package jalview.util;

import java.util.Iterator;
import java.util.List;
import java.util.Objects;

/**
 * A generic immutable pair of values.
 * 
 * @author mmwarowny
 *
 * @param <T>
 *          first value type
 * @param <U>
 *          second value type
 */
public class Pair<T, U> implements Iterable<Object>
{
  final T val0;

  final U val1;

  public Pair(T val0, U val1)
  {
    this.val0 = val0;
    this.val1 = val1;
  }
  
  /**
   * Return value at the specified index cast to type R
   * @param <R> return type
   * @param index item index
   * @return value at given index
   * @throws ClassCastException value cannot be cast to R
   * @throws IndexOutOfBoundsException index outside tuple size
   */
  @SuppressWarnings("unchecked")
  public <R> R get(int index) throws ClassCastException, IndexOutOfBoundsException
  {
    if (index == 0)
      return (R) val0;
    if (index == 1)
      return (R) val1;
    throw new IndexOutOfBoundsException(index);
  }

  /**
   * @return 0th value of the pair
   */
  public T get0()
  {
    return val0;
  }

  /**
   * @return 1st value of the pair
   */
  public U get1()
  {
    return val1;
  }
  
  /**
   * @return tuple size
   */
  public int size()
  {
    return 2;
  }

  @Override
  public boolean equals(Object obj)
  {
    if (obj instanceof Pair)
    {
      Pair<?, ?> other = (Pair<?, ?>) obj;
      return Objects.equals(val0, other.val0) &&
          Objects.equals(val1, other.val1);
    }
    return false;
  }

  @Override
  public Iterator<Object> iterator()
  {
    return List.of(val0, val1).iterator();
  }
}