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.linq4j;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.AbstractList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.RandomAccess;
  import java.util.function.ObjIntConsumer;
  
  /**
   * Pair of an element and an ordinal.
   *
   * @param <E> Element type
   */
  public class Ord<E> implements Map.Entry<Integer, E> {
    public final int i;
    public final E e;
  
    /**
     * Creates an Ord.
     */
    public Ord(int i, E e) {
      this.i = i;
      this.e = e;
    }
  
    /**
     * Creates an Ord.
     */
    public static <E> Ord<E> of(int n, E e) {
      return new Ord<>(n, e);
    }
  
    @Override public int hashCode() {
      return Objects.hash(e, i);
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof Ord
          && i == ((Ord<?>) obj).i
          && Objects.equals(e, ((Ord<?>) obj).e);
    }
  
    /**
     * Creates an iterable of {@code Ord}s over an iterable.
     */
    public static <E> Iterable<Ord<E>> zip(final Iterable<? extends E> iterable) {
      return () -> zip(iterable.iterator());
    }
  
    /**
     * Creates an iterator of {@code Ord}s over an iterator.
     */
    public static <E> Iterator<Ord<E>> zip(final Iterator<? extends E> iterator) {
      return new Iterator<Ord<E>>() {
        int n = 0;
  
        @Override public boolean hasNext() {
          return iterator.hasNext();
        }
  
        @Override public Ord<E> next() {
          return Ord.of(n++, iterator.next());
        }
  
        @Override public void remove() {
          iterator.remove();
        }
      };
    }
  
    /**
     * Returns a numbered list based on an array.
     */
    public static <E> List<Ord<E>> zip(final E[] elements) {
      return new OrdArrayList<>(elements);
    }
  
    /**
     * Returns a numbered list.
     */
    public static <E> List<Ord<E>> zip(final List<? extends E> elements) {
      return elements instanceof RandomAccess
          ? new OrdRandomAccessList<>(elements)
          : new OrdList<>(elements);
    }
  
    /**
     * Iterates over an array in reverse order.
     *
     * <p>Given the array ["a", "b", "c"], returns (2, "c") then (1, "b") then
     * (0, "a").
     */
    @SafeVarargs // heap pollution is not possible because we only read
    public static <E> Iterable<Ord<E>> reverse(E... elements) {
      return reverse(ImmutableList.copyOf(elements));
    }
  
    /**
     * Iterates over a list in reverse order.
     *
     * <p>Given the list ["a", "b", "c"], returns (2, "c") then (1, "b") then
     * (0, "a").
     */
    public static <E> Iterable<Ord<E>> reverse(Iterable<? extends E> elements) {
      final ImmutableList<E> elementList = ImmutableList.copyOf(elements);
      return () -> new Iterator<Ord<E>>() {
        int i = elementList.size() - 1;
  
        @Override public boolean hasNext() {
          return i >= 0;
        }
  
        @Override public Ord<E> next() {
          return Ord.of(i, elementList.get(i--));
        }
      };
    }
  
    @Override public Integer getKey() {
      return i;
    }
  
    @Override public E getValue() {
      return e;
    }
  
    @Override public E setValue(E value) {
      throw new UnsupportedOperationException();
    }
  
    /** Applies an action to every element of an iterable, passing the zero-based
     * ordinal of the element to the action.
     *
     * @see List#forEach(java.util.function.Consumer)
     * @see Map#forEach(java.util.function.BiConsumer)
     *
     * @param iterable Iterable
     * @param action The action to be performed for each element
     * @param <T> Element type
     */
    public static <T> void forEach(Iterable<T> iterable,
        ObjIntConsumer<? super T> action) {
      int i = 0;
      for (T t : iterable) {
        action.accept(t, i++);
      }
    }
  
    /** Applies an action to every element of an array, passing the zero-based
     * ordinal of the element to the action.
     *
     * @see List#forEach(java.util.function.Consumer)
     * @see Map#forEach(java.util.function.BiConsumer)
     *
     * @param ts Array
     * @param action The action to be performed for each element
     * @param <T> Element type
     */
    public static <T> void forEach(T[] ts,
        ObjIntConsumer<? super T> action) {
      for (int i = 0; i < ts.length; i++) {
        action.accept(ts[i], i);
      }
    }
  
    /** List of {@link Ord} backed by a list of elements.
     *
     * @param <E> element type */
    private static class OrdList<E> extends AbstractList<Ord<E>> {
      private final List<? extends E> elements;
  
      OrdList(List<? extends E> elements) {
        this.elements = elements;
      }
  
      @Override public Ord<E> get(int index) {
        return Ord.of(index, elements.get(index));
      }
  
      @Override public int size() {
        return elements.size();
      }
    }
  
    /** List of {@link Ord} backed by a random-access list of elements.
     *
     * @param <E> element type */
    private static class OrdRandomAccessList<E> extends OrdList<E>
        implements RandomAccess {
      OrdRandomAccessList(List<? extends E> elements) {
        super(elements);
      }
    }
  
    /** List of {@link Ord} backed by an array of elements.
     *
     * @param <E> element type */
    private static class OrdArrayList<E> extends AbstractList<Ord<E>>
        implements RandomAccess {
      private final E[] elements;
  
      OrdArrayList(E[] elements) {
        this.elements = elements;
      }
  
      @Override public Ord<E> get(int index) {
        return Ord.of(index, elements[index]);
      }
  
      @Override public int size() {
        return elements.length;
      }
    }
  }
  