from fnmatch import fnmatch

import OpenSSL

class CertInvalidException(Exception):
  """ Exception raised when a certificate could not be parsed/loaded. """
  pass

class KeyInvalidException(Exception):
  """ Exception raised when a key could not be parsed/loaded or successfully applied to a cert. """
  pass


def load_certificate(cert_contents):
  """ Loads the certificate from the given contents and returns it or raises a CertInvalidException
      on failure.
  """
  try:
    cert = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_PEM, cert_contents)
    return SSLCertificate(cert)
  except OpenSSL.crypto.Error as ex:
    raise CertInvalidException(ex.args[0][0][2])


_SUBJECT_ALT_NAME = 'subjectAltName'

class SSLCertificate(object):
  """ Helper class for easier working with SSL certificates. """
  def __init__(self, openssl_cert):
    self.openssl_cert = openssl_cert

  def validate_private_key(self, private_key_path):
    """ Validates that the private key found at the given file path applies to this certificate.
        Raises a KeyInvalidException on failure.
    """
    context = OpenSSL.SSL.Context(OpenSSL.SSL.TLSv1_METHOD)
    context.use_certificate(self.openssl_cert)

    try:
      context.use_privatekey_file(private_key_path)
      context.check_privatekey()
    except OpenSSL.SSL.Error as ex:
      raise KeyInvalidException(ex.args[0][0][2])

  def matches_name(self, check_name):
    """ Returns true if this SSL certificate matches the given DNS hostname. """
    for dns_name in self.names:
      if fnmatch(check_name, dns_name):
        return True

    return False

  @property
  def expired(self):
    """ Returns whether the SSL certificate has expired. """
    return self.openssl_cert.has_expired()

  @property
  def common_name(self):
    """ Returns the defined common name for the certificate, if any. """
    return self.openssl_cert.get_subject().commonName

  @property
  def names(self):
    """ Returns all the DNS named to which the certificate applies. May be empty. """
    dns_names = set()
    common_name = self.common_name
    if common_name is not None:
      dns_names.add(common_name)

    # Find the DNS extension, if any.
    for i in range(0, self.openssl_cert.get_extension_count()):
      ext = self.openssl_cert.get_extension(i)
      if ext.get_short_name() == _SUBJECT_ALT_NAME:
        value = str(ext)
        for san_name in value.split(','):
          san_name_trimmed = san_name.strip()
          if san_name_trimmed.startswith('DNS:'):
            dns_names.add(san_name_trimmed[4:])

    return dns_names