package com.atlassian.vcache.internal.memcached;
   
   import com.atlassian.marshalling.api.MarshallingPair;
   import com.atlassian.vcache.ExternalCacheException;
   import com.atlassian.vcache.ExternalCacheSettings;
   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.VCacheCoreUtils;
  import com.atlassian.vcache.internal.core.metrics.CacheType;
  import com.atlassian.vcache.internal.core.metrics.MetricsRecorder;
  import com.atlassian.vcache.internal.core.service.AbstractStableReadExternalCache;
  import com.atlassian.vcache.internal.core.service.VersionedExternalCacheRequestContext;
  import net.spy.memcached.MemcachedClientIF;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Map;
  import java.util.Optional;
  import java.util.Set;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.function.Supplier;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  
  import static com.atlassian.vcache.internal.core.VCacheCoreUtils.isEmpty;
  import static com.atlassian.vcache.internal.core.VCacheCoreUtils.unmarshall;
  import static com.atlassian.vcache.internal.memcached.MemcachedUtils.expiryTime;
  import static com.atlassian.vcache.internal.memcached.MemcachedUtils.putOperationForPolicy;
  import static java.util.Objects.requireNonNull;
  
  /**
   * Implementation that backs onto Memcached.
   *
   * @param <V> the value type
   * @since 1.0.0
   */
  class MemcachedStableReadExternalCache<V>
          extends AbstractStableReadExternalCache<V> {
      private static final Logger log = LoggerFactory.getLogger(MemcachedStableReadExternalCache.class);
  
      private final Supplier<MemcachedClientIF> clientSupplier;
      private final Supplier<RequestContext> contextSupplier;
      private final ExternalCacheKeyGenerator keyGenerator;
      private final MarshallingPair<V> valueMarshalling;
      private final int ttlSeconds;
  
      MemcachedStableReadExternalCache(
              MemcachedVCacheServiceSettings serviceSettings,
              Supplier<RequestContext> contextSupplier,
              ExternalCacheKeyGenerator keyGenerator,
              String name,
              MarshallingPair<V> valueMarshalling,
              ExternalCacheSettings settings,
              MetricsRecorder metricsRecorder) {
          super(name, metricsRecorder, serviceSettings.getLockTimeout(), serviceSettings.getExternalCacheExceptionListener());
          this.clientSupplier = requireNonNull(serviceSettings.getClientSupplier());
          this.contextSupplier = requireNonNull(contextSupplier);
          this.keyGenerator = requireNonNull(keyGenerator);
          this.valueMarshalling = requireNonNull(valueMarshalling);
          this.ttlSeconds = VCacheCoreUtils.roundUpToSeconds(settings.getDefaultTtl().get());
      }
  
      @Override
      public boolean internalPut(String internalKey, V value, PutPolicy policy) {
          final String externalKey = ensureCacheContext().externalEntryKeyFor(internalKey);
          final byte[] valueBytes = valueMarshalling.getMarshaller().marshallToBytes(value);
  
          try {
              final Future<Boolean> putOp = putOperationForPolicy(
                      policy, clientSupplier.get(), externalKey, expiryTime(ttlSeconds), valueBytes);
              return putOp.get();
          } catch (InterruptedException | ExecutionException e) {
              throw new ExternalCacheException(ExternalCacheException.Reason.UNCLASSIFIED_FAILURE, e);
          }
      }
  
      @Override
      protected void internalRemove(Iterable<String> internalKeys) {
          // There is no bulk delete in the api, so need to remove each one async
          if (isEmpty(internalKeys)) {
              return;
          }
  
          // Lodge all the requests for delete
          final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
          final Map<String, Future<Boolean>> deleteOps =
                  StreamSupport.stream(internalKeys.spliterator(), false)
                          .distinct()
                          .collect(Collectors.toMap(
                                  k -> k,
                                  k -> clientSupplier.get().delete(cacheContext.externalEntryKeyFor(k))
                          ));
  
          // Need to loop verifying the outcome. If an exception was thrown for an operation,
          // then do not record the removal.
          Exception failureException = null;
         for (Map.Entry<String, Future<Boolean>> delOp : deleteOps.entrySet()) {
             try {
                 // Do not care whether the delOp returns true or false. Either way, no entry with the specified key
                 // now exists on the Memcache server.
                 delOp.getValue().get();
                 cacheContext.recordValue(delOp.getKey(), Optional.empty());
             } catch (ExecutionException | InterruptedException ex) {
                 log.info("Cache {}: unable to remove key {}", name, delOp.getKey(), ex);
                 failureException = ex;
             }
         }
 
         // Finally, if there was a failure, then re-throw the last one reported (as good as any!)
         if (failureException != null) {
             throw new ExternalCacheException(ExternalCacheException.Reason.NETWORK_FAILURE, failureException);
         }
     }
 
     @Override
     protected void internalRemoveAll() {
         final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         cacheContext.updateCacheVersion(MemcachedUtils.cacheVersionIncrementer(clientSupplier));
     }
 
     @Override
     protected Logger getLogger() {
         return log;
     }
 
     @Override
     protected VersionedExternalCacheRequestContext<V> ensureCacheContext() {
         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);
             return new VersionedExternalCacheRequestContext<>(
                     keyGenerator, name, requestContext::partitionIdentifier,
                     MemcachedUtils.cacheVersionSupplier(clientSupplier),
                     lockTimeout);
         });
     }
 
     @Override
     protected V handleCreation(String internalKey, V candidateValue)
             throws ExecutionException, InterruptedException {
         final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         final byte[] candidateValueBytes = valueMarshalling.getMarshaller().marshallToBytes(candidateValue);
         final String externalKey = cacheContext.externalEntryKeyFor(internalKey);
 
         // Loop until either able to add the candidate value, or retrieve one that has been added by another thread
         for (; ; ) {
             metricsRecorder.record(name, CacheType.EXTERNAL, MetricLabel.NUMBER_OF_REMOTE_GET, 1);
             final Future<Boolean> addOp = clientSupplier.get().add(externalKey, expiryTime(ttlSeconds), 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;
             }
 
             getLogger().info("Cache {}, unable to add candidate for key {}, retrieve what was added", name, internalKey);
             metricsRecorder.record(name, CacheType.EXTERNAL, MetricLabel.NUMBER_OF_REMOTE_GET, 1);
             final Optional<V> otherAddedValue = unmarshall((byte[]) clientSupplier.get().get(externalKey), valueMarshalling);
             if (otherAddedValue.isPresent()) {
                 return otherAddedValue.get();
             }
 
             getLogger().info("Cache {}, unable to retrieve recently added candidate for key {}, looping", name, internalKey);
         }
 
         return candidateValue;
     }
 
     @Override
     protected final ExternalCacheException mapException(Exception ex) {
         return MemcachedUtils.mapException(ex);
     }
 
     @Override
     protected final Optional<V> directGet(String externalKey) {
         return unmarshall((byte[]) clientSupplier.get().get(externalKey), valueMarshalling);
     }
 
     @Override
     protected final Map<String, Optional<V>> directGetBulk(Set<String> externalKeys) {
         return MemcachedUtils.directGetBulk(externalKeys, clientSupplier, valueMarshalling);
     }
 }