/*
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 Copyright (c) 2005-2009 Terence Parr
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     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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package org.antlr.runtime.misc;

import java.util.List;
import java.util.ArrayList;
import java.util.NoSuchElementException;

A queue that can dequeue and get(i) in O(1) and grow arbitrarily large.
 A linked list is fast at dequeue but slow at get(i).  An array is
 the reverse.  This is O(1) for both operations.
 List grows until you dequeue last element at end of buffer. Then
 it resets to start filling at 0 again.  If adds/removes are balanced, the
 buffer will not grow too large.
 No iterator stuff as that's not how we'll use it.
/** A queue that can dequeue and get(i) in O(1) and grow arbitrarily large.
 *  A linked list is fast at dequeue but slow at get(i).  An array is
 *  the reverse.  This is O(1) for both operations.
 *
 *  List grows until you dequeue last element at end of buffer. Then
 *  it resets to start filling at 0 again.  If adds/removes are balanced, the
 *  buffer will not grow too large.
 *
 *  No iterator stuff as that's not how we'll use it.
 */
public class FastQueue<T> {
    
dynamically-sized buffer of elements /** dynamically-sized buffer of elements */
    protected List<T> data = new ArrayList<T>();
    
index of next element to fill /** index of next element to fill */
    protected int p = 0;
	protected int range = -1; // how deep have we gone?	

    public void reset() { clear(); }
    public void clear() { p = 0; data.clear(); }

    
Get and remove first element in queue /** Get and remove first element in queue */
    public T remove() {
        T o = elementAt(0);
        p++;
        // have we hit end of buffer?
        if ( p == data.size() ) {
            // 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 add(T o) { data.add(o); }

    public int size() { return data.size() - p; }

	public int range() { return range; }

    public T head() { return elementAt(0); }

    
Return element i elements ahead of current element. i==0 gets current element. This is not an absolute index into FastQueue<T>.data since p defines the start of the real list. /**
     * Return element {@code i} elements ahead of current element. {@code i==0}
     * gets current element. This is not an absolute index into {@link #data}
     * since {@code p} defines the start of the real list.
     */
    public T elementAt(int i) {
		int absIndex = p + i;
		if ( absIndex >= data.size() ) {
            throw new NoSuchElementException("queue index "+ absIndex +" > last index "+(data.size()-1));
        }
        if ( absIndex < 0 ) {
            throw new NoSuchElementException("queue index "+ absIndex +" < 0");
        }
		if ( absIndex>range ) range = absIndex;
        return data.get(absIndex);
    }

    
Return string of current buffer contents; non-destructive /** Return string of current buffer contents; non-destructive */
	@Override
    public String toString() {
        StringBuilder buf = new StringBuilder();
        int n = size();
        for (int i=0; i<n; i++) {
            buf.append(elementAt(i));
            if ( (i+1)<n ) buf.append(" ");
        }
        return buf.toString();
    }
}