package com.atlassian.plugins.rest.module;
   
   import java.util.Arrays;
   import java.util.Collection;
   import java.util.Collections;
   
   import javax.annotation.Nullable;
   
   import org.osgi.framework.*;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.base.Function;
  import com.google.common.base.Preconditions;
  import com.google.common.collect.Iterables;
  import com.google.common.collect.Lists;
  
  import static com.google.common.collect.ImmutableList.copyOf;
  
  class OsgiServiceAccessor<S> {
      private static final String FILTER = "(|(plugin=com.atlassian.plugins.rest)(" + Constants.BUNDLE_SYMBOLICNAME + "=%s))";
  
      private final Logger logger = LoggerFactory.getLogger(this.getClass());
  
      private final Class<S> serviceType;
      private final BundleContext bundleContext;
  
      private ServiceReference[] references;
      private final OsgiFactory<? extends S> factory;
  
      OsgiServiceAccessor(final Class<S> serviceType, final BundleContext bundleContext, final OsgiFactory<? extends S> factory) {
          this.serviceType = Preconditions.checkNotNull(serviceType);
          this.bundleContext = Preconditions.checkNotNull(bundleContext);
          this.factory = Preconditions.checkNotNull(factory);
      }
  
      Collection<? extends S> get() {
          try {
              references = bundleContext.getServiceReferences(serviceType.getName(), createFilterString(bundleContext.getBundle()));
              if (references == null) // no service found
              {
                  return Collections.emptySet();
              } else {
                  return copyOf(Iterables.transform(Arrays.asList(references), new Function<ServiceReference, S>() {
                      public S apply(@Nullable ServiceReference serviceReference) {
                          return factory.getInstance(bundleContext, serviceReference);
                      }
                  }));
              }
          } catch (InvalidSyntaxException e) {
              logger.error("Could not get service references", e);
              return Collections.emptyList();
          }
      }
  
      void release() {
          if (references != null) {
              for (ServiceReference reference : references) {
                  bundleContext.ungetService(reference);
              }
          }
      }
  
      private String createFilterString(Bundle currentBundle) {
          return String.format(FILTER, currentBundle.getSymbolicName());
      }
  }