/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j.helpers;

import org.apache.log4j.spi.LoggingEvent;

/**
 * 
 * CyclicBuffer is used by other appenders to hold {@link LoggingEvent
 * LoggingEvents} for immediate or differed display.
 * 
 * <p>
 * This buffer gives read access to any element in the buffer not just the first
 * or last element.
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @since 0.9.0
 * 
 */
public class CyclicBuffer {

    LoggingEvent[] ea;
    int first;
    int last;
    int numElems;
    int maxSize;

    /**
     * Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
     * 
     * The <code>maxSize</code> argument must a positive integer.
     * 
     * @param maxSize The maximum number of elements in the buffer.
     */
    public CyclicBuffer(int maxSize) throws IllegalArgumentException {
	if (maxSize < 1) {
	    throw new IllegalArgumentException("The maxSize argument (" + maxSize + ") is not a positive integer.");
	}
	this.maxSize = maxSize;
	ea = new LoggingEvent[maxSize];
	first = 0;
	last = 0;
	numElems = 0;
    }

    /**
     * Add an <code>event</code> as the last event in the buffer.
     * 
     */
    public void add(LoggingEvent event) {
	ea[last] = event;
	if (++last == maxSize)
	    last = 0;

	if (numElems < maxSize)
	    numElems++;
	else if (++first == maxSize)
	    first = 0;
    }

    /**
     * Get the <i>i</i>th oldest event currently in the buffer. If <em>i</em> is
     * outside the range 0 to the number of elements currently in the buffer, then
     * <code>null</code> is returned.
     * 
     * 
     */
    public LoggingEvent get(int i) {
	if (i < 0 || i >= numElems)
	    return null;

	return ea[(first + i) % maxSize];
    }

    public int getMaxSize() {
	return maxSize;
    }

    /**
     * Get the oldest (first) element in the buffer. The oldest element is removed
     * from the buffer.
     */
    public LoggingEvent get() {
	LoggingEvent r = null;
	if (numElems > 0) {
	    numElems--;
	    r = ea[first];
	    ea[first] = null;
	    if (++first == maxSize)
		first = 0;
	}
	return r;
    }

    /**
     * Get the number of elements in the buffer. This number is guaranteed to be in
     * the range 0 to <code>maxSize</code> (inclusive).
     */
    public int length() {
	return numElems;
    }

    /**
     * Resize the cyclic buffer to <code>newSize</code>.
     * 
     * @throws IllegalArgumentException if <code>newSize</code> is negative.
     */
    public void resize(int newSize) {
	if (newSize < 0) {
	    throw new IllegalArgumentException("Negative array size [" + newSize + "] not allowed.");
	}
	if (newSize == numElems)
	    return; // nothing to do

	LoggingEvent[] temp = new LoggingEvent[newSize];

	int loopLen = newSize < numElems ? newSize : numElems;

	for (int i = 0; i < loopLen; i++) {
	    temp[i] = ea[first];
	    ea[first] = null;
	    if (++first == numElems)
		first = 0;
	}
	ea = temp;
	first = 0;
	numElems = loopLen;
	maxSize = newSize;
	if (loopLen == newSize) {
	    last = 0;
	} else {
	    last = loopLen;
	}
    }
}
