/*
    * ====================================================================
    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.http.impl.client.cache;
  
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.security.NoSuchAlgorithmException;
  import java.security.SecureRandom;
  import java.util.Formatter;
  import java.util.Locale;
  
  import org.apache.http.annotation.Contract;
  import org.apache.http.annotation.ThreadingBehavior;
  
  /**
   * Should produce reasonably unique tokens.
   */
  @Contract(threading = ThreadingBehavior.SAFE)
  class BasicIdGenerator {
  
      private final String hostname;
      private final SecureRandom rnd;
      private long count;
  
      public BasicIdGenerator() {
          super();
          String hostname;
          try {
              hostname = InetAddress.getLocalHost().getHostName();
          } catch (final UnknownHostException ex) {
              hostname = "localhost";
          }
          this.hostname = hostname;
          try {
              this.rnd = SecureRandom.getInstance("SHA1PRNG");
          } catch (final NoSuchAlgorithmException ex) {
              throw new Error(ex);
          }
          this.rnd.setSeed(System.currentTimeMillis());
      }
  
      public synchronized void generate(final StringBuilder buffer) {
          this.count++;
          final int rndnum = this.rnd.nextInt();
          buffer.append(System.currentTimeMillis());
          buffer.append('.');
          final Formatter formatter = new Formatter(buffer, Locale.US);
          formatter.format("%1$016x-%2$08x", Long.valueOf(this.count), Integer.valueOf(rndnum));
          formatter.close();
          buffer.append('.');
          buffer.append(this.hostname);
      }
  
      public String generate() {
          final StringBuilder buffer = new StringBuilder();
          generate(buffer);
          return buffer.toString();
      }
  
  }