/*
* 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.flink.api.common.operators.util;
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.typeutils.TypeComparator;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.util.TraversableOnceException;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
/**
* The KeyValueIterator returns a key and all values that belong to the key (share the same key).
*/
@Internal
public final class ListKeyGroupedIterator<E> {
private final List<E> input;
private final TypeSerializer<E> serializer; // != null if the elements should be copied
private final TypeComparator<E> comparator;
private ValuesIterator valuesIterator;
private int currentPosition = 0;
private E lookahead;
private boolean done;
/**
* Initializes the ListKeyGroupedIterator..
*
* @param input The list with the input elements.
* @param comparator The comparator for the data type iterated over.
*/
public ListKeyGroupedIterator(List<E> input, TypeSerializer<E> serializer, TypeComparator<E> comparator) {
if (input == null || comparator == null) {
throw new NullPointerException();
}
this.input = input;
this.serializer = serializer;
this.comparator = comparator;
this.done = input.isEmpty() ? true : false;
}
/**
* Moves the iterator to the next key. This method may skip any values that have not yet been returned by the
* iterator created by the {@link #getValues()} method. Hence, if called multiple times it "removes" key groups.
*
* @return true, if the input iterator has an other group of records with the same key.
*/
public boolean nextKey() throws IOException {
if (lookahead != null) {
// common case: whole value-iterator was consumed and a new key group is available.
this.comparator.setReference(this.lookahead);
this.valuesIterator.next = this.lookahead;
this.lookahead = null;
this.valuesIterator.iteratorAvailable = true;
return true;
}
// first element, empty/done, or the values iterator was not entirely consumed
if (this.done) {
return false;
}
if (this.valuesIterator != null) {
// values was not entirely consumed. move to the next key
// Required if user code / reduce() method did not read the whole value iterator.
E next;
while (true) {
if (currentPosition < input.size() && (next = this.input.get(currentPosition++)) != null) {
if (!this.comparator.equalToReference(next)) {
// the keys do not match, so we have a new group. store the current key
this.comparator.setReference(next);
this.valuesIterator.next = next;
this.valuesIterator.iteratorAvailable = true;
return true;
}
}
else {
// input exhausted
this.valuesIterator.next = null;
this.valuesIterator = null;
this.done = true;
return false;
}
}
}
else {
// first element
// get the next element
E first = input.get(currentPosition++);
if (first != null) {
this.comparator.setReference(first);
this.valuesIterator = new ValuesIterator(first, serializer);
return true;
}
else {
// empty input, set everything null
this.done = true;
return false;
}
}
}
private E advanceToNext() {
if (currentPosition < input.size()) {
E next = input.get(currentPosition++);
if (comparator.equalToReference(next)) {
// same key
return next;
} else {
// moved to the next key, no more values here
lookahead = next;
return null;
}
}
else {
// backing iterator is consumed
this.done = true;
return null;
}
}
/**
* Returns an iterator over all values that belong to the current key. The iterator is initially <code>null</code>
* (before the first call to {@link #nextKey()} and after all keys are consumed. In general, this method returns
* always a non-null value, if a previous call to {@link #nextKey()} return <code>true</code>.
*
* @return Iterator over all values that belong to the current key.
*/
public ValuesIterator getValues() {
return this.valuesIterator;
}
// --------------------------------------------------------------------------------------------
public final class ValuesIterator implements Iterator<E>, Iterable<E> {
private E next;
private boolean iteratorAvailable = true;
private final TypeSerializer<E> serializer;
private ValuesIterator(E first, TypeSerializer<E> serializer) {
this.next = first;
this.serializer = serializer;
}
@Override
public boolean hasNext() {
return next != null;
}
@Override
public E next() {
if (this.next != null) {
E current = this.next;
this.next = ListKeyGroupedIterator.this.advanceToNext();
return serializer.copy(current);
} else {
throw new NoSuchElementException();
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public Iterator<E> iterator() {
if (iteratorAvailable) {
iteratorAvailable = false;
return this;
} else {
throw new TraversableOnceException();
}
}
public E getCurrent() {
return next;
}
}
}