package org.checkerframework.javacutil;

import java.util.Objects;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.qual.Pure;
import org.checkerframework.dataflow.qual.SideEffectFree;

/** Simple pair class for multiple returns. */
// TODO: as class is immutable, use @Covariant annotation.
public class Pair<V1, V2> {
  /** The first element in the pair. */
  public final V1 first;
  /** The second element in the pair. */
  public final V2 second;

  private Pair(V1 v1, V2 v2) {
    this.first = v1;
    this.second = v2;
  }

  public static <V1, V2> Pair<V1, V2> of(V1 v1, V2 v2) {
    return new Pair<>(v1, v2);
  }

  @SideEffectFree
  @Override
  public String toString() {
    return "Pair(" + first + ", " + second + ")";
  }

  private int hashCode = -1;

  @Pure
  @Override
  public int hashCode() {
    if (hashCode == -1) {
      hashCode = Objects.hash(first, second);
    }
    return hashCode;
  }

  @Override
  public boolean equals(@Nullable Object o) {
    if (this == o) {
      return true;
    }
    if (!(o instanceof Pair)) {
      return false;
    }
    @SuppressWarnings("unchecked")
    Pair<V1, V2> other = (Pair<V1, V2>) o;
    return Objects.equals(this.first, other.first) && Objects.equals(this.second, other.second);
  }
}