/*
    * 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 com.google.common.annotations.Beta;
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.annotations.GwtIncompatible;
  import com.google.common.base.Function;
  import com.google.common.base.Joiner;
  import com.google.common.base.Optional;
  import com.google.common.base.Predicate;
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.List;
  import java.util.SortedSet;
  
  import javax.annotation.CheckReturnValue;
  import javax.annotation.Nullable;
  
  /**
   * {@code FluentIterable} provides a rich interface for manipulating {@code Iterable} instances in a
   * chained fashion. A {@code FluentIterable} can be created from an {@code Iterable}, or from a set
   * of elements. The following types of methods are provided on {@code FluentIterable}:
   * <ul>
   * <li>chained methods which return a new {@code FluentIterable} based in some way on the contents
   * of the current one (for example {@link #transform})
   * <li>conversion methods which copy the {@code FluentIterable}'s contents into a new collection or
   * array (for example {@link #toList})
   * <li>element extraction methods which facilitate the retrieval of certain elements (for example
   * {@link #last})
   * <li>query methods which answer questions about the {@code FluentIterable}'s contents (for example
   * {@link #anyMatch})
   * </ul>
   *
   * <p>Here is an example that merges the lists returned by two separate database calls, transforms
   * it by invoking {@code toString()} on each element, and returns the first 10 elements as an
   * {@code ImmutableList}: <pre>   {@code
   *
   *   FluentIterable
   *       .from(database.getClientList())
   *       .filter(activeInLastMonth())
   *       .transform(Functions.toStringFunction())
   *       .limit(10)
   *       .toList();}</pre>
   *
   * <p>Anything which can be done using {@code FluentIterable} could be done in a different fashion
   * (often with {@link Iterables}), however the use of {@code FluentIterable} makes many sets of
   * operations significantly more concise.
   *
   * @author Marcin Mikosik
   * @since 12.0
   */
  @GwtCompatible(emulated = true)
  public abstract class FluentIterable<E> implements Iterable<E> {
    // We store 'iterable' and use it instead of 'this' to allow Iterables to perform instanceof
    // checks on the _original_ iterable when FluentIterable.from is used.
    private final Iterable<E> iterable;
  
    /** Constructor for use by subclasses. */
    protected FluentIterable() {
      this.iterable = this;
    }
  
    FluentIterable(Iterable<E> iterable) {
      this.iterable = checkNotNull(iterable);
    }
  
    /**
     * Returns a fluent iterable that wraps {@code iterable}, or {@code iterable} itself if it
     * is already a {@code FluentIterable}.
     */
    public static <E> FluentIterable<E> from(final Iterable<E> iterable) {
      return (iterable instanceof FluentIterable) ? (FluentIterable<E>) iterable
          : new FluentIterable<E>(iterable) {
            @Override
            public Iterator<E> iterator() {
              return iterable.iterator();
            }
          };
    }
 
   /**
    * Construct a fluent iterable from another fluent iterable. This is obviously never necessary,
    * but is intended to help call out cases where one migration from {@code Iterable} to
    * {@code FluentIterable} has obviated the need to explicitly convert to a {@code FluentIterable}.
    *
    * @deprecated instances of {@code FluentIterable} don't need to be converted to
    *     {@code FluentIterable}
    */
   @Deprecated
   public static <E> FluentIterable<E> from(FluentIterable<E> iterable) {
     return checkNotNull(iterable);
   }
 
   /**
    * Returns a fluent iterable containing {@code elements} in the specified order.
    *
    * @since 18.0
    */
   @Beta
   public static <E> FluentIterable<E> of(E[] elements) {
     return from(Lists.newArrayList(elements));
   }
 
   /**
    * Returns a string representation of this fluent iterable, with the format
    * {@code [e1, e2, ..., en]}.
    */
   @Override
   public String toString() {
     return Iterables.toString(iterable);
   }
 
   /**
    * Returns the number of elements in this fluent iterable.
    */
   public final int size() {
     return Iterables.size(iterable);
   }
 
   /**
    * Returns {@code true} if this fluent iterable contains any object for which
    * {@code equals(element)} is true.
    */
   public final boolean contains(@Nullable Object element) {
     return Iterables.contains(iterable, element);
   }
 
   /**
    * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of
    * this fluent iterable.
    *
    * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After
    * {@code remove()} is called, subsequent cycles omit the removed element, which is no longer in
    * this fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until
    * this fluent iterable is empty.
    *
    * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You
    * should use an explicit {@code break} or be certain that you will eventually remove all the
    * elements.
    */
   @CheckReturnValue
   public final FluentIterable<E> cycle() {
     return from(Iterables.cycle(iterable));
   }
 
   /**
    * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable,
    * followed by those of {@code other}. The iterators are not polled until necessary.
    *
    * <p>The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding
    * {@code Iterator} supports it.
    *
    * @since 18.0
    */
   @Beta
   @CheckReturnValue
   public final FluentIterable<E> append(Iterable<? extends E> other) {
     return from(Iterables.concat(iterable, other));
   }
 
   /**
    * Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable,
    * followed by {@code elements}.
    *
    * @since 18.0
    */
   @Beta
   @CheckReturnValue
   public final FluentIterable<E> append(E... elements) {
     return from(Iterables.concat(iterable, Arrays.asList(elements)));
   }
 
   /**
    * Returns the elements from this fluent iterable that satisfy a predicate. The
    * resulting fluent iterable's iterator does not support {@code remove()}.
    */
   @CheckReturnValue
   public final FluentIterable<E> filter(Predicate<? super E> predicate) {
     return from(Iterables.filter(iterable, predicate));
   }
 
   /**
    * Returns the elements from this fluent iterable that are instances of class {@code type}.
    *
    * @param type the type of elements desired
    */
   @GwtIncompatible("Class.isInstance")
   @CheckReturnValue
   public final <T> FluentIterable<T> filter(Class<T> type) {
     return from(Iterables.filter(iterable, type));
   }
 
   /**
    * Returns {@code true} if any element in this fluent iterable satisfies the predicate.
    */
   public final boolean anyMatch(Predicate<? super E> predicate) {
     return Iterables.any(iterable, predicate);
   }
 
   /**
    * Returns {@code true} if every element in this fluent iterable satisfies the predicate.
    * If this fluent iterable is empty, {@code true} is returned.
    */
   public final boolean allMatch(Predicate<? super E> predicate) {
     return Iterables.all(iterable, predicate);
   }
 
   /**
    * Returns an {@link Optional} containing the first element in this fluent iterable that
    * satisfies the given predicate, if such an element exists.
    *
    * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null}
    * is matched in this fluent iterable, a {@link NullPointerException} will be thrown.
    */
   public final Optional<E> firstMatch(Predicate<? super E> predicate) {
     return Iterables.tryFind(iterable, predicate);
   }
 
   /**
    * Returns a fluent iterable that applies {@code function} to each element of this
    * fluent iterable.
    *
    * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's
    * iterator does. After a successful {@code remove()} call, this fluent iterable no longer
    * contains the corresponding element.
    */
   public final <T> FluentIterable<T> transform(Function<? super E, T> function) {
     return from(Iterables.transform(iterable, function));
   }
 
   /**
    * Applies {@code function} to each element of this fluent iterable and returns
    * a fluent iterable with the concatenated combination of results.  {@code function}
    * returns an Iterable of results.
    *
    * <p>The returned fluent iterable's iterator supports {@code remove()} if this
    * function-returned iterables' iterator does. After a successful {@code remove()} call,
    * the returned fluent iterable no longer contains the corresponding element.
    *
    * @since 13.0 (required {@code Function<E, Iterable<T>>} until 14.0)
    */
   public <T> FluentIterable<T> transformAndConcat(
       Function<? super E, ? extends Iterable<? extends T>> function) {
     return from(Iterables.concat(transform(function)));
   }
 
   /**
    * Returns an {@link Optional} containing the first element in this fluent iterable.
    * If the iterable is empty, {@code Optional.absent()} is returned.
    *
    * @throws NullPointerException if the first element is null; if this is a possibility, use
    *     {@code iterator().next()} or {@link Iterables#getFirst} instead.
    */
   public final Optional<E> first() {
     Iterator<E> iterator = iterable.iterator();
     return iterator.hasNext()
         ? Optional.of(iterator.next())
         : Optional.<E>absent();
   }
 
   /**
    * Returns an {@link Optional} containing the last element in this fluent iterable.
    * If the iterable is empty, {@code Optional.absent()} is returned.
    *
    * @throws NullPointerException if the last element is null; if this is a possibility, use
    *     {@link Iterables#getLast} instead.
    */
   public final Optional<E> last() {
     // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE
 
     // TODO(kevinb): Support a concurrently modified collection?
     if (iterable instanceof List) {
       List<E> list = (List<E>) iterable;
       if (list.isEmpty()) {
         return Optional.absent();
       }
       return Optional.of(list.get(list.size() - 1));
     }
     Iterator<E> iterator = iterable.iterator();
     if (!iterator.hasNext()) {
       return Optional.absent();
     }
 
     /*
      * TODO(kevinb): consider whether this "optimization" is worthwhile. Users
      * with SortedSets tend to know they are SortedSets and probably would not
      * call this method.
      */
     if (iterable instanceof SortedSet) {
       SortedSet<E> sortedSet = (SortedSet<E>) iterable;
       return Optional.of(sortedSet.last());
     }
 
     while (true) {
       E current = iterator.next();
       if (!iterator.hasNext()) {
         return Optional.of(current);
       }
     }
   }
 
   /**
    * Returns a view of this fluent iterable that skips its first {@code numberToSkip}
    * elements. If this fluent iterable contains fewer than {@code numberToSkip} elements,
    * the returned fluent iterable skips all of its elements.
    *
    * <p>Modifications to this fluent iterable before a call to {@code iterator()} are
    * reflected in the returned fluent iterable. That is, the its iterator skips the first
    * {@code numberToSkip} elements that exist when the iterator is created, not when {@code skip()}
    * is called.
    *
    * <p>The returned fluent iterable's iterator supports {@code remove()} if the
    * {@code Iterator} of this fluent iterable supports it. Note that it is <i>not</i>
    * possible to delete the last skipped element by immediately calling {@code remove()} on the
    * returned fluent iterable's iterator, as the {@code Iterator} contract states that a call
    * to {@code * remove()} before a call to {@code next()} will throw an
    * {@link IllegalStateException}.
    */
   @CheckReturnValue
   public final FluentIterable<E> skip(int numberToSkip) {
     return from(Iterables.skip(iterable, numberToSkip));
   }
 
   /**
    * Creates a fluent iterable with the first {@code size} elements of this
    * fluent iterable. If this fluent iterable does not contain that many elements,
    * the returned fluent iterable will have the same behavior as this fluent iterable.
    * The returned fluent iterable's iterator supports {@code remove()} if this
    * fluent iterable's iterator does.
    *
    * @param size the maximum number of elements in the returned fluent iterable
    * @throws IllegalArgumentException if {@code size} is negative
    */
   @CheckReturnValue
   public final FluentIterable<E> limit(int size) {
     return from(Iterables.limit(iterable, size));
   }
 
   /**
    * Determines whether this fluent iterable is empty.
    */
   public final boolean isEmpty() {
     return !iterable.iterator().hasNext();
   }
 
   /**
    * Returns an {@code ImmutableList} containing all of the elements from this fluent iterable in
    * proper sequence.
    *
    * @since 14.0 (since 12.0 as {@code toImmutableList()}).
    */
   public final ImmutableList<E> toList() {
     return ImmutableList.copyOf(iterable);
   }
 
   /**
    * Returns an {@code ImmutableList} containing all of the elements from this {@code
    * FluentIterable} in the order specified by {@code comparator}.  To produce an {@code
    * ImmutableList} sorted by its natural ordering, use {@code toSortedList(Ordering.natural())}.
    *
    * @param comparator the function by which to sort list elements
    * @throws NullPointerException if any element is null
    * @since 14.0 (since 13.0 as {@code toSortedImmutableList()}).
    */
   public final ImmutableList<E> toSortedList(Comparator<? super E> comparator) {
     return Ordering.from(comparator).immutableSortedCopy(iterable);
   }
 
   /**
    * Returns an {@code ImmutableSet} containing all of the elements from this fluent iterable with
    * duplicates removed.
    *
    * @since 14.0 (since 12.0 as {@code toImmutableSet()}).
    */
   public final ImmutableSet<E> toSet() {
     return ImmutableSet.copyOf(iterable);
   }
 
   /**
    * Returns an {@code ImmutableSortedSet} containing all of the elements from this {@code
    * FluentIterable} in the order specified by {@code comparator}, with duplicates (determined by
    * {@code comparator.compare(x, y) == 0}) removed. To produce an {@code ImmutableSortedSet} sorted
    * by its natural ordering, use {@code toSortedSet(Ordering.natural())}.
    *
    * @param comparator the function by which to sort set elements
    * @throws NullPointerException if any element is null
    * @since 14.0 (since 12.0 as {@code toImmutableSortedSet()}).
    */
   public final ImmutableSortedSet<E> toSortedSet(Comparator<? super E> comparator) {
     return ImmutableSortedSet.copyOf(comparator, iterable);
   }
 
   /**
    * Returns an immutable map for which the elements of this {@code FluentIterable} are the keys in
    * the same order, mapped to values by the given function. If this iterable contains duplicate
    * elements, the returned map will contain each distinct element once in the order it first
    * appears.
    *
    * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code
    *     valueFunction} produces {@code null} for any key
    * @since 14.0
    */
   public final <V> ImmutableMap<E, V> toMap(Function<? super E, V> valueFunction) {
     return Maps.toMap(iterable, valueFunction);
   }
 
   /**
    * Creates an index {@code ImmutableListMultimap} that contains the results of applying a
    * specified function to each item in this {@code FluentIterable} of values. Each element of this
    * iterable will be stored as a value in the resulting multimap, yielding a multimap with the same
    * size as this iterable. The key used to store that value in the multimap will be the result of
    * calling the function on that value. The resulting multimap is created as an immutable snapshot.
    * In the returned multimap, keys appear in the order they are first encountered, and the values
    * corresponding to each key appear in the same order as they are encountered.
    *
    * @param keyFunction the function used to produce the key for each value
    * @throws NullPointerException if any of the following cases is true:
    *     <ul>
    *       <li>{@code keyFunction} is null
    *       <li>An element in this fluent iterable is null
    *       <li>{@code keyFunction} returns {@code null} for any element of this iterable
    *     </ul>
    * @since 14.0
    */
   public final <K> ImmutableListMultimap<K, E> index(Function<? super E, K> keyFunction) {
     return Multimaps.index(iterable, keyFunction);
   }
 
   /**
    * Returns an immutable map for which the {@link java.util.Map#values} are the elements of this
    * {@code FluentIterable} in the given order, and each key is the product of invoking a supplied
    * function on its corresponding value.
    *
    * @param keyFunction the function used to produce the key for each value
    * @throws IllegalArgumentException if {@code keyFunction} produces the same key for more than one
    *     value in this fluent iterable
    * @throws NullPointerException if any element of this fluent iterable is null, or if
    *     {@code keyFunction} produces {@code null} for any value
    * @since 14.0
    */
   public final <K> ImmutableMap<K, E> uniqueIndex(Function<? super E, K> keyFunction) {
     return Maps.uniqueIndex(iterable, keyFunction);
   }
 
   /**
    * Returns an array containing all of the elements from this fluent iterable in iteration order.
    *
    * @param type the type of the elements
    * @return a newly-allocated array into which all the elements of this fluent iterable have
    *     been copied
    */
   @GwtIncompatible("Array.newArray(Class, int)")
   public final E[] toArray(Class<E> type) {
     return Iterables.toArray(iterable, type);
   }
 
   /**
    * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to
    * calling {@code Iterables.addAll(collection, this)}.
    *
    * @param collection the collection to copy elements to
    * @return {@code collection}, for convenience
    * @since 14.0
    */
   public final <C extends Collection<? super E>> C copyInto(C collection) {
     checkNotNull(collection);
     if (iterable instanceof Collection) {
       collection.addAll(Collections2.cast(iterable));
     } else {
       for (E item : iterable) {
         collection.add(item);
       }
     }
     return collection;
   }
 
   /**
    * Returns a {@link String} containing all of the elements of this fluent iterable joined with
    * {@code joiner}.
    *
    * @since 18.0
    */
   @Beta
   public final String join(Joiner joiner) {
     return joiner.join(this);
   }
 
   /**
    * Returns the element at the specified position in this fluent iterable.
    *
    * @param position position of the element to return
    * @return the element at the specified position in this fluent iterable
    * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to
    *     the size of this fluent iterable
    */
   public final E get(int position) {
     return Iterables.get(iterable, position);
   }
 
   /**
    * Function that transforms {@code Iterable<E>} into a fluent iterable.
    */
   private static class FromIterableFunction<E>
       implements Function<Iterable<E>, FluentIterable<E>> {
     @Override
     public FluentIterable<E> apply(Iterable<E> fromObject) {
       return FluentIterable.from(fromObject);
     }
   }
 }