# Copyright 2016 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Library with a variant of appengine_rpc using httplib2.

The httplib2 module offers some of the features in appengine_rpc, with
one important one being a simple integration point for OAuth2 integration.
"""

from __future__ import absolute_import
# pylint: disable=g-bad-name,g-import-not-at-top

import io
import logging
import os
import random
import re
import time
import urllib

import httplib2

from oauth2client import client
from oauth2client import file as oauth2client_file
from oauth2client import tools
from googlecloudsdk.third_party.appengine.tools.value_mixin import ValueMixin
from googlecloudsdk.third_party.appengine._internal import six_subset

# pylint:disable=g-import-not-at-top
# pylint:disable=invalid-name
# Inline these directly rather than placing in six_subset since importing
# urllib into six_subset seems to mess with the overridden version of
# urllib/httplib that the NaCl runtime sandbox inserts for SSL purposes.
if six_subset.PY3:
  HTTPError = urllib.error.HTTPError
  urlencode_fn = urllib.parse.urlencode
else:
  import urllib2
  HTTPError = urllib2.HTTPError
  urlencode_fn = urllib.urlencode
# pylint:disable=g-import-not-at-top
# pylint:disable=invalid-name

logger = logging.getLogger('googlecloudsdk.third_party.appengine.tools.appengine_rpc')


_TIMEOUT_WAIT_TIME = 5


class Error(Exception):
  pass


class AuthPermanentFail(Error):
  """Authentication will not succeed in the current context."""


class MemoryCache(object):
  """httplib2 Cache implementation which only caches locally."""

  def __init__(self):
    self.cache = {}

  def get(self, key):
    return self.cache.get(key)

  def set(self, key, value):
    self.cache[key] = value

  def delete(self, key):
    self.cache.pop(key, None)


def RaiseHttpError(url, response_info, response_body, extra_msg=''):
  """Raise a urllib2.HTTPError based on an httplib2 response tuple."""
  if response_body is not None:
    stream = io.BytesIO()
    stream.write(response_body)
    stream.seek(0)
  else:
    stream = None
  if not extra_msg:
    msg = response_info.reason
  else:
    msg = response_info.reason + ' ' + extra_msg
  raise HTTPError(url, response_info.status, msg, response_info, stream)


class HttpRpcServerHttpLib2(object):
  """A variant of HttpRpcServer which uses httplib2.

  This follows the same interface as appengine_rpc.AbstractRpcServer,
  but is a totally separate implementation.
  """

  def __init__(self, host, auth_function, user_agent, source,
               host_override=None, extra_headers=None, save_cookies=False,
               auth_tries=None, account_type=None, debug_data=True, secure=True,
               ignore_certs=False, rpc_tries=3, conflict_max_errors=10,
               timeout_max_errors=2, http_class=None, http_object=None):
    """Creates a new HttpRpcServerHttpLib2.

    Args:
      host: The host to send requests to.
      auth_function: Saved but ignored; may be used by subclasses.
      user_agent: The user-agent string to send to the server. Specify None to
        omit the user-agent header.
      source: Saved but ignored; may be used by subclasses.
      host_override: The host header to send to the server (defaults to host).
      extra_headers: A dict of extra headers to append to every request. Values
        supplied here will override other default headers that are supplied.
      save_cookies: Saved but ignored; may be used by subclasses.
      auth_tries: The number of times to attempt auth_function before failing.
      account_type: Saved but ignored; may be used by subclasses.
      debug_data: Whether debugging output should include data contents.
      secure: If the requests sent using Send should be sent over HTTPS.
      ignore_certs: If the certificate mismatches should be ignored.
      rpc_tries: The number of rpc retries upon http server error (i.e.
        Response code >= 500 and < 600) before failing.
      conflict_max_errors: The number of rpc retries upon http server error
        (i.e. Response code 409) before failing.
      timeout_max_errors: The number of rpc retries upon http server timeout
        (i.e. Response code 408) before failing.
      http_class: the httplib2.Http subclass to use. Defaults to httplib2.Http.
      http_object: an httlib2.Http object to use to make requests. If this is
        provided, http_class is ignored.
    """
    self.host = host
    self.auth_function = auth_function
    self.user_agent = user_agent
    self.source = source
    self.host_override = host_override
    self.extra_headers = extra_headers or {}
    self.save_cookies = save_cookies
    self.auth_max_errors = auth_tries
    self.account_type = account_type
    self.debug_data = debug_data
    self.secure = secure
    self.ignore_certs = ignore_certs
    self.rpc_max_errors = rpc_tries
    self.scheme = secure and 'https' or 'http'
    self.conflict_max_errors = conflict_max_errors
    self.timeout_max_errors = timeout_max_errors
    self.http_class = http_class if http_class is not None else httplib2.Http
    self.http_object = http_object

    self.certpath = None
    self.cert_file_available = False
    if not self.ignore_certs:
      # Use the App Engine managed cacerts file instead of the 'httplib2' copy.
      # should probably let the httplib2 copy get used.
      self.certpath = os.path.normpath(os.path.join(
          os.path.dirname(__file__), '..', '..', '..', 'lib', 'cacerts',
          'cacerts.txt'))
      self.cert_file_available = os.path.exists(self.certpath)

    self.memory_cache = MemoryCache()

  def _Authenticate(self, http, saw_error):
    """Pre or Re-auth stuff...

    Args:
      http: An 'Http' object from httplib2.
      saw_error: If the user has already tried to contact the server.
        If they have, it's OK to prompt them. If not, we should not be asking
        them for auth info--it's possible it'll suceed w/o auth.
    """
    # Note that this should possibly have direct access to headers, etc.
    # But most of the 'httplib2' methods work on the 'Http' object.
    raise NotImplementedError()

  def Send(self, request_path, payload='',
           content_type='application/octet-stream',
           timeout=None,
           **kwargs):
    """Sends an RPC and returns the response.

    Args:
      request_path: The path to send the request to, eg /api/appversion/create.
      payload: The body of the request, or None to send an empty request.
      content_type: The Content-Type header to use.
      timeout: timeout in seconds; default None i.e. no timeout.
        (Note: for large requests on OS X, the timeout doesn't work right.)
      Any keyword arguments are converted into query string parameters.

    Returns:
      The response body, as a string.

    Raises:
      AuthPermanentFail: If authorization failed in a permanent way.
      urllib2.HTTPError: On most HTTP errors.
    """
    # TODO(user): To prevent raising httplib2.CertificateValidationUnsupported
    # we need to track self.cert_file_available and send
    # disable_ssl_certificate_validation on the Http(constructor).
    # Though perhaps we should require proper SSL support if you're using oauth.

    self.http = self.http_object or self.http_class(
        cache=self.memory_cache, ca_certs=self.certpath,
        disable_ssl_certificate_validation=(not self.cert_file_available))
    self.http.follow_redirects = False
    self.http.timeout = timeout
    url = '%s://%s%s' % (self.scheme, self.host, request_path)
    if kwargs:
      url += '?' + urlencode_fn(sorted(kwargs.items()))
    headers = {}
    if self.extra_headers:
      headers.update(self.extra_headers)
    # This header is necessary to prevent XSRF attacks, since the browser
    # cannot include this header, that means the request had to come from
    # another agent like appcfg.py.
    headers['X-appcfg-api-version'] = '1'
    # POST if there's a payload (which may be empty). GET if there's no payload.
    if payload is not None:
      method = 'POST'
      # For some reason, content-length is not sent automatically.
      headers['content-length'] = str(len(payload))
      headers['Content-Type'] = content_type
    else:
      method = 'GET'
    if self.host_override:
      headers['Host'] = self.host_override

    rpc_errors = 0
    auth_errors = [0]
    conflict_errors = 0
    timeout_errors = 0

    def NeedAuth():
      """Marker that we need auth; it'll actually be tried next time around."""
      auth_errors[0] += 1
      logger.debug('Attempting to auth. This is try %s of %s.',
                   auth_errors[0], self.auth_max_errors)
      if auth_errors[0] > self.auth_max_errors:
        RaiseHttpError(url, response_info, response, 'Too many auth attempts.')

    while (rpc_errors < self.rpc_max_errors and
           conflict_errors < self.conflict_max_errors and
           timeout_errors < self.timeout_max_errors):
      self._Authenticate(self.http, auth_errors[0] > 0)
      logger.debug('Sending request to %s headers=%s body=%s',
                   url, headers,
                   self.debug_data and payload or payload and 'ELIDED' or '')
      try:
        response_info, response = self.http.request(
            url, method=method, body=payload, headers=headers)
      except client.AccessTokenRefreshError as e:
        # Consider this a 401.
        logger.info('Got access token error', exc_info=1)
        response_info = httplib2.Response({'status': 401})
        response_info.reason = str(e)
        response = ''

      status = response_info.status
      if status == 200:
        return response
      logger.debug('Got http error %s.', response_info.status)
      if status == 401:
        NeedAuth()
        continue
      elif status == 408:
        timeout_errors += 1
        logger.debug('Got timeout error %s of %s. Retrying in %s seconds',
                     timeout_errors, self.timeout_max_errors,
                     _TIMEOUT_WAIT_TIME)
        time.sleep(_TIMEOUT_WAIT_TIME)
        continue
      elif status == 409:
        conflict_errors += 1
        # Retry with jitter.
        wait_time = random.randint(0, 10)
        logger.debug('Got conflict error %s of %s. Retrying in %s seconds.',
                     conflict_errors, self.conflict_max_errors, wait_time)
        time.sleep(wait_time)
        continue
      elif status >= 500 and status < 600:
        # Server Error - try again.
        rpc_errors += 1
        logger.debug('Retrying. This is attempt %s of %s.',
                     rpc_errors, self.rpc_max_errors)
        continue
      elif status == 302:
        # Server may also return a 302 redirect to indicate authentication
        # is required.
        loc = response_info.get('location')
        logger.debug('Got 302 redirect. Location: %s', loc)
        if (loc.startswith('https://www.google.com/accounts/ServiceLogin') or
            re.match(r'https://www\.google\.com/a/[a-z0-9.-]+/ServiceLogin',
                     loc)):
          NeedAuth()
          continue
        elif loc.startswith('http://%s/_ah/login' % (self.host,)):
          # We can probably stuff a fake header in here.
          RaiseHttpError(url, response_info, response,
                         'dev_appserver login not supported')
        else:
          RaiseHttpError(url, response_info, response,
                         'Unexpected redirect to %s' % loc)
      else:
        logger.debug('Unexpected results: %s', response_info)
        RaiseHttpError(url, response_info, response,
                       'Unexpected HTTP status %s' % status)
    logging.info('Too many retries for url %s', url)
    RaiseHttpError(url, response_info, response)


class NoStorage(client.Storage):
  """A no-op implementation of storage."""

  def locked_get(self):
    return None

  def locked_put(self, credentials):
    pass


class HttpRpcServerOAuth2(HttpRpcServerHttpLib2):
  """A variant of HttpRpcServer which uses oauth2.

  This variant is specifically meant for interactive command line usage,
  as it will attempt to open a browser and ask the user to enter
  information from the resulting web page.
  """

  class OAuth2Parameters(ValueMixin):
    """Class encapsulating parameters related to OAuth2 authentication."""

    def __init__(self, access_token, client_id, client_secret, scope,
                 refresh_token, credential_file, token_uri=None,
                 credentials=None):
      self.access_token = access_token
      self.client_id = client_id
      self.client_secret = client_secret
      self.scope = scope
      self.refresh_token = refresh_token
      self.credential_file = credential_file
      self.token_uri = token_uri
      self.credentials = credentials

  class FlowFlags(object):

    def __init__(self, options):
      self.logging_level = logging.getLevelName(logging.getLogger().level)
      self.noauth_local_webserver = (not options.auth_local_webserver
                                     if options else True)
      self.auth_host_port = [8080, 8090]
      self.auth_host_name = 'localhost'

  def __init__(self, host, oauth2_parameters, user_agent, source,
               host_override=None, extra_headers=None, save_cookies=False,
               auth_tries=None, account_type=None, debug_data=True, secure=True,
               ignore_certs=False, rpc_tries=3, timeout_max_errors=2,
               options=None, http_class=None, http_object=None):
    """Creates a new HttpRpcServerOAuth2.

    Args:
      host: The host to send requests to.
      oauth2_parameters: An object of type OAuth2Parameters (defined above)
        that specifies all parameters related to OAuth2 authentication. (This
        replaces the auth_function parameter in the parent class.)
      user_agent: The user-agent string to send to the server. Specify None to
        omit the user-agent header.
      source: Saved but ignored.
      host_override: The host header to send to the server (defaults to host).
      extra_headers: A dict of extra headers to append to every request. Values
        supplied here will override other default headers that are supplied.
      save_cookies: If the refresh token should be saved.
      auth_tries: The number of times to attempt auth_function before failing.
      account_type: Ignored.
      debug_data: Whether debugging output should include data contents.
      secure: If the requests sent using Send should be sent over HTTPS.
      ignore_certs: If the certificate mismatches should be ignored.
      rpc_tries: The number of rpc retries upon http server error (i.e.
        Response code >= 500 and < 600) before failing.
      timeout_max_errors: The number of rpc retries upon http server timeout
        (i.e. Response code 408) before failing.
      options: the command line options.
      http_class: the httplib2.Http subclass to use. Defaults to httplib2.Http.
      http_object: an httlib2.Http object to use to make requests. If this is
        provided, http_class is ignored.
    """
    super(HttpRpcServerOAuth2, self).__init__(
        host, None, user_agent, source, host_override=host_override,
        extra_headers=extra_headers, auth_tries=auth_tries,
        debug_data=debug_data, secure=secure, ignore_certs=ignore_certs,
        rpc_tries=rpc_tries, timeout_max_errors=timeout_max_errors,
        save_cookies=save_cookies, http_class=http_class,
        http_object=http_object)

    if not isinstance(oauth2_parameters, self.OAuth2Parameters):
      raise TypeError('oauth2_parameters must be an OAuth2Parameters: %r' %
                      oauth2_parameters)
    self.oauth2_parameters = oauth2_parameters

    if save_cookies:
      oauth2_credential_file = (oauth2_parameters.credential_file
                                or '~/.appcfg_oauth2_tokens')
      self.storage = oauth2client_file.Storage(
          os.path.expanduser(oauth2_credential_file))
    else:
      self.storage = NoStorage()

    if oauth2_parameters.credentials:
      self.credentials = oauth2_parameters.credentials
    elif any((oauth2_parameters.access_token, oauth2_parameters.refresh_token,
              oauth2_parameters.token_uri)):
      token_uri = (oauth2_parameters.token_uri or
                   ('https://%s/o/oauth2/token' %
                    os.getenv('APPENGINE_AUTH_SERVER', 'accounts.google.com')))
      self.credentials = client.OAuth2Credentials(
          oauth2_parameters.access_token,
          oauth2_parameters.client_id,
          oauth2_parameters.client_secret,
          oauth2_parameters.refresh_token,
          None,
          token_uri,
          self.user_agent)
    else:
      self.credentials = self.storage.get()

    self.flags = self.FlowFlags(options)

  def _Authenticate(self, http, needs_auth):
    """Pre or Re-auth stuff...

    This will attempt to avoid making any OAuth related HTTP connections or
    user interactions unless it's needed.

    Args:
      http: An 'Http' object from httplib2.
      needs_auth: If the user has already tried to contact the server.
        If they have, it's OK to prompt them. If not, we should not be asking
        them for auth info--it's possible it'll suceed w/o auth, but if we have
        some credentials we'll use them anyway.

    Raises:
      AuthPermanentFail: The user has requested non-interactive auth but
        the token is invalid.
    """
    if needs_auth and (not self.credentials or self.credentials.invalid):
      # If we were given either an access token or a refresh token on the
      # command line then we assume that we don't want interactive login.
      # Likewise we interpret a non-default token_uri as meaning we are using
      # something like the GCE Metadata Service so again it is not interactive.
      if self.oauth2_parameters.access_token:
        logger.debug('_Authenticate skipping auth because user explicitly '
                     'supplied an access token.')
        raise AuthPermanentFail('Access token is invalid.')
      if self.oauth2_parameters.refresh_token:
        logger.debug('_Authenticate skipping auth because user explicitly '
                     'supplied a refresh token.')
        raise AuthPermanentFail('Refresh token is invalid.')
      if self.oauth2_parameters.token_uri:
        logger.debug('_Authenticate skipping auth because user explicitly '
                     'supplied a Token URI, for example for service account '
                     'authentication with Compute Engine')
        raise AuthPermanentFail('Token URI did not yield a valid token: ' +
                                self.oauth_parameters.token_uri)
      logger.debug('_Authenticate requesting auth')
      flow = client.OAuth2WebServerFlow(
          client_id=self.oauth2_parameters.client_id,
          client_secret=self.oauth2_parameters.client_secret,
          scope=_ScopesToString(self.oauth2_parameters.scope),
          user_agent=self.user_agent)
      self.credentials = tools.run_flow(flow, self.storage, self.flags)
    if self.credentials and not self.credentials.invalid:
      # We will configure this automatically if either we think the access token
      # is valid, or we think we need a token and have a refresh token
      if not self.credentials.access_token_expired or needs_auth:
        logger.debug('_Authenticate configuring auth; needs_auth=%s',
                     needs_auth)
        self.credentials.authorize(http)
        return
    logger.debug('_Authenticate skipped auth; needs_auth=%s', needs_auth)


def _ScopesToString(scopes):
  """Converts scope value to a string."""
  # TODO(user): replace with oauth2client.util.scopes_to_string when we
  # have a more recent oauth2client.
  if isinstance(scopes, six_subset.string_types):
    return scopes
  else:
    return ' '.join(scopes)
