/*
    * 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
    *
    *      https://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.commons.lang3.tuple;
  
  import java.io.Serializable;
  import java.util.Objects;
  
  import org.apache.commons.lang3.builder.CompareToBuilder;
  
  /**
   * A triple consisting of three elements.
   *
   * <p>
   * This class is an abstract implementation defining the basic API.
   * It refers to the elements as 'left', 'middle' and 'right'.
   * </p>
   *
   * <p>
   * Subclass implementations may be mutable or immutable.
   * However, there is no restriction on the type of the stored objects that may be stored.
   * If mutable objects are stored in the triple, then the triple itself effectively becomes mutable.
   * </p>
   *
   * @param <L> The left element type.
   * @param <M> The middle element type.
   * @param <R> The right element type.
   * @since 3.2
   */
  public abstract class Triple<L, M, R> implements Comparable<Triple<L, M, R>>, Serializable {
  
      /** Serialization version */
      private static final long serialVersionUID = 1L;
  
      /**
       * An empty array.
       * <p>
       * Consider using {@link #emptyArray()} to avoid generics warnings.
       * </p>
       *
       * @since 3.10
       */
      public static final Triple<?, ?, ?>[] EMPTY_ARRAY = {};
  
      /**
       * Returns the empty array singleton that can be assigned without compiler warning.
       *
       * @param <L> The left element type.
       * @param <M> The middle element type.
       * @param <R> The right element type.
       * @return The empty array singleton that can be assigned without compiler warning.
       * @since 3.10
       */
      @SuppressWarnings("unchecked")
      public static <L, M, R> Triple<L, M, R>[] emptyArray() {
          return (Triple<L, M, R>[]) EMPTY_ARRAY;
      }
  
      /**
       * Obtains an immutable triple of three objects inferring the generic types.
       *
       * @param <L> The left element type.
       * @param <M> The middle element type.
       * @param <R> The right element type.
       * @param left  The left element, may be null.
       * @param middle The middle element, may be null.
       * @param right  The right element, may be null.
       * @return An immutable triple formed from the three parameters, not null.
       */
      public static <L, M, R> Triple<L, M, R> of(final L left, final M middle, final R right) {
          return ImmutableTriple.of(left, middle, right);
      }
  
      /**
       * Obtains an immutable triple of three non-null objects inferring the generic types.
       *
       * @param <L> The left element type.
       * @param <M> The middle element type.
       * @param <R> The right element type.
       * @param left  The left element, may not be null.
       * @param middle  The middle element, may not be null.
       * @param right  The right element, may not be null.
       * @return An immutable triple formed from the three parameters, not null.
       * @throws NullPointerException Thrown if any input is null.
       * @since 3.13.0
       */
     public static <L, M, R> Triple<L, M, R> ofNonNull(final L left, final M middle, final R right) {
         return ImmutableTriple.ofNonNull(left, middle, right);
     }
 
     /**
      * Constructs a new instance.
      */
     public Triple() {
         // empty
     }
 
     /**
      * Compares the triple based on the left element, followed by the middle element,
      * finally the right element.
      * The types must be {@link Comparable}.
      *
      * @param other  The other triple, not null.
      * @return negative if this is less, zero if equal, positive if greater.
      */
     @Override
     public int compareTo(final Triple<L, M, R> other) {
       return new CompareToBuilder().append(getLeft(), other.getLeft())
           .append(getMiddle(), other.getMiddle())
           .append(getRight(), other.getRight()).toComparison();
     }
 
     /**
      * Compares this triple to another based on the three elements.
      *
      * @param obj  The object to compare to, null returns false.
      * @return true if the elements of the triple are equal.
      */
     @Override
     public boolean equals(final Object obj) {
         if (obj == this) {
             return true;
         }
         if (obj instanceof Triple<?, ?, ?>) {
             final Triple<?, ?, ?> other = (Triple<?, ?, ?>) obj;
             return Objects.equals(getLeft(), other.getLeft())
                 && Objects.equals(getMiddle(), other.getMiddle())
                 && Objects.equals(getRight(), other.getRight());
         }
         return false;
     }
 
     /**
      * Gets the left element from this triple.
      *
      * @return The left element, may be null.
      */
     public abstract L getLeft();
 
     /**
      * Gets the middle element from this triple.
      *
      * @return The middle element, may be null.
      */
     public abstract M getMiddle();
 
     /**
      * Gets the right element from this triple.
      *
      * @return The right element, may be null.
      */
     public abstract R getRight();
 
     /**
      * Returns a suitable hash code.
      * <p>
      * The hash code is adapted from the definition in {@code Map.Entry}.
      * </p>
      *
      * @return The hash code.
      */
     @Override
     public int hashCode() {
         // See Map.Entry API specification
         return Objects.hashCode(getLeft()) ^ Objects.hashCode(getMiddle()) ^ Objects.hashCode(getRight());
     }
 
     /**
      * Returns a String representation of this triple using the format {@code (left,middle,right)}.
      *
      * @return A string describing this object, not null.
      */
     @Override
     public String toString() {
         return "(" + getLeft() + "," + getMiddle() + "," + getRight() + ")";
     }
 
     /**
      * Formats the receiver using the given format.
      *
      * <p>
      * This uses {@link java.util.Formattable} to perform the formatting. Three variables may
      * be used to embed the left and right elements. Use {@code %1$s} for the left
      * element, {@code %2$s} for the middle and {@code %3$s} for the right element.
      * The default format used by {@code toString()} is {@code (%1$s,%2$s,%3$s)}.
      * </p>
      *
      * @param format  The format string, optionally containing {@code %1$s}, {@code %2$s} and {@code %3$s}, not null.
      * @return The formatted string, not null.
      */
     public String toString(final String format) {
         return String.format(format, getLeft(), getMiddle(), getRight());
     }
 
 }