/*
 * Copyright 2008-2017 Ping Identity Corporation
 * All Rights Reserved.
 */
/*
 * Copyright (C) 2008-2017 Ping Identity Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License (GPLv2 only)
 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses>.
 */
package com.unboundid.util.ssl;


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintStream;
import java.security.MessageDigest;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.Date;
import java.util.concurrent.ConcurrentHashMap;
import javax.net.ssl.X509TrustManager;
import javax.security.auth.x500.X500Principal;

import com.unboundid.util.NotMutable;
import com.unboundid.util.ThreadSafety;
import com.unboundid.util.ThreadSafetyLevel;

import static com.unboundid.util.Debug.*;
import static com.unboundid.util.StaticUtils.*;
import static com.unboundid.util.ssl.SSLMessages.*;



/**
 * This class provides an SSL trust manager that will interactively prompt the
 * user to determine whether to trust any certificate that is presented to it.
 * It provides the ability to cache information about certificates that had been
 * previously trusted so that the user is not prompted about the same
 * certificate repeatedly, and it can be configured to store trusted
 * certificates in a file so that the trust information can be persisted.
 */
@NotMutable()
@ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
public final class PromptTrustManager
       implements X509TrustManager
{
  /**
   * The message digest that will be used for MD5 hashes.
   */
  private static final MessageDigest MD5;



  /**
   * The message digest that will be used for SHA-1 hashes.
   */
  private static final MessageDigest SHA1;



  /**
   * The message digest that will be used for 256-bit SHA-2 hashes.
   */
  private static final MessageDigest SHA256;



  /**
   * A pre-allocated empty certificate array.
   */
  private static final X509Certificate[] NO_CERTIFICATES =
       new X509Certificate[0];



  static
  {
    MessageDigest d = null;
    try
    {
      d = MessageDigest.getInstance("MD5");
    }
    catch (final Exception e)
    {
      debugException(e);
      throw new RuntimeException(e);
    }
    MD5 = d;

    d = null;
    try
    {
      d = MessageDigest.getInstance("SHA-1");
    }
    catch (final Exception e)
    {
      debugException(e);
      throw new RuntimeException(e);
    }
    SHA1 = d;

    d = null;
    try
    {
      d = MessageDigest.getInstance("SHA-256");
    }
    catch (final Exception e)
    {
      debugException(e);
      throw new RuntimeException(e);
    }
    SHA256 = d;
  }



  // Indicates whether to examine the validity dates for the certificate in
  // addition to whether the certificate has been previously trusted.
  private final boolean examineValidityDates;

  // The set of previously-accepted certificates.  The certificates will be
  // mapped from an all-lowercase hexadecimal string representation of the
  // certificate signature to a flag that indicates whether the certificate has
  // already been manually trusted even if it is outside of the validity window.
  private final ConcurrentHashMap<String,Boolean> acceptedCerts;

  // The input stream from which the user input will be read.
  private final InputStream in;

  // The print stream that will be used to display the prompt.
  private final PrintStream out;

  // The path to the file to which the set of accepted certificates should be
  // persisted.
  private final String acceptedCertsFile;



  /**
   * Creates a new instance of this prompt trust manager.  It will cache trust
   * information in memory but not on disk.
   */
  public PromptTrustManager()
  {
    this(null, true, null, null);
  }



  /**
   * Creates a new instance of this prompt trust manager.  It may optionally
   * cache trust information on disk.
   *
   * @param  acceptedCertsFile  The path to a file in which the certificates
   *                            that have been previously accepted will be
   *                            cached.  It may be {@code null} if the cache
   *                            should only be maintained in memory.
   */
  public PromptTrustManager(final String acceptedCertsFile)
  {
    this(acceptedCertsFile, true, null, null);
  }



  /**
   * Creates a new instance of this prompt trust manager.  It may optionally
   * cache trust information on disk, and may also be configured to examine or
   * ignore validity dates.
   *
   * @param  acceptedCertsFile     The path to a file in which the certificates
   *                               that have been previously accepted will be
   *                               cached.  It may be {@code null} if the cache
   *                               should only be maintained in memory.
   * @param  examineValidityDates  Indicates whether to reject certificates if
   *                               the current time is outside the validity
   *                               window for the certificate.
   * @param  in                    The input stream that will be used to read
   *                               input from the user.  If this is {@code null}
   *                               then {@code System.in} will be used.
   * @param  out                   The print stream that will be used to display
   *                               the prompt to the user.  If this is
   *                               {@code null} then System.out will be used.
   */
  public PromptTrustManager(final String acceptedCertsFile,
                            final boolean examineValidityDates,
                            final InputStream in, final PrintStream out)
  {
    this.acceptedCertsFile    = acceptedCertsFile;
    this.examineValidityDates = examineValidityDates;

    if (in == null)
    {
      this.in = System.in;
    }
    else
    {
      this.in = in;
    }

    if (out == null)
    {
      this.out = System.out;
    }
    else
    {
      this.out = out;
    }

    acceptedCerts = new ConcurrentHashMap<String,Boolean>();

    if (acceptedCertsFile != null)
    {
      BufferedReader r = null;
      try
      {
        final File f = new File(acceptedCertsFile);
        if (f.exists())
        {
          r = new BufferedReader(new FileReader(f));
          while (true)
          {
            final String line = r.readLine();
            if (line == null)
            {
              break;
            }
            acceptedCerts.put(line, false);
          }
        }
      }
      catch (final Exception e)
      {
        debugException(e);
      }
      finally
      {
        if (r != null)
        {
          try
          {
            r.close();
          }
          catch (final Exception e)
          {
            debugException(e);
          }
        }
      }
    }
  }



  /**
   * Writes an updated copy of the trusted certificate cache to disk.
   *
   * @throws  IOException  If a problem occurs.
   */
  private void writeCacheFile()
          throws IOException
  {
    final File tempFile = new File(acceptedCertsFile + ".new");

    BufferedWriter w = null;
    try
    {
      w = new BufferedWriter(new FileWriter(tempFile));

      for (final String certBytes : acceptedCerts.keySet())
      {
        w.write(certBytes);
        w.newLine();
      }
    }
    finally
    {
      if (w != null)
      {
        w.close();
      }
    }

    final File cacheFile = new File(acceptedCertsFile);
    if (cacheFile.exists())
    {
      final File oldFile = new File(acceptedCertsFile + ".previous");
      if (oldFile.exists())
      {
        oldFile.delete();
      }

      cacheFile.renameTo(oldFile);
    }

    tempFile.renameTo(cacheFile);
  }



  /**
   * Indicates whether this trust manager would interactively prompt the user
   * about whether to trust the provided certificate chain.
   *
   * @param  chain  The chain of certificates for which to make the
   *                determination.
   *
   * @return  {@code true} if this trust manger would interactively prompt the
   *          user about whether to trust the certificate chain, or
   *          {@code false} if not (e.g., because the certificate is already
   *          known to be trusted).
   */
  public synchronized boolean wouldPrompt(final X509Certificate[] chain)
  {
    // See if the certificate is in the cache.  If it isn't then we will
    // prompt no matter what.
    final X509Certificate c = chain[0];
    final String certBytes = toLowerCase(toHex(c.getSignature()));
    final Boolean acceptedRegardlessOfValidity = acceptedCerts.get(certBytes);
    if (acceptedRegardlessOfValidity == null)
    {
      return true;
    }


    // If we shouldn't check validity dates, or if the certificate has already
    // been accepted when it's outside the validity window, then we won't
    // prompt.
    if (acceptedRegardlessOfValidity || (! examineValidityDates))
    {
      return false;
    }


    // If the certificate is within the validity window, then we won't prompt.
    // If it's outside the validity window, then we will prompt to make sure the
    // user still wants to trust it.
    final Date currentDate = new Date();
    return (! (currentDate.before(c.getNotBefore()) ||
               currentDate.after(c.getNotAfter())));
  }



  /**
   * Performs the necessary validity check for the provided certificate array.
   *
   * @param  chain       The chain of certificates for which to make the
   *                     determination.
   * @param  serverCert  Indicates whether the certificate was presented as a
   *                     server certificate or as a client certificate.
   *
   * @throws  CertificateException  If the provided certificate chain should not
   *                                be trusted.
   */
  private synchronized void checkCertificateChain(final X509Certificate[] chain,
                                                  final boolean serverCert)
          throws CertificateException
  {
    // See if the certificate is currently within the validity window.
    String validityWarning = null;
    final Date currentDate = new Date();
    final X509Certificate c = chain[0];
    if (examineValidityDates)
    {
      if (currentDate.before(c.getNotBefore()))
      {
        validityWarning = WARN_PROMPT_NOT_YET_VALID.get();
      }
      else if (currentDate.after(c.getNotAfter()))
      {
        validityWarning = WARN_PROMPT_EXPIRED.get();
      }
    }


    // If the certificate is within the validity window, or if we don't care
    // about validity dates, then see if it's in the cache.
    if ((! examineValidityDates) || (validityWarning == null))
    {
      final String certBytes = toLowerCase(toHex(c.getSignature()));
      final Boolean accepted = acceptedCerts.get(certBytes);
      if (accepted != null)
      {
        if ((validityWarning == null) || (! examineValidityDates) ||
            Boolean.TRUE.equals(accepted))
        {
          // The certificate was found in the cache.  It's either in the
          // validity window, we don't care about the validity window, or has
          // already been manually trusted outside of the validity window.
          // We'll consider it trusted without the need to re-prompt.
          return;
        }
      }
    }


    // If we've gotten here, then we need to display a prompt to the user.
    if (serverCert)
    {
      out.println(INFO_PROMPT_SERVER_HEADING.get());
    }
    else
    {
      out.println(INFO_PROMPT_CLIENT_HEADING.get());
    }

    out.println('\t' + INFO_PROMPT_SUBJECT.get(
         c.getSubjectX500Principal().getName(X500Principal.CANONICAL)));
    out.println("\t\t" + INFO_PROMPT_MD5_FINGERPRINT.get(
         getFingerprint(c, MD5)));
    out.println("\t\t" + INFO_PROMPT_SHA1_FINGERPRINT.get(
         getFingerprint(c, SHA1)));
    out.println("\t\t" + INFO_PROMPT_SHA256_FINGERPRINT.get(
         getFingerprint(c, SHA256)));

    for (int i=1; i < chain.length; i++)
    {
      out.println('\t' + INFO_PROMPT_ISSUER_SUBJECT.get(i,
           chain[i].getSubjectX500Principal().getName(
                X500Principal.CANONICAL)));
      out.println("\t\t" + INFO_PROMPT_MD5_FINGERPRINT.get(
           getFingerprint(chain[i], MD5)));
      out.println("\t\t" + INFO_PROMPT_SHA1_FINGERPRINT.get(
           getFingerprint(chain[i], SHA1)));
    }

    out.println(INFO_PROMPT_VALIDITY.get(String.valueOf(c.getNotBefore()),
         String.valueOf(c.getNotAfter())));

    if (chain.length == 1)
    {
      out.println();
      out.println(WARN_PROMPT_SELF_SIGNED.get());
    }

    if (validityWarning != null)
    {
      out.println();
      out.println(validityWarning);
    }

    final BufferedReader reader = new BufferedReader(new InputStreamReader(in));
    while (true)
    {
      try
      {
        out.println();
        out.print(INFO_PROMPT_MESSAGE.get());
        out.flush();
        final String line = reader.readLine();
        if (line == null)
        {
          // The input stream has been closed, so we can't prompt for trust,
          // and should assume it is not trusted.
          throw new CertificateException(
               ERR_CERTIFICATE_REJECTED_BY_END_OF_STREAM.get(
                    SSLUtil.certificateToString(chain[0])));
        }
        else if (line.equalsIgnoreCase("y") || line.equalsIgnoreCase("yes"))
        {
          // The certificate should be considered trusted.
          break;
        }
        else if (line.equalsIgnoreCase("n") || line.equalsIgnoreCase("no"))
        {
          // The certificate should not be trusted.
          throw new CertificateException(
               ERR_CERTIFICATE_REJECTED_BY_USER.get(
                    SSLUtil.certificateToString(chain[0])));
        }
      }
      catch (final CertificateException ce)
      {
        throw ce;
      }
      catch (final Exception e)
      {
        debugException(e);
      }
    }

    final String certBytes = toLowerCase(toHex(c.getSignature()));
    acceptedCerts.put(certBytes, (validityWarning != null));

    if (acceptedCertsFile != null)
    {
      try
      {
        writeCacheFile();
      }
      catch (final Exception e)
      {
        debugException(e);
      }
    }
  }



  /**
   * Computes the fingerprint for the provided certificate using the given
   * digest.
   *
   * @param  c  The certificate for which to obtain the fingerprint.
   * @param  d  The message digest to use when creating the fingerprint.
   *
   * @return  The generated certificate fingerprint.
   *
   * @throws  CertificateException  If a problem is encountered while generating
   *                                the certificate fingerprint.
   */
  private static String getFingerprint(final X509Certificate c,
                                       final MessageDigest d)
          throws CertificateException
  {
    final byte[] encodedCertBytes = c.getEncoded();

    final byte[] digestBytes;
    synchronized (d)
    {
      digestBytes = d.digest(encodedCertBytes);
    }

    final StringBuilder buffer = new StringBuilder(3 * encodedCertBytes.length);
    toHex(digestBytes, ":", buffer);
    return buffer.toString();
  }



  /**
   * Indicate whether to prompt about certificates contained in the cache if the
   * current time is outside the validity window for the certificate.
   *
   * @return  {@code true} if the certificate validity time should be examined
   *          for cached certificates and the user should be prompted if they
   *          are expired or not yet valid, or {@code false} if cached
   *          certificates should be accepted even outside of the validity
   *          window.
   */
  public boolean examineValidityDates()
  {
    return examineValidityDates;
  }



  /**
   * Checks to determine whether the provided client certificate chain should be
   * trusted.
   *
   * @param  chain     The client certificate chain for which to make the
   *                   determination.
   * @param  authType  The authentication type based on the client certificate.
   *
   * @throws  CertificateException  If the provided client certificate chain
   *                                should not be trusted.
   */
  @Override()
  public void checkClientTrusted(final X509Certificate[] chain,
                                 final String authType)
         throws CertificateException
  {
    checkCertificateChain(chain, false);
  }



  /**
   * Checks to determine whether the provided server certificate chain should be
   * trusted.
   *
   * @param  chain     The server certificate chain for which to make the
   *                   determination.
   * @param  authType  The key exchange algorithm used.
   *
   * @throws  CertificateException  If the provided server certificate chain
   *                                should not be trusted.
   */
  @Override()
  public void checkServerTrusted(final X509Certificate[] chain,
                                 final String authType)
         throws CertificateException
  {
    checkCertificateChain(chain, true);
  }



  /**
   * Retrieves the accepted issuer certificates for this trust manager.  This
   * will always return an empty array.
   *
   * @return  The accepted issuer certificates for this trust manager.
   */
  @Override()
  public X509Certificate[] getAcceptedIssuers()
  {
    return NO_CERTIFICATES;
  }
}