/*
 * Copyright (c) 2018, PostgreSQL Global Development Group
 * See the LICENSE file in the project root for more information.
 */

package org.postgresql.ssl;

import org.postgresql.util.GT;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.net.IDN;
import java.security.cert.CertificateParsingException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.naming.InvalidNameException;
import javax.naming.ldap.LdapName;
import javax.naming.ldap.Rdn;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLPeerUnverifiedException;
import javax.net.ssl.SSLSession;
import javax.security.auth.x500.X500Principal;

public class PGjdbcHostnameVerifier implements HostnameVerifier {
  private static final Logger LOGGER = Logger.getLogger(PGjdbcHostnameVerifier.class.getName());

  public static final PGjdbcHostnameVerifier INSTANCE = new PGjdbcHostnameVerifier();

  private static final int TYPE_DNS_NAME = 2;
  private static final int TYPE_IP_ADDRESS = 7;

  public static final Comparator<String> HOSTNAME_PATTERN_COMPARATOR = new Comparator<String>() {
    private int countChars(String value, char ch) {
      int count = 0;
      int pos = -1;
      while (true) {
        pos = value.indexOf(ch, pos + 1);
        if (pos == -1) {
          break;
        }
        count++;
      }
      return count;
    }

    @Override
    public int compare(String o1, String o2) {
      // The more the dots the better: a.b.c.postgresql.org is more specific than postgresql.org
      int d1 = countChars(o1, '.');
      int d2 = countChars(o2, '.');
      if (d1 != d2) {
        return d1 > d2 ? 1 : -1;
      }

      // The less the stars the better: postgresql.org is more specific than *.*.postgresql.org
      int s1 = countChars(o1, '*');
      int s2 = countChars(o2, '*');
      if (s1 != s2) {
        return s1 < s2 ? 1 : -1;
      }

      // The longer the better: postgresql.org is more specific than sql.org
      int l1 = o1.length();
      int l2 = o2.length();
      if (l1 != l2) {
        return l1 > l2 ? 1 : -1;
      }

      return 0;
    }
  };

  @Override
  public boolean verify(String hostname, SSLSession session) {
    X509Certificate[] peerCerts;
    try {
      peerCerts = (X509Certificate[]) session.getPeerCertificates();
    } catch (SSLPeerUnverifiedException e) {
      LOGGER.log(Level.SEVERE,
          GT.tr("Unable to parse X509Certificate for hostname {0}", hostname), e);
      return false;
    }
    if (peerCerts == null || peerCerts.length == 0) {
      LOGGER.log(Level.SEVERE,
          GT.tr("No certificates found for hostname {0}", hostname));
      return false;
    }

    String canonicalHostname;
    if (hostname.startsWith("[") && hostname.endsWith("]")) {
      // IPv6 address like [2001:db8:0:1:1:1:1:1]
      canonicalHostname = hostname.substring(1, hostname.length() - 1);
    } else {
      // This converts unicode domain name to ASCII
      try {
        canonicalHostname = IDN.toASCII(hostname);
        if (LOGGER.isLoggable(Level.FINEST)) {
          LOGGER.log(Level.FINEST, "Canonical host name for {0} is {1}",
              new Object[]{hostname, canonicalHostname});
        }
      } catch (IllegalArgumentException e) {
        // e.g. hostname is invalid
        LOGGER.log(Level.SEVERE,
            GT.tr("Hostname {0} is invalid", hostname), e);
        return false;
      }
    }

    X509Certificate serverCert = peerCerts[0];

    // Check for Subject Alternative Names (see RFC 6125)

    Collection<List<?>> subjectAltNames;
    try {
      subjectAltNames = serverCert.getSubjectAlternativeNames();
      if (subjectAltNames == null) {
        subjectAltNames = Collections.emptyList();
      }
    } catch (CertificateParsingException e) {
      LOGGER.log(Level.SEVERE,
          GT.tr("Unable to parse certificates for hostname {0}", hostname), e);
      return false;
    }

    boolean anyDnsSan = false;
    /*
     * Each item in the SAN collection is a 2-element list.
     * See {@link X509Certificate#getSubjectAlternativeNames}
     * The first element in each list is a number indicating the type of entry.
     */
    for (List<?> sanItem : subjectAltNames) {
      if (sanItem.size() != 2) {
        continue;
      }
      Integer sanType = (Integer) sanItem.get(0);
      if (sanType == null) {
        // just in case
        continue;
      }
      if (sanType != TYPE_IP_ADDRESS && sanType != TYPE_DNS_NAME) {
        continue;
      }
      String san = (String) sanItem.get(1);
      if (sanType == TYPE_IP_ADDRESS && san != null && san.startsWith("*")) {
        // Wildcards should not be present in the IP Address field
        continue;
      }
      anyDnsSan |= sanType == TYPE_DNS_NAME;
      if (verifyHostName(canonicalHostname, san)) {
        if (LOGGER.isLoggable(Level.FINEST)) {
          LOGGER.log(Level.FINEST,
              GT.tr("Server name validation pass for {0}, subjectAltName {1}", hostname, san));
        }
        return true;
      }
    }

    if (anyDnsSan) {
      /*
       * RFC2818, section 3.1 (I bet you won't recheck :)
       * If a subjectAltName extension of type dNSName is present, that MUST
       * be used as the identity. Otherwise, the (most specific) Common Name
       * field in the Subject field of the certificate MUST be used. Although
       * the use of the Common Name is existing practice, it is deprecated and
       * Certification Authorities are encouraged to use the dNSName instead.
       */
      LOGGER.log(Level.SEVERE,
          GT.tr("Server name validation failed: certificate for host {0} dNSName entries subjectAltName,"
              + " but none of them match. Assuming server name validation failed", hostname));
      return false;
    }

    // Last attempt: no DNS Subject Alternative Name entries detected, try common name
    LdapName dn;
    try {
      dn = new LdapName(serverCert.getSubjectX500Principal().getName(X500Principal.RFC2253));
    } catch (InvalidNameException e) {
      LOGGER.log(Level.SEVERE,
          GT.tr("Server name validation failed: unable to extract common name"
              + " from X509Certificate for hostname {0}", hostname), e);
      return false;
    }

    List<String> commonNames = new ArrayList<String>(1);
    for (Rdn rdn : dn.getRdns()) {
      if ("CN".equals(rdn.getType())) {
        commonNames.add((String) rdn.getValue());
      }
    }
    if (commonNames.isEmpty()) {
      LOGGER.log(Level.SEVERE,
          GT.tr("Server name validation failed: certificate for hostname {0} has no DNS subjectAltNames,"
                  + " and it CommonName is missing as well",
              hostname));
      return false;
    }
    if (commonNames.size() > 1) {
      /*
       * RFC2818, section 3.1
       * If a subjectAltName extension of type dNSName is present, that MUST
       * be used as the identity. Otherwise, the (most specific) Common Name
       * field in the Subject field of the certificate MUST be used
       *
       * The sort is from less specific to most specific.
       */
      Collections.sort(commonNames, HOSTNAME_PATTERN_COMPARATOR);
    }
    String commonName = commonNames.get(commonNames.size() - 1);
    boolean result = verifyHostName(canonicalHostname, commonName);
    if (!result) {
      LOGGER.log(Level.SEVERE,
          GT.tr("Server name validation failed: hostname {0} does not match common name {1}",
              hostname, commonName));
    }
    return result;
  }

  public boolean verifyHostName(@Nullable String hostname, @Nullable String pattern) {
    if (hostname == null || pattern == null) {
      return false;
    }
    int lastStar = pattern.lastIndexOf('*');
    if (lastStar == -1) {
      // No wildcard => just compare hostnames
      return hostname.equalsIgnoreCase(pattern);
    }
    if (lastStar > 0) {
      // Wildcards like foo*.com are not supported yet
      return false;
    }
    if (pattern.indexOf('.') == -1) {
      // Wildcard certificates should contain at least one dot
      return false;
    }
    // pattern starts with *, so hostname should be at least (pattern.length-1) long
    if (hostname.length() < pattern.length() - 1) {
      return false;
    }
    // Use case insensitive comparison
    final boolean ignoreCase = true;
    // Below code is "hostname.endsWithIgnoreCase(pattern.withoutFirstStar())"

    // E.g. hostname==sub.host.com; pattern==*.host.com
    // We need to start the offset of ".host.com" in hostname
    // For this we take hostname.length() - pattern.length()
    // and +1 is required since pattern is known to start with *
    int toffset = hostname.length() - pattern.length() + 1;

    // Wildcard covers just one domain level
    // a.b.c.com should not be covered by *.c.com
    if (hostname.lastIndexOf('.', toffset - 1) >= 0) {
      // If there's a dot in between 0..toffset
      return false;
    }

    return hostname.regionMatches(ignoreCase, toffset,
        pattern, 1, pattern.length() - 1);
  }

}
