/**
 * 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.hadoop.hive.shims;

import java.util.HashMap;
import java.util.Map;

import org.apache.hadoop.hive.thrift.HadoopThriftAuthBridge;
import org.apache.hadoop.util.VersionInfo;

/**
 * ShimLoader.
 *
 */
public abstract class ShimLoader {
  private static HadoopShims hadoopShims;
  private static JettyShims jettyShims;

  /**
   * The names of the classes for shimming Hadoop for each major version.
   */
  private static final HashMap<String, String> HADOOP_SHIM_CLASSES =
      new HashMap<String, String>();

  static {
    HADOOP_SHIM_CLASSES.put("0.20", "org.apache.hadoop.hive.shims.Hadoop20Shims");
    HADOOP_SHIM_CLASSES.put("0.20S", "org.apache.hadoop.hive.shims.Hadoop20SShims");
    HADOOP_SHIM_CLASSES.put("0.23", "org.apache.hadoop.hive.shims.Hadoop23Shims");
  }

  /**
   * The names of the classes for shimming Jetty for each major version of
   * Hadoop.
   */
  private static final HashMap<String, String> JETTY_SHIM_CLASSES =
      new HashMap<String, String>();

  static {
    JETTY_SHIM_CLASSES.put("0.20", "org.apache.hadoop.hive.shims.Jetty20Shims");
    JETTY_SHIM_CLASSES.put("0.20S", "org.apache.hadoop.hive.shims.Jetty20SShims");
    JETTY_SHIM_CLASSES.put("0.23", "org.apache.hadoop.hive.shims.Jetty23Shims");
  }

  /**
   * Factory method to get an instance of HadoopShims based on the
   * version of Hadoop on the classpath.
   */
  public static HadoopShims getHadoopShims() {
    if (hadoopShims == null) {
      synchronized(ShimLoader.class) {
        if (hadoopShims == null) {
          hadoopShims = loadShims(HADOOP_SHIM_CLASSES, HadoopShims.class);
        }
      }
    }
    return hadoopShims;
  }

  /**
   * Factory method to get an instance of JettyShims based on the version
   * of Hadoop on the classpath.
   */
  public static JettyShims getJettyShims() {
    if (jettyShims == null) {
      synchronized(ShimLoader.class) {
        if (jettyShims == null) {
          jettyShims = loadShims(JETTY_SHIM_CLASSES, JettyShims.class);
        }
      }
    }
    return jettyShims;
  }

  public static synchronized HadoopThriftAuthBridge getHadoopThriftAuthBridge() {
      if (getHadoopShims().isSecureShimImpl()) {
          return createShim("org.apache.hadoop.hive.thrift.HadoopThriftAuthBridge20S",
                            HadoopThriftAuthBridge.class);
        } else {
          return new HadoopThriftAuthBridge();
        }
      }

  private static <T> T loadShims(Map<String, String> classMap, Class<T> xface) {
    String vers = getMajorVersion();
    String className = classMap.get(vers);
    return createShim(className, xface);
  }

    private static <T> T createShim(String className, Class<T> xface) {
    try {
      Class<?> clazz = Class.forName(className);
      return xface.cast(clazz.newInstance());
    } catch (Exception e) {
      throw new RuntimeException("Could not load shims in class " +
          className, e);
    }
  }

  /**
   * Return the major version of Hadoop currently on the classpath.
   * This is simply the first two components of the version number
   * (e.g "0.18" or "0.20")
   */
  public static String getMajorVersion() {
    String vers = VersionInfo.getVersion();

    String[] parts = vers.split("\\.");
    if (parts.length < 2) {
      throw new RuntimeException("Illegal Hadoop Version: " + vers +
          " (expected A.B.* format)");
    }

    switch (Integer.parseInt(parts[0])) {
        case 0:
            break;
        case 1:
            return "0.20S";
        case 2:
            return "0.23";
        default:
            throw new IllegalArgumentException("Unrecognized Hadoop major version number: " + vers);
    }
    String majorVersion = parts[0] + "." + parts[1];

    // If we are running a security release, we won't have UnixUserGroupInformation
    // (removed by HADOOP-6299 when switching to JAAS for Login)
    try {
      Class.forName("org.apache.hadoop.security.UnixUserGroupInformation");
    } catch (ClassNotFoundException cnf) {
      if ("0.20".equals(majorVersion)) {
        majorVersion += "S";
      }
    }
    return majorVersion;
  }

  private ShimLoader() {
    // prevent instantiation
  }
}