content: /*
   * 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.distributedlog.namespace;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.base.Objects;
  import com.google.common.collect.Sets;
  import java.net.URI;
  import java.util.Arrays;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import org.apache.bookkeeper.common.util.ReflectionUtils;
  import org.apache.commons.lang3.StringUtils;
  import org.apache.distributedlog.DistributedLogConstants;
  import org.apache.distributedlog.impl.BKNamespaceDriver;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  
  /**
   * The basic service for managing a set of namespace drivers.
   */
  public class NamespaceDriverManager {
  
      private static final Logger logger = LoggerFactory.getLogger(NamespaceDriverManager.class);
  
      static class NamespaceDriverInfo {
  
          final Class<? extends NamespaceDriver> driverClass;
          final String driverClassName;
  
          NamespaceDriverInfo(Class<? extends NamespaceDriver> driverClass) {
              this.driverClass = driverClass;
              this.driverClassName = this.driverClass.getName();
          }
  
          @Override
          public String toString() {
              StringBuilder sb = new StringBuilder();
              sb.append("driver[")
                      .append(driverClassName)
                      .append("]");
              return sb.toString();
          }
      }
  
      private static final ConcurrentMap<String, NamespaceDriverInfo> drivers;
      private static boolean initialized = false;
  
      static {
          drivers = new ConcurrentHashMap<String, NamespaceDriverInfo>();
          initialize();
      }
  
      static void initialize() {
          if (initialized) {
              return;
          }
          loadInitialDrivers();
          initialized = true;
          logger.info("DistributedLog NamespaceDriverManager initialized");
      }
  
      private static void loadInitialDrivers() {
          Set<String> driverList = Sets.newHashSet();
          // add default bookkeeper based driver
          driverList.add(BKNamespaceDriver.class.getName());
          // load drivers from system property
          String driversStr = System.getProperty("distributedlog.namespace.drivers");
          if (null != driversStr) {
              String[] driversArray = StringUtils.split(driversStr, ':');
              driverList.addAll(Arrays.asList(driversArray));
          }
          // initialize the drivers
          for (String driverClsName : driverList) {
              try {
                  NamespaceDriver driver =
                          ReflectionUtils.newInstance(driverClsName, NamespaceDriver.class);
                  NamespaceDriverInfo driverInfo = new NamespaceDriverInfo(driver.getClass());
                  drivers.put(driver.getScheme().toLowerCase(), driverInfo);
              } catch (Exception ex) {
                  logger.warn("Failed to load namespace driver {} : ", driverClsName, ex);
              }
          }
      }
  
      /**
       * Prevent the NamespaceDriverManager class from being instantiated.
       */
      private NamespaceDriverManager() {}
  
      /**
       * Register the namespace {@code driver}.
       *
       * @param driver the namespace driver
       */
      public static void registerDriver(String backend, Class<? extends NamespaceDriver> driver) {
          if (!initialized) {
              initialize();
          }
  
          String scheme = backend.toLowerCase();
          NamespaceDriverInfo oldDriverInfo = drivers.get(scheme);
          if (null != oldDriverInfo) {
              return;
          }
          NamespaceDriverInfo newDriverInfo = new NamespaceDriverInfo(driver);
          oldDriverInfo = drivers.putIfAbsent(scheme, newDriverInfo);
          if (null != oldDriverInfo) {
              logger.debug("Driver for {} is already there.", scheme);
          }
      }
  
      /**
       * Retrieve the namespace driver for {@code scheme}.
       *
       * @param scheme the scheme for the namespace driver
       * @return the namespace driver
       * @throws NullPointerException when scheme is null
       */
      public static NamespaceDriver getDriver(String scheme) {
          checkNotNull(scheme, "Driver Scheme is null");
          if (!initialized) {
              initialize();
          }
          NamespaceDriverInfo driverInfo = drivers.get(scheme.toLowerCase());
          if (null == driverInfo) {
              throw new IllegalArgumentException("Unknown backend " + scheme);
          }
          return ReflectionUtils.newInstance(driverInfo.driverClass);
      }
  
      /**
       * Retrieve the namespace driver for {@code uri}.
       *
       * @param uri the distributedlog uri
       * @return the namespace driver for {@code uri}
       * @throws NullPointerException if the distributedlog {@code uri} is null or doesn't have scheme
       *          or there is no namespace driver registered for the scheme
       * @throws IllegalArgumentException if the distributedlog {@code uri} scheme is illegal
       */
      public static NamespaceDriver getDriver(URI uri) {
          // Validate the uri and load the backend according to scheme
          checkNotNull(uri, "DistributedLog uri is null");
          String scheme = uri.getScheme();
          checkNotNull(scheme, "Invalid distributedlog uri : " + uri);
          scheme = scheme.toLowerCase();
          String[] schemeParts = StringUtils.split(scheme, '-');
          checkArgument(schemeParts.length > 0,
                  "Invalid distributedlog scheme found : " + uri);
          checkArgument(Objects.equal(DistributedLogConstants.SCHEME_PREFIX, schemeParts[0].toLowerCase()),
                  "Unknown distributedlog scheme found : " + uri);
          // bookkeeper is the default backend
          String backend = DistributedLogConstants.BACKEND_BK;
          if (schemeParts.length > 1) {
              backend = schemeParts[1];
          }
          return getDriver(backend);
      }
  
  }
  