/**
 * 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.security;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.util.ReflectionUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * An implementation of {@link GroupMappingServiceProvider} which
 * composites other group mapping providers for determining group membership.
 * This allows to combine existing provider implementations and composite 
 * a virtually new provider without customized development to deal with complex situation. 
 */
@InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
@InterfaceStability.Evolving
public class CompositeGroupsMapping
    implements GroupMappingServiceProvider, Configurable {
  
  public static final String MAPPING_PROVIDERS_CONFIG_KEY = GROUP_MAPPING_CONFIG_PREFIX + ".providers";
  public static final String MAPPING_PROVIDERS_COMBINED_CONFIG_KEY = MAPPING_PROVIDERS_CONFIG_KEY + ".combined";
  public static final String MAPPING_PROVIDER_CONFIG_PREFIX = GROUP_MAPPING_CONFIG_PREFIX + ".provider";
  
  private static final Logger LOG =
      LoggerFactory.getLogger(CompositeGroupsMapping.class);

  private List<GroupMappingServiceProvider> providersList = 
		  new ArrayList<GroupMappingServiceProvider>();
  
  private Configuration conf;
  private boolean combined;


  /**
   * Returns list of groups for a user.
   * 
   * @param user get groups for this user
   * @return list of groups for a given user
   */
  @Override
  public synchronized List<String> getGroups(String user) throws IOException {
    Set<String> groupSet = new TreeSet<String>();

    List<String> groups = null;
    for (GroupMappingServiceProvider provider : providersList) {
      try {
        groups = provider.getGroups(user);
      } catch (Exception e) {
        LOG.warn("Unable to get groups for user {} via {} because: {}",
            user, provider.getClass().getSimpleName(), e.toString());
        LOG.debug("Stacktrace: ", e);
      }        
      if (groups != null && ! groups.isEmpty()) {
        groupSet.addAll(groups);
        if (!combined) break;
      }
    }

    List<String> results = new ArrayList<String>(groupSet.size());
    results.addAll(groupSet);
    return results;
  }
  
  /**
   * Caches groups, no need to do that for this provider
   */
  @Override
  public void cacheGroupsRefresh() throws IOException {
    // does nothing in this provider of user to groups mapping
  }

  /** 
   * Adds groups to cache, no need to do that for this provider
   *
   * @param groups unused
   */
  @Override
  public void cacheGroupsAdd(List<String> groups) throws IOException {
    // does nothing in this provider of user to groups mapping
  }

  @Override
  public synchronized Configuration getConf() {
    return conf;
  }

  @Override
  public synchronized void setConf(Configuration conf) {
    this.conf = conf;
    
    this.combined = conf.getBoolean(MAPPING_PROVIDERS_COMBINED_CONFIG_KEY, true);
    
    loadMappingProviders();
  }
  
  private void loadMappingProviders() {
    String[] providerNames = conf.getStrings(MAPPING_PROVIDERS_CONFIG_KEY, new String[]{});

    String providerKey;
    for (String name : providerNames) {
      providerKey = MAPPING_PROVIDER_CONFIG_PREFIX + "." + name;
      Class<?> providerClass = conf.getClass(providerKey, null);
      if (providerClass == null) {
        LOG.error("The mapping provider, " + name + " does not have a valid class");
      } else {
        addMappingProvider(name, providerClass);
      }
    }
  }
    
  private void addMappingProvider(String providerName, Class<?> providerClass) {
    Configuration newConf = prepareConf(providerName);
    GroupMappingServiceProvider provider = 
        (GroupMappingServiceProvider) ReflectionUtils.newInstance(providerClass, newConf);
    providersList.add(provider);

  }

  /*
   * For any provider specific configuration properties, such as "hadoop.security.group.mapping.ldap.url" 
   * and the like, allow them to be configured as "hadoop.security.group.mapping.provider.PROVIDER-X.ldap.url",
   * so that a provider such as LdapGroupsMapping can be used to composite a complex one with other providers.
   */
  private Configuration prepareConf(String providerName) {
    Configuration newConf = new Configuration();
    Iterator<Map.Entry<String, String>> entries = conf.iterator();
    String providerKey = MAPPING_PROVIDER_CONFIG_PREFIX + "." + providerName;
    while (entries.hasNext()) {
      Map.Entry<String, String> entry = entries.next();
      String key = entry.getKey();
      // get a property like "hadoop.security.group.mapping.provider.PROVIDER-X.ldap.url"
      if (key.startsWith(providerKey) && !key.equals(providerKey)) {
        // restore to be the one like "hadoop.security.group.mapping.ldap.url" 
        // so that can be used by original provider.
        key = key.replace(".provider." + providerName, "");
        newConf.set(key, entry.getValue());
      }
    }
    return newConf;
  }  
}