/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.omid.tools.hbase;
  
  import org.apache.hadoop.security.UserGroupInformation;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import javax.annotation.Nullable;
  import java.io.IOException;
  
  public final class HBaseLogin {
  
      private static final Logger LOG = LoggerFactory.getLogger(HBaseLogin.class);
  
      private static volatile UserGroupInformation ugi;
  
      @Nullable
      public static UserGroupInformation loginIfNeeded(SecureHBaseConfig config) throws IOException {
  
          if (UserGroupInformation.isSecurityEnabled()) {
              LOG.info("Security enabled when connecting to HBase");
              if (ugi == null) { // Use lazy initialization with double-checked locking
                  synchronized (HBaseLogin.class) {
                      if (ugi == null) {
                          LOG.info("Login with Kerberos. User={}, keytab={}", config.getPrincipal(), config.getKeytab());
                          UserGroupInformation.loginUserFromKeytab(config.getPrincipal(), config.getKeytab());
                          ugi = UserGroupInformation.getCurrentUser();
                      }
                  }
              } else {
                  LOG.info("User {}, already trusted (Kerberos). Avoiding 2nd login as it causes problems", ugi.toString());
              }
          } else {
              LOG.warn("Security NOT enabled when connecting to HBase. Act at your own risk. NULL UGI returned");
          }
          return ugi;
      }
  
  }