/*
 * Copyright (C) 2007 The Guava Authors
 *
 * 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 com.google.common.collect;

import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Objects;

/**
 * Implementation of {@code Multimap} that does not allow duplicate key-value
 * entries and that returns collections whose iterators follow the ordering in
 * which the data was added to the multimap.
 *
 * <p>
 * The collections returned by {@code keySet}, {@code keys}, and {@code
 * asMap} iterate through the keys in the order they were first added to the
 * multimap. Similarly, {@code get}, {@code removeAll}, and {@code
 * replaceValues} return collections that iterate through the values in the
 * order they were added. The collections generated by {@code entries} and
 * {@code values} iterate across the key-value mappings in the order they were
 * added to the multimap.
 *
 * <p>
 * The iteration ordering of the collections generated by {@code keySet},
 * {@code keys}, and {@code asMap} has a few subtleties. As long as the set of
 * keys remains unchanged, adding or removing mappings does not affect the key
 * iteration order. However, if you remove all values associated with a key and
 * then add the key back to the multimap, that key will come last in the key
 * iteration order.
 *
 * <p>
 * The multimap does not store duplicate key-value pairs. Adding a new key-value
 * pair equal to an existing key-value pair has no effect.
 *
 * <p>
 * Keys and values may be null. All optional multimap methods are supported, and
 * all returned views are modifiable.
 *
 * <p>
 * This class is not threadsafe when any concurrent operations update the
 * multimap. Concurrent read operations will work correctly. To allow concurrent
 * update operations, wrap your multimap with a call to
 * {@link Multimaps#synchronizedSetMultimap}.
 *
 * <p>
 * See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap">
 * {@code Multimap}</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true, emulated = true)
public final class LinkedHashMultimap<K, V> extends AbstractSetMultimap<K, V> {

	/**
	 * Creates a new, empty {@code LinkedHashMultimap} with the default initial
	 * capacities.
	 */
	public static <K, V> LinkedHashMultimap<K, V> create() {
		return new LinkedHashMultimap<K, V>(DEFAULT_KEY_CAPACITY, DEFAULT_VALUE_SET_CAPACITY);
	}

	/**
	 * Constructs an empty {@code LinkedHashMultimap} with enough capacity to hold
	 * the specified numbers of keys and values without rehashing.
	 *
	 * @param expectedKeys         the expected number of distinct keys
	 * @param expectedValuesPerKey the expected average number of values per key
	 * @throws IllegalArgumentException if {@code expectedKeys} or {@code
	 *      expectedValuesPerKey}    is negative
	 */
	public static <K, V> LinkedHashMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
		return new LinkedHashMultimap<K, V>(Maps.capacity(expectedKeys), Maps.capacity(expectedValuesPerKey));
	}

	/**
	 * Constructs a {@code LinkedHashMultimap} with the same mappings as the
	 * specified multimap. If a key-value mapping appears multiple times in the
	 * input multimap, it only appears once in the constructed multimap. The new
	 * multimap has the same {@link Multimap#entries()} iteration order as the input
	 * multimap, except for excluding duplicate mappings.
	 *
	 * @param multimap the multimap whose contents are copied to this multimap
	 */
	public static <K, V> LinkedHashMultimap<K, V> create(Multimap<? extends K, ? extends V> multimap) {
		LinkedHashMultimap<K, V> result = create(multimap.keySet().size(), DEFAULT_VALUE_SET_CAPACITY);
		result.putAll(multimap);
		return result;
	}

	private interface ValueSetLink<K, V> {
		ValueSetLink<K, V> getPredecessorInValueSet();

		ValueSetLink<K, V> getSuccessorInValueSet();

		void setPredecessorInValueSet(ValueSetLink<K, V> entry);

		void setSuccessorInValueSet(ValueSetLink<K, V> entry);
	}

	private static <K, V> void succeedsInValueSet(ValueSetLink<K, V> pred, ValueSetLink<K, V> succ) {
		pred.setSuccessorInValueSet(succ);
		succ.setPredecessorInValueSet(pred);
	}

	private static <K, V> void succeedsInMultimap(ValueEntry<K, V> pred, ValueEntry<K, V> succ) {
		pred.setSuccessorInMultimap(succ);
		succ.setPredecessorInMultimap(pred);
	}

	private static <K, V> void deleteFromValueSet(ValueSetLink<K, V> entry) {
		succeedsInValueSet(entry.getPredecessorInValueSet(), entry.getSuccessorInValueSet());
	}

	private static <K, V> void deleteFromMultimap(ValueEntry<K, V> entry) {
		succeedsInMultimap(entry.getPredecessorInMultimap(), entry.getSuccessorInMultimap());
	}

	/**
	 * LinkedHashMultimap entries are in no less than three coexisting linked lists:
	 * a bucket in the hash table for a Set<V> associated with a key, the linked
	 * list of insertion-ordered entries in that Set<V>, and the linked list of
	 * entries in the LinkedHashMultimap as a whole.
	 */
	@VisibleForTesting
	static final class ValueEntry<K, V> extends ImmutableEntry<K, V> implements ValueSetLink<K, V> {
		final int smearedValueHash;

		@Nullable
		ValueEntry<K, V> nextInValueBucket;

		ValueSetLink<K, V> predecessorInValueSet;
		ValueSetLink<K, V> successorInValueSet;

		ValueEntry<K, V> predecessorInMultimap;
		ValueEntry<K, V> successorInMultimap;

		ValueEntry(@Nullable K key, @Nullable V value, int smearedValueHash,
				@Nullable ValueEntry<K, V> nextInValueBucket) {
			super(key, value);
			this.smearedValueHash = smearedValueHash;
			this.nextInValueBucket = nextInValueBucket;
		}

		boolean matchesValue(@Nullable Object v, int smearedVHash) {
			return smearedValueHash == smearedVHash && Objects.equal(getValue(), v);
		}

		@Override
		public ValueSetLink<K, V> getPredecessorInValueSet() {
			return predecessorInValueSet;
		}

		@Override
		public ValueSetLink<K, V> getSuccessorInValueSet() {
			return successorInValueSet;
		}

		@Override
		public void setPredecessorInValueSet(ValueSetLink<K, V> entry) {
			predecessorInValueSet = entry;
		}

		@Override
		public void setSuccessorInValueSet(ValueSetLink<K, V> entry) {
			successorInValueSet = entry;
		}

		public ValueEntry<K, V> getPredecessorInMultimap() {
			return predecessorInMultimap;
		}

		public ValueEntry<K, V> getSuccessorInMultimap() {
			return successorInMultimap;
		}

		public void setSuccessorInMultimap(ValueEntry<K, V> multimapSuccessor) {
			this.successorInMultimap = multimapSuccessor;
		}

		public void setPredecessorInMultimap(ValueEntry<K, V> multimapPredecessor) {
			this.predecessorInMultimap = multimapPredecessor;
		}
	}

	private static final int DEFAULT_KEY_CAPACITY = 16;
	private static final int DEFAULT_VALUE_SET_CAPACITY = 2;
	@VisibleForTesting
	static final double VALUE_SET_LOAD_FACTOR = 1.0;

	@VisibleForTesting
	transient int valueSetCapacity = DEFAULT_VALUE_SET_CAPACITY;
	private transient ValueEntry<K, V> multimapHeaderEntry;

	private LinkedHashMultimap(int keyCapacity, int valueSetCapacity) {
		super(new LinkedHashMap<K, Collection<V>>(keyCapacity));
		checkNonnegative(valueSetCapacity, "expectedValuesPerKey");

		this.valueSetCapacity = valueSetCapacity;
		this.multimapHeaderEntry = new ValueEntry<K, V>(null, null, 0, null);
		succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>
	 * Creates an empty {@code LinkedHashSet} for a collection of values for one
	 * key.
	 *
	 * @return a new {@code LinkedHashSet} containing a collection of values for one
	 *         key
	 */
	@Override
	Set<V> createCollection() {
		return new LinkedHashSet<V>(valueSetCapacity);
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>
	 * Creates a decorated insertion-ordered set that also keeps track of the order
	 * in which key-value pairs are added to the multimap.
	 *
	 * @param key key to associate with values in the collection
	 * @return a new decorated set containing a collection of values for one key
	 */
	@Override
	Collection<V> createCollection(K key) {
		return new ValueSet(key, valueSetCapacity);
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>
	 * If {@code values} is not empty and the multimap already contains a mapping
	 * for {@code key}, the {@code keySet()} ordering is unchanged. However, the
	 * provided values always come last in the {@link #entries()} and
	 * {@link #values()} iteration orderings.
	 */
	@Override
	public Set<V> replaceValues(@Nullable K key, Iterable<? extends V> values) {
		return super.replaceValues(key, values);
	}

	/**
	 * Returns a set of all key-value pairs. Changes to the returned set will update
	 * the underlying multimap, and vice versa. The entries set does not support the
	 * {@code add} or {@code addAll} operations.
	 *
	 * <p>
	 * The iterator generated by the returned set traverses the entries in the order
	 * they were added to the multimap.
	 *
	 * <p>
	 * Each entry is an immutable snapshot of a key-value mapping in the multimap,
	 * taken at the time the entry is returned by a method call to the collection or
	 * its iterator.
	 */
	@Override
	public Set<Map.Entry<K, V>> entries() {
		return super.entries();
	}

	/**
	 * Returns a collection of all values in the multimap. Changes to the returned
	 * collection will update the underlying multimap, and vice versa.
	 *
	 * <p>
	 * The iterator generated by the returned collection traverses the values in the
	 * order they were added to the multimap.
	 */
	@Override
	public Collection<V> values() {
		return super.values();
	}

	@VisibleForTesting
	final class ValueSet extends Sets.ImprovedAbstractSet<V> implements ValueSetLink<K, V> {
		/*
		 * We currently use a fixed load factor of 1.0, a bit higher than normal to
		 * reduce memory consumption.
		 */

		private final K key;
		@VisibleForTesting
		ValueEntry<K, V>[] hashTable;
		private int size = 0;
		private int modCount = 0;

		// We use the set object itself as the end of the linked list, avoiding an
		// unnecessary
		// entry object per key.
		private ValueSetLink<K, V> firstEntry;
		private ValueSetLink<K, V> lastEntry;

		ValueSet(K key, int expectedValues) {
			this.key = key;
			this.firstEntry = this;
			this.lastEntry = this;
			// Round expected values up to a power of 2 to get the table size.
			int tableSize = Hashing.closedTableSize(expectedValues, VALUE_SET_LOAD_FACTOR);

			@SuppressWarnings("unchecked")
			ValueEntry<K, V>[] hashTable = new ValueEntry[tableSize];
			this.hashTable = hashTable;
		}

		private int mask() {
			return hashTable.length - 1;
		}

		@Override
		public ValueSetLink<K, V> getPredecessorInValueSet() {
			return lastEntry;
		}

		@Override
		public ValueSetLink<K, V> getSuccessorInValueSet() {
			return firstEntry;
		}

		@Override
		public void setPredecessorInValueSet(ValueSetLink<K, V> entry) {
			lastEntry = entry;
		}

		@Override
		public void setSuccessorInValueSet(ValueSetLink<K, V> entry) {
			firstEntry = entry;
		}

		@Override
		public Iterator<V> iterator() {
			return new Iterator<V>() {
				ValueSetLink<K, V> nextEntry = firstEntry;
				ValueEntry<K, V> toRemove;
				int expectedModCount = modCount;

				private void checkForComodification() {
					if (modCount != expectedModCount) {
						throw new ConcurrentModificationException();
					}
				}

				@Override
				public boolean hasNext() {
					checkForComodification();
					return nextEntry != ValueSet.this;
				}

				@Override
				public V next() {
					if (!hasNext()) {
						throw new NoSuchElementException();
					}
					ValueEntry<K, V> entry = (ValueEntry<K, V>) nextEntry;
					V result = entry.getValue();
					toRemove = entry;
					nextEntry = entry.getSuccessorInValueSet();
					return result;
				}

				@Override
				public void remove() {
					checkForComodification();
					checkRemove(toRemove != null);
					ValueSet.this.remove(toRemove.getValue());
					expectedModCount = modCount;
					toRemove = null;
				}
			};
		}

		@Override
		public int size() {
			return size;
		}

		@Override
		public boolean contains(@Nullable Object o) {
			int smearedHash = Hashing.smearedHash(o);
			for (ValueEntry<K, V> entry = hashTable[smearedHash
					& mask()]; entry != null; entry = entry.nextInValueBucket) {
				if (entry.matchesValue(o, smearedHash)) {
					return true;
				}
			}
			return false;
		}

		@Override
		public boolean add(@Nullable V value) {
			int smearedHash = Hashing.smearedHash(value);
			int bucket = smearedHash & mask();
			ValueEntry<K, V> rowHead = hashTable[bucket];
			for (ValueEntry<K, V> entry = rowHead; entry != null; entry = entry.nextInValueBucket) {
				if (entry.matchesValue(value, smearedHash)) {
					return false;
				}
			}

			ValueEntry<K, V> newEntry = new ValueEntry<K, V>(key, value, smearedHash, rowHead);
			succeedsInValueSet(lastEntry, newEntry);
			succeedsInValueSet(newEntry, this);
			succeedsInMultimap(multimapHeaderEntry.getPredecessorInMultimap(), newEntry);
			succeedsInMultimap(newEntry, multimapHeaderEntry);
			hashTable[bucket] = newEntry;
			size++;
			modCount++;
			rehashIfNecessary();
			return true;
		}

		private void rehashIfNecessary() {
			if (Hashing.needsResizing(size, hashTable.length, VALUE_SET_LOAD_FACTOR)) {
				@SuppressWarnings("unchecked")
				ValueEntry<K, V>[] hashTable = new ValueEntry[this.hashTable.length * 2];
				this.hashTable = hashTable;
				int mask = hashTable.length - 1;
				for (ValueSetLink<K, V> entry = firstEntry; entry != this; entry = entry.getSuccessorInValueSet()) {
					ValueEntry<K, V> valueEntry = (ValueEntry<K, V>) entry;
					int bucket = valueEntry.smearedValueHash & mask;
					valueEntry.nextInValueBucket = hashTable[bucket];
					hashTable[bucket] = valueEntry;
				}
			}
		}

		@Override
		public boolean remove(@Nullable Object o) {
			int smearedHash = Hashing.smearedHash(o);
			int bucket = smearedHash & mask();
			ValueEntry<K, V> prev = null;
			for (ValueEntry<K, V> entry = hashTable[bucket]; entry != null; prev = entry, entry = entry.nextInValueBucket) {
				if (entry.matchesValue(o, smearedHash)) {
					if (prev == null) {
						// first entry in the bucket
						hashTable[bucket] = entry.nextInValueBucket;
					} else {
						prev.nextInValueBucket = entry.nextInValueBucket;
					}
					deleteFromValueSet(entry);
					deleteFromMultimap(entry);
					size--;
					modCount++;
					return true;
				}
			}
			return false;
		}

		@Override
		public void clear() {
			Arrays.fill(hashTable, null);
			size = 0;
			for (ValueSetLink<K, V> entry = firstEntry; entry != this; entry = entry.getSuccessorInValueSet()) {
				ValueEntry<K, V> valueEntry = (ValueEntry<K, V>) entry;
				deleteFromMultimap(valueEntry);
			}
			succeedsInValueSet(this, this);
			modCount++;
		}
	}

	@Override
	Iterator<Map.Entry<K, V>> entryIterator() {
		return new Iterator<Map.Entry<K, V>>() {
			ValueEntry<K, V> nextEntry = multimapHeaderEntry.successorInMultimap;
			ValueEntry<K, V> toRemove;

			@Override
			public boolean hasNext() {
				return nextEntry != multimapHeaderEntry;
			}

			@Override
			public Map.Entry<K, V> next() {
				if (!hasNext()) {
					throw new NoSuchElementException();
				}
				ValueEntry<K, V> result = nextEntry;
				toRemove = result;
				nextEntry = nextEntry.successorInMultimap;
				return result;
			}

			@Override
			public void remove() {
				checkRemove(toRemove != null);
				LinkedHashMultimap.this.remove(toRemove.getKey(), toRemove.getValue());
				toRemove = null;
			}
		};
	}

	@Override
	Iterator<V> valueIterator() {
		return Maps.valueIterator(entryIterator());
	}

	@Override
	public void clear() {
		super.clear();
		succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
	}

	/**
	 * @serialData the expected values per key, the number of distinct keys, the
	 *             number of entries, and the entries in order
	 */
	@GwtIncompatible("java.io.ObjectOutputStream")
	private void writeObject(ObjectOutputStream stream) throws IOException {
		stream.defaultWriteObject();
		stream.writeInt(valueSetCapacity);
		stream.writeInt(keySet().size());
		for (K key : keySet()) {
			stream.writeObject(key);
		}
		stream.writeInt(size());
		for (Map.Entry<K, V> entry : entries()) {
			stream.writeObject(entry.getKey());
			stream.writeObject(entry.getValue());
		}
	}

	@GwtIncompatible("java.io.ObjectInputStream")
	private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
		stream.defaultReadObject();
		multimapHeaderEntry = new ValueEntry<K, V>(null, null, 0, null);
		succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
		valueSetCapacity = stream.readInt();
		int distinctKeys = stream.readInt();
		Map<K, Collection<V>> map = new LinkedHashMap<K, Collection<V>>(Maps.capacity(distinctKeys));
		for (int i = 0; i < distinctKeys; i++) {
			@SuppressWarnings("unchecked")
			K key = (K) stream.readObject();
			map.put(key, createCollection(key));
		}
		int entries = stream.readInt();
		for (int i = 0; i < entries; i++) {
			@SuppressWarnings("unchecked")
			K key = (K) stream.readObject();
			@SuppressWarnings("unchecked")
			V value = (V) stream.readObject();
			map.get(key).add(value);
		}
		setMap(map);
	}

	@GwtIncompatible("java serialization not supported")
	private static final long serialVersionUID = 1;
}
