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.kafka.common.telemetry.internals;
  
  import java.time.Instant;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Optional;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * A LastValueTracker uses a ConcurrentHashMap to maintain historic values for a given key, and return
   * a previous value and an Instant for that value.
   *
   * @param <T> The type of the value.
   */
  public class LastValueTracker<T> {
      private final Map<MetricKey, InstantAndValue<T>> counters = new ConcurrentHashMap<>();
  
      /**
       * Return the last instant/value for the given MetricKey, or Optional.empty if there isn't one.
       *
       * @param metricKey the key for which to calculate a getAndSet.
       * @param now the timestamp for the new value.
       * @param value the current value.
       * @return the timestamp of the previous entry and its value. If there
       *     isn't a previous entry, then this method returns {@link Optional#empty()}
       */
      public Optional<InstantAndValue<T>> getAndSet(MetricKey metricKey, Instant now, T value) {
          InstantAndValue<T> instantAndValue = new InstantAndValue<>(now, value);
          InstantAndValue<T> valueOrNull = counters.put(metricKey, instantAndValue);
  
          // there wasn't already an entry, so return empty.
          if (valueOrNull == null) {
              return Optional.empty();
          }
  
          // Return the previous instance and the value.
          return Optional.of(valueOrNull);
      }
  
      public InstantAndValue<T> remove(MetricKey metricKey) {
          return counters.remove(metricKey);
      }
  
      public boolean contains(MetricKey metricKey) {
          return counters.containsKey(metricKey);
      }
  
      public void reset() {
          counters.clear();
      }
  
      public static class InstantAndValue<T> {
  
          private final Instant intervalStart;
          private final T value;
  
          public InstantAndValue(Instant intervalStart, T value) {
              this.intervalStart = Objects.requireNonNull(intervalStart);
              this.value = Objects.requireNonNull(value);
          }
  
          public Instant getIntervalStart() {
              return intervalStart;
          }
  
          public T getValue() {
              return value;
          }
      }
  
  }