package com.atlassian.vcache;
   
   import com.atlassian.annotations.PublicApi;
   
   import java.time.Duration;
   import java.util.Optional;
   
   import static com.atlassian.vcache.SettingsUtils.ifPresent;
   import static java.util.Objects.requireNonNull;
  
  /**
   * An immutable representation of settings for an {@link ExternalCache}.
   *
   * @since 1.0
   */
  @PublicApi
  public class ExternalCacheSettings {
      private final Optional<Duration> defaultTtl;
      private final Optional<Integer> entryCountHint;
      private final Optional<ChangeRate> dataChangeRateHint;
      private final Optional<ChangeRate> entryGrowthRateHint;
  
      ExternalCacheSettings(
              Optional<Duration> defaultTtl,
              Optional<Integer> entryCountHint,
              Optional<ChangeRate> dataChangeRateHint,
              Optional<ChangeRate> entryGrowthRateHint) {
          this.defaultTtl = requireNonNull(defaultTtl);
          this.entryCountHint = requireNonNull(entryCountHint);
          this.dataChangeRateHint = requireNonNull(dataChangeRateHint);
          this.entryGrowthRateHint = requireNonNull(entryGrowthRateHint);
      }
  
      /**
       * Returns a new {@link ExternalCacheSettings} instance where the current settings
       * are overridden with settings specified in <tt>overrides</tt>.
       *
       * @param overrides contains the settings to override
       * @return a new {@link ExternalCacheSettings} instance with the <tt>overrides</tt> settings applied.
       */
      public ExternalCacheSettings override(ExternalCacheSettings overrides) {
          return new ExternalCacheSettings(
                  ifPresent(overrides.getDefaultTtl(), getDefaultTtl()),
                  ifPresent(overrides.getEntryCountHint(), getEntryCountHint()),
                  ifPresent(overrides.getDataChangeRateHint(), getDataChangeRateHint()),
                  ifPresent(overrides.getEntryGrowthRateHint(), getEntryGrowthRateHint()));
      }
  
      /**
       * Returns the default time-to-live for entries when added. The time-to-live is calculated on the time the
       * entry was added or updated.
       *
       * @return the default time-to-live for entries when added.
       */
      public Optional<Duration> getDefaultTtl() {
          return defaultTtl;
      }
  
      /**
       * Returns the hint for the expected number of entries
       *
       * @return the hint for the expected number of entries
       */
      public Optional<Integer> getEntryCountHint() {
          return entryCountHint;
      }
  
      /**
       * Returns the hint for the expected change rate for data updates.
       *
       * @return the hint for the expected change rate for data updates.
       */
      public Optional<ChangeRate> getDataChangeRateHint() {
          return dataChangeRateHint;
      }
  
      /**
       * Returns the hint for the expected change rate for entry additions.
       *
       * @return the hint for the expected change rate for entry additions.
       */
      public Optional<ChangeRate> getEntryGrowthRateHint() {
          return entryGrowthRateHint;
      }
  }