# Copyright 2010 Google Inc. All Rights Reserved.

"""An OAuth 2.0 client

Tools for interacting with OAuth 2.0 protected
resources.
"""

__author__ = 'jcgregorio@google.com (Joe Gregorio)'

import copy
import datetime
import httplib2
import logging
import urllib
import urlparse

try: # pragma: no cover
  import simplejson
except ImportError: # pragma: no cover
  try:
    # Try to import from django, should work on App Engine
    from django.utils import simplejson
  except ImportError:
    # Should work for Python2.6 and higher.
    import json as simplejson

try:
    from urlparse import parse_qsl
except ImportError:
    from cgi import parse_qsl


class Error(Exception):
  """Base error for this module."""
  pass


class RequestError(Error):
  """Error occurred during request."""
  pass


class MissingParameter(Error):
  pass


def _abstract():
  raise NotImplementedError('You need to override this function')


class Credentials(object):
  """Base class for all Credentials objects.

  Subclasses must define an authorize() method
  that applies the credentials to an HTTP transport.
  """

  def authorize(self, http):
    """Take an httplib2.Http instance (or equivalent) and
    authorizes it for the set of credentials, usually by
    replacing http.request() with a method that adds in
    the appropriate headers and then delegates to the original
    Http.request() method.
    """
    _abstract()

class Flow(object):
  """Base class for all Flow objects."""
  pass


class Storage(object):
  """Base class for all Storage objects.

  Store and retrieve a single credential.
  """


  def get(self):
    """Retrieve credential.

    Returns:
      apiclient.oauth.Credentials
    """
    _abstract()

  def put(self, credentials):
    """Write a credential.

    Args:
      credentials: Credentials, the credentials to store.
    """
    _abstract()


class OAuth2Credentials(Credentials):
  """Credentials object for OAuth 2.0

  Credentials can be applied to an httplib2.Http object
  using the authorize() method, which then signs each
  request from that object with the OAuth 2.0 access token.

  OAuth2Credentials objects may be safely pickled and unpickled.
  """

  def __init__(self, access_token, client_id, client_secret, refresh_token,
      token_expiry, token_uri, user_agent):
    """Create an instance of OAuth2Credentials

    This constructor is not usually called by the user, instead
    OAuth2Credentials objects are instantiated by
    the OAuth2WebServerFlow.

    Args:
      token_uri: string, URI of token endpoint.
      client_id: string, client identifier.
      client_secret: string, client secret.
      access_token: string, access token.
      token_expiry: datetime, when the access_token expires.
      refresh_token: string, refresh token.
      user_agent: string, The HTTP User-Agent to provide for this application.


    Notes:
      store: callable, a callable that when passed a Credential
        will store the credential back to where it came from.
        This is needed to store the latest access_token if it
        has expired and been refreshed.
    """
    self.access_token = access_token
    self.client_id = client_id
    self.client_secret = client_secret
    self.refresh_token = refresh_token
    self.store = None
    self.token_expiry = token_expiry
    self.token_uri = token_uri
    self.user_agent = user_agent

  def set_store(self, store):
    """Set the storage for the credential.

    Args:
      store: callable, a callable that when passed a Credential
        will store the credential back to where it came from.
        This is needed to store the latest access_token if it
        has expired and been refreshed.
    """
    self.store = store

  def __getstate__(self):
    """Trim the state down to something that can be pickled.
    """
    d = copy.copy(self.__dict__)
    del d['store']
    return d

  def __setstate__(self, state):
    """Reconstitute the state of the object from being pickled.
    """
    self.__dict__.update(state)
    self.store = None

  def _refresh(self, http_request):
    """Refresh the access_token using the refresh_token.

    Args:
       http: An instance of httplib2.Http.request
           or something that acts like it.
    """
    body = urllib.urlencode({
      'grant_type': 'refresh_token',
      'client_id': self.client_id,
      'client_secret': self.client_secret,
      'refresh_token' : self.refresh_token
      })
    headers = {
        'user-agent': self.user_agent,
        'content-type': 'application/x-www-form-urlencoded'
    }
    resp, content = http_request(
        self.token_uri, method='POST', body=body, headers=headers)
    if resp.status == 200:
      # TODO(jcgregorio) Raise an error if loads fails?
      d = simplejson.loads(content)
      self.access_token = d['access_token']
      self.refresh_token = d.get('refresh_token', self.refresh_token)
      if 'expires_in' in d:
        self.token_expiry = datetime.timedelta(
            seconds = int(d['expires_in'])) + datetime.datetime.now()
      else:
        self.token_expiry = None
      if self.store is not None:
        self.store(self)
    else:
      logging.error('Failed to retrieve access token: %s' % content)
      raise RequestError('Invalid response %s.' % resp['status'])

  def authorize(self, http):
    """Authorize an httplib2.Http instance with these credentials.

    Args:
       http: An instance of httplib2.Http
           or something that acts like it.

    Returns:
       A modified instance of http that was passed in.

    Example:

      h = httplib2.Http()
      h = credentials.authorize(h)

    You can't create a new OAuth
    subclass of httplib2.Authenication because
    it never gets passed the absolute URI, which is
    needed for signing. So instead we have to overload
    'request' with a closure that adds in the
    Authorization header and then calls the original version
    of 'request()'.
    """
    request_orig = http.request

    # The closure that will replace 'httplib2.Http.request'.
    def new_request(uri, method='GET', body=None, headers=None,
                    redirections=httplib2.DEFAULT_MAX_REDIRECTS,
                    connection_type=None):
      """Modify the request headers to add the appropriate
      Authorization header."""
      if headers == None:
        headers = {}
      headers['authorization'] = 'OAuth ' + self.access_token
      if 'user-agent' in headers:
        headers['user-agent'] = self.user_agent + ' ' + headers['user-agent']
      else:
        headers['user-agent'] = self.user_agent
      resp, content = request_orig(uri, method, body, headers,
                                   redirections, connection_type)
      if resp.status == 401:
        logging.info("Refreshing because we got a 401")
        self._refresh(request_orig)
        return request_orig(uri, method, body, headers,
                            redirections, connection_type)
      else:
        return (resp, content)

    http.request = new_request
    return http


class OAuth2WebServerFlow(Flow):
  """Does the Web Server Flow for OAuth 2.0.

  OAuth2Credentials objects may be safely pickled and unpickled.
  """

  def __init__(self, client_id, client_secret, scope, user_agent,
      auth_uri='https://www.google.com/accounts/o8/oauth2/authorization',
      token_uri='https://www.google.com/accounts/o8/oauth2/token',
      **kwargs):
    """Constructor for OAuth2WebServerFlow

    Args:
      client_id: string, client identifier.
      client_secret: string client secret.
      scope: string, scope of the credentials being requested.
      user_agent: string, HTTP User-Agent to provide for this application.
      auth_uri: string, URI for authorization endpoint. For convenience
        defaults to Google's endpoints but any OAuth 2.0 provider can be used.
      token_uri: string, URI for token endpoint. For convenience
        defaults to Google's endpoints but any OAuth 2.0 provider can be used.
      **kwargs: dict, The keyword arguments are all optional and required
                        parameters for the OAuth calls.
    """
    self.client_id = client_id
    self.client_secret = client_secret
    self.scope = scope
    self.user_agent = user_agent
    self.auth_uri = auth_uri
    self.token_uri = token_uri
    self.params = kwargs
    self.redirect_uri = None

  def step1_get_authorize_url(self, redirect_uri='oob'):
    """Returns a URI to redirect to the provider.

    Args:
      redirect_uri: string, Either the string 'oob' for a non-web-based
                    application, or a URI that handles the callback from
                    the authorization server.

    If redirect_uri is 'oob' then pass in the
    generated verification code to step2_exchange,
    otherwise pass in the query parameters received
    at the callback uri to step2_exchange.
    """

    self.redirect_uri = redirect_uri
    query = {
      'response_type': 'code',
      'client_id': self.client_id,
      'redirect_uri': redirect_uri,
      'scope': self.scope,
      }
    query.update(self.params)
    parts = list(urlparse.urlparse(self.auth_uri))
    query.update(dict(parse_qsl(parts[4]))) # 4 is the index of the query part
    parts[4] = urllib.urlencode(query)
    return urlparse.urlunparse(parts)

  def step2_exchange(self, code):
    """Exhanges a code for OAuth2Credentials.

    Args:
      code: string or dict, either the code as a string, or a dictionary
        of the query parameters to the redirect_uri, which contains
        the code.
    """

    if not (isinstance(code, str) or isinstance(code, unicode)):
      code = code['code']

    body = urllib.urlencode({
      'grant_type': 'authorization_code',
      'client_id': self.client_id,
      'client_secret': self.client_secret,
      'code': code,
      'redirect_uri': self.redirect_uri,
      'scope': self.scope
      })
    headers = {
      'user-agent': self.user_agent,
      'content-type': 'application/x-www-form-urlencoded'
    }
    h = httplib2.Http()
    resp, content = h.request(self.token_uri, method='POST', body=body, headers=headers)
    if resp.status == 200:
      # TODO(jcgregorio) Raise an error if simplejson.loads fails?
      d = simplejson.loads(content)
      access_token = d['access_token']
      refresh_token = d.get('refresh_token', None)
      token_expiry = None
      if 'expires_in' in d:
        token_expiry = datetime.datetime.now() + datetime.timedelta(seconds = int(d['expires_in']))

      logging.info('Successfully retrieved access token: %s' % content)
      return OAuth2Credentials(access_token, self.client_id, self.client_secret,
                               refresh_token, token_expiry, self.token_uri,
                               self.user_agent)
    else:
      logging.error('Failed to retrieve access token: %s' % content)
      raise RequestError('Invalid response %s.' % resp['status'])