#! /usr/bin/python
#
# Copyright (C) 2008 Google Inc.
#
# 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. 

"""This module provides a common interface for all HTTP requests. 

  HttpResponse: Represents the server's response to an HTTP request.  Provides
      an interface identical to httplib. HTTPResponse which is the response
      expected from higher level classes which use HttpClient.request. 

  GenericHttpClient: Provides an interface (superclass) for an object 
      responsible for making HTTP requests.  Subclasses of this object are
      used in AtomService and GDataService to make requests to the server.  By
      changing the http_client member object, the AtomService is able to make
      HTTP requests using different logic (for example, when running on 
      Google App Engine, the http_client makes requests using the App Engine
      urlfetch API).  
"""


__author__ = 'api.jscudder (Jeff Scudder)'


import StringIO


USER_AGENT = '%s GData-Python/1.3.2'


class Error(Exception):
  pass


class UnparsableUrlObject(Error):
  pass


class ContentLengthRequired(Error):
  pass
  

class HttpResponse(object):
  def __init__(self, body=None, status=None, reason=None, headers=None):
    """Constructor for an HttpResponse object.  

    HttpResponse represents the server's response to an HTTP request from
    the client.  The HttpClient.request method returns a httplib. HTTPResponse
    object and this HttpResponse class is designed to mirror the interface
    exposed by httplib. HTTPResponse. 

    Args:
      body: A file like object, with a read() method.  The body could also
          be a string, and the constructor will wrap it so that 
          HttpResponse.read(self) will return the full string. 
      status: The HTTP status code as an int.  Example: 200, 201, 404. 
      reason: The HTTP status message which follows the code.  Example: 
          OK, Created, Not Found
      headers: A dictionary containing the HTTP headers in the server's 
          response.  A common header in the response is Content-Length. 
    """
    if body:
      if hasattr(body, 'read'):
        self._body = body
      else:
        self._body = StringIO.StringIO(body)
    else:
      self._body = None
    if status is not None:
      self.status = int(status)
    else:
      self.status = None
    self.reason = reason
    self._headers = headers or {}

  def getheader(self, name, default=None):
    if name in self._headers:
      return self._headers[name]
    else:
      return default
    
  def read(self, amt=None):
    if not amt:
      return self._body.read()
    else:
      return self._body.read(amt)


class GenericHttpClient(object):
  debug = False

  def __init__(self, http_client, headers=None):
    """
    
    Args:
      http_client: An object which provides a request method to make an HTTP 
          request.  The request method in GenericHttpClient performs a 
          call-through to the contained HTTP client object. 
      headers: A dictionary containing HTTP headers which should be included
          in every HTTP request.  Common persistent headers include 
          'User-Agent'. 
    """
    self.http_client = http_client
    self.headers = headers or {}

  def request(self, operation, url, data=None, headers=None):
    all_headers = self.headers.copy()
    if headers:
      all_headers.update(headers)
    return self.http_client.request(operation, url, data=data, 
        headers=all_headers)

  def get(self, url, headers=None):
    return self.request('GET', url, headers=headers)

  def post(self, url, data, headers=None):
    return self.request('POST', url, data=data, headers=headers)

  def put(self, url, data, headers=None):
    return self.request('PUT', url, data=data, headers=headers)

  def delete(self, url, headers=None):
    return self.request('DELETE', url, headers=headers)


class GenericToken(object):
  """Represents an Authorization token to be added to HTTP requests. 
  
  Some Authorization headers included calculated fields (digital
  signatures for example) which are based on the parameters of the HTTP
  request.  Therefore the token is responsible for signing the request
  and adding the Authorization header.  
  """
  def perform_request(self, http_client, operation, url, data=None, 
                      headers=None):
    """For the GenericToken, no Authorization token is set.""" 
    return http_client.request(operation, url, data=data, headers=headers)

  def valid_for_scope(self, url):
    """Tells the caller if the token authorizes access to the desired URL. 
    
    Since the generic token doesn't add an auth header, it is not valid for
    any scope. 
    """
    return False


