content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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 org.apache.calcite.util;
  
  import com.google.common.collect.ImmutableList;
  
  import java.util.AbstractList;
  import java.util.List;
  
  /**
   * Read-only list that is the concatenation of sub-lists.
   *
   * <p>The list is read-only; attempts to call methods such as
   * {@link #add(Object)} or {@link #set(int, Object)} will throw.
   *
   * <p>Changes to the backing lists, including changes in length, will be
   * reflected in this list.
   *
   * <p>This class is not thread-safe. Changes to backing lists will cause
   * unspecified behavior.
   *
   * @param <T> Element type
   */
  public class CompositeList<T> extends AbstractList<T> {
    private final ImmutableList<List<T>> lists;
  
    /**
     * Creates a CompositeList.
     *
     * @param lists Constituent lists
     */
    private CompositeList(ImmutableList<List<T>> lists) {
      this.lists = lists;
    }
  
    /**
     * Creates a CompositeList.
     *
     * @param lists Constituent lists
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    @SafeVarargs
    public static <T> CompositeList<T> of(List<? extends T>... lists) {
      //noinspection unchecked
      return new CompositeList<T>((ImmutableList) ImmutableList.copyOf(lists));
    }
  
    /**
     * Creates a CompositeList.
     *
     * @param lists Constituent lists
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    public static <T> CompositeList<T> ofCopy(Iterable<List<T>> lists) {
      final ImmutableList<List<T>> list = ImmutableList.copyOf(lists);
      return new CompositeList<>(list);
    }
  
    /**
     * Creates a CompositeList of zero lists.
     *
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    public static <T> List<T> of() {
      return ImmutableList.of();
    }
  
    /**
     * Creates a CompositeList of one list.
     *
     * @param list0 List
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    public static <T> List<T> of(List<T> list0) {
      return list0;
    }
  
    /**
     * Creates a CompositeList of two lists.
     *
     * @param list0 First list
     * @param list1 Second list
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    public static <T> CompositeList<T> of(List<? extends T> list0,
        List<? extends T> list1) {
      //noinspection unchecked
      return new CompositeList<T>((ImmutableList) ImmutableList.of(list0, list1));
    }
  
    /**
     * Creates a CompositeList of three lists.
     *
     * @param list0 First list
     * @param list1 Second list
     * @param list2 Third list
     * @param <T>   Element type
     * @return List consisting of all lists
     */
    public static <T> CompositeList<T> of(List<? extends T> list0,
        List<? extends T> list1,
        List<? extends T> list2) {
      //noinspection unchecked
      return new CompositeList<T>((ImmutableList) ImmutableList.of(list0, list1, list2));
    }
  
    @Override public T get(int index) {
      for (List<? extends T> list : lists) {
        int nextIndex = index - list.size();
        if (nextIndex < 0) {
          return list.get(index);
        }
        index = nextIndex;
      }
      throw new IndexOutOfBoundsException();
    }
  
    @Override public int size() {
      int n = 0;
      for (List<? extends T> list : lists) {
        n += list.size();
      }
      return n;
    }
  }
  