/**
    * Copyright The Apache Software Foundation
    *
    * 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;
  
  import java.io.DataOutput;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.commons.collections.iterators.UnmodifiableIterator;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.Bytes;
  
  /**
   * Do a shallow merge of multiple KV configuration pools. This is a very useful
   * utility class to easily add per-object configurations in addition to wider
   * scope settings. This is different from Configuration.addResource()
   * functionality, which performs a deep merge and mutates the common data
   * structure.
   * <p>
   * The iterator on CompoundConfiguration is unmodifiable. Obtaining iterator is an expensive
   * operation.
   * <p>
   * For clarity: the shallow merge allows the user to mutate either of the
   * configuration objects and have changes reflected everywhere. In contrast to a
   * deep merge, that requires you to explicitly know all applicable copies to
   * propagate changes.
   * 
   * WARNING: The values set in the CompoundConfiguration are do not handle Property variable
   * substitution.  However, if they are set in the underlying configuration substitutions are
   * done. 
   */
  @InterfaceAudience.Private
  public class CompoundConfiguration extends Configuration {
  
    private Configuration mutableConf = null;
  
    /**
     * Default Constructor. Initializes empty configuration
     */
    public CompoundConfiguration() {
    }
  
    // Devs: these APIs are the same contract as their counterparts in
    // Configuration.java
    private interface ImmutableConfigMap extends Iterable<Map.Entry<String,String>> {
      String get(String key);
      String getRaw(String key);
      Class<?> getClassByName(String name) throws ClassNotFoundException;
      int size();
    }
  
    private final List<ImmutableConfigMap> configs
      = new ArrayList<ImmutableConfigMap>();
  
    static class ImmutableConfWrapper implements  ImmutableConfigMap {
     private final Configuration c;
      
      ImmutableConfWrapper(Configuration conf) {
        c = conf;
      }
  
      @Override
      public Iterator<Map.Entry<String,String>> iterator() {
        return c.iterator();
      }
      
      @Override
      public String get(String key) {
        return c.get(key);
      }
  
      @Override
      public String getRaw(String key) {
        return c.getRaw(key);
      }
  
     @Override
     public Class<?> getClassByName(String name)
         throws ClassNotFoundException {
       return c.getClassByName(name);
     }
 
     @Override
     public int size() {
       return c.size();
     }
 
     @Override
     public String toString() {
       return c.toString();
     }
   }
 
   /**
    * If set has been called, it will create a mutableConf.  This converts the mutableConf to an
    * immutable one and resets it to allow a new mutable conf.  This is used when a new map or
    * conf is added to the compound configuration to preserve proper override semantics.
    */
   void freezeMutableConf() {
     if (mutableConf == null) {
       // do nothing if there is no current mutableConf
       return;
     }
 
     this.configs.add(0, new ImmutableConfWrapper(mutableConf));
     mutableConf = null;
   }
 
   /**
    * Add Hadoop Configuration object to config list.
    * The added configuration overrides the previous ones if there are name collisions.
    * @param conf configuration object
    * @return this, for builder pattern
    */
   public CompoundConfiguration add(final Configuration conf) {
     freezeMutableConf();
 
     if (conf instanceof CompoundConfiguration) {
       this.configs.addAll(0, ((CompoundConfiguration) conf).configs);
       return this;
     }
     // put new config at the front of the list (top priority)
     this.configs.add(0, new ImmutableConfWrapper(conf));
     return this;
   }
 
   /**
    * Add Bytes map to config list. This map is generally
    * created by HTableDescriptor or HColumnDescriptor, but can be abstractly
    * used. The added configuration overrides the previous ones if there are
    * name collisions.
    *
    * @param map
    *          Bytes map
    * @return this, for builder pattern
    */
   public CompoundConfiguration addBytesMap(
       final Map<Bytes, Bytes> map) {
     freezeMutableConf();
 
     // put new map at the front of the list (top priority)
     this.configs.add(0, new ImmutableConfigMap() {
       private final Map<Bytes, Bytes> m = map;
 
       @Override
       public Iterator<Map.Entry<String,String>> iterator() {
         Map<String, String> ret = new HashMap<String, String>();
         for (Map.Entry<Bytes, Bytes> entry : map.entrySet()) {
           String key = Bytes.toString(entry.getKey().get());
           String val = entry.getValue() == null ? null : Bytes.toString(entry.getValue().get());
           ret.put(key, val);
         }
         return ret.entrySet().iterator();
       }
       
       @Override
       public String get(String key) {
         Bytes ibw = new Bytes(Bytes
             .toBytes(key));
         if (!m.containsKey(ibw))
           return null;
         Bytes value = m.get(ibw);
         if (value == null || value.get() == null)
           return null;
         return Bytes.toString(value.get());
       }
 
       @Override
       public String getRaw(String key) {
         return get(key);
       }
 
       @Override
       public Class<?> getClassByName(String name)
       throws ClassNotFoundException {
         return null;
       }
 
       @Override
       public int size() {
         return m.size();
       }
 
       @Override
       public String toString() {
         return m.toString();
       }
     });
     return this;
   }
 
   /**
    * Add String map to config list. This map is generally created by HTableDescriptor
    * or HColumnDescriptor, but can be abstractly used. The added configuration
    * overrides the previous ones if there are name collisions.
    *
    * @return this, for builder pattern
    */
   public CompoundConfiguration addStringMap(final Map<String, String> map) {
     freezeMutableConf();
 
     // put new map at the front of the list (top priority)
     this.configs.add(0, new ImmutableConfigMap() {
       private final Map<String, String> m = map;
 
       @Override
       public Iterator<Map.Entry<String,String>> iterator() {
         return map.entrySet().iterator();
       }
 
       @Override
       public String get(String key) {
         return m.get(key);
       }
 
       @Override
       public String getRaw(String key) {
         return get(key);
       }
 
       @Override
       public Class<?> getClassByName(String name)
       throws ClassNotFoundException {
         return null;
       }
 
       @Override
       public int size() {
         return m.size();
       }
 
       @Override
       public String toString() {
         return m.toString();
       }
     });
     return this;
   }
 
   @Override
   public String toString() {
     StringBuffer sb = new StringBuffer();
     sb.append("CompoundConfiguration: " + this.configs.size() + " configs");
     for (ImmutableConfigMap m : this.configs) {
       sb.append(this.configs);
     }
     return sb.toString();
   }
 
   @Override
   public String get(String key) {
     if (mutableConf != null) {
       String value = mutableConf.get(key);
       if (value != null) {
         return value;
       }
     }
 
     for (ImmutableConfigMap m : this.configs) {
       String value = m.get(key);
       if (value != null) {
         return value;
       }
     }
     return null;
   }
 
   @Override
   public String getRaw(String key) {
     if (mutableConf != null) {
       String value = mutableConf.getRaw(key);
       if (value != null) {
         return value;
       }
     }
 
     for (ImmutableConfigMap m : this.configs) {
       String value = m.getRaw(key);
       if (value != null) {
         return value;
       }
     }
     return null;
   }
 
   @Override
   public Class<?> getClassByName(String name) throws ClassNotFoundException {
     if (mutableConf != null) {
       Class<?> value = mutableConf.getClassByName(name);
       if (value != null) {
         return value;
       }
     }
 
     for (ImmutableConfigMap m : this.configs) {
       Class<?> value = m.getClassByName(name);
       if (value != null) {
         return value;
       }
     }
     throw new ClassNotFoundException();
   }
 
   // TODO: This method overestimates the number of configuration settings -- if a value is masked
   // by an overriding config or map, it will be counted multiple times. 
   @Override
   public int size() {
     int ret = 0;
 
     if (mutableConf != null) {
       ret += mutableConf.size();
     }
 
     for (ImmutableConfigMap m : this.configs) {
       ret += m.size();
     }
     return ret;
   }
 
   /**
    * Get the value of the <code>name</code>. If the key is deprecated,
    * it returns the value of the first key which replaces the deprecated key
    * and is not null.
    * If no such property exists,
    * then <code>defaultValue</code> is returned.
 
    * The CompooundConfiguration does not do property substitution.  To do so we need
    * Configuration.getProps to be protected or package visible.  Though in hadoop2 it is
    * protected, in hadoop1 the method is private and not accessible.
    * 
    * All of the get* methods call this overridden get method.
    * 
    * @param name property name.
    * @param defaultValue default value.
    * @return property value, or <code>defaultValue</code> if the property 
    *         doesn't exist.                    
    **/
   @Override
   public String get(String name, String defaultValue) {
     String ret = get(name);
     return ret == null ? defaultValue : ret;
   }
 
   @Override
   public Iterator<Map.Entry<String, String>> iterator() {
     Map<String, String> ret = new HashMap<String, String>();
 
     // add in reverse order so that oldest get overridden.
     if (!configs.isEmpty()) {
       for (int i = configs.size() - 1; i >= 0; i--) {
         ImmutableConfigMap map = configs.get(i);
         Iterator<Map.Entry<String, String>> iter = map.iterator();
         while (iter.hasNext()) {
           Map.Entry<String, String> entry = iter.next();
           ret.put(entry.getKey(), entry.getValue());
         }
       }
     }
 
     // add mutations to this CompoundConfiguration last.
     if (mutableConf != null) {
       Iterator<Map.Entry<String, String>> miter = mutableConf.iterator();
       while (miter.hasNext()) {
         Map.Entry<String, String> entry = miter.next();
         ret.put(entry.getKey(), entry.getValue());
       }
     }
 
     return UnmodifiableIterator.decorate(ret.entrySet().iterator());
   }
 
   @Override
   public void set(String name, String value) {
     if (mutableConf == null) {
       // not thread safe
       mutableConf = new Configuration(false); // an empty configuration
     }
     mutableConf.set(name,  value);
   }
 
   /***********************************************************************************************
    * These methods are unsupported, and no code using CompoundConfiguration depend upon them.
    * Quickly abort upon any attempts to use them. 
    **********************************************************************************************/
 
   @Override
   public void clear() {
     throw new UnsupportedOperationException("Immutable Configuration");
   }
 
   @Override
   public void write(DataOutput out) throws IOException {
     throw new UnsupportedOperationException("Immutable Configuration");
   }
 
   @Override
   public void writeXml(OutputStream out) throws IOException {
     throw new UnsupportedOperationException("Immutable Configuration");
   }
 };