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

 Redistribution and use in source and binary forms, with or without
 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
 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
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package org.antlr.runtime.misc;

import org.antlr.runtime.Token;

import java.util.NoSuchElementException;

public abstract class LookaheadStream<T> extends FastQueue<T> {
    public static final int UNINITIALIZED_EOF_ELEMENT_INDEX = Integer.MAX_VALUE;

    protected int currentElementIndex = 0;

    protected T prevElement;

    public T eof = null;

    protected int lastMarker;

    protected int markDepth = 0;

    public void reset() {
        super.reset();
        currentElementIndex = 0;
        p = 0;
        prevElement=null;        
    }
    
    public abstract T nextElement();

    public abstract boolean isEOF(T o);

    public T remove() {
        T o = elementAt(0);
        p++;
        // have we hit end of buffer and not backtracking?
        if ( p == data.size() && markDepth==0 ) {
            // if so, it's an opportunity to start filling at index 0 again
            clear(); // size goes to 0, but retains memory
        }
        return o;
    }

    public void consume() {
        syncAhead(1);
        prevElement = remove();
        currentElementIndex++;
    }

    protected void syncAhead(int need) {
        int n = (p+need-1) - data.size() + 1; // how many more elements we need?
        if ( n > 0 ) fill(n);                 // out of elements?
    }

    public void fill(int n) {
        for (int i=1; i<=n; i++) {
            T o = nextElement();
            if ( isEOF(o) ) eof = o;
            data.add(o);
        }
    }

    public int size() { throw new UnsupportedOperationException("streams are of unknown size"); }

    public T LT(int k) {
                if ( k==0 ) {
                        return null;
                }
                if ( k<0 ) return LB(-k);
                //System.out.print("LT(p="+p+","+k+")=");
        syncAhead(k);
        if ( (p+k-1) > data.size() ) return eof;
        return elementAt(k-1);
        }

    public int index() { return currentElementIndex; }

        public int mark() {
        markDepth++;
        lastMarker = p; // track where we are in buffer not absolute token index
        return lastMarker;
        }

        public void release(int marker) {
                // no resources to release
        }

        public void rewind(int marker) {
        markDepth--;
        seek(marker); // assume marker is top
        // release(marker); // waste of call; it does nothing in this class
    }

        public void rewind() {
        seek(lastMarker); // rewind but do not release marker
    }

    public void seek(int index) { p = index; }

    protected T LB(int k) {
        if ( k==1 ) return prevElement;
        throw new NoSuchElementException("can't look backwards more than one token in this stream");
    }
}

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