/**
    * 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.hbase.procedure;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.List;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  
  /**
   * Provides the common setup framework and runtime services for globally
   * barriered procedure invocation from HBase services.
   * @param <E> the specific procedure management extension that a concrete
   * implementation provides
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public abstract class ProcedureManagerHost<E extends ProcedureManager> {
  
    public static final String REGIONSERVER_PROCEDURE_CONF_KEY =
        "hbase.procedure.regionserver.classes";
    public static final String MASTER_PROCEUDRE_CONF_KEY =
        "hbase.procedure.master.classes";
  
    private static final Log LOG = LogFactory.getLog(ProcedureManagerHost.class);
  
    protected Set<E> procedures = new HashSet<E>();
  
    /**
     * Load system procedures. Read the class names from configuration.
     * Called by constructor.
     */
    protected void loadUserProcedures(Configuration conf, String confKey) {
      Class<?> implClass = null;
  
      // load default procedures from configure file
      String[] defaultProcClasses = conf.getStrings(confKey);
      if (defaultProcClasses == null || defaultProcClasses.length == 0)
        return;
  
      List<E> configured = new ArrayList<E>();
      for (String className : defaultProcClasses) {
        className = className.trim();
        ClassLoader cl = this.getClass().getClassLoader();
        Thread.currentThread().setContextClassLoader(cl);
        try {
          implClass = cl.loadClass(className);
          configured.add(loadInstance(implClass));
          LOG.info("User procedure " + className + " was loaded successfully.");
        } catch (ClassNotFoundException e) {
          LOG.warn("Class " + className + " cannot be found. " +
              e.getMessage());
        } catch (IOException e) {
          LOG.warn("Load procedure " + className + " failed. " +
              e.getMessage());
        }
      }
  
      // add entire set to the collection
      procedures.addAll(configured);
    }
  
    @SuppressWarnings("unchecked")
    public E loadInstance(Class<?> implClass) throws IOException {
      // create the instance
      E impl;
      Object o = null;
      try {
        o = implClass.newInstance();
        impl = (E)o;
      } catch (InstantiationException e) {
        throw new IOException(e);
      } catch (IllegalAccessException e) {
        throw new IOException(e);
      }
  
      return impl;
   }
 
   // Register a procedure manager object
   public void register(E obj) {
     procedures.add(obj);
   }
 
   public Set<E> getProcedureManagers() {
     Set<E> returnValue = new HashSet<E>();
     for (E e: procedures) {
       returnValue.add(e);
     }
     return returnValue;
   }
 
   public abstract void loadProcedures(Configuration conf);
 }