#!/usr/bin/env python
#
# Copyright 2010 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.
#

"""Transport library for ProtoRPC.

Contains underlying infrastructure used for communicating RPCs over low level
transports such as HTTP.

Includes HTTP transport built over urllib2.
"""

import httplib
import logging
import os
import socket
import sys
import urlparse

from . import messages
from . import protobuf
from . import remote
from . import util

__all__ = [
  'RpcStateError',

  'HttpTransport',
  'LocalTransport',
  'Rpc',
  'Transport',
]


class RpcStateError(messages.Error):
  """Raised when trying to put RPC in to an invalid state."""


class Rpc(object):
  """Represents a client side RPC.

  An RPC is created by the transport class and is used with a single RPC.  While
  an RPC is still in process, the response is set to None.  When it is complete
  the response will contain the response message.
  """

  def __init__(self, request):
    """Constructor.

    Args:
      request: Request associated with this RPC.
    """
    self.__request = request
    self.__response = None
    self.__state = remote.RpcState.RUNNING
    self.__error_message = None
    self.__error_name = None

  @property
  def request(self):
    """Request associated with RPC."""
    return self.__request

  @property
  def response(self):
    """Response associated with RPC."""
    self.wait()
    self.__check_status()
    return self.__response

  @property
  def state(self):
    """State associated with RPC."""
    return self.__state

  @property
  def error_message(self):
    """Error, if any, associated with RPC."""
    self.wait()
    return self.__error_message

  @property
  def error_name(self):
    """Error name, if any, associated with RPC."""
    self.wait()
    return self.__error_name

  def wait(self):
    """Wait for an RPC to finish."""
    if self.__state == remote.RpcState.RUNNING:
      self._wait_impl()

  def _wait_impl(self):
    """Implementation for wait()."""
    raise NotImplementedError()

  def __check_status(self):
    error_class = remote.RpcError.from_state(self.__state)
    if error_class is not None:
      if error_class is remote.ApplicationError:
        raise error_class(self.__error_message, self.__error_name)
      else:
        raise error_class(self.__error_message)

  def __set_state(self, state, error_message=None, error_name=None):
    if self.__state != remote.RpcState.RUNNING:
      raise RpcStateError(
        'RPC must be in RUNNING state to change to %s' % state)
    if state == remote.RpcState.RUNNING:
      raise RpcStateError('RPC is already in RUNNING state')
    self.__state = state
    self.__error_message = error_message
    self.__error_name = error_name

  def set_response(self, response):
    # TODO: Even more specific type checking.
    if not isinstance(response, messages.Message):
      raise TypeError('Expected Message type, received %r' % (response))

    self.__response = response
    self.__set_state(remote.RpcState.OK)

  def set_status(self, status):
    status.check_initialized()
    self.__set_state(status.state, status.error_message, status.error_name)


class Transport(object):
  """Transport base class.

  Provides basic support for implementing a ProtoRPC transport such as one
  that can send and receive messages over HTTP.

  Implementations override _start_rpc.  This method receives a RemoteInfo
  instance and a request Message. The transport is expected to set the rpc
  response or raise an exception before termination.
  """

  @util.positional(1)
  def __init__(self, protocol=protobuf):
    """Constructor.

    Args:
      protocol: If string, will look up a protocol from the default Protocols
        instance by name.  Can also be an instance of remote.ProtocolConfig.
        If neither, it must be an object that implements a protocol interface
        by implementing encode_message, decode_message and set CONTENT_TYPE.
        For example, the modules protobuf and protojson can be used directly.
    """
    if isinstance(protocol, basestring):
      protocols = remote.Protocols.get_default()
      try:
        protocol = protocols.lookup_by_name(protocol)
      except KeyError:
        protocol = protocols.lookup_by_content_type(protocol)
    if isinstance(protocol, remote.ProtocolConfig):
      self.__protocol = protocol.protocol
      self.__protocol_config = protocol
    else:
      self.__protocol = protocol
      self.__protocol_config = remote.ProtocolConfig(
        protocol, 'default', default_content_type=protocol.CONTENT_TYPE)

  @property
  def protocol(self):
    """Protocol associated with this transport."""
    return self.__protocol

  @property
  def protocol_config(self):
    """Protocol associated with this transport."""
    return self.__protocol_config

  def send_rpc(self, remote_info, request):
    """Initiate sending an RPC over the transport.

    Args:
      remote_info: RemoteInfo instance describing remote method.
      request: Request message to send to service.

    Returns:
      An Rpc instance intialized with the request..
    """
    request.check_initialized()

    rpc = self._start_rpc(remote_info, request)

    return rpc

  def _start_rpc(self, remote_info, request):
    """Start a remote procedure call.

    Args:
      remote_info: RemoteInfo instance describing remote method.
      request: Request message to send to service.

    Returns:
      An Rpc instance initialized with the request.
    """
    raise NotImplementedError()


class HttpTransport(Transport):
  """Transport for communicating with HTTP servers."""

  @util.positional(2)
  def __init__(self,
               service_url,
               protocol=protobuf,
               connection_class=httplib.HTTPConnection):
    """Constructor.

    Args:
      service_url: URL where the service is located.  All communication via
        the transport will go to this URL.
      protocol: The protocol implementation.  Must implement encode_message and
        decode_message.  Can also be an instance of remote.ProtocolConfig.
    """
    super(HttpTransport, self).__init__(protocol=protocol)
    self.__service_url = service_url
    self.__connection_class = connection_class

  def __get_rpc_status(self, response, content):
    """Get RPC status from HTTP response.

    Args:
      response: HTTPResponse object.
      content: Content read from HTTP response.

    Returns:
      RpcStatus object parsed from response, else an RpcStatus with a generic
      HTTP error.
    """
    # Status above 400 may have RpcStatus content.
    if response.status >= 400:
      content_type = response.getheader('content-type')
      if content_type == self.protocol_config.default_content_type:
        try:
          rpc_status = self.protocol.decode_message(remote.RpcStatus, content)
        except Exception, decode_err:
          logging.warning(
            'An error occurred trying to parse status: %s\n%s',
            str(decode_err), content)
        else:
          if rpc_status.is_initialized():
            return rpc_status
          else:
            logging.warning(
              'Body does not result in an initialized RpcStatus message:\n%s',
              content)

    # If no RpcStatus message present, attempt to forward any content.  If empty
    # use standard error message.
    if not content.strip():
      content = httplib.responses.get(response.status, 'Unknown Error')
    return remote.RpcStatus(state=remote.RpcState.SERVER_ERROR,
                            error_message='HTTP Error %s: %s' % (
                              response.status, content or 'Unknown Error'))

  def __set_response(self, remote_info, connection, rpc):
    """Set response on RPC.

    Sets response or status from HTTP request.  Implements the wait method of
    Rpc instance.

    Args:
      remote_info: Remote info for invoked RPC.
      connection: HTTPConnection that is making request.
      rpc: Rpc instance.
    """
    response = connection.getresponse()

    content = response.read()

    if response.status == httplib.OK:
      response = self.protocol.decode_message(remote_info.response_type,
                                              content)
      rpc.set_response(response)
    else:
      status = self.__get_rpc_status(response, content)
      rpc.set_status(status)

    connection.close()

  def _start_rpc(self, remote_info, request):
    """Start a remote procedure call.

    Args:
      remote_info: A RemoteInfo instance for this RPC.
      request: The request message for this RPC.

    Returns:
      An Rpc instance initialized with a Request.
    """
    method_url = '%s.%s' % (self.__service_url, remote_info.method.func_name)
    encoded_request = self.protocol.encode_message(request)

    url = urlparse.urlparse(method_url)
    if url.scheme == 'https':
      connection_type = httplib.HTTPSConnection
    else:
      connection_type = httplib.HTTPConnection
    connection = connection_type(url.hostname, url.port)
    try:
      connection.request(
        'POST',
        url.path,
        encoded_request,
        headers={'Content-type': self.protocol_config.default_content_type,
                 'Content-length': len(encoded_request)})

      rpc = Rpc(request)

      wait_impl = lambda: self.__set_response(remote_info, connection, rpc)
      rpc._wait_impl = wait_impl

      return rpc
    except remote.RpcError:
      # Pass through all ProtoRPC errors
      connection.close()
      raise
    except socket.error, err:
      connection.close()
      raise remote.NetworkError('Socket error: %s %r' % (type(err).__name__,
                                                         err.args),
                                err)
    except Exception, err:
      connection.close()
      raise remote.NetworkError('Error communicating with HTTP server',
                                err)


class LocalTransport(Transport):
  """Local transport that sends messages directly to services.

  Useful in tests or creating code that can work with either local or remote
  services.  Using LocalTransport is preferrable to simply instantiating a
  single instance of a service and reusing it.  The entire request process
  involves instantiating a new instance of a service, initializing it with
  request state and then invoking the remote method for every request.
  """

  def __init__(self, service_factory):
    """Constructor.

    Args:
      service_factory: Service factory or class.
    """
    super(LocalTransport, self).__init__()
    self.__service_class = getattr(service_factory,
                                   'service_class',
                                   service_factory)
    self.__service_factory = service_factory

  @property
  def service_class(self):
    return self.__service_class

  @property
  def service_factory(self):
    return self.__service_factory

  def _start_rpc(self, remote_info, request):
    """Start a remote procedure call.

    Args:
      remote_info: RemoteInfo instance describing remote method.
      request: Request message to send to service.

    Returns:
      An Rpc instance initialized with the request.
    """
    rpc = Rpc(request)
    def wait_impl():
      instance = self.__service_factory()
      try:
        initalize_request_state = instance.initialize_request_state
      except AttributeError:
        pass
      else:
        host = unicode(os.uname()[1])
        initalize_request_state(remote.RequestState(remote_host=host,
                                                    remote_address=u'127.0.0.1',
                                                    server_host=host,
                                                    server_port=-1))
      try:
        response = remote_info.method(instance, request)
        assert isinstance(response, remote_info.response_type)
      except remote.ApplicationError:
        raise
      except:
        exc_type, exc_value, traceback = sys.exc_info()
        message = 'Unexpected error %s: %s' % (exc_type.__name__, exc_value)
        raise remote.ServerError, message, traceback
      rpc.set_response(response)
    rpc._wait_impl = wait_impl
    return rpc
