package com.atlassian.vcache.internal.memcached;
   
   import java.util.Collections;
   import java.util.HashMap;
   import java.util.HashSet;
   import java.util.List;
   import java.util.Map;
   import java.util.Optional;
   import java.util.Set;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.Future;
  import java.util.function.Function;
  import java.util.function.Supplier;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  import javax.annotation.Nonnull;
  
  import com.atlassian.vcache.CasIdentifier;
  import com.atlassian.vcache.DirectExternalCache;
  import com.atlassian.vcache.ExternalCacheException;
  import com.atlassian.vcache.ExternalCacheSettings;
  import com.atlassian.vcache.IdentifiedValue;
  import com.atlassian.vcache.Marshaller;
  import com.atlassian.vcache.PutPolicy;
  import com.atlassian.vcache.internal.RequestContext;
  import com.atlassian.vcache.internal.core.DefaultIdentifiedValue;
  import com.atlassian.vcache.internal.core.ExternalCacheKeyGenerator;
  import com.atlassian.vcache.internal.core.VCacheUtils;
  import com.atlassian.vcache.internal.core.service.AbstractExternalCache;
  
  import com.google.common.annotations.VisibleForTesting;
  import net.spy.memcached.CASResponse;
  import net.spy.memcached.CASValue;
  import net.spy.memcached.MemcachedClientIF;
  import net.spy.memcached.OperationTimeoutException;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import static com.atlassian.vcache.internal.core.VCacheUtils.isEmpty;
  import static com.atlassian.vcache.internal.core.VCacheUtils.marshall;
  import static com.atlassian.vcache.internal.core.VCacheUtils.unmarshall;
  import static com.atlassian.vcache.internal.memcached.MemcachedUtils.identifiedValueFrom;
  import static com.atlassian.vcache.internal.memcached.MemcachedUtils.putOperationForPolicy;
  import static com.atlassian.vcache.internal.memcached.MemcachedUtils.safeExtractId;
  import static java.util.Objects.requireNonNull;
  
  /**
   * Implementation of the {@link DirectExternalCache} that uses Memcached.
   *
   * @param <V> the value type
   *
   * @since 1.0
   */
  class MemcachedDirectExternalCache<V>
          extends AbstractExternalCache<V>
          implements DirectExternalCache<V>
  {
      private static final Logger log = LoggerFactory.getLogger(MemcachedDirectExternalCache.class);
  
      private final Supplier<MemcachedClientIF> clientSupplier;
      private final Supplier<RequestContext> contextSupplier;
      private final ExternalCacheKeyGenerator keyGenerator;
      private final Marshaller<V> valueMarshaller;
      private final ExternalCacheSettings settings;
      private final int defaultTtl;
  
      MemcachedDirectExternalCache(
              Supplier<MemcachedClientIF> clientSupplier,
              Supplier<RequestContext> contextSupplier,
              ExternalCacheKeyGenerator keyGenerator,
              String name,
              Marshaller<V> valueMarshaller,
              ExternalCacheSettings settings)
      {
          super(name);
          this.clientSupplier = requireNonNull(clientSupplier);
          this.contextSupplier = requireNonNull(contextSupplier);
          this.keyGenerator = requireNonNull(keyGenerator);
          this.valueMarshaller = requireNonNull(valueMarshaller);
          this.settings = requireNonNull(settings);
          this.defaultTtl = VCacheUtils.roundUpToSeconds(settings.getDefaultTtl().get());
      }
  
      @Nonnull
      @Override
      public CompletableFuture<Optional<V>> get(String internalKey)
      {
          return perform(() -> {
              final String externalKey = buildExternalKey(internalKey);
              return unmarshall(clientSupplier.get().get(externalKey), valueMarshaller);
          });
      }
  
      @Nonnull
      @Override
      public CompletableFuture<V> get(String internalKey, Supplier<V> supplier)
      {
          return perform(() -> {
              final String externalKey = buildExternalKey(internalKey);
             final Optional<V> existingValue = unmarshall(clientSupplier.get().get(externalKey), valueMarshaller);
             if (existingValue.isPresent())
             {
                 return existingValue.get();
             }
 
             log.trace("Cache {}, creating candidate for key {}", name, internalKey);
             final V candidateValue = requireNonNull(supplier.get());
             final byte[] candidateValueBytes = valueMarshaller.marshall(candidateValue);
 
             // Loop until either able to add the candidate value, or retrieve one that has been added by another thread
             for (; ; )
             {
                 final Future<Boolean> addOp = clientSupplier.get().add(externalKey, defaultTtl, candidateValueBytes);
                 if (addOp.get())
                 {
                     // I break here, rather than just return, due to battling with the compiler. Unless written
                     // this way, the compiler will not allow the lambda structure.
                     break;
                 }
 
                 log.info("Cache {}, unable to add candidate for key {}, retrieve what was added", name, internalKey);
                 final Optional<V> otherAddedValue = unmarshall(clientSupplier.get().get(externalKey), valueMarshaller);
                 if (otherAddedValue.isPresent())
                 {
                     return otherAddedValue.get();
                 }
 
                 log.info("Cache {}, unable to retrieve recently added candidate for key {}, looping", name, internalKey);
             }
             return candidateValue;
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Optional<IdentifiedValue<V>>> getIdentified(String internalKey)
     {
         return perform(() -> {
             final String externalKey = buildExternalKey(internalKey);
             final CASValue<Object> casValue = clientSupplier.get().gets(externalKey);
             if (casValue == null)
             {
                 return Optional.empty();
             }
 
             final CasIdentifier identifier = new MemcachedCasIdentifier(casValue.getCas());
             final IdentifiedValue<V> iv = new DefaultIdentifiedValue<>(
                     identifier, valueMarshaller.unmarshall((byte[]) casValue.getValue()));
             return Optional.of(iv);
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Map<String, Optional<V>>> getBulk(Iterable<String> internalKeys)
     {
         return perform(() -> {
             if (isEmpty(internalKeys))
             {
                 return new HashMap<>();
             }
 
             // De-duplicate the keys and calculate the externalKeys
             final ExternalCacheRequestContext cacheContext = ensureCacheContext();
 
             final Set<String> externalKeys = StreamSupport.stream(internalKeys.spliterator(), false)
                     .map(cacheContext::externalEntryKeyFor)
                     .collect(Collectors.toSet());
 
             // Returns map of keys that contain values, so need to handle the missing ones
             final Map<String, Object> haveValues = clientSupplier.get().getBulk(externalKeys);
 
             return externalKeys.stream().collect(Collectors.toMap(
                     cacheContext::internalEntryKeyFor,
                     k -> unmarshall(haveValues.get(k), valueMarshaller)));
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Map<String, V>> getBulk(Function<Set<String>, Map<String, V>> factory, Iterable<String> internalKeys)
     {
         return perform(() -> {
             if (isEmpty(internalKeys))
             {
                 return new HashMap<>();
             }
 
             // De-duplicate the keys and calculate the externalKeys
             final ExternalCacheRequestContext cacheContext = ensureCacheContext();
 
             final Set<String> externalKeys = Collections.unmodifiableSet(
                     StreamSupport.stream(internalKeys.spliterator(), false)
                             .map(cacheContext::externalEntryKeyFor)
                             .collect(Collectors.toSet()));
 
             // Returns map of keys that contain values, so need to calculate the
             // missing ones
             final Map<String, Object> haveValues = clientSupplier.get().getBulk(externalKeys);
             log.trace("{} of {} entries have values", haveValues.size(), externalKeys.size());
             final Set<String> missingExternalKeys = new HashSet<>(externalKeys);
             missingExternalKeys.removeAll(haveValues.keySet());
 
             // Add the existing values to the grand result
             final Map<String, V> grandResult = haveValues.entrySet().stream().collect(Collectors.toMap(
                     e -> cacheContext.internalEntryKeyFor(e.getKey()),
                     e -> unmarshall(e.getValue(), valueMarshaller).get()
             ));
 
             if (!missingExternalKeys.isEmpty())
             {
                 // 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);
 
                 // Okay, got the missing values, now need to add them to Memcached
                 final Map<String, Future<Boolean>> internalKeyToFutureMap = missingValues.entrySet().stream().collect(Collectors.toMap(
                         Map.Entry::getKey,
                         e -> clientSupplier.get().set(
                                 cacheContext.externalEntryKeyFor(e.getKey()), defaultTtl, marshall(e.getValue(), valueMarshaller))
                 ));
 
                 // Now wait for the outcomes and then add to the grand result
                 for (Map.Entry<String, Future<Boolean>> e : internalKeyToFutureMap.entrySet())
                 {
                     e.getValue().get(); // Don't care about the result as it will always be true
                 }
 
                 grandResult.putAll(missingValues);
             }
 
             return grandResult;
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Map<String, Optional<IdentifiedValue<V>>>> getBulkIdentified(Iterable<String> internalKeys)
     {
         return perform(() -> {
             if (isEmpty(internalKeys))
             {
                 return new HashMap<>();
             }
 
             // There is not equivalent call in Spy Memcached client. So need to do the calls async.
             final ExternalCacheRequestContext cacheContext = ensureCacheContext();
 
             // De-duplicate the keys, create map on internalKey to the future
             final Map<String, Future<CASValue<Object>>> internalKeyToFuture =
                     StreamSupport.stream(internalKeys.spliterator(), false)
                             .distinct()
                             .collect(Collectors.toMap(
                                     k -> k,
                                     k -> clientSupplier.get().asyncGets(cacheContext.externalEntryKeyFor(k))
                             ));
 
             return internalKeyToFuture.entrySet().stream().collect(Collectors.toMap(
                     Map.Entry::getKey,
                     e -> identifiedValueFrom(e.getValue(), valueMarshaller)
             ));
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Boolean> put(String internalKey, V value, PutPolicy policy)
     {
         return perform(() -> {
             final String externalKey = buildExternalKey(internalKey);
             final byte[] valueBytes = valueMarshaller.marshall(value);
 
             final Future<Boolean> putOp =
                     putOperationForPolicy(policy, clientSupplier.get(), externalKey, defaultTtl, valueBytes);
 
             return putOp.get();
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Boolean> removeIf(String internalKey, CasIdentifier casId)
     {
         return perform(() -> {
             final String partitionedKey = buildExternalKey(internalKey);
             final Future<Boolean> delOp = clientSupplier.get().delete(partitionedKey, safeExtractId(casId));
             return delOp.get();
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Boolean> replaceIf(String internalKey, CasIdentifier casId, V newValue)
     {
         return perform(() -> {
             final String externalKey = buildExternalKey(internalKey);
             final CASResponse casOp = clientSupplier.get().cas(
                     externalKey, safeExtractId(casId), defaultTtl, valueMarshaller.marshall(newValue));
             return casOp == CASResponse.OK;
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Void> remove(Iterable<String> internalKeys)
     {
         // There is no bulk delete in the api, so need to remove each one async
         return perform(() -> {
             if (isEmpty(internalKeys))
             {
                 return null;
             }
 
             // Lodge all the requests for delete
             final List<Future<Boolean>> deleteOps =
                     StreamSupport.stream(internalKeys.spliterator(), false)
                             .map(this::buildExternalKey)
                             .map(k -> clientSupplier.get().delete(k))
                             .collect(Collectors.toList());
 
             // Now wait for the outcome
             for (Future<Boolean> delOp : deleteOps)
             {
                 delOp.get(); // don't care if succeeded or not
             }
 
             return null;
         });
     }
 
     @Nonnull
     @Override
     public CompletableFuture<Void> removeAll()
     {
         return perform(() -> {
             final ExternalCacheRequestContext cacheContext = ensureCacheContext();
             cacheContext.updateCacheVersion(
                     clientSupplier.get().incr(cacheContext.externalCacheVersionKey(), 1, 1));
             return null;
         });
     }
 
     @VisibleForTesting
     void refreshCacheVersion()
     {
         // Refresh the cacheVersion. Useful if want to get the current state of the external cache in testing.
         final ExternalCacheRequestContext cacheContext = ensureCacheContext();
         cacheContext.updateCacheVersion(
                 clientSupplier.get().incr(cacheContext.externalCacheVersionKey(), 0, 1));
     }
 
     private String buildExternalKey(String internalKey) throws OperationTimeoutException
     {
         final ExternalCacheRequestContext cacheContext = ensureCacheContext();
         return cacheContext.externalEntryKeyFor(internalKey);
     }
 
     @Nonnull
     protected ExternalCacheRequestContext ensureCacheContext() throws OperationTimeoutException
     {
         final RequestContext requestContext = contextSupplier.get();
 
         return requestContext.computeIfAbsent(this, () -> {
             // Need to build a new context, which involves getting the current cache version, or setting it if it does
             // not exist.
             log.trace("Cache {}: Setting up a new context", name);
             final ExternalCacheRequestContext newCacheContext =
                     new ExternalCacheRequestContext(keyGenerator, name, requestContext::partitionIdentifier);
             newCacheContext.updateCacheVersion(
                     clientSupplier.get().incr(newCacheContext.externalCacheVersionKey(), 0, 1));
             return newCacheContext;
         });
     }
 
     @Nonnull
     @Override
     protected Logger getLogger()
     {
         return log;
     }
 
     @Nonnull
     @Override
     protected ExternalCacheException mapException(Exception ex)
     {
         return MemcachedUtils.mapException(ex);
     }
 }