package com.atlassian.vcache.internal.guava;
   
   import com.atlassian.marshalling.api.MarshallingPair;
   import com.atlassian.vcache.ExternalCacheException;
   import com.atlassian.vcache.PutPolicy;
   import com.atlassian.vcache.internal.MetricLabel;
   import com.atlassian.vcache.internal.RequestContext;
   import com.atlassian.vcache.internal.core.ExternalCacheKeyGenerator;
   import com.atlassian.vcache.internal.core.cas.IdentifiedData;
  import com.atlassian.vcache.internal.core.metrics.CacheType;
  import com.atlassian.vcache.internal.core.metrics.MetricsRecorder;
  import com.atlassian.vcache.internal.core.service.AbstractExternalCacheRequestContext;
  import com.atlassian.vcache.internal.core.service.AbstractStableReadExternalCache;
  import com.atlassian.vcache.internal.core.service.UnversionedExternalCacheRequestContext;
  import com.google.common.cache.Cache;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Collections;
  import java.util.Map;
  import java.util.Optional;
  import java.util.Set;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.CompletionStage;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.function.Function;
  import java.util.function.Supplier;
  import java.util.stream.Collectors;
  
  import static com.atlassian.vcache.internal.core.cas.IdentifiedUtils.marshall;
  import static com.atlassian.vcache.internal.core.cas.IdentifiedUtils.unmarshall;
  import static java.util.Objects.requireNonNull;
  
  /**
   * Guava implementation of {@link com.atlassian.vcache.StableReadExternalCache}.
   *
   * @param <V> the value type
   * @since 1.0.0
   */
  public class GuavaStableReadExternalCache<V>
          extends AbstractStableReadExternalCache<V> {
      private static final Logger log = LoggerFactory.getLogger(GuavaStableReadExternalCache.class);
  
      private final Cache<String, IdentifiedData> delegate;
      private final Supplier<RequestContext> contextSupplier;
      private final ExternalCacheKeyGenerator keyGenerator;
      private final Optional<MarshallingPair<V>> valueMarshalling;
  
      public GuavaStableReadExternalCache(
              String name,
              Cache<String, IdentifiedData> delegate,
              Supplier<RequestContext> contextSupplier,
              ExternalCacheKeyGenerator keyGenerator,
              Optional<MarshallingPair<V>> valueMarshalling,
              MetricsRecorder metricsRecorder) {
          super(name, metricsRecorder);
          this.contextSupplier = requireNonNull(contextSupplier);
          this.keyGenerator = requireNonNull(keyGenerator);
          this.valueMarshalling = requireNonNull(valueMarshalling);
          this.delegate = requireNonNull(delegate);
      }
  
      @Override
      protected CompletionStage<Boolean> internalPut(String internalKey, V value, PutPolicy policy) {
          final AbstractExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
          return perform(
                  () -> {
                      // This stores the result of the remote operation. If it fails then we can roll back. We use Atomic because in the
                      // future we may be async.
                      final AtomicBoolean remotePutResult = new AtomicBoolean(true);
  
                      // computeValue allows us to get the current CompletableFuture (if there is one) and chain the next
                      // put() onto the old future. If the old future is still running then we preserve
                      // ordering (and so consistency). Also any blocked gets will get the new value when the chain
                      // completes. The map locks the update to the future so updates are nicely serialized.
                      cacheContext.computeValue(internalKey, (k, oldValue) -> {
                          if (oldValue != null) {
                              return oldValue.thenApply(oldV -> {
                                  remotePutResult.set(remotePut(cacheContext.externalEntryKeyFor(internalKey), value, policy));
                                  return Optional.of(value);
                              });
                          } else {
                              remotePutResult.set(remotePut(cacheContext.externalEntryKeyFor(internalKey), value, policy));
                              return CompletableFuture.completedFuture(Optional.of(value));
                          }
                      });
                      return remotePutResult.get();
                  },
                  (result) -> {
                      if (!result) {
                          cacheContext.forgetValue(internalKey);
                      }
                  });
      }
  
      @Override
      protected CompletionStage<Void> internalRemove(Iterable<String> internalKeys) {
          return perform(() -> {
             // There is no bulk delete in the api, so need to remove each one
             final AbstractExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
             for (String key : internalKeys) {
                 delegate.asMap().remove(cacheContext.externalEntryKeyFor(key));
                 cacheContext.forgetValue(key);
             }
             return null;
         });
     }
 
     @Override
     protected CompletionStage<Void> internalRemoveAll() {
         return perform(() -> {
             final AbstractExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
             delegate.asMap().clear();
             cacheContext.forgetAllValues();
             return null;
         });
     }
 
     @Override
     protected Logger getLogger() {
         return log;
     }
 
     @Override
     protected AbstractExternalCacheRequestContext<V> ensureCacheContext() {
         final RequestContext requestContext = contextSupplier.get();
 
         return requestContext.computeIfAbsent(this, () -> {
             log.trace("Cache {}: Setting up a new context", getName());
             return new UnversionedExternalCacheRequestContext<>(
                     keyGenerator, getName(), requestContext::partitionIdentifier);
         });
     }
 
     @Override
     protected V handleCreation(String internalKey, Supplier<V> supplier)
             throws ExecutionException, InterruptedException {
         final AbstractExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         final V candidateValue = requireNonNull(supplier.get());
         final IdentifiedData candidateIdentifiedData = marshall(candidateValue, valueMarshalling);
 
         final String externalKey = cacheContext.externalEntryKeyFor(internalKey);
         final Optional<V> otherAddedValue =
                 unmarshall(delegate.asMap().putIfAbsent(externalKey, candidateIdentifiedData), valueMarshalling);
 
         if (otherAddedValue.isPresent()) {
             getLogger().info("Cache {}, unable to add candidate for key {}, use what was added", name, internalKey);
             return otherAddedValue.get();
         }
 
         return candidateValue;
     }
 
     @Override
     protected Map<String, V> handleCreation(Function<Set<String>, Map<String, V>> factory, Set<String> externalKeys)
             throws ExecutionException, InterruptedException {
         // Get the missing values from the external cache.
         // Returns map of keys that contain values, so need to handle the missing ones
         final AbstractExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         metricsRecorder.record(name, CacheType.EXTERNAL, MetricLabel.NUMBER_OF_REMOTE_GET, 1);
 
         final Map<String, Optional<V>> candidateValues = directGetBulk(externalKeys);
 
         final Set<String> missingExternalKeys = candidateValues.entrySet().stream()
                 .filter(e -> !e.getValue().isPresent())
                 .map(Map.Entry::getKey)
                 .collect(Collectors.toSet());
 
         // Add the retrieved values to the grand result
         final Map<String, V> grandResult = candidateValues.entrySet().stream()
                 .filter(e -> e.getValue().isPresent())
                 .collect(Collectors.toMap(
                         e -> cacheContext.internalEntryKeyFor(e.getKey()),
                         e -> e.getValue().get()));
 
         if (!missingExternalKeys.isEmpty()) {
             getLogger().trace("Cache {}: getBulk(Function): calling factory to create {} values",
                     name, missingExternalKeys.size());
             // Okay, need to get the missing values and mapping from externalKeys to internalKeys
             final Set<String> missingInternalKeys = Collections.unmodifiableSet(
                     missingExternalKeys.stream().map(cacheContext::internalEntryKeyFor).collect(Collectors.toSet()));
             final Map<String, V> missingValues = factory.apply(missingInternalKeys);
             if (missingInternalKeys.size() != missingValues.size()) {
                 getLogger().warn("Cache {}: getBulk(Function): mismatch on generated values, expected ",
                         name, missingInternalKeys.size() + " but got " + missingValues.size());
                 throw new ExternalCacheException(ExternalCacheException.Reason.FUNCTION_INCORRECT_RESULT);
             }
 
             // Okay, got the missing values, now need to add them
             missingValues.entrySet().stream().forEach(e ->
                     delegate.put(
                             cacheContext.externalEntryKeyFor(e.getKey()),
                             marshall(e.getValue(), valueMarshalling)));
 
             grandResult.putAll(missingValues);
         }
         return grandResult;
     }
 
     @Override
     protected final ExternalCacheException mapException(Exception ex) {
         return GuavaUtils.mapException(ex);
     }
 
     @Override
     protected final Optional<V> directGet(String externalKey) {
         return unmarshall(delegate.getIfPresent(externalKey), valueMarshalling);
     }
 
     @Override
     protected final Map<String, Optional<V>> directGetBulk(Set<String> externalKeys) {
         return GuavaUtils.directGetBulk(externalKeys, delegate, valueMarshalling);
     }
 
     private boolean remotePut(String externalKey, V value, PutPolicy policy) {
         final IdentifiedData identifiedData = marshall(value, valueMarshalling);
         return GuavaUtils.directPut(externalKey, identifiedData, policy, delegate);
     }
 }