package com.atlassian.vcache.internal.core.service;
   
   import com.atlassian.vcache.internal.core.ExternalCacheKeyGenerator;
   import io.atlassian.util.concurrent.Lazy;
   
   import javax.annotation.Nullable;
   import java.time.Duration;
   import java.util.function.Function;
   import java.util.function.Supplier;
  
  /**
   * Represents the request context for an {@link com.atlassian.vcache.ExternalCache} that maintains a
   * cache version.
   *
   * @param <V> the value type
   * @since 1.0.0
   */
  public class VersionedExternalCacheRequestContext<V> extends AbstractExternalCacheRequestContext<V> {
      protected final String externalCacheVersionKey;
      private final Supplier<Long> cacheVersionSupplier;
  
      @Nullable
      private Long cacheVersion;
  
      public VersionedExternalCacheRequestContext(ExternalCacheKeyGenerator keyGenerator,
                                                  String name,
                                                  Supplier<String> partitionSupplier,
                                                  Function<String, Long> cacheVersionSupplier,
                                                  Duration lockTimeout) {
          super(keyGenerator, name, partitionSupplier, lockTimeout);
          this.externalCacheVersionKey =
                  keyGenerator.cacheVersionKey(partitionSupplier.get(), name);
          // memoize the cache version so we don't re-evaluate the function (and re-invoke the external cache) every time we need it
          this.cacheVersionSupplier = Lazy.supplier(() -> cacheVersionSupplier.apply(externalCacheVersionKey));
      }
  
      @Override
      protected long cacheVersion() {
          return cacheVersion == null
                  ? cacheVersionSupplier.get()
                  : cacheVersion;
      }
  
      public void updateCacheVersion(final Function<String, Long> cacheVersionSupplier) {
          this.cacheVersion = cacheVersionSupplier.apply(externalCacheVersionKey);
          clearKeyMaps();
      }
  }