/*
 * Copyright (C) 2009 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.collect.Lists;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.RandomAccess;

import javax.annotation.Nullable;

/**
 * GWT emulated version of {@link ImmutableList}.
 *
 * @author Hayward Chan
 */
@SuppressWarnings("serial") // we're overriding default serialization
public abstract class ImmutableList<E> extends ForwardingImmutableCollection<E>
    implements List<E>, RandomAccess {
  
  private transient final List<E> delegate;

  ImmutableList(List<E> delegate) {
    super(delegate);
    this.delegate = Collections.unmodifiableList(delegate);
  }

  ImmutableList() {
    this(Collections.<E>emptyList());
  }

  // Casting to any type is safe because the list will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <E> ImmutableList<E> of() {
    return (ImmutableList<E>) EmptyImmutableList.INSTANCE;
  }

  public static <E> ImmutableList<E> of(E element) {
    return new SingletonImmutableList<E>(element);
  }

  public static <E> ImmutableList<E> of(E e1, E e2) {
    return new RegularImmutableList<E>(
        ImmutableList.<E>nullCheckedList(e1, e2));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3) {
    return new RegularImmutableList<E>(
        ImmutableList.<E>nullCheckedList(e1, e2, e3));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) {
    return new RegularImmutableList<E>(
        ImmutableList.<E>nullCheckedList(e1, e2, e3, e4));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5) {
    return new RegularImmutableList<E>(
        ImmutableList.<E>nullCheckedList(e1, e2, e3, e4, e5));
  }

  public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
    return new RegularImmutableList<E>(
        ImmutableList.<E>nullCheckedList(e1, e2, e3, e4, e5, e6));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
    return new RegularImmutableList<E>(
         ImmutableList.<E>nullCheckedList(e1, e2, e3, e4, e5, e6, e7));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
    return new RegularImmutableList<E>(
         ImmutableList.<E>nullCheckedList(e1, e2, e3, e4, e5, e6, e7, e8));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
    return new RegularImmutableList<E>(
         ImmutableList.<E>nullCheckedList(e1, e2, e3, e4, e5, e6, e7, e8, e9));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
    return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(
        e1, e2, e3, e4, e5, e6, e7, e8, e9, e10));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) {
    return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(
        e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11));
  }

  public static <E> ImmutableList<E> of(
      E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11,
      E e12, E... others) {
    final int paramCount = 12;
    Object[] array = new Object[paramCount + others.length];
    arrayCopy(array, 0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11, e12);
    arrayCopy(array, paramCount, others);
    return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(array));
  }

  public static <E> ImmutableList<E> of(E[] elements) {
    checkNotNull(elements); // for GWT
    switch (elements.length) {
      case 0:
        return ImmutableList.of();
      case 1:
        return new SingletonImmutableList<E>(elements[0]);
      default:
        return new RegularImmutableList<E>(
            ImmutableList.<E>nullCheckedList(elements));
    }
  }

  private static void arrayCopy(Object[] dest, int pos, Object... source) {
    System.arraycopy(source, 0, dest, pos, source.length);
  }

  public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) {
    checkNotNull(elements); // for GWT
    return (elements instanceof Collection)
        ? copyOf((Collection<? extends E>) elements)
        : copyOf(elements.iterator());
  }

  public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) {
    return copyFromCollection(Lists.newArrayList(elements));
  }

  public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
    if (elements instanceof ImmutableCollection) {
      /*
       * TODO: When given an ImmutableList that's a sublist, copy the referenced
       * portion of the array into a new array to save space?
       */
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableCollection<E> list = (ImmutableCollection<E>) elements;
      return list.asList();
    }
    return copyFromCollection(elements);
  }

  public static <E> ImmutableList<E> copyOf(E[] elements) {
    checkNotNull(elements); // eager for GWT
    return copyOf(Arrays.asList(elements));
  }

  private static <E> ImmutableList<E> copyFromCollection(
      Collection<? extends E> collection) {
    Object[] elements = collection.toArray();
    switch (elements.length) {
      case 0:
        return of();
      case 1:
        @SuppressWarnings("unchecked") // collection had only Es in it
        ImmutableList<E> list = new SingletonImmutableList<E>((E) elements[0]);
        return list;
      default:
        return new RegularImmutableList<E>(ImmutableList.<E>nullCheckedList(elements));
    }
  }

  // Factory method that skips the null checks.  Used only when the elements
  // are guaranteed to be null.
  static <E> ImmutableList<E> unsafeDelegateList(List<? extends E> list) {
    switch (list.size()) {
      case 0:
        return of();
      case 1:
        return new SingletonImmutableList<E>(list.iterator().next());
      default:
        @SuppressWarnings("unchecked")
        List<E> castedList = (List<E>) list;
        return new RegularImmutableList<E>(castedList);
    }
  }

  static <E> ImmutableList<E> backedBy(E[] elements) {
    return unsafeDelegateList(Arrays.asList(elements));
  }

  private static <E> List<E> nullCheckedList(Object... array) {
    for (int i = 0, len = array.length; i < len; i++) {
      if (array[i] == null) {
        throw new NullPointerException("at index " + i);
      }
    }
    @SuppressWarnings("unchecked")
    E[] castedArray = (E[]) array;
    return Arrays.asList(castedArray);
  }

  public int indexOf(@Nullable Object object) {
    return delegate.indexOf(object);
  }

  public int lastIndexOf(@Nullable Object object) {
    return delegate.lastIndexOf(object);
  }

  public final boolean addAll(int index, Collection<? extends E> newElements) {
    throw new UnsupportedOperationException();
  }

  public final E set(int index, E element) {
    throw new UnsupportedOperationException();
  }

  public final void add(int index, E element) {
    throw new UnsupportedOperationException();
  }

  public final E remove(int index) {
    throw new UnsupportedOperationException();
  }

  public E get(int index) {
    return delegate.get(index);
  }

  public ImmutableList<E> subList(int fromIndex, int toIndex) {
    return unsafeDelegateList(delegate.subList(fromIndex, toIndex));
  }

  public ListIterator<E> listIterator() {
    return delegate.listIterator();
  }

  public ListIterator<E> listIterator(int index) {
    return delegate.listIterator(index);
  }

  @Override public ImmutableList<E> asList() {
    return this;
  }
  
  public ImmutableList<E> reverse(){
    List<E> list = Lists.newArrayList(this);
    Collections.reverse(list);
    return unsafeDelegateList(list);
  }

  @Override public Object[] toArray() {
    // Note that ArrayList.toArray() doesn't work here because it returns E[]
    // instead of Object[].
    return delegate.toArray(new Object[size()]);
  }

  @Override public boolean equals(Object obj) {
    return delegate.equals(obj);
  }

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

  public static <E> Builder<E> builder() {
    return new Builder<E>();
  }

  public static final class Builder<E> extends ImmutableCollection.Builder<E> {
    private final ArrayList<E> contents = Lists.newArrayList();

    public Builder() {}

    @Override public Builder<E> add(E element) {
      contents.add(checkNotNull(element));
      return this;
    }

    @Override public Builder<E> addAll(Iterable<? extends E> elements) {
      super.addAll(elements);
      return this;
    }

    @Override public Builder<E> add(E... elements) {
      checkNotNull(elements);  // for GWT
      super.add(elements);
      return this;
    }

    @Override public Builder<E> addAll(Iterator<? extends E> elements) {
      super.addAll(elements);
      return this;
    }

    @Override public ImmutableList<E> build() {
      return copyOf(contents);
    }
  }
}