src/main/java/org/apache/sling/query/impl/util/LazyList.java

/*-
 * 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.sling.query.impl.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;

public class LazyList<E> implements List<E> {

    private final class LazyListIterator implements ListIterator<E> {
        private int index = 0;

        private LazyListIterator() {
            this.index = 0;
        }

        private LazyListIterator(int index) {
            this.index = index;
        }

        @Override
        public boolean hasNext() {
            fillToSize(index + 1);
            return arrayList.size() > index;
        }

        @Override
        public E next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            return arrayList.get(index++);
        }

        @Override
        public boolean hasPrevious() {
            return index > 0;
        }

        @Override
        public E previous() {
            if (!hasPrevious()) {
                throw new NoSuchElementException();
            }
            fillToSize(index);
            return arrayList.get(--index);
        }

        @Override
        public int nextIndex() {
            return index;
        }

        @Override
        public int previousIndex() {
            return index - 1;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }

        @Override
        public void set(E e) {
            throw new UnsupportedOperationException();
        }

        @Override
        public void add(E e) {
            throw new UnsupportedOperationException();
        }
    }

    private final List<E> arrayList;

    private final Iterator<E> iterator;

    public LazyList(Iterator<E> iterator) {
        this.arrayList = new ArrayList<E>();
        this.iterator = iterator;
    }

    private void fillAll() {
        while (fillNext() != -1)
            ;
    }

    private void fillToSize(int size) {
        for (int s = arrayList.size(); s < size; s++) {
            if (fillNext() == -1) {
                break;
            }
        }
    }

    private int fillNext() {
        if (iterator.hasNext()) {
            E element = iterator.next();
            arrayList.add(element);
            return arrayList.size() - 1;
        }
        return -1;
    }

    @Override
    public int size() {
        fillAll();
        return arrayList.size();
    }

    @Override
    public boolean isEmpty() {
        return arrayList.isEmpty() && !iterator.hasNext();
    }

    @Override
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }

    @Override
    public Iterator<E> iterator() {
        return new LazyListIterator();
    }

    @Override
    public Object[] toArray() {
        fillAll();
        return arrayList.toArray();
    }

    @Override
    public <T> T[] toArray(T[] a) {
        fillAll();
        return arrayList.toArray(a);
    }

    @Override
    public boolean containsAll(Collection<?> c) {
        for (Object o : c) {
            if (!contains(o)) {
                return false;
            }
        }
        return true;
    }

    @Override
    public E get(int index) {
        fillToSize(index + 1);
        return arrayList.get(index);
    }

    @Override
    public int indexOf(Object o) {
        int index = arrayList.indexOf(o);
        if (index > -1) {
            return index;
        }
        int addedIndex;
        while ((addedIndex = fillNext()) != -1) {
            E element = arrayList.get(addedIndex);
            if (element == null && o == null) {
                return addedIndex;
            } else if (element != null && element.equals(o)) {
                return addedIndex;
            }
        }
        return -1;
    }

    @Override
    public int lastIndexOf(Object o) {
        fillAll();
        return arrayList.lastIndexOf(o);
    }

    @Override
    public ListIterator<E> listIterator() {
        return new LazyListIterator();
    }

    @Override
    public ListIterator<E> listIterator(int index) {
        return new LazyListIterator(index);
    }

    @Override
    public List<E> subList(int fromIndex, int toIndex) {
        fillToSize(toIndex);
        return arrayList.subList(fromIndex, toIndex);
    }

    @Override
    public boolean equals(Object o) {
        fillAll();
        return arrayList.equals(o);
    }

    @Override
    public int hashCode() {
        fillAll();
        return arrayList.hashCode();
    }

    @Override
    public boolean add(E e) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean remove(Object o) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean addAll(Collection<? extends E> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean addAll(int index, Collection<? extends E> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean removeAll(Collection<?> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean retainAll(Collection<?> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void clear() {
        throw new UnsupportedOperationException();
    }

    @Override
    public E set(int index, E element) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void add(int index, E element) {
        throw new UnsupportedOperationException();
    }

    @Override
    public E remove(int index) {
        throw new UnsupportedOperationException();
    }

}