package com.atlassian.vcache.internal.redis;
   
   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 org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import redis.clients.jedis.Jedis;
  import redis.clients.jedis.Pipeline;
  import redis.clients.jedis.Response;
  
  import java.util.Collections;
  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.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 java.util.stream.StreamSupport;
  
  import static com.atlassian.vcache.internal.core.VCacheCoreUtils.isEmpty;
  import static com.atlassian.vcache.internal.core.VCacheCoreUtils.marshall;
  import static com.atlassian.vcache.internal.core.VCacheCoreUtils.unmarshall;
  import static java.util.Objects.requireNonNull;
  
  /**
   * Redis implementation of {@link com.atlassian.vcache.StableReadExternalCache}.
   *
   * @param <V> the value type
   * @since 1.0.0
   */
  class RedisStableReadExternalCache<V>
          extends AbstractStableReadExternalCache<V> {
      private static final Logger log = LoggerFactory.getLogger(RedisStableReadExternalCache.class);
  
      private final Supplier<Jedis> clientSupplier;
      private final Supplier<RequestContext> contextSupplier;
      private final ExternalCacheKeyGenerator keyGenerator;
      private final MarshallingPair<V> valueMarshalling;
      private final int defaultTtl;
  
      RedisStableReadExternalCache(
              Supplier<Jedis> clientSupplier,
              Supplier<RequestContext> contextSupplier,
              ExternalCacheKeyGenerator keyGenerator,
              String name,
              MarshallingPair<V> valueMarshalling,
              ExternalCacheSettings settings,
              MetricsRecorder metricsRecorder) {
          super(name, metricsRecorder);
          this.clientSupplier = requireNonNull(clientSupplier);
          this.contextSupplier = requireNonNull(contextSupplier);
          this.keyGenerator = requireNonNull(keyGenerator);
          this.valueMarshalling = requireNonNull(valueMarshalling);
          this.defaultTtl = VCacheCoreUtils.roundUpToSeconds(settings.getDefaultTtl().get());
      }
  
      @Override
      public CompletionStage<Boolean> internalPut(String internalKey, V value, PutPolicy policy) {
          final VersionedExternalCacheRequestContext<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);
                      cacheContext.computeValue(internalKey, (key, oldValue) -> {
  
                          // 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.
                          if (oldValue != null) {
                              return oldValue.thenApply((oldV) -> {
                                  remotePutResult.set(remotePut(cacheContext.externalEntryKeyFor(key), value, policy));
                                  return Optional.of(value);
                              });
                          } else {
                              remotePutResult.set(remotePut(cacheContext.externalEntryKeyFor(key), value, policy));
                              return CompletableFuture.completedFuture(Optional.of(value));
                          }
                      });
                      return remotePutResult.get();
                  },
                  (result) -> {
                      if (!result) {
                         cacheContext.forgetValue(internalKey);
                     }
                 });
     }
 
     private boolean remotePut(String externalKey, V value, PutPolicy policy) {
         final byte[] valueBytes = valueMarshalling.getMarshaller().marshallToBytes(value);
         return RedisUtils.putOperationForPolicy(
                 policy, clientSupplier, externalKey, defaultTtl, valueBytes);
     }
 
     @Override
     protected CompletionStage<Void> internalRemove(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
             try (Jedis client = clientSupplier.get()) {
                 final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
                 final List<byte[]> externalKeysList = StreamSupport.stream(internalKeys.spliterator(), false)
                         .map(cacheContext::externalEntryKeyFor)
                         .map(String::getBytes)
                         .collect(Collectors.toList());
                 final byte[][] externalKeysAsBytes = externalKeysList.toArray(new byte[externalKeysList.size()][]);
 
                 final long numDeleted = client.del(externalKeysAsBytes);
                 if (numDeleted != externalKeysAsBytes.length) {
                     log.info("Cache {}: only able to delete {} of {} keys", name, numDeleted, externalKeysAsBytes.length);
                 }
 
                 // Forget the values removed
                 StreamSupport.stream(internalKeys.spliterator(), false)
                         .forEach(k -> cacheContext.recordValue(k, Optional.empty()));
             }
 
             return null;
         });
     }
 
     @Override
     protected CompletionStage<Void> internalRemoveAll() {
         return perform(() -> {
             final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
             cacheContext.updateCacheVersion(
                     RedisUtils.incrementCacheVersion(clientSupplier, cacheContext.externalCacheVersionKey()));
             cacheContext.forgetAllValues();
             return null;
         });
     }
 
     @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);
             final VersionedExternalCacheRequestContext<V> newCacheContext = new VersionedExternalCacheRequestContext<>(
                     keyGenerator, name, requestContext::partitionIdentifier);
             newCacheContext.updateCacheVersion(
                     RedisUtils.obtainCacheVersion(
                             clientSupplier,
                             newCacheContext.externalCacheVersionKey(),
                             defaultTtl + 1));
             return newCacheContext;
         });
     }
 
     @Override
     protected V handleCreation(String internalKey, Supplier<V> supplier)
             throws ExecutionException, InterruptedException {
         final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         final V candidateValue = requireNonNull(supplier.get());
         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
         try (Jedis client = clientSupplier.get()) {
             for (; ; ) {
                 final long addOp = client.setnx(externalKey.getBytes(), candidateValueBytes);
                 if (addOp == 1) {
                     // 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);
                 final Optional<V> otherAddedValue = unmarshall(client.get(externalKey.getBytes()), 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 Map<String, V> handleCreation(Function<Set<String>, Map<String, V>> factory, Set<String> externalKeys)
             throws ExecutionException, InterruptedException {
         // Get the known values from the external cache.
         final VersionedExternalCacheRequestContext<V> cacheContext = ensureCacheContext();
         metricsRecorder.record(name, CacheType.EXTERNAL, MetricLabel.NUMBER_OF_REMOTE_GET, 1);
         final Map<String, Optional<V>> candidateValues =
                 RedisUtils.directGetBulk(externalKeys, clientSupplier, valueMarshalling);
 
         // Add the known 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()));
         getLogger().trace("Cache {}: getBulk(Function): {} of {} entries have values",
                 name, grandResult.size(), externalKeys.size());
 
         // Calculate the missing keys
         final List<String> missingExternalKeys = candidateValues.entrySet().stream()
                 .filter(e -> !e.getValue().isPresent())
                 .map(Map.Entry::getKey)
                 .collect(Collectors.toList());
 
         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 to Redis
             try (Jedis client = clientSupplier.get()) {
                 final Pipeline pipeline = client.pipelined();
                 final Map<String, Response<String>> internalKeyToResponseMap =
                         missingValues.entrySet().stream().collect(Collectors.toMap(
                                 Map.Entry::getKey,
                                 e -> pipeline.setex(
                                         cacheContext.externalEntryKeyFor(e.getKey()).getBytes(),
                                         defaultTtl,
                                         marshall(e.getValue(), valueMarshalling))
                         ));
                 pipeline.sync();
 
                 internalKeyToResponseMap.entrySet().stream()
                         .filter(e -> !RedisUtils.OK.equals(e.getValue().get()))
                         .forEach(e -> log.warn("Cache {}: Unable to set key {}", name, e.getKey()));
             }
 
             grandResult.putAll(missingValues);
         }
 
         return grandResult;
     }
 
     @Override
     public CompletionStage<Map<String, Optional<V>>> getBulk(String... keys) {
         return super.getBulk(keys);
     }
 
     @Override
     public CompletionStage<Map<String, V>> getBulk(Function<Set<String>, Map<String, V>> factory, String... keys) {
         return super.getBulk(factory, keys);
     }
 
     @Override
     protected final ExternalCacheException mapException(Exception ex) {
         return RedisUtils.mapException(ex);
     }
 
     @Override
     protected final Optional<V> directGet(String externalKey) {
         try (Jedis client = clientSupplier.get()) {
             return unmarshall(client.get(externalKey.getBytes()), valueMarshalling);
         }
     }
 
     @Override
     protected final Map<String, Optional<V>> directGetBulk(Set<String> externalKeys) {
         return RedisUtils.directGetBulk(externalKeys, clientSupplier, valueMarshalling);
     }
 }