/*
 * Copyright (C) 2011 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.math.IntMath;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.LazyInit;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

/**
 * A {@link SortedMultiset} whose contents will never change, with many other important properties
 * detailed at {@link ImmutableCollection}.
 *
 * <p><b>Warning:</b> as with any sorted collection, you are strongly advised not to use a {@link
 * Comparator} or {@link Comparable} type whose comparison behavior is <i>inconsistent with
 * equals</i>. That is, {@code a.compareTo(b)} or {@code comparator.compare(a, b)} should equal zero
 * <i>if and only if</i> {@code a.equals(b)}. If this advice is not followed, the resulting
 * collection will not correctly obey its specification.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/ImmutableCollectionsExplained">
 * immutable collections</a>.
 *
 * @author Louis Wasserman
 * @since 12.0
 */
@GwtIncompatible // hasn't been tested yet
public abstract class ImmutableSortedMultiset<E> extends ImmutableSortedMultisetFauxverideShim<E>
    implements SortedMultiset<E> {
  // TODO(lowasser): GWT compatibility

  /**
   * Returns the empty immutable sorted multiset.
   */
  @SuppressWarnings("unchecked")
  public static <E> ImmutableSortedMultiset<E> of() {
    return (ImmutableSortedMultiset) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
  }

  /**
   * Returns an immutable sorted multiset containing a single element.
   */
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E element) {
    RegularImmutableSortedSet<E> elementSet =
        (RegularImmutableSortedSet<E>) ImmutableSortedSet.of(element);
    long[] cumulativeCounts = {0, 1};
    return new RegularImmutableSortedMultiset<E>(elementSet, cumulativeCounts, 0, 1);
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  @SuppressWarnings("unchecked")
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E e1, E e2) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  @SuppressWarnings("unchecked")
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E e1, E e2, E e3) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  @SuppressWarnings("unchecked")
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(
      E e1, E e2, E e3, E e4) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3, e4));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  @SuppressWarnings("unchecked")
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(
      E e1, E e2, E e3, E e4, E e5) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2, e3, e4, e5));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  @SuppressWarnings("unchecked")
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E... remaining) {
    int size = remaining.length + 6;
    List<E> all = Lists.newArrayListWithCapacity(size);
    Collections.addAll(all, e1, e2, e3, e4, e5, e6);
    Collections.addAll(all, remaining);
    return copyOf(Ordering.natural(), all);
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any of {@code elements} is null
   */
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> copyOf(E[] elements) {
    return copyOf(Ordering.natural(), Arrays.asList(elements));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering. To create a copy of a {@code SortedMultiset} that preserves the
   * comparator, call {@link #copyOfSorted} instead. This method iterates over {@code elements} at
   * most once.
   *
   * <p>Note that if {@code s} is a {@code Multiset<String>}, then {@code
   * ImmutableSortedMultiset.copyOf(s)} returns an {@code ImmutableSortedMultiset<String>}
   * containing each of the strings in {@code s}, while {@code ImmutableSortedMultiset.of(s)}
   * returns an {@code ImmutableSortedMultiset<Multiset<String>>} containing one element (the given
   * multiset itself).
   *
   * <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>This method is not type-safe, as it may be called on elements that are not mutually
   * comparable.
   *
   * @throws ClassCastException if the elements are not mutually comparable
   * @throws NullPointerException if any of {@code elements} is null
   */
  public static <E> ImmutableSortedMultiset<E> copyOf(Iterable<? extends E> elements) {
    // Hack around E not being a subtype of Comparable.
    // Unsafe, see ImmutableSortedMultisetFauxverideShim.
    @SuppressWarnings("unchecked")
    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
    return copyOf(naturalOrder, elements);
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * <p>This method is not type-safe, as it may be called on elements that are not mutually
   * comparable.
   *
   * @throws ClassCastException if the elements are not mutually comparable
   * @throws NullPointerException if any of {@code elements} is null
   */
  public static <E> ImmutableSortedMultiset<E> copyOf(Iterator<? extends E> elements) {
    // Hack around E not being a subtype of Comparable.
    // Unsafe, see ImmutableSortedMultisetFauxverideShim.
    @SuppressWarnings("unchecked")
    Ordering<E> naturalOrder = (Ordering<E>) Ordering.<Comparable>natural();
    return copyOf(naturalOrder, elements);
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by the given {@code
   * Comparator}.
   *
   * @throws NullPointerException if {@code comparator} or any of {@code elements} is null
   */
  public static <E> ImmutableSortedMultiset<E> copyOf(
      Comparator<? super E> comparator, Iterator<? extends E> elements) {
    checkNotNull(comparator);
    return new Builder<E>(comparator).addAll(elements).build();
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by the given {@code
   * Comparator}. This method iterates over {@code elements} at most once.
   *
   * <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.
   *
   * @throws NullPointerException if {@code comparator} or any of {@code elements} is null
   */
  @SuppressWarnings("unchecked")
  public static <E> ImmutableSortedMultiset<E> copyOf(
      Comparator<? super E> comparator, Iterable<? extends E> elements) {
    if (elements instanceof ImmutableSortedMultiset) {
      @SuppressWarnings("unchecked") // immutable collections are always safe for covariant casts
      ImmutableSortedMultiset<E> multiset = (ImmutableSortedMultiset<E>) elements;
      if (comparator.equals(multiset.comparator())) {
        if (multiset.isPartialView()) {
          return copyOfSortedEntries(comparator, multiset.entrySet().asList());
        } else {
          return multiset;
        }
      }
    }
    return new ImmutableSortedMultiset.Builder<E>(comparator).addAll(elements).build();
  }

  /**
   * Returns an immutable sorted multiset containing the elements of a sorted multiset, sorted by
   * the same {@code Comparator}. That behavior differs from {@link #copyOf(Iterable)}, which
   * always uses the natural ordering of the elements.
   *
   * <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>This method is safe to use even when {@code sortedMultiset} is a synchronized or concurrent
   * collection that is currently being modified by another thread.
   *
   * @throws NullPointerException if {@code sortedMultiset} or any of its elements is null
   */
  public static <E> ImmutableSortedMultiset<E> copyOfSorted(SortedMultiset<E> sortedMultiset) {
    return copyOfSortedEntries(
        sortedMultiset.comparator(), Lists.newArrayList(sortedMultiset.entrySet()));
  }

  private static <E> ImmutableSortedMultiset<E> copyOfSortedEntries(
      Comparator<? super E> comparator, Collection<Entry<E>> entries) {
    if (entries.isEmpty()) {
      return emptyMultiset(comparator);
    }
    ImmutableList.Builder<E> elementsBuilder = new ImmutableList.Builder<E>(entries.size());
    long[] cumulativeCounts = new long[entries.size() + 1];
    int i = 0;
    for (Entry<E> entry : entries) {
      elementsBuilder.add(entry.getElement());
      cumulativeCounts[i + 1] = cumulativeCounts[i] + entry.getCount();
      i++;
    }
    return new RegularImmutableSortedMultiset<E>(
        new RegularImmutableSortedSet<E>(elementsBuilder.build(), comparator),
        cumulativeCounts,
        0,
        entries.size());
  }

  @SuppressWarnings("unchecked")
  static <E> ImmutableSortedMultiset<E> emptyMultiset(Comparator<? super E> comparator) {
    if (Ordering.natural().equals(comparator)) {
      return (ImmutableSortedMultiset<E>) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
    } else {
      return new RegularImmutableSortedMultiset<E>(comparator);
    }
  }

  ImmutableSortedMultiset() {}

  @Override
  public final Comparator<? super E> comparator() {
    return elementSet().comparator();
  }

  @Override
  public abstract ImmutableSortedSet<E> elementSet();

  @LazyInit
  transient ImmutableSortedMultiset<E> descendingMultiset;

  @Override
  public ImmutableSortedMultiset<E> descendingMultiset() {
    ImmutableSortedMultiset<E> result = descendingMultiset;
    if (result == null) {
      return descendingMultiset =
          this.isEmpty()
              ? emptyMultiset(Ordering.from(comparator()).reverse())
              : new DescendingImmutableSortedMultiset<E>(this);
    }
    return result;
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is guaranteed to throw an {@link UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  public final Entry<E> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is guaranteed to throw an {@link UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  public final Entry<E> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public abstract ImmutableSortedMultiset<E> headMultiset(E upperBound, BoundType boundType);

  @Override
  public ImmutableSortedMultiset<E> subMultiset(
      E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {
    checkArgument(
        comparator().compare(lowerBound, upperBound) <= 0,
        "Expected lowerBound <= upperBound but %s > %s",
        lowerBound,
        upperBound);
    return tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound, upperBoundType);
  }

  @Override
  public abstract ImmutableSortedMultiset<E> tailMultiset(E lowerBound, BoundType boundType);

  /**
   * Returns a builder that creates immutable sorted multisets with an explicit comparator. If the
   * comparator has a more general type than the set being generated, such as creating a {@code
   * SortedMultiset<Integer>} with a {@code Comparator<Number>}, use the {@link Builder}
   * constructor instead.
   *
   * @throws NullPointerException if {@code comparator} is null
   */
  public static <E> Builder<E> orderedBy(Comparator<E> comparator) {
    return new Builder<E>(comparator);
  }

  /**
   * Returns a builder that creates immutable sorted multisets whose elements are ordered by the
   * reverse of their natural ordering.
   *
   * <p>Note: the type parameter {@code E} extends {@code Comparable<?>} rather than {@code
   * Comparable<? super E>} as a workaround for javac <a
   * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6468354">bug 6468354</a>.
   */
  public static <E extends Comparable<?>> Builder<E> reverseOrder() {
    return new Builder<E>(Ordering.natural().reverse());
  }

  /**
   * Returns a builder that creates immutable sorted multisets whose elements are ordered by their
   * natural ordering. The sorted multisets use {@link Ordering#natural()} as the comparator. This
   * method provides more type-safety than {@link #builder}, as it can be called only for classes
   * that implement {@link Comparable}.
   *
   * <p>Note: the type parameter {@code E} extends {@code Comparable<?>} rather than {@code
   * Comparable<? super E>} as a workaround for javac <a
   * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6468354">bug 6468354</a>.
   */
  public static <E extends Comparable<?>> Builder<E> naturalOrder() {
    return new Builder<E>(Ordering.natural());
  }

  /**
   * A builder for creating immutable multiset instances, especially {@code public static final}
   * multisets ("constant multisets"). Example:
   *
   * <pre> {@code
   *
   *   public static final ImmutableSortedMultiset<Bean> BEANS =
   *       new ImmutableSortedMultiset.Builder<Bean>(colorComparator())
   *           .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 12.0
   */
  public static class Builder<E> extends ImmutableMultiset.Builder<E> {
    /*
     * We keep an array of elements and counts.  Periodically -- when we need more room in the 
     * array, or when we're building, or the like -- we sort, deduplicate, and combine the counts.
     * Negative counts indicate a setCount operation with ~counts[i].
     */

    private final Comparator<? super E> comparator;
    
    @VisibleForTesting
    E[] elements;
    private int[] counts;
    
    /* 
     * The number of used positions in the elements array.  We deduplicate periodically, so this
     * may fluctuate up and down. 
     */
    private int length;
    
    // True if we just called build() and the elements array is being used by a created ISM, meaning
    // we shouldn't modify that array further.
    private boolean forceCopyElements;

    /**
     * Creates a new builder. The returned builder is equivalent to the builder generated by
     * {@link ImmutableSortedMultiset#orderedBy(Comparator)}.
     */
    @SuppressWarnings("unchecked")
    public Builder(Comparator<? super E> comparator) {
      super(true); // doesn't allocate hash table in supertype
      this.comparator = checkNotNull(comparator);
      this.elements = (E[]) new Object[ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY];
      this.counts = new int[ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY];
    }
    
    /**
     * Check if we need to do deduplication and coalescing, and if so, do it.
     */
    private void maintenance() {
      if (length == elements.length) {
        dedupAndCoalesce(true);
      } else if (forceCopyElements) {
        this.elements = Arrays.copyOf(elements, elements.length);
        // we don't currently need to copy the counts array, because we don't use it directly
        // in built ISMs
      } 
      forceCopyElements = false;
    }

    private void dedupAndCoalesce(boolean maybeExpand) {
      if (length == 0) {
        return;
      }
      E[] sortedElements = Arrays.copyOf(elements, length);
      Arrays.sort(sortedElements, comparator);
      int uniques = 1;
      for (int i = 1; i < sortedElements.length; i++) {
        if (comparator.compare(sortedElements[uniques - 1], sortedElements[i]) < 0) {
          sortedElements[uniques] = sortedElements[i];
          uniques++;
        }
      }
      Arrays.fill(sortedElements, uniques, length, null); 
      if (maybeExpand && uniques * 4 > length * 3) {
        // lots of nonduplicated elements, expand the array by 50%
        sortedElements =
            Arrays.copyOf(sortedElements, IntMath.saturatedAdd(length, length / 2 + 1));
      }
      int[] sortedCounts = new int[sortedElements.length];
      for (int i = 0; i < length; i++) {
        int index =
            Arrays.binarySearch(sortedElements, 0, uniques, elements[i], comparator);
        if (counts[i] >= 0) {
          sortedCounts[index] += counts[i];
        } else {
          sortedCounts[index] = ~counts[i];
        }
      }
      // Note that we're not getting rid, yet, of elements with count 0.  We'll do that in build().
      this.elements = sortedElements;
      this.counts = sortedCounts;
      this.length = uniques;
    }

    /**
     * Adds {@code element} to the {@code ImmutableSortedMultiset}.
     *
     * @param element the element to add
     * @return this {@code Builder} object
     * @throws NullPointerException if {@code element} is null
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<E> add(E element) {
      return addCopies(element, 1);
    }

    /**
     * Adds a number of occurrences of an element to this {@code ImmutableSortedMultiset}.
     *
     * @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
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<E> addCopies(E element, int occurrences) {
      checkNotNull(element);
      CollectPreconditions.checkNonnegative(occurrences, "occurrences");
      if (occurrences == 0) {
        return this;
      }
      maintenance();
      elements[length] = element;
      counts[length] = occurrences;
      length++;
      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
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<E> setCount(E element, int count) {
      checkNotNull(element);
      CollectPreconditions.checkNonnegative(count, "count");
      maintenance();
      elements[length] = element;
      counts[length] = ~count;
      length++;
      return this;
    }

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

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

    /**
     * Adds each element of {@code elements} to the {@code ImmutableSortedMultiset}.
     *
     * @param elements the elements to add to the {@code ImmutableSortedMultiset}
     * @return this {@code Builder} object
     * @throws NullPointerException if {@code elements} is null or contains a null element
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<E> addAll(Iterator<? extends E> elements) {
      while (elements.hasNext()) {
        add(elements.next());
      }
      return this;
    }
    
    private void dedupAndCoalesceAndDeleteEmpty() {
      dedupAndCoalesce(false);
      
      // If there was a setCount(elem, 0), those elements are still present.  Eliminate them.
      int size = 0;
      for (int i = 0; i < length; i++) {
        if (counts[i] > 0) {
          elements[size] = elements[i];
          counts[size] = counts[i];
          size++;
        }
      }
      Arrays.fill(elements, size, length, null);
      Arrays.fill(counts, size, length, 0);
      length = size;
    }

    /**
     * Returns a newly-created {@code ImmutableSortedMultiset} based on the contents of the {@code
     * Builder}.
     */
    @Override
    public ImmutableSortedMultiset<E> build() {
      dedupAndCoalesceAndDeleteEmpty();
      if (length == 0) {
        return emptyMultiset(comparator);
      }
      RegularImmutableSortedSet<E> elementSet =
          (RegularImmutableSortedSet<E>)
              ImmutableSortedSet.construct(comparator, length, elements);
      long[] cumulativeCounts = new long[length + 1];
      for (int i = 0; i < length; i++) {
        cumulativeCounts[i + 1] = cumulativeCounts[i] + counts[i];
      }
      forceCopyElements = true;
      return new RegularImmutableSortedMultiset<E>(elementSet, cumulativeCounts, 0, length);
    }
  }

  private static final class SerializedForm<E> implements Serializable {
    final Comparator<? super E> comparator;
    final E[] elements;
    final int[] counts;

    @SuppressWarnings("unchecked")
    SerializedForm(SortedMultiset<E> multiset) {
      this.comparator = multiset.comparator();
      int n = multiset.entrySet().size();
      elements = (E[]) new Object[n];
      counts = new int[n];
      int i = 0;
      for (Entry<E> entry : multiset.entrySet()) {
        elements[i] = entry.getElement();
        counts[i] = entry.getCount();
        i++;
      }
    }

    Object readResolve() {
      int n = elements.length;
      Builder<E> builder = new Builder<>(comparator);
      for (int i = 0; i < n; i++) {
        builder.addCopies(elements[i], counts[i]);
      }
      return builder.build();
    }
  }

  @Override
  Object writeReplace() {
    return new SerializedForm<E>(this);
  }
}