package com.atlassian.vcache.internal.core.metrics;
   
   import javax.annotation.concurrent.NotThreadSafe;
   import java.util.Optional;
   import java.util.function.Consumer;
   import java.util.function.Supplier;
   
   import static java.util.Objects.requireNonNull;
   
  /**
   * Wrapper for a supplier used to create missing values. Calls the supplied handler with
   * the elapsed time taken in nanoseconds, and {@link Optional#empty()} means it was was not called.
   *
   * @param <V> the value type
   * @since 1.0.0
   */
  @NotThreadSafe
  public class TimedSupplier<V> implements Supplier<V>, AutoCloseable {
      private final Supplier<? extends V> delegate;
      private final Consumer<Optional<Long>> handler;
  
      private Optional<Long> elapsedDuration = Optional.empty();
  
      public TimedSupplier(Supplier<V> delegate, Consumer<Optional<Long>> handler) {
          this.delegate = requireNonNull(delegate);
          this.handler = requireNonNull(handler);
      }
  
      @Override
      public V get() {
          try (ElapsedTimer ignored = new ElapsedTimer(t -> elapsedDuration = Optional.of(t))) {
              return delegate.get();
          }
      }
  
      @Override
      public void close() {
          handler.accept(elapsedDuration);
      }
  
      public boolean wasInvoked() {
          return elapsedDuration.isPresent();
      }
  }