content: /**
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.aurora.scheduler.http;
  
  import javax.inject.Inject;
  import javax.ws.rs.GET;
  import javax.ws.rs.Path;
  import javax.ws.rs.Produces;
  import javax.ws.rs.core.MediaType;
  import javax.ws.rs.core.Response;
  
  import com.google.common.base.Function;
  import com.google.common.base.Joiner;
  import com.google.common.collect.FluentIterable;
  import com.google.common.collect.Iterables;
  import com.google.common.collect.Ordering;
  
  import org.apache.aurora.gen.MaintenanceMode;
  import org.apache.aurora.scheduler.storage.Storage;
  import org.apache.aurora.scheduler.storage.entities.IAttribute;
  import org.apache.aurora.scheduler.storage.entities.IHostAttributes;
  import org.apache.aurora.scheduler.storage.entities.IServerInfo;
  
  import static java.util.Objects.requireNonNull;
  
  import static org.apache.aurora.common.base.MorePreconditions.checkNotBlank;
  
  /**
   * HTTP interface to serve as a HUD for the Mesos agents tracked in the scheduler.
   */
  @Path("/agents")
  public class Agents extends JerseyTemplateServlet {
    private final String clusterName;
    private final Storage storage;
  
    /**
     * Injected constructor.
     *
     * @param serverInfo server meta-data that contains the cluster name
     * @param storage store to fetch the host attributes from
     */
    @Inject
    public Agents(IServerInfo serverInfo, Storage storage) {
      super("agents");
      this.clusterName = checkNotBlank(serverInfo.getClusterName());
      this.storage = requireNonNull(storage);
    }
  
    private Iterable<IHostAttributes> getHostAttributes() {
      return storage.read(storeProvider -> storeProvider.getAttributeStore().getHostAttributes());
    }
  
    /**
     * Fetches the listing of known agents.
     *
     * @return HTTP response.
     */
    @GET
    @Produces(MediaType.TEXT_HTML)
    public Response get() {
      return fillTemplate(template -> {
        template.setAttribute("cluster_name", clusterName);
  
        template.setAttribute("agents",
            FluentIterable.from(getHostAttributes()).transform(Agent::new).toList());
      });
    }
  
    private static final Ordering<IAttribute> ATTR_ORDER = Ordering.natural().onResultOf(
        new Function<IAttribute, String>() {
          @Override
          public String apply(IAttribute attr) {
            return attr .getName();
          }
        });
  
    /**
     * Template object to represent a agent.
     */
    private static class Agent {
      private final IHostAttributes attributes;
  
      Agent(IHostAttributes attributes) {
        this.attributes = attributes;
      }
  
      public String getHost() {
        return attributes.getHost();
      }
  
      public String getId() {
        return attributes.getSlaveId();
      }
  
      public MaintenanceMode getMode() {
        return attributes.getMode();
      }
  
      private static final Function<IAttribute, String> ATTR_TO_STRING =
          attr -> attr.getName() + "=[" + Joiner.on(",").join(attr.getValues()) + "]";
  
      public String getAttributes() {
        return Joiner.on(", ").join(
            Iterables.transform(ATTR_ORDER.sortedCopy(attributes.getAttributes()), ATTR_TO_STRING));
      }
    }
  }
  