package org.eclipse.aether.repository;
   
   /*
    * 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.
   */
  
  import java.nio.charset.StandardCharsets;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  
  import org.eclipse.aether.RepositorySystemSession;
  
  /**
   * A helper to calculate a fingerprint/digest for the authentication data of a repository/proxy. Such a fingerprint can
   * be used to detect changes in the authentication data across JVM restarts without exposing sensitive information.
   */
  public final class AuthenticationDigest
  {
  
      private final MessageDigest digest;
  
      private final RepositorySystemSession session;
  
      private final RemoteRepository repository;
  
      private final Proxy proxy;
  
      /**
       * Gets the fingerprint for the authentication of the specified repository.
       * 
       * @param session The repository system session during which the fingerprint is requested, must not be {@code null}.
       * @param repository The repository whose authentication is to be fingerprinted, must not be {@code null}.
       * @return The fingerprint of the repository authentication or an empty string if no authentication is configured,
       *         never {@code null}.
       */
      public static String forRepository( RepositorySystemSession session, RemoteRepository repository )
      {
          String digest = "";
          Authentication auth = repository.getAuthentication();
          if ( auth != null )
          {
              AuthenticationDigest authDigest = new AuthenticationDigest( session, repository, null );
              auth.digest( authDigest );
              digest = authDigest.digest();
          }
          return digest;
      }
  
      /**
       * Gets the fingerprint for the authentication of the specified repository's proxy.
       * 
       * @param session The repository system session during which the fingerprint is requested, must not be {@code null}.
       * @param repository The repository whose proxy authentication is to be fingerprinted, must not be {@code null}.
       * @return The fingerprint of the proxy authentication or an empty string if no proxy is present or if no proxy
       *         authentication is configured, never {@code null}.
       */
      public static String forProxy( RepositorySystemSession session, RemoteRepository repository )
      {
          String digest = "";
          Proxy proxy = repository.getProxy();
          if ( proxy != null )
          {
              Authentication auth = proxy.getAuthentication();
              if ( auth != null )
              {
                  AuthenticationDigest authDigest = new AuthenticationDigest( session, repository, proxy );
                  auth.digest( authDigest );
                  digest = authDigest.digest();
              }
          }
          return digest;
      }
  
      private AuthenticationDigest( RepositorySystemSession session, RemoteRepository repository, Proxy proxy )
      {
          this.session = session;
          this.repository = repository;
          this.proxy = proxy;
          digest = newDigest();
      }
  
      private static MessageDigest newDigest()
      {
          try
         {
             return MessageDigest.getInstance( "SHA-1" );
         }
         catch ( NoSuchAlgorithmException e )
         {
             try
             {
                 return MessageDigest.getInstance( "MD5" );
             }
             catch ( NoSuchAlgorithmException ne )
             {
                 throw new IllegalStateException( ne );
             }
         }
     }
 
     /**
      * Gets the repository system session during which the authentication fingerprint is calculated.
      * 
      * @return The repository system session, never {@code null}.
      */
     public RepositorySystemSession getSession()
     {
         return session;
     }
 
     /**
      * Gets the repository requiring authentication. If {@link #getProxy()} is not {@code null}, the data gathered by
      * this authentication digest does not apply to the repository's host but rather the proxy.
      * 
      * @return The repository to be contacted, never {@code null}.
      */
     public RemoteRepository getRepository()
     {
         return repository;
     }
 
     /**
      * Gets the proxy (if any) to be authenticated with.
      * 
      * @return The proxy or {@code null} if authenticating directly with the repository's host.
      */
     public Proxy getProxy()
     {
         return proxy;
     }
 
     /**
      * Updates the digest with the specified strings.
      * 
      * @param strings The strings to update the digest with, may be {@code null} or contain {@code null} elements.
      */
     public void update( String... strings )
     {
         if ( strings != null )
         {
             for ( String string : strings )
             {
                 if ( string != null )
                 {
                     digest.update( string.getBytes( StandardCharsets.UTF_8 ) );
                 }
             }
         }
     }
 
     /**
      * Updates the digest with the specified characters.
      * 
      * @param chars The characters to update the digest with, may be {@code null}.
      */
     @SuppressWarnings( "checkstyle:magicnumber" )
     public void update( char... chars )
     {
         if ( chars != null )
         {
             for ( char c : chars )
             {
                 digest.update( (byte) ( c >> 8 ) );
                 digest.update( (byte) ( c & 0xFF ) );
             }
         }
     }
 
     /**
      * Updates the digest with the specified bytes.
      * 
      * @param bytes The bytes to update the digest with, may be {@code null}.
      */
     public void update( byte... bytes )
     {
         if ( bytes != null )
         {
             digest.update( bytes );
         }
     }
 
     @SuppressWarnings( "checkstyle:magicnumber" )
     private String digest()
     {
         byte[] bytes = digest.digest();
         StringBuilder buffer = new StringBuilder( bytes.length * 2 );
         for ( byte aByte : bytes )
         {
             int b = aByte & 0xFF;
             if ( b < 0x10 )
             {
                 buffer.append( '0' );
             }
             buffer.append( Integer.toHexString( b ) );
         }
         return buffer.toString();
     }
 
 }