/**
 * 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.hdfs;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.StringTokenizer;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.security.UserGroupInformation;

@InterfaceAudience.Private
public class DFSUtil {
  /**
   * Whether the pathname is valid.  Currently prohibits relative paths, 
   * and names which contain a ":" or "/" 
   */
  public static boolean isValidName(String src) {
      
    // Path must be absolute.
    if (!src.startsWith(Path.SEPARATOR)) {
      return false;
    }
      
    // Check for ".." "." ":" "/"
    StringTokenizer tokens = new StringTokenizer(src, Path.SEPARATOR);
    while(tokens.hasMoreTokens()) {
      String element = tokens.nextToken();
      if (element.equals("..") || 
          element.equals(".")  ||
          (element.indexOf(":") >= 0)  ||
          (element.indexOf("/") >= 0)) {
        return false;
      }
    }
    return true;
  }

  /**
   * Utility class to facilitate junit test error simulation.
   */
  @InterfaceAudience.Private
  public static class ErrorSimulator {
    private static boolean[] simulation = null; // error simulation events
    public static void initializeErrorSimulationEvent(int numberOfEvents) {
      simulation = new boolean[numberOfEvents]; 
      for (int i = 0; i < numberOfEvents; i++) {
        simulation[i] = false;
      }
    }
    
    public static boolean getErrorSimulation(int index) {
      if(simulation == null)
        return false;
      assert(index < simulation.length);
      return simulation[index];
    }
    
    public static void setErrorSimulation(int index) {
      assert(index < simulation.length);
      simulation[index] = true;
    }
    
    public static void clearErrorSimulation(int index) {
      assert(index < simulation.length);
      simulation[index] = false;
    }
  }
  
  /**
   * If a keytab has been provided, login as that user.
   */
  public static void login(final Configuration conf,
                           final String keytabFileKey,
                           final String userNameKey)
                           throws IOException {
    String keytabFilename = conf.get(keytabFileKey);
    
    if(keytabFilename == null)
      return;
    
    String user = conf.get(userNameKey, System.getProperty("user.name"));
    UserGroupInformation.loginUserFromKeytab(user, keytabFilename);
  }

  /**
   * Converts a byte array to a string using UTF8 encoding.
   */
  public static String bytes2String(byte[] bytes) {
    try {
      return new String(bytes, "UTF8");
    } catch(UnsupportedEncodingException e) {
      assert false : "UTF8 encoding is not supported ";
    }
    return null;
  }

  /**
   * Converts a string to a byte array using UTF8 encoding.
   */
  public static byte[] string2Bytes(String str) {
    try {
      return str.getBytes("UTF8");
    } catch(UnsupportedEncodingException e) {
      assert false : "UTF8 encoding is not supported ";
    }
    return null;
  }
}