import logging

from urlparse import urljoin
from posixpath import join

from abc import ABCMeta, abstractmethod
from six import add_metaclass

import requests

from data.database import CloseForLongOperation
from util.abchelpers import nooper
from util.failover import failover, FailoverException
from util.security.instancekeys import InstanceKeys
from util.security.registry_jwt import (build_context_and_subject, generate_bearer_token,
                                        SIGNER_TUF_ROOT)


DEFAULT_HTTP_HEADERS = {'Connection': 'close'}
MITM_CERT_PATH = '/conf/mitm.cert'
TOKEN_VALIDITY_LIFETIME_S = 60 * 60  # 1 hour

logger = logging.getLogger(__name__)


class InvalidMetadataException(Exception):
  """ Exception raised when the upstream API metadata that doesn't parse correctly. """
  pass


class Non200ResponseException(Exception):
  """ Exception raised when the upstream API returns a non-200 HTTP status code. """
  def __init__(self, response):
    super(Non200ResponseException, self).__init__()
    self.response = response


class TUFMetadataAPI(object):
  """ Helper class for talking to the TUF Metadata service (Apostille). """
  def __init__(self, app, config, client=None):
    feature_enabled = config.get('FEATURE_SIGNING', False)
    if feature_enabled:
      self.state = ImplementedTUFMetadataAPI(app, config, client=client)
    else:
      self.state = NoopTUFMetadataAPI()

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


@add_metaclass(ABCMeta)
class TUFMetadataAPIInterface(object):
  """ Helper class for talking to the TUF Metadata service (Apostille). """

  @abstractmethod
  def get_default_tags_with_expiration(self, namespace, repository, targets_file=None):
    """
    Gets the tag -> sha mappings for a repo, as well as the expiration of the signatures.
    Does not verify the metadata, this is purely for display purposes.

    Args:
      namespace: namespace containing the repository
      repository: the repo to get tags for
      targets_file: the specific delegation to read from. Default: targets/releases.json

    Returns:
      targets, expiration or None, None
    """
    pass

  @abstractmethod
  def get_all_tags_with_expiration(self, namespace, repository, targets_file=None, targets_map=None):
    """
    Gets the tag -> sha mappings of all delegations for a repo, as well as the expiration of the signatures.
    Does not verify the metadata, this is purely for display purposes.
    
    Args:
      namespace: namespace containing the repository
      repository: the repo to get tags for
      targets_file: the specific target or delegation to read from. Default: targets.json
    
    Returns:
      targets
    """
    pass
  
  @abstractmethod
  def delete_metadata(self, namespace, repository):
    """
    Deletes the TUF metadata for a repo

    Args:
      namespace: namespace containing the repository
      repository: the repo to delete metadata for

    Returns:
       True if successful, False otherwise
    """
    pass


@nooper
class NoopTUFMetadataAPI(TUFMetadataAPIInterface):
  """ No-op version of the TUF API. """
  pass


class ImplementedTUFMetadataAPI(TUFMetadataAPIInterface):
  def __init__(self, app, config, client=None):
    self._app = app
    self._instance_keys = InstanceKeys(app)
    self._config = config
    self._client = client or config['HTTPCLIENT']
    self._gun_prefix = config['TUF_GUN_PREFIX'] or config['SERVER_HOSTNAME']

  def get_default_tags_with_expiration(self, namespace, repository, targets_file=None):
    """
    Gets the tag -> sha mappings for a repo, as well as the expiration of the signatures.
    Does not verify the metadata, this is purely for display purposes.

    Args:
      namespace: namespace containing the repository
      repository: the repo to get tags for
      targets_file: the specific delegation to read from. Default: targets/releases.json

    Returns:
      targets, expiration or None, None
    """

    if not targets_file:
      targets_file = 'targets/releases.json'

    signed = self._get_signed(namespace, repository, targets_file)
    if not signed:
      return None, None

    return signed.get('targets'), signed.get('expires')
  
  def get_all_tags_with_expiration(self, namespace, repository, targets_file=None, targets_map=None):
    """
    Gets the tag -> sha mappings of all delegations for a repo, as well as the expiration of the signatures.
    Does not verify the metadata, this is purely for display purposes.

    Args:
      namespace: namespace containing the repository
      repository: the repo to get tags for
      targets_file: the specific target or delegation to read from. Default: targets.json

    Returns:
      targets
    """

    if not targets_file:
      targets_file = 'targets.json'

    targets_name = targets_file
    if targets_name.endswith('.json'):
      targets_name = targets_name[:-5]
      
    if not targets_map:
      targets_map = {}
      
    signed = self._get_signed(namespace, repository, targets_file)
    if not signed:
      targets_map[targets_name] = None
      return targets_map

    if signed.get('targets'):
      targets_map[targets_name] = {
        'targets':  signed.get('targets'),
        'expiration':  signed.get('expires'),
      }

    delegation_names = [role.get('name') for role in signed.get('delegations').get('roles')]

    for delegation in delegation_names:
      targets_map = self.get_all_tags_with_expiration(namespace, repository, targets_file=delegation + '.json', targets_map=targets_map)
   
    return targets_map

  def delete_metadata(self, namespace, repository):
    """
    Deletes the TUF metadata for a repo

    Args:
      namespace: namespace containing the repository
      repository: the repo to delete metadata for

    Returns:
       True if successful, False otherwise
    """
    gun = self._gun(namespace, repository)
    try:
      self._delete(gun)
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to delete metadata for %s', gun)
      return False
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to delete metadata for %s', gun)
      return False
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Failed to delete metadata for %s', gun)
      return False
    except Non200ResponseException as ex:
      logger.exception('Failed request for %s: %s %s', gun, ex.response, str(ex))
      return False
    return True

  def _gun(self, namespace, repository):
    return join(self._gun_prefix, namespace, repository)
  
  def _get_signed(self, namespace, repository, targets_file):
    gun = self._gun(namespace, repository)

    try:
      response = self._get(gun, targets_file)
      signed = self._parse_signed(response.json())
      return signed
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to get metadata for %s', gun)
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to get metadata for %s', gun)
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Failed to get metadata for %s', gun)
    except Non200ResponseException as ex:
      logger.exception('Failed request for %s: %s %s', gun, ex.response, str(ex))
    except InvalidMetadataException as ex:
      logger.exception('Failed to parse targets from metadata: %s', str(ex))
    return None

  def _parse_signed(self, json_response):
    """ Attempts to parse the targets from a metadata response """
    signed = json_response.get('signed')
    if not signed:
      raise InvalidMetadataException("Could not find `signed` in metadata: %s" % json_response)
    return signed

  def _auth_header(self, gun, actions):
    """ Generate a registry auth token for apostille"""
    access = [{
      'type': 'repository',
      'name': gun,
      'actions': actions,
    }]
    context, subject = build_context_and_subject(auth_context=None, tuf_roots={gun: SIGNER_TUF_ROOT})
    token = generate_bearer_token(self._config["SERVER_HOSTNAME"], subject, context, access,
                                  TOKEN_VALIDITY_LIFETIME_S, self._instance_keys)
    return {'Authorization': 'Bearer %s' % token}

  def _get(self, gun, metadata_file):
    return self._call('GET', '/v2/%s/_trust/tuf/%s' % (gun, metadata_file), headers=self._auth_header(gun, ['pull']))

  def _delete(self, gun):
    return self._call('DELETE', '/v2/%s/_trust/tuf/' % (gun), headers=self._auth_header(gun, ['*']))

  def _request(self, method, endpoint, path, body, headers, params, timeout):
    """ Issues an HTTP request to the signing endpoint. """
    url = urljoin(endpoint, path)
    logger.debug('%sing signing URL %s', method.upper(), url)

    headers.update(DEFAULT_HTTP_HEADERS)
    resp = self._client.request(method, url, json=body, params=params, timeout=timeout,
                                verify=True, headers=headers)
    if resp.status_code // 100 != 2:
      raise Non200ResponseException(resp)
    return resp

  def _call(self, method, path, params=None, body=None, headers=None):
    """ Issues an HTTP request to signing service and handles failover for GET requests.
    """
    timeout = self._config.get('TUF_API_TIMEOUT_SECONDS', 1)
    endpoint = self._config['TUF_SERVER']

    with CloseForLongOperation(self._config):
      # If the request isn't a read do not fail over.
      if method != 'GET':
        return self._request(method, endpoint, path, body, headers, params, timeout)

      # The request is read-only and can failover.
      all_endpoints = [endpoint] + self._config.get('TUF_READONLY_FAILOVER_ENDPOINTS', [])
      return _failover_read_request(*[((self._request, endpoint, path, body, headers, params, timeout), {})
                                      for endpoint in all_endpoints])


@failover
def _failover_read_request(request_fn, endpoint, path, body, headers, params, timeout):
  """ This function auto-retries read-only requests until they return a 2xx status code. """
  try:
    return request_fn('GET', endpoint, path, body, headers, params, timeout)
  except (requests.exceptions.RequestException, Non200ResponseException) as ex:
    raise FailoverException(ex)