import logging
from urlparse import urljoin

import requests

from data.database import CloseForLongOperation
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, QUAY_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):
    self._app = app
    self._instance_keys = InstanceKeys(app)
    self._config = config
    self._client = client or config['HTTPCLIENT']

  def get_default_tags(self, namespace, repository):
    """ Gets the tag -> sha mappings in the 'targets/releases' delegation 
    """
    gun = "%s/%s" % (namespace, repository)
    try:
      response = self._get(gun, "targets/releases.json")
      json_response = response.json()
      targets = self._parse_targets(json_response)
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to get metadata for %s', gun)
      return None, True
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to get metadata for %s', gun)
      return None, True
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Failed to get metadata for %s', gun)
      return None, False
    except Non200ResponseException as ex:
      return None, ex.response.status_code != 404 and ex.response.status_code != 400
    except InvalidMetadataException as ex:
      logger.exception('Failed to parse targets from metadata', str(ex))
      return None, False 
    
    return targets, False
  
  def _parse_targets(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)
    targets = signed.get('targets')
    if not targets:
      raise InvalidMetadataException("Could not find `targets` in metadata: %s" % json_response)
    return targets
  
  def _auth_header(self, gun):
    """ Generate a registry auth token for apostille"""
    access = [{
      'type': 'repository',
      'name': '%s/%s' % (self._config['SERVER_HOSTNAME'], gun),
      'actions': ['pull'],
    }]
    context, subject = build_context_and_subject(user=None, token=None, oauthtoken=None, tuf_root=QUAY_TUF_ROOT)
    token = generate_bearer_token("quay", 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))
    
  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=MITM_CERT_PATH, 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.
    """
    if self._config is None:
      raise Exception('Cannot call unconfigured signing service')

    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)