.UnbufferedTokenStream
 @see org.antlr.runtime.BufferedTokenStream
/** The most common stream of tokens where every token is buffered up
 *  and tokens are filtered for a certain channel (the parser will only
 *  see these tokens).
 *
 *  Even though it buffers all of the tokens, this token stream pulls tokens
 *  from the tokens source on demand. In other words, until you ask for a
 *  token using consume(), LT(), etc. the stream does not pull from the lexer.
 *
 *  The only difference between this stream and BufferedTokenStream superclass
 *  is that this stream knows how to ignore off channel tokens. There may be
 *  a performance advantage to using the superclass if you don't pass
 *  whitespace and comments etc. to the parser on a hidden channel (i.e.,
 *  you set $channel instead of calling skip() in lexer rules.)
 *
 *  @see org.antlr.runtime.UnbufferedTokenStream
 *  @see org.antlr.runtime.BufferedTokenStream
 */
public class CommonTokenStream extends BufferedTokenStream {
    
Skip tokens on any channel but this one; this is how we skip whitespace... /** Skip tokens on any channel but this one; this is how we skip whitespace... */
    protected int channel = Token.DEFAULT_CHANNEL;

    public CommonTokenStream() { }

    public CommonTokenStream(TokenSource tokenSource) {
        super(tokenSource);
    }

    public CommonTokenStream(TokenSource tokenSource, int channel) {
        this(tokenSource);
        this.channel = channel;
    }

    
Always leave p on an on-channel token. /** Always leave p on an on-channel token. */
	@Override
    public void consume() {
        if ( p == -1 ) setup();
        p++;
        sync(p);
        while ( tokens.get(p).getChannel()!=channel ) {
            p++;
            sync(p);
        }
    }

	@Override
    protected Token LB(int k) {
        if ( k==0 || (p-k)<0 ) return null;

        int i = p;
        int n = 1;
        // find k good tokens looking backwards
        while ( n<=k ) {
            // skip off-channel tokens
            i = skipOffTokenChannelsReverse(i-1);
            n++;
        }
        if ( i<0 ) return null;
        return tokens.get(i);
    }

	@Override
    public Token LT(int k) {
        //System.out.println("enter LT("+k+")");
        if ( p == -1 ) setup();
        if ( k == 0 ) return null;
        if ( k < 0 ) return LB(-k);
        int i = p;
        int n = 1; // we know tokens[p] is a good one
        // find k good tokens
        while ( n<k ) {
            // skip off-channel tokens
            i = skipOffTokenChannels(i+1);
            n++;
        }
		if ( i>range ) range = i;
        return tokens.get(i);
    }

    
Given a starting index, return the index of the first on-channel
 token.
/** Given a starting index, return the index of the first on-channel
     *  token.
     */
    protected int skipOffTokenChannels(int i) {
        sync(i);
        while ( tokens.get(i).getChannel()!=channel ) { // also stops at EOF (it's onchannel)
            i++;
            sync(i);
        }
        return i;
    }

    protected int skipOffTokenChannelsReverse(int i) {
        while ( i>=0 && tokens.get(i).getChannel()!=channel ) {
            i--;
        }
        return i;
    }

	@Override
	public void reset() {
		super.reset();
		p = skipOffTokenChannels(0);
	}

	@Override
	protected void setup() {
        p = 0;
        sync(0);
        int i = 0;
        while ( tokens.get(i).getChannel()!=channel ) {
            i++;
            sync(i);
        }
        p = i;
    }

	
Count EOF just once. /** Count EOF just once. */
	public int getNumberOfOnChannelTokens() {
		int n = 0;
		fill();
		for (int i = 0; i < tokens.size(); i++) {
			Token t = tokens.get(i);
			if ( t.getChannel()==channel ) n++;
			if ( t.getType()==Token.EOF ) break;
		}
		return n;
	}

    
Reset this token stream by setting its token source. /** Reset this token stream by setting its token source. */
	@Override
    public void setTokenSource(TokenSource tokenSource) {
        super.setTokenSource(tokenSource);
        channel = Token.DEFAULT_CHANNEL;
    }
}