import gpgme
import os
import features
import logging

logger = logging.getLogger(__name__)

from StringIO import StringIO

class GPG2Signer(object):
  """ Helper class for signing data using GPG2. """
  def __init__(self, config, config_provider):
    if not config.get('GPG2_PRIVATE_KEY_NAME'):
      raise Exception('Missing configuration key GPG2_PRIVATE_KEY_NAME')

    if not config.get('GPG2_PRIVATE_KEY_FILENAME'):
      raise Exception('Missing configuration key GPG2_PRIVATE_KEY_FILENAME')

    if not config.get('GPG2_PUBLIC_KEY_FILENAME'):
      raise Exception('Missing configuration key GPG2_PUBLIC_KEY_FILENAME')

    self._ctx = gpgme.Context()
    self._ctx.armor = True
    self._private_key_name = config['GPG2_PRIVATE_KEY_NAME']
    self._public_key_filename = config['GPG2_PUBLIC_KEY_FILENAME']
    self._config_provider = config_provider

    if not config_provider.volume_file_exists(config['GPG2_PRIVATE_KEY_FILENAME']):
      raise Exception('Missing key file %s' % config['GPG2_PRIVATE_KEY_FILENAME'])

    with config_provider.get_volume_file(config['GPG2_PRIVATE_KEY_FILENAME'], mode='rb') as fp:
      self._ctx.import_(fp)

  @property
  def name(self):
    return 'gpg2'

  def open_public_key_file(self):
    return self._config_provider.get_volume_file(self._public_key_filename, mode='rb')

  def detached_sign(self, stream):
    """ Signs the given stream, returning the signature. """
    ctx = self._ctx
    try:
      ctx.signers = [ctx.get_key(self._private_key_name)]
    except:
      raise Exception('Invalid private key name')

    signature = StringIO()
    new_sigs = ctx.sign(stream, signature, gpgme.SIG_MODE_DETACH)
    signature.seek(0)
    return signature.getvalue()


class Signer(object):
  def __init__(self, app=None, config_provider=None):
    self.app = app
    if app is not None:
      self.state = self.init_app(app, config_provider)
    else:
      self.state = None

  def init_app(self, app, config_provider):
    preference = app.config.get('SIGNING_ENGINE', None)
    if preference is None:
      return None

    if not features.ACI_CONVERSION:
      return None

    try:
      return SIGNING_ENGINES[preference](app.config, key_directory)
    except Exception:
      logger.exception('Could not initialize signing engine')

  def __getattr__(self, name):
    return getattr(self.state, name, None)


SIGNING_ENGINES = {
  'gpg2': GPG2Signer
}