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Groovy: A powerful, dynamic language for the JVM
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/*  

   Licensed 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.codehaus.groovy.util;

import java.util.ArrayList;
import java.util.Iterator;

/**
 * This class provides a very simple linked list of memory managed elements.
 * This class does not support concurrent modifications nor will it check 
 * for them. This class is also not thread safe.
 * 
 * @author Jochen Theodorou
 * @since 1.6
 */
public class ManagedLinkedList {
    
    private final class Element extends ManagedReference {
        Element next;
        Element previous;
        public Element(ReferenceBundle bundle, V value) {
            super(bundle, value);            
        }
        public void finalizeReference() {
            if (previous!=null && previous.next!=null) {
                previous.next = next;
            }
            if (next!=null && next.previous!=null) {
                next.previous = previous;
            }
            if (this==head) head = next;
            next=null;
            if (this==tail) tail = previous;
            previous=null;
            super.finalizeReference();
        }
    }
    
    private final class Iter implements Iterator {
        private Element current;
        private boolean currentHandled=false;
        Iter() {
            current = head;
        }
        public boolean hasNext() {
            if (current==null) return false;
            if (currentHandled) {
                return current.next!=null;
            } else {
                return current!=null;
            }
        }
        public T next() {
            if (currentHandled) current = current.next;
            currentHandled=true;
            if (current==null)  return null;
            return current.get();
        }
        public void remove() {
            if (current!=null) current.finalizeReference();
        }
        
    }
    
    private Element tail;
    private Element head;
    private ReferenceBundle bundle;
    
    public ManagedLinkedList(ReferenceBundle bundle) {
        this.bundle = bundle;
    }
    
    /**
     * adds a value to the list
     * @param value the value
     */
    public void add(T value) {
        Element element = new Element(bundle,value);
        element.previous = tail;
        if (tail!=null) tail.next = element;
        tail = element;
        if (head==null) head=element;
    }
    
    /**
     * returns an iterator, which allows the removal of elements.
     * The next() method of the iterator may return null values. This
     * is especially the case if the value was removed
     * @return the Iterator
     */
    public Iterator iterator() {
        return new Iter();
    }
    
    /**
     * this will return an array of non null elements of this list
     * @return the array
     */
    public T[] toArray(T[] tArray) {
        ArrayList array = new ArrayList(100);
        for (Iterator it = iterator(); it.hasNext();) {
            T val = it.next();
            if (val!=null) array.add(val);
        }
        return array.toArray(tArray);
    }
    
    /**
     * returns if the list is empty
     * @return true if the list is empty
     */
    public boolean isEmpty() {
        return head==null;
    }
}