/*
 * Copyright (C) 2008 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.base.Preconditions.checkNotNull;

import java.io.Serializable;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.primitives.Ints;

/**
 * An immutable hash-based multiset. Does not permit null elements.
 *
 * <p>
 * Its iterator orders elements according to the first appearance of the element
 * among the items passed to the factory method or builder. When the multiset
 * contains multiple instances of an element, those instances are consecutive in
 * the iteration order.
 *
 * <p>
 * See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/ImmutableCollectionsExplained">
 * immutable collections</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
// TODO(user): write an efficient asList() implementation
public abstract class ImmutableMultiset<E> extends ImmutableCollection<E> implements Multiset<E> {

	private static final ImmutableMultiset<Object> EMPTY = new RegularImmutableMultiset<Object>(
			ImmutableMap.<Object, Integer>of(), 0);

	/**
	 * Returns the empty immutable multiset.
	 */
	@SuppressWarnings("unchecked") // all supported methods are covariant
	public static <E> ImmutableMultiset<E> of() {
		return (ImmutableMultiset<E>) EMPTY;
	}

	/**
	 * Returns an immutable multiset containing a single element.
	 *
	 * @throws NullPointerException if {@code element} is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") // generic array created but never written
	public static <E> ImmutableMultiset<E> of(E element) {
		return copyOfInternal(element);
	}

	/**
	 * Returns an immutable multiset containing the given elements, in order.
	 *
	 * @throws NullPointerException if any element is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") //
	public static <E> ImmutableMultiset<E> of(E e1, E e2) {
		return copyOfInternal(e1, e2);
	}

	/**
	 * Returns an immutable multiset containing the given elements, in order.
	 *
	 * @throws NullPointerException if any element is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") //
	public static <E> ImmutableMultiset<E> of(E e1, E e2, E e3) {
		return copyOfInternal(e1, e2, e3);
	}

	/**
	 * Returns an immutable multiset containing the given elements, in order.
	 *
	 * @throws NullPointerException if any element is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") //
	public static <E> ImmutableMultiset<E> of(E e1, E e2, E e3, E e4) {
		return copyOfInternal(e1, e2, e3, e4);
	}

	/**
	 * Returns an immutable multiset containing the given elements, in order.
	 *
	 * @throws NullPointerException if any element is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") //
	public static <E> ImmutableMultiset<E> of(E e1, E e2, E e3, E e4, E e5) {
		return copyOfInternal(e1, e2, e3, e4, e5);
	}

	/**
	 * Returns an immutable multiset containing the given elements, in order.
	 *
	 * @throws NullPointerException if any element is null
	 * @since 6.0 (source-compatible since 2.0)
	 */
	@SuppressWarnings("unchecked") //
	public static <E> ImmutableMultiset<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E... others) {
		return new Builder<E>().add(e1).add(e2).add(e3).add(e4).add(e5).add(e6).add(others).build();
	}

	/**
	 * Returns an immutable multiset containing the given elements.
	 *
	 * <p>
	 * The multiset is ordered by the first occurrence of each element. For example,
	 * {@code ImmutableMultiset.copyOf([2, 3, 1, 3])} yields a multiset with
	 * elements in the order {@code 2, 3, 3, 1}.
	 *
	 * @throws NullPointerException if any of {@code elements} is null
	 * @since 6.0
	 */
	public static <E> ImmutableMultiset<E> copyOf(E[] elements) {
		return copyOf(Arrays.asList(elements));
	}

	/**
	 * Returns an immutable multiset containing the given elements.
	 *
	 * <p>
	 * The multiset is ordered by the first occurrence of each element. For example,
	 * {@code ImmutableMultiset.copyOf(Arrays.asList(2, 3, 1, 3))} yields a multiset
	 * with elements in the order {@code 2, 3, 3, 1}.
	 *
	 * <p>
	 * Despite the method name, this method attempts to avoid actually copying the
	 * data when it is safe to do so. The exact circumstances under which a copy
	 * will or will not be performed are undocumented and subject to change.
	 *
	 * <p>
	 * <b>Note:</b> Despite what the method name suggests, if {@code elements} is an
	 * {@code ImmutableMultiset}, no copy will actually be performed, and the given
	 * multiset itself will be returned.
	 *
	 * @throws NullPointerException if any of {@code elements} is null
	 */
	public static <E> ImmutableMultiset<E> copyOf(Iterable<? extends E> elements) {
		if (elements instanceof ImmutableMultiset) {
			@SuppressWarnings("unchecked") // all supported methods are covariant
			ImmutableMultiset<E> result = (ImmutableMultiset<E>) elements;
			if (!result.isPartialView()) {
				return result;
			}
		}

		Multiset<? extends E> multiset = (elements instanceof Multiset) ? Multisets.cast(elements)
				: LinkedHashMultiset.create(elements);

		return copyOfInternal(multiset);
	}

	private static <E> ImmutableMultiset<E> copyOfInternal(E... elements) {
		return copyOf(Arrays.asList(elements));
	}

	private static <E> ImmutableMultiset<E> copyOfInternal(Multiset<? extends E> multiset) {
		return copyFromEntries(multiset.entrySet());
	}

	static <E> ImmutableMultiset<E> copyFromEntries(Collection<? extends Entry<? extends E>> entries) {
		long size = 0;
		ImmutableMap.Builder<E, Integer> builder = ImmutableMap.builder();
		for (Entry<? extends E> entry : entries) {
			int count = entry.getCount();
			if (count > 0) {
				// Since ImmutableMap.Builder throws an NPE if an element is null, no
				// other null checks are needed.
				builder.put(entry.getElement(), count);
				size += count;
			}
		}

		if (size == 0) {
			return of();
		}
		return new RegularImmutableMultiset<E>(builder.build(), Ints.saturatedCast(size));
	}

	/**
	 * Returns an immutable multiset containing the given elements.
	 *
	 * <p>
	 * The multiset is ordered by the first occurrence of each element. For example,
	 * {@code ImmutableMultiset.copyOf(Arrays.asList(2, 3, 1, 3).iterator())} yields
	 * a multiset with elements in the order {@code 2, 3, 3, 1}.
	 *
	 * @throws NullPointerException if any of {@code elements} is null
	 */
	public static <E> ImmutableMultiset<E> copyOf(Iterator<? extends E> elements) {
		Multiset<E> multiset = LinkedHashMultiset.create();
		Iterators.addAll(multiset, elements);
		return copyOfInternal(multiset);
	}

	ImmutableMultiset() {
	}

	@Override
	public UnmodifiableIterator<E> iterator() {
		final Iterator<Entry<E>> entryIterator = entrySet().iterator();
		return new UnmodifiableIterator<E>() {
			int remaining;
			E element;

			@Override
			public boolean hasNext() {
				return (remaining > 0) || entryIterator.hasNext();
			}

			@Override
			public E next() {
				if (remaining <= 0) {
					Entry<E> entry = entryIterator.next();
					element = entry.getElement();
					remaining = entry.getCount();
				}
				remaining--;
				return element;
			}
		};
	}

	@Override
	public boolean contains(@Nullable Object object) {
		return count(object) > 0;
	}

	@Override
	public boolean containsAll(Collection<?> targets) {
		return elementSet().containsAll(targets);
	}

	/**
	 * Guaranteed to throw an exception and leave the collection unmodified.
	 *
	 * @throws UnsupportedOperationException always
	 * @deprecated Unsupported operation.
	 */
	@Deprecated
	@Override
	public final int add(E element, int occurrences) {
		throw new UnsupportedOperationException();
	}

	/**
	 * Guaranteed to throw an exception and leave the collection unmodified.
	 *
	 * @throws UnsupportedOperationException always
	 * @deprecated Unsupported operation.
	 */
	@Deprecated
	@Override
	public final int remove(Object element, int occurrences) {
		throw new UnsupportedOperationException();
	}

	/**
	 * Guaranteed to throw an exception and leave the collection unmodified.
	 *
	 * @throws UnsupportedOperationException always
	 * @deprecated Unsupported operation.
	 */
	@Deprecated
	@Override
	public final int setCount(E element, int count) {
		throw new UnsupportedOperationException();
	}

	/**
	 * Guaranteed to throw an exception and leave the collection unmodified.
	 *
	 * @throws UnsupportedOperationException always
	 * @deprecated Unsupported operation.
	 */
	@Deprecated
	@Override
	public final boolean setCount(E element, int oldCount, int newCount) {
		throw new UnsupportedOperationException();
	}

	@GwtIncompatible("not present in emulated superclass")
	@Override
	int copyIntoArray(Object[] dst, int offset) {
		for (Multiset.Entry<E> entry : entrySet()) {
			Arrays.fill(dst, offset, offset + entry.getCount(), entry.getElement());
			offset += entry.getCount();
		}
		return offset;
	}

	@Override
	public boolean equals(@Nullable Object object) {
		return Multisets.equalsImpl(this, object);
	}

	@Override
	public int hashCode() {
		return Sets.hashCodeImpl(entrySet());
	}

	@Override
	public String toString() {
		return entrySet().toString();
	}

	private transient ImmutableSet<Entry<E>> entrySet;

	@Override
	public ImmutableSet<Entry<E>> entrySet() {
		ImmutableSet<Entry<E>> es = entrySet;
		return (es == null) ? (entrySet = createEntrySet()) : es;
	}

	private final ImmutableSet<Entry<E>> createEntrySet() {
		return isEmpty() ? ImmutableSet.<Entry<E>>of() : new EntrySet();
	}

	abstract Entry<E> getEntry(int index);

	private final class EntrySet extends ImmutableSet<Entry<E>> {
		@Override
		boolean isPartialView() {
			return ImmutableMultiset.this.isPartialView();
		}

		@Override
		public UnmodifiableIterator<Entry<E>> iterator() {
			return asList().iterator();
		}

		@Override
		ImmutableList<Entry<E>> createAsList() {
			return new ImmutableAsList<Entry<E>>() {
				@Override
				public Entry<E> get(int index) {
					return getEntry(index);
				}

				@Override
				ImmutableCollection<Entry<E>> delegateCollection() {
					return EntrySet.this;
				}
			};
		}

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

		@Override
		public boolean contains(Object o) {
			if (o instanceof Entry) {
				Entry<?> entry = (Entry<?>) o;
				if (entry.getCount() <= 0) {
					return false;
				}
				int count = count(entry.getElement());
				return count == entry.getCount();
			}
			return false;
		}

		@Override
		public int hashCode() {
			return ImmutableMultiset.this.hashCode();
		}

		// We can't label this with @Override, because it doesn't override anything
		// in the GWT emulated version.
		// TODO(cpovirk): try making all copies of this method @GwtIncompatible instead
		Object writeReplace() {
			return new EntrySetSerializedForm<E>(ImmutableMultiset.this);
		}

		private static final long serialVersionUID = 0;
	}

	static class EntrySetSerializedForm<E> implements Serializable {
		final ImmutableMultiset<E> multiset;

		EntrySetSerializedForm(ImmutableMultiset<E> multiset) {
			this.multiset = multiset;
		}

		Object readResolve() {
			return multiset.entrySet();
		}
	}

	private static class SerializedForm implements Serializable {
		final Object[] elements;
		final int[] counts;

		SerializedForm(Multiset<?> multiset) {
			int distinct = multiset.entrySet().size();
			elements = new Object[distinct];
			counts = new int[distinct];
			int i = 0;
			for (Entry<?> entry : multiset.entrySet()) {
				elements[i] = entry.getElement();
				counts[i] = entry.getCount();
				i++;
			}
		}

		Object readResolve() {
			LinkedHashMultiset<Object> multiset = LinkedHashMultiset.create(elements.length);
			for (int i = 0; i < elements.length; i++) {
				multiset.add(elements[i], counts[i]);
			}
			return ImmutableMultiset.copyOf(multiset);
		}

		private static final long serialVersionUID = 0;
	}

	// We can't label this with @Override, because it doesn't override anything
	// in the GWT emulated version.
	Object writeReplace() {
		return new SerializedForm(this);
	}

	/**
	 * Returns a new builder. The generated builder is equivalent to the builder
	 * created by the {@link Builder} constructor.
	 */
	public static <E> Builder<E> builder() {
		return new Builder<E>();
	}

	/**
	 * A builder for creating immutable multiset instances, especially {@code
	 * public static final} multisets ("constant multisets"). Example:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	public static final ImmutableMultiset<Bean> BEANS = new ImmutableMultiset.Builder<Bean>()
	 * 			.addCopies(Bean.COCOA, 4).addCopies(Bean.GARDEN, 6).addCopies(Bean.RED, 8)
	 * 			.addCopies(Bean.BLACK_EYED, 10).build();
	 * }
	 * </pre>
	 *
	 * <p>
	 * Builder instances can be reused; it is safe to call {@link #build} multiple
	 * times to build multiple multisets in series.
	 *
	 * @since 2.0 (imported from Google Collections Library)
	 */
	public static class Builder<E> extends ImmutableCollection.Builder<E> {
		final Multiset<E> contents;

		/**
		 * Creates a new builder. The returned builder is equivalent to the builder
		 * generated by {@link ImmutableMultiset#builder}.
		 */
		public Builder() {
			this(LinkedHashMultiset.<E>create());
		}

		Builder(Multiset<E> contents) {
			this.contents = contents;
		}

		/**
		 * Adds {@code element} to the {@code ImmutableMultiset}.
		 *
		 * @param element the element to add
		 * @return this {@code Builder} object
		 * @throws NullPointerException if {@code element} is null
		 */
		@Override
		public Builder<E> add(E element) {
			contents.add(checkNotNull(element));
			return this;
		}

		/**
		 * Adds a number of occurrences of an element to this {@code
		 * ImmutableMultiset}.
		 *
		 * @param element     the element to add
		 * @param occurrences the number of occurrences of the element to add. May be
		 *                    zero, in which case no change will be made.
		 * @return this {@code Builder} object
		 * @throws NullPointerException     if {@code element} is null
		 * @throws IllegalArgumentException if {@code occurrences} is negative, or if
		 *                                  this operation would result in more than
		 *                                  {@link Integer#MAX_VALUE} occurrences of the
		 *                                  element
		 */
		public Builder<E> addCopies(E element, int occurrences) {
			contents.add(checkNotNull(element), occurrences);
			return this;
		}

		/**
		 * Adds or removes the necessary occurrences of an element such that the element
		 * attains the desired count.
		 *
		 * @param element the element to add or remove occurrences of
		 * @param count   the desired count of the element in this multiset
		 * @return this {@code Builder} object
		 * @throws NullPointerException     if {@code element} is null
		 * @throws IllegalArgumentException if {@code count} is negative
		 */
		public Builder<E> setCount(E element, int count) {
			contents.setCount(checkNotNull(element), count);
			return this;
		}

		/**
		 * Adds each element of {@code elements} to the {@code ImmutableMultiset}.
		 *
		 * @param elements the elements to add
		 * @return this {@code Builder} object
		 * @throws NullPointerException if {@code elements} is null or contains a null
		 *                              element
		 */
		@Override
		public Builder<E> add(E... elements) {
			super.add(elements);
			return this;
		}

		/**
		 * Adds each element of {@code elements} to the {@code ImmutableMultiset}.
		 *
		 * @param elements the {@code Iterable} to add to the {@code
		 *     ImmutableMultiset}
		 * @return this {@code Builder} object
		 * @throws NullPointerException if {@code elements} is null or contains a null
		 *                              element
		 */
		@Override
		public Builder<E> addAll(Iterable<? extends E> elements) {
			if (elements instanceof Multiset) {
				Multiset<? extends E> multiset = Multisets.cast(elements);
				for (Entry<? extends E> entry : multiset.entrySet()) {
					addCopies(entry.getElement(), entry.getCount());
				}
			} else {
				super.addAll(elements);
			}
			return this;
		}

		/**
		 * Adds each element of {@code elements} to the {@code ImmutableMultiset}.
		 *
		 * @param elements the elements to add to the {@code ImmutableMultiset}
		 * @return this {@code Builder} object
		 * @throws NullPointerException if {@code elements} is null or contains a null
		 *                              element
		 */
		@Override
		public Builder<E> addAll(Iterator<? extends E> elements) {
			super.addAll(elements);
			return this;
		}

		/**
		 * Returns a newly-created {@code ImmutableMultiset} based on the contents of
		 * the {@code Builder}.
		 */
		@Override
		public ImmutableMultiset<E> build() {
			return copyOf(contents);
		}
	}
}
