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package org.dcache.util;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import java.util.stream.Stream;
/**
* <p>A list whose elements, once assigned, cannot be re-indexed.</p>
*
* <p>Add operations append to the end of the list as usual, but removes
* do not collapse the list. Hence index numbers are monotonically
* increasing at each add.</p>
*
* <p>Iteration is based on a realized list detached from the underlying
* data structures, and thus side-effects through the iterator will
* not change the list itself.</p>
*
* <p>This realized (iterable) list is guaranteed to respect the order
* of insertion, but the value returned by indexOf() may not be
* equal to the implicit index of the iterable list returned for
* iteration or streaming unless the value of <code>includeNulls</code>
* is set to true (false by default). In that case, it then becomes
* imperative that the caller check for <code>null</code> values, as
* any index assigned to an element which has been removed will be
* marked by <code>null</code>.</p>
*
* <p>Any operation which requires the reassignment of list positions
* to existing elements is unsupported. Mutation of the list via the
* <code>set</code> operation is also unsupported.</p>
*
* <p>This list contains unique elements. Adding the same element twice
* overwrites the previous index. Nulls cannot be added to the list.</p>
*
* <p>Not thread-safe.</p>
*/
public final class NonReindexableList<E> implements List<E> {
private static final String UNSUPPORTED_ERROR_MSG
= "This list can only be modified by appending or removing.";
private final Map<E, Integer> index = new HashMap<>();
private final Map<Integer, E> list = new HashMap<>();
private int counter = 0;
private boolean includeNulls = false;
@Override
public boolean add(E e) {
return append(e);
}
@Override
public void add(int index, E element) {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
@Override
public boolean addAll(Collection<? extends E> c) {
int added = appendAll(c);
return added > 0;
}
@Override
public boolean addAll(int index, Collection<? extends E> c) {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
@Override
public void clear() {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
@Override
public boolean contains(Object o) {
return index.containsKey(o);
}
@Override
public boolean containsAll(Collection<?> collection) {
for (Object o : collection) {
if (!index.containsKey(o)) {
return false;
}
}
return true;
}
@Override
public boolean equals(Object o) {
return list.values().equals(o);
}
@Override
public void forEach(Consumer<? super E> action) {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
@Override
public E get(int index) {
if (index >= counter) {
throw new IndexOutOfBoundsException(index + " >= " + counter);
}
E element = list.get(index);
if (element == null && !includeNulls) {
throw new NoSuchElementException("at index " + index);
}
return element;
}
@Override
public int hashCode() {
return list.hashCode();
}
@Override
public int indexOf(Object o) {
if (index.containsKey(o)) {
return index.get(o);
}
/*
* Differs from the normal list, which would return -1.
*/
throw new NoSuchElementException(String.valueOf(o));
}
@Override
public boolean isEmpty() {
return list.isEmpty();
}
public boolean isIncludeNulls() {
return includeNulls;
}
@Override
public Iterator<E> iterator() {
return realizeList().iterator();
}
@Override
public int lastIndexOf(Object o) {
return indexOf(o);
}
@Override
public ListIterator<E> listIterator() {
return realizeList().listIterator();
}
@Override
public ListIterator<E> listIterator(int index) {
return realizeList().listIterator(index);
}
@Override
public Stream<E> parallelStream() {
return realizeList().parallelStream();
}
@Override
public boolean remove(Object element) {
Integer i = index.remove(element);
if (i != null) {
list.remove(i);
return true;
}
return false;
}
@Override
public E remove(int index) {
E element = list.remove(index);
if (element != null) {
this.index.remove(element);
}
return element;
}
@Override
public boolean removeAll(Collection<?> c) {
int changes = 0;
for (Object o : c) {
if (remove(o)) {
++changes;
}
}
return changes > 0;
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
throw new UnsupportedOperationException();
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
@Override
public boolean retainAll(Collection<?> c) {
throw new UnsupportedOperationException();
}
@Override
public E set(int index, E element) {
throw new UnsupportedOperationException(UNSUPPORTED_ERROR_MSG);
}
public void setIncludeNulls(boolean includeNulls) {
this.includeNulls = includeNulls;
}
@Override
public int size() {
return list.size();
}
@Override
public void sort(Comparator<? super E> c) {
throw new UnsupportedOperationException(
"This list uses a fixed monotonically increasing "
+ "order of insertion indexing.");
}
@Override
public Spliterator<E> spliterator() {
return realizeList().spliterator();
}
@Override
public Stream<E> stream() {
return realizeList().stream();
}
@Override
public List<E> subList(int fromIndex, int toIndex) {
return realizeList().subList(fromIndex, toIndex);
}
@Override
public Object[] toArray() {
return list.values().toArray();
}
@Override
public <T> T[] toArray(T[] a) {
return list.values().toArray(a);
}
private boolean append(E element) {
if (element == null) {
throw new IllegalArgumentException("Cannot add null "
+ "values to this list.");
}
if (index.containsKey(element)) {
return false;
}
int next = counter++;
list.put(next, element);
index.put(element, next);
return true;
}
private int appendAll(Collection<? extends E> collection) {
int added = 0;
for (E element: collection) {
if (append(element)) {
++added;
}
}
return added;
}
private List<E> realizeList() {
List<E> iterable = new ArrayList<>();
for (int i = 0; i < counter; i++) {
E element = list.get(i);
if (element != null || includeNulls) {
iterable.add(element);
}
}
return iterable;
}
}