/*
 * 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.chainsaw;

import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


/**
 * CyclicBuffer implementation that is Object generic, and implements the List interface.
 * <p>
 * Original CyclicBuffer @author Ceki G&uuml;lc&uuml;
 * <p>
 * This implementation (although there's very little change) @author Paul Smith &lt;psmith@apache.org&gt;
 */
public class CyclicBufferList extends AbstractList implements List {
    Object[] ea;
    int first;
    int last;
    int numElems;
    int maxSize;

    /**
     * Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
     * <p>
     * The <code>maxSize</code> argument must a positive integer.
     *
     * @param maxSize The maximum number of elements in the buffer.
     */
    public CyclicBufferList(int maxSize) {
        if (maxSize < 1) {
            throw new IllegalArgumentException(
                "The maxSize argument (" + maxSize + ") is not a positive integer.");
        }
        this.maxSize = maxSize;
        clear();
    }

    public CyclicBufferList() {
        this(5000);
    }

    /**
     * Removes the element at the specified position in this list.
     * Shifts any subsequent elements to the left (subtracts one from their
     * indices).
     *
     * @param index the index of the element to removed.
     * @return the element that was removed from the list.
     * @throws IndexOutOfBoundsException if index out of range <tt>(index
     *                                   &lt; 0 || index &gt;= size())</tt>.
     */
    public Object remove(int index) {
        Object oldValue = ea[index];

        List list = new ArrayList(Arrays.asList(ea));
        list.remove(index);
        ea = list.toArray(ea);
        numElems = ea.length;

        numElems--;
        if (--last <= 0) {
            last = numElems;
        }

        if (first == maxSize) {
            first = 0;
        }
        return oldValue;
    }

    public Object set(int index, Object element) {
        Object previous = ea[index];
        ea[index] = element;

        return previous;
    }

    /**
     * Add an <code>event</code> as the last event in the buffer.
     */
    public boolean add(Object event) {
        ea[last] = event;

        if (++last == maxSize) {
            last = 0;
        }

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

        return true;
    }

    /**
     * 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 Object get(int i) {
        if ((i < 0) || (i >= numElems)) {
            return null;
        }

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

    public int getMaxSize() {
        return maxSize;
    }

    public int getLast() {
        return last;
    }

    /**
     * Get the oldest (first) element in the buffer. The oldest element
     * is removed from the buffer.
     */
    public Object get() {
        Object 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 size() {
        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
        }

        Object[] temp = new Object[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;
        }
    }

    /* (non-Javadoc)
     * @see java.util.Collection#clear()
     */
    public void clear() {
        ea = new Object[maxSize];
        first = 0;
        last = 0;
        numElems = 0;

    }

}