/**
 * 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.activemq.kaha.impl.index;

import org.apache.activemq.kaha.StoreEntry;

/**
 * A linked list used by IndexItems
 * 
 * @version $Revision: 1.2 $
 */
public final class VMIndexLinkedList implements Cloneable, IndexLinkedList {
    private transient IndexItem root;
    private transient int size;

    /**
     * Constructs an empty list.
     * @param header 
     */
    public VMIndexLinkedList(IndexItem header) {
        this.root = header;
        this.root.next=this.root.prev=this.root;
    }
    
    public  void setRoot(IndexItem newRoot) {
        this.root=newRoot;
    }

    public synchronized IndexItem getRoot() {
        return root;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#getFirst()
     */
    public synchronized IndexItem getFirst() {
        if (size == 0) {
            return null;
        }
        return root.next;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#getLast()
     */
    public synchronized IndexItem getLast() {
        if (size == 0) {
            return null;
        }
        return root.prev;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#removeFirst()
     */
    public synchronized StoreEntry removeFirst() {
        if (size == 0) {
            return null;
        }
        StoreEntry result = root.next;
        remove(root.next);
        return result;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#removeLast()
     */
    public synchronized Object removeLast() {
        if (size == 0) {
            return null;
        }
        StoreEntry result = root.prev;
        remove(root.prev);
        return result;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#addFirst(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized void addFirst(IndexItem item) {
        addBefore(item, root.next);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#addLast(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized void addLast(IndexItem item) {
        addBefore(item, root);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#size()
     */
    public synchronized int size() {
        return size;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#isEmpty()
     */
    public synchronized boolean isEmpty() {
        return size == 0;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#add(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized boolean add(IndexItem item) {
        addBefore(item, root);
        return true;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#clear()
     */
    public synchronized void clear() {
        root.next=root.prev=root;
        size = 0;
    }

    // Positional Access Operations
    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#get(int)
     */
    public synchronized IndexItem get(int index) {
        return entry(index);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#add(int,
     *      org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized void add(int index, IndexItem element) {
        addBefore(element, index == size ? root : entry(index));
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#remove(int)
     */
    public synchronized Object remove(int index) {
        IndexItem e = entry(index);
        remove(e);
        return e;
    }

    /**
     * Return the indexed entry.
     */
    private IndexItem entry(int index) {
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
        }
        IndexItem e = root;
        if (index < size / 2) {
            for (int i = 0; i <= index; i++) {
                e = e.next;
            }
        } else {
            for (int i = size; i > index; i--) {
                e = e.prev;
            }
        }
        return e;
    }

    // Search Operations
    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#indexOf(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized int indexOf(StoreEntry o) {
        int index = 0;
        for (IndexItem e = root.next; e != root; e = e.next) {
            if (o == e) {
                return index;
            }
            index++;
        }
        return -1;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#getNextEntry(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized IndexItem getNextEntry(IndexItem entry) {
        return entry.next != root ? entry.next : null;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#getPrevEntry(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized IndexItem getPrevEntry(IndexItem entry) {
        return entry.prev != root ? entry.prev : null;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#addBefore(org.apache.activemq.kaha.impl.IndexItem,
     *      org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized void addBefore(IndexItem insert, IndexItem e) {
        insert.next = e;
        insert.prev = e.prev;
        insert.prev.next = insert;
        insert.next.prev = insert;
        size++;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.activemq.kaha.impl.IndexLinkedList#remove(org.apache.activemq.kaha.impl.IndexItem)
     */
    public synchronized void remove(IndexItem e) {
        if (e == root || e.equals(root)) {
            return;
        }
        
        e.prev.next = e.next;
        e.next.prev = e.prev;
        size--;
    }

    /**
     * @return clone
     */
    public synchronized Object clone() {
        IndexLinkedList clone = new VMIndexLinkedList(this.root);
        for (IndexItem e = root.next; e != root; e = e.next) {
            clone.add(e);
        }
        return clone;
    }

    public synchronized StoreEntry getEntry(StoreEntry current) {
        return current;
    }

    /**
     * Update the indexes of a StoreEntry
     * 
     * @param current
     */
    public synchronized StoreEntry refreshEntry(StoreEntry current) {
        return current;
    }
}
