/**
 * 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.dfs;

import java.util.*;

class Host2NodesMap {
  private HashMap<String, DatanodeDescriptor[]> map
    = new HashMap<String, DatanodeDescriptor[]>();
  private Random r = new Random();
                      
  /** Check if node is already in the map. */
  synchronized boolean contains(DatanodeDescriptor node) {
    if (node==null) {
      return false;
    }
      
    String host = node.getHost();
    DatanodeDescriptor[] nodes = map.get(host);
    if (nodes != null) {
      for(DatanodeDescriptor containedNode:nodes) {
        if (node==containedNode) {
          return true;
        }
      }
    }
    return false;
  }
    
  /** add node to the map 
   * return true if the node is added; false otherwise.
   */
  synchronized boolean add(DatanodeDescriptor node) {
    if (node==null || contains(node)) {
      return false;
    }
      
    String host = node.getHost();
    DatanodeDescriptor[] nodes = map.get(host);
    DatanodeDescriptor[] newNodes;
    if (nodes==null) {
      newNodes = new DatanodeDescriptor[1];
      newNodes[0]=node;
    } else { // rare case: more than one datanode on the host
      newNodes = new DatanodeDescriptor[nodes.length+1];
      System.arraycopy(nodes, 0, newNodes, 0, nodes.length);
      newNodes[nodes.length] = node;
    }
    map.put(host, newNodes);
    return true;
  }
    
  /** remove node from the map 
   * return true if the node is removed; false otherwise.
   */
  synchronized boolean remove(DatanodeDescriptor node) {
    if (node==null) {
      return false;
    }
      
    String host = node.getHost();
    DatanodeDescriptor[] nodes = map.get(host);
    if (nodes==null) {
      return false;
    }
    if (nodes.length==1) {
      if (nodes[0]==node) {
        map.remove(host);
        return true;
      } else {
        return false;
      }
    }
    //rare case
    int i=0;
    for(; i<nodes.length; i++) {
      if (nodes[i]==node) {
        break;
      }
    }
    if (i==nodes.length) {
      return false;
    } else {
      DatanodeDescriptor[] newNodes;
      newNodes = new DatanodeDescriptor[nodes.length-1];
      System.arraycopy(nodes, 0, newNodes, 0, i);
      System.arraycopy(nodes, i+1, newNodes, i, nodes.length-i-1);
      map.put(host, newNodes);
      return true;
    }
  }
    
  /** get a data node by its host.
   * @return DatanodeDescriptor if found; otherwise null.
   */
  synchronized DatanodeDescriptor getDatanodeByHost(String host) {
    if (host==null) {
      return null;
    }
      
    DatanodeDescriptor[] nodes = map.get(host);
    // no entry
    if (nodes== null) {
      return null;
    }
    // one node
    if (nodes.length == 1) {
      return nodes[0];
    }
    // more than one node
    return nodes[r.nextInt(nodes.length)];
  }
    
  /**
   * Find data node by its name.
   * 
   * @return DatanodeDescriptor if found or null otherwise 
   */
  public DatanodeDescriptor getDatanodeByName(String name) {
    if (name==null) {
      return null;
    }
      
    int colon = name.indexOf(":");
    String host;
    if (colon < 0) {
      host = name;
    } else {
      host = name.substring(0, colon);
    }

    DatanodeDescriptor[] nodes = map.get(host);
    // no entry
    if (nodes== null) {
      return null;
    }
    for(DatanodeDescriptor containedNode:nodes) {
      if (name.equals(containedNode.getName())) {
        return containedNode;
      }
    }
    return null;
  }
}
