/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package java.util.stream;

import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.IntFunction;

/**
 * Factory methods for transforming streams into duplicate-free streams, using
 * {@link Object#equals(Object)} to determine equality.
 *
 * @since 1.8
 */
final class DistinctOps {

 private DistinctOps() { }

 /**
 * Appends a "distinct" operation to the provided stream, and returns the
 * new stream.
 *
 * @param <T> the type of both input and output elements
 * @param upstream a reference stream with element type T
 * @return the new stream
 */
 static <T> ReferencePipeline<T, T> makeRef(AbstractPipeline<?, T, ?> upstream) {
 return new ReferencePipeline.StatefulOp<T, T>(upstream, StreamShape.REFERENCE,
 StreamOpFlag.IS_DISTINCT | StreamOpFlag.NOT_SIZED) {

 <P_IN> Node<T> reduce(PipelineHelper<T> helper, Spliterator<P_IN> spliterator) {
 // If the stream is SORTED then it should also be ORDERED so the following will also
 // preserve the sort order
 TerminalOp<T, LinkedHashSet<T>> reduceOp
 = ReduceOps.<T, LinkedHashSet<T>>makeRef(LinkedHashSet::new, LinkedHashSet::add,
 LinkedHashSet::addAll);
 return Nodes.node(reduceOp.evaluateParallel(helper, spliterator));
 }

 @Override
 <P_IN> Node<T> opEvaluateParallel(PipelineHelper<T> helper,
 Spliterator<P_IN> spliterator,
 IntFunction<T[]> generator) {
 if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
 // No-op
 return helper.evaluate(spliterator, false, generator);
 }
 else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
 return reduce(helper, spliterator);
 }
 else {
 // Holder of null state since ConcurrentHashMap does not support null values
 AtomicBoolean seenNull = new AtomicBoolean(false);
 ConcurrentHashMap<T, Boolean> map = new ConcurrentHashMap<>();
 TerminalOp<T, Void> forEachOp = ForEachOps.makeRef(t -> {
 if (t == null)
 seenNull.set(true);
 else
 map.putIfAbsent(t, Boolean.TRUE);
 }, false);
 forEachOp.evaluateParallel(helper, spliterator);

 // If null has been seen then copy the key set into a HashSet that supports null values
 // and add null
 Set<T> keys = map.keySet();
 if (seenNull.get()) {
 // TODO Implement a more efficient set-union view, rather than copying
 keys = new HashSet<>(keys);
 keys.add(null);
 }
 return Nodes.node(keys);
 }
 }

 @Override
 <P_IN> Spliterator<T> opEvaluateParallelLazy(PipelineHelper<T> helper, Spliterator<P_IN> spliterator) {
 if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
 // No-op
 return helper.wrapSpliterator(spliterator);
 }
 else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
 // Not lazy, barrier required to preserve order
 return reduce(helper, spliterator).spliterator();
 }
 else {
 // Lazy
 return new StreamSpliterators.DistinctSpliterator<>(helper.wrapSpliterator(spliterator));
 }
 }

 @Override
 Sink<T> opWrapSink(int flags, Sink<T> sink) {
 Objects.requireNonNull(sink);

 if (StreamOpFlag.DISTINCT.isKnown(flags)) {
 return sink;
 } else if (StreamOpFlag.SORTED.isKnown(flags)) {
 return new Sink.ChainedReference<T, T>(sink) {
 boolean seenNull;
 T lastSeen;

 @Override
 public void begin(long size) {
 seenNull = false;
 lastSeen = null;
 downstream.begin(-1);
 }

 @Override
 public void end() {
 seenNull = false;
 lastSeen = null;
 downstream.end();
 }

 @Override
 public void accept(T t) {
 if (t == null) {
 if (!seenNull) {
 seenNull = true;
 downstream.accept(lastSeen = null);
 }
 } else if (lastSeen == null || !t.equals(lastSeen)) {
 downstream.accept(lastSeen = t);
 }
 }
 };
 } else {
 return new Sink.ChainedReference<T, T>(sink) {
 Set<T> seen;

 @Override
 public void begin(long size) {
 seen = new HashSet<>();
 downstream.begin(-1);
 }

 @Override
 public void end() {
 seen = null;
 downstream.end();
 }

 @Override
 public void accept(T t) {
 if (!seen.contains(t)) {
 seen.add(t);
 downstream.accept(t);
 }
 }
 };
 }
 }
 };
 }
}