import logging

from urlparse import urljoin

import requests

from flask import url_for

from data.database import CloseForLongOperation
from data import model
from data.model.storage import get_storage_locations
from util.failover import failover, FailoverException
from util.secscan.validator import SecurityConfigValidator
from util.security.instancekeys import InstanceKeys
from util.security.registry_jwt import generate_bearer_token, build_context_and_subject
from util import get_app_url


TOKEN_VALIDITY_LIFETIME_S = 60  # Amount of time the security scanner has to call the layer URL

UNKNOWN_PARENT_LAYER_ERROR_MSG = 'worker: parent layer is unknown, it must be processed first'

MITM_CERT_PATH = '/conf/mitm.cert'
DEFAULT_HTTP_HEADERS = {'Connection': 'close'}

logger = logging.getLogger(__name__)


class AnalyzeLayerException(Exception):
  """ Exception raised when a layer fails to analyze due to a request issue. """

class AnalyzeLayerRetryException(Exception):
  """ Exception raised when a layer fails to analyze due to a request issue, and the request should
      be retried.
  """

class MissingParentLayerException(AnalyzeLayerException):
  """ Exception raised when the parent of the layer is missing from the security scanner. """

class InvalidLayerException(AnalyzeLayerException):
  """ Exception raised when the layer itself cannot be handled by the security scanner. """

class APIRequestFailure(Exception):
  """ Exception raised when there is a failure to conduct an API request. """


_API_METHOD_INSERT = 'layers'
_API_METHOD_GET_LAYER = 'layers/%s'
_API_METHOD_DELETE_LAYER = 'layers/%s'
_API_METHOD_MARK_NOTIFICATION_READ = 'notifications/%s'
_API_METHOD_GET_NOTIFICATION = 'notifications/%s'
_API_METHOD_PING = 'metrics'


def compute_layer_id(layer):
  """ Returns the ID for the layer in the security scanner. """
  return '%s.%s' % (layer.docker_image_id, layer.storage.uuid)


class SecurityScannerAPI(object):
  """ Helper class for talking to the Security Scan service (Clair). """
  def __init__(self, app, config, storage, client=None, skip_validation=False):
    if not skip_validation:
      config_validator = SecurityConfigValidator(config)
      if not config_validator.valid():
        logger.warning('Invalid config provided to SecurityScannerAPI')
        return

    self._app = app
    self._config = config
    self._instance_keys = InstanceKeys(app)
    self._client = client or config['HTTPCLIENT']
    self._storage = storage
    self._default_storage_locations = config['DISTRIBUTED_STORAGE_PREFERENCE']
    self._target_version = config.get('SECURITY_SCANNER_ENGINE_VERSION_TARGET', 2)

  def _get_image_url_and_auth(self, image):
    """ Returns a tuple of the url and the auth header value that must be used
        to fetch the layer data itself. If the image can't be addressed, we return
        None.
    """
    path = model.storage.get_layer_path(image.storage)
    locations = self._default_storage_locations

    if not self._storage.exists(locations, path):
      locations = get_storage_locations(image.storage.uuid)
      if not locations or not self._storage.exists(locations, path):
        logger.warning('Could not find a valid location to download layer %s out of %s',
                       compute_layer_id(image), locations)
        return None, None

    uri = self._storage.get_direct_download_url(locations, path)
    auth_header = None
    if uri is None:
      # Use the registry API instead, with a signed JWT giving access
      repo_name = image.repository.name
      namespace_name = image.repository.namespace_user.username
      repository_and_namespace = '/'.join([namespace_name, repo_name])

      # Generate the JWT which will authorize this
      audience = self._app.config['SERVER_HOSTNAME']
      context, subject = build_context_and_subject(None, None, None)
      access = [{
        'type': 'repository',
        'name': repository_and_namespace,
        'actions': ['pull'],
      }]

      auth_token = generate_bearer_token(audience, subject, context, access,
                                         TOKEN_VALIDITY_LIFETIME_S, self._instance_keys)
      auth_header = 'Bearer ' + auth_token

      with self._app.test_request_context('/'):
        relative_layer_url = url_for('v2.download_blob', repository=repository_and_namespace,
                                     digest=image.storage.content_checksum)
      uri = urljoin(get_app_url(self._config), relative_layer_url)

    return uri, auth_header

  def _new_analyze_request(self, layer):
    """ Create the request body to submit the given layer for analysis. If the layer's URL cannot
        be found, returns None.
    """
    url, auth_header = self._get_image_url_and_auth(layer)
    if url is None:
      return None

    layer_request = {
      'Name': compute_layer_id(layer),
      'Path': url,
      'Format': 'Docker',
    }

    if auth_header is not None:
      layer_request['Headers'] = {
        'Authorization': auth_header,
      }

    if layer.parent.docker_image_id and layer.parent.storage.uuid:
      layer_request['ParentName'] = compute_layer_id(layer.parent)

    return {
      'Layer': layer_request,
    }

  def cleanup_layers(self, layers):
    """ Callback invoked by garbage collection to cleanup any layers that no longer
        need to be stored in the security scanner.
    """
    if self._config is None:
      # Security scanner not enabled.
      return

    for layer in layers:
      self.delete_layer(layer)

  def ping(self):
    """ Calls GET on the metrics endpoint of the security scanner to ensure it is running
        and properly configured. Returns the HTTP response.
    """
    try:
      return self._call('GET', _API_METHOD_PING)
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to connect to security scanner endpoint')
      raise Exception('Timeout when trying to connect to security scanner endpoint')
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to connect to security scanner endpoint')
      raise Exception('Connection error when trying to connect to security scanner endpoint')
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Exception when trying to connect to security scanner endpoint')
      raise Exception('Exception when trying to connect to security scanner endpoint')

  def delete_layer(self, layer):
    """ Calls DELETE on the given layer in the security scanner, removing it from
        its database.
    """
    layer_id = compute_layer_id(layer)
    try:
      response = self._call('DELETE', _API_METHOD_DELETE_LAYER % layer_id)
      return response.status_code / 100 == 2
    except requests.exceptions.RequestException:
      logger.exception('Failed to delete layer: %s', layer_id)
      return False

  def analyze_layer(self, layer):
    """ Posts the given layer to the security scanner for analysis, blocking until complete.
        Returns the analysis version on success or raises an exception deriving from
        AnalyzeLayerException on failure. Callers should handle all cases of AnalyzeLayerException.
    """
    request = self._new_analyze_request(layer)
    if not request:
      raise AnalyzeLayerException

    logger.info('Analyzing layer %s', request['Layer']['Name'])
    try:
      response = self._call('POST', _API_METHOD_INSERT, body=request)
      json_response = response.json()
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to post layer data response for %s', layer.id)
      raise AnalyzeLayerRetryException
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to post layer data response for %s', layer.id)
      raise AnalyzeLayerRetryException
    except (requests.exceptions.RequestException, ValueError) as re:
      logger.exception('Failed to post layer data response for %s: %s', layer.id, re)
      raise AnalyzeLayerException

    # Handle any errors from the security scanner.
    if response.status_code != 201:
      message = json_response.get('Error').get('Message', '')
      logger.warning('A warning event occurred when analyzing layer %s (status code %s): %s',
                     request['Layer']['Name'], response.status_code, message)

      # 400 means the layer could not be analyzed due to a bad request.
      if response.status_code == 400:
        if message == UNKNOWN_PARENT_LAYER_ERROR_MSG:
          raise MissingParentLayerException('Bad request to security scanner: %s' % message)
        else:
          raise AnalyzeLayerException('Bad request to security scanner: %s' % message)

      # 422 means that the layer could not be analyzed:
      # - the layer could not be extracted (might be a manifest or an invalid .tar.gz)
      # - the layer operating system / package manager is unsupported
      elif response.status_code == 422:
        raise InvalidLayerException

      # Otherwise, it is some other error and we should retry.
      else:
        raise AnalyzeLayerRetryException

    # Return the parsed API version.
    return json_response['Layer']['IndexedByVersion']

  def check_layer_vulnerable(self, layer_id, cve_name):
    """ Checks to see if the layer with the given ID is vulnerable to the specified CVE. """
    layer_data = self._get_layer_data(layer_id, include_vulnerabilities=True)
    if layer_data is None or 'Layer' not in layer_data or 'Features' not in layer_data['Layer']:
      return False

    for feature in layer_data['Layer']['Features']:
      for vuln in feature.get('Vulnerabilities', []):
        if vuln['Name'] == cve_name:
          return True

    return False

  def get_notification(self, notification_name, layer_limit=100, page=None):
    """ Gets the data for a specific notification, with optional page token.
        Returns a tuple of the data (None on failure) and whether to retry.
    """
    try:
      params = {
        'limit': layer_limit
      }

      if page is not None:
        params['page'] = page

      response = self._call('GET', _API_METHOD_GET_NOTIFICATION % notification_name, params=params)
      json_response = response.json()
    except requests.exceptions.Timeout:
      logger.exception('Timeout when trying to get notification for %s', notification_name)
      return None, True
    except requests.exceptions.ConnectionError:
      logger.exception('Connection error when trying to get notification for %s', notification_name)
      return None, True
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Failed to get notification for %s', notification_name)
      return None, False

    if response.status_code != 200:
      return None, response.status_code != 404 and response.status_code != 400

    return json_response, False

  def mark_notification_read(self, notification_name):
    """ Marks a security scanner notification as read. """
    try:
      response = self._call('DELETE', _API_METHOD_MARK_NOTIFICATION_READ % notification_name)
      return response.status_code / 100 == 2
    except requests.exceptions.RequestException:
      logger.exception('Failed to mark notification as read: %s', notification_name)
      return False

  def get_layer_data(self, layer, include_features=False, include_vulnerabilities=False):
    """ Returns the layer data for the specified layer. On error, returns None. """
    layer_id = compute_layer_id(layer)
    return self._get_layer_data(layer_id, include_features, include_vulnerabilities)

  def _get_layer_data(self, layer_id, include_features=False, include_vulnerabilities=False):
    try:
      params = {}
      if include_features:
        params = {'features': True}

      if include_vulnerabilities:
        params = {'vulnerabilities': True}

      response = self._call('GET', _API_METHOD_GET_LAYER % layer_id, params=params)
      logger.debug('Got response %s for vulnerabilities for layer %s',
                   response.status_code, layer_id)
      json_response = response.json()
    except requests.exceptions.Timeout:
      raise APIRequestFailure('API call timed out')
    except requests.exceptions.ConnectionError:
      raise APIRequestFailure('Could not connect to security service')
    except (requests.exceptions.RequestException, ValueError):
      logger.exception('Failed to get layer data response for %s', layer_id)
      raise APIRequestFailure()

    if response.status_code == 404:
      return None

    return json_response

  def _request(self, method, endpoint, path, body, params, timeout):
    """ Issues an HTTP request to the security endpoint. """
    if self._config is None:
      raise Exception('Cannot call unconfigured security system')

    url = _join_api_url(endpoint, self._config.get('SECURITY_SCANNER_API_VERSION', 'v1'), path)
    signer_proxy_url = self._config.get('JWTPROXY_SIGNER', 'localhost:8080')

    logger.debug('%sing security URL %s', method.upper(), url)
    return self._client.request(method, url, json=body, params=params, timeout=timeout,
                                verify=MITM_CERT_PATH, headers=DEFAULT_HTTP_HEADERS,
                                proxies={'https': 'https://' + signer_proxy_url,
                                         'http': 'http://' + signer_proxy_url})

  def _call(self, method, path, params=None, body=None):
    """ Issues an HTTP request to the security endpoint handling the logic of using an alternative
        BATCH endpoint for non-GET requests and failover for GET requests.
    """
    if self._config is None:
      raise Exception('Cannot call unconfigured security system')

    timeout = self._config['SECURITY_SCANNER_API_TIMEOUT_SECONDS']
    endpoint = self._config['SECURITY_SCANNER_ENDPOINT']

    with CloseForLongOperation(self._config):
      # If the request isn't a read, attempt to use a batch stack and do not fail over.
      if method != 'GET':
        if self._config.get('SECURITY_SCANNER_ENDPOINT_BATCH') is not None:
          endpoint = self._config['SECURITY_SCANNER_ENDPOINT_BATCH']
          timeout = self._config.get('SECURITY_SCANNER_API_BATCH_TIMEOUT_SECONDS') or timeout
        return self._request(method, endpoint, path, body, params, timeout)

      # The request is read-only and can failover.
      all_endpoints = [endpoint] + self._config['SECURITY_SCANNER_READONLY_FAILOVER_ENDPOINTS']
      try:
        return  _failover_read_request(*[((self._request, endpoint, path, body, params, timeout), {})
                                        for endpoint in all_endpoints])
      except FailoverException:
        raise APIRequestFailure()


def _join_api_url(endpoint, api_version, path):
  pathless_url = urljoin(endpoint, '/' + api_version) + '/'
  return urljoin(pathless_url, path)


@failover
def _failover_read_request(request_fn, endpoint, path, body, params, timeout):
  """ This function auto-retries read-only requests until they return a 2xx status code. """
  resp = request_fn('GET', endpoint, path, body, params, timeout)
  if resp.status_code / 100 != 2:
    raise FailoverException('status code was not 2xx')
  return resp