"""Library for handling batch HTTP requests for apitools."""

import collections
import email.generator as generator
import email.mime.multipart as mime_multipart
import email.mime.nonmultipart as mime_nonmultipart
import email.parser as email_parser
import itertools
import StringIO
import time
import urllib
import urlparse
import uuid

from six.moves import http_client

from googlecloudapis.apitools.base.py import exceptions
from googlecloudapis.apitools.base.py import http_wrapper

__all__ = [
    'BatchApiRequest',
]


class RequestResponseAndHandler(collections.namedtuple(
    'RequestResponseAndHandler', ['request', 'response', 'handler'])):
  """Container for data related to completing an HTTP request.

  This contains an HTTP request, its response, and a callback for handling
  the response from the server.

  Attributes:
    request: An http_wrapper.Request object representing the HTTP request.
    response: The http_wrapper.Response object returned from the server.
    handler: A callback function accepting two arguments, response
      and exception. Response is an http_wrapper.Response object, and
      exception is an apiclient.errors.HttpError object if an error
      occurred, or otherwise None.
  """


class BatchApiRequest(object):

  class ApiCall(object):
    """Holds request and response information for each request.

    ApiCalls are ultimately exposed to the client once the HTTP batch request
    has been completed.

    Attributes:
      http_request: A client-supplied http_wrapper.Request to be
          submitted to the server.
      response: A http_wrapper.Response object given by the server as a
          response to the user request, or None if an error occurred.
      exception: An apiclient.errors.HttpError object if an error
          occurred, or None.
    """

    def __init__(self, request, retryable_codes, service, method_config):
      """Initialize an individual API request.

      Args:
        request: An http_wrapper.Request object.
        retryable_codes: A list of integer HTTP codes that can be retried.
        service: A service inheriting from base_api.BaseApiService.
        method_config: Method config for the desired API request.
      """
      self.__retryable_codes = list(
          set(retryable_codes + [http_client.UNAUTHORIZED]))
      self.__http_response = None
      self.__service = service
      self.__method_config = method_config

      self.http_request = request
      # TODO(user): Add some validation to these fields.
      self.__response = None
      self.__exception = None

    @property
    def is_error(self):
      return self.exception is not None

    @property
    def response(self):
      return self.__response

    @property
    def exception(self):
      return self.__exception

    @property
    def authorization_failed(self):
      return (self.__http_response and (
          self.__http_response.status_code == http_client.UNAUTHORIZED))

    @property
    def terminal_state(self):
      return (self.__http_response and (
          self.__http_response.status_code not in self.__retryable_codes))

    def HandleResponse(self, http_response, exception):
      """Handles an incoming http response to the request in http_request.

      This is intended to be used as a callback function for
      BatchHttpRequest.Add.

      Args:
        http_response: Deserialized http_wrapper.Response object.
        exception: apiclient.errors.HttpError object if an error occurred.
      """
      self.__http_response = http_response
      self.__exception = exception
      if self.terminal_state and not self.__exception:
        self.__response = self.__service.ProcessHttpResponse(
            self.__method_config, self.__http_response)

  def __init__(self, batch_url=None, retryable_codes=None):
    """Initialize a batch API request object.

    Args:
      batch_url: Base URL for batch API calls.
      retryable_codes: A list of integer HTTP codes that can be retried.
    """
    self.api_requests = []
    self.retryable_codes = retryable_codes or []
    self.batch_url = batch_url or 'https://www.googleapis.com/batch'

  def Add(self, service, method, request, global_params=None):
    """Add a request to the batch.

    Args:
      service: A class inheriting base_api.BaseApiService.
      method: A string indicated desired method from the service. See
          the example in the class docstring.
      request: An input message appropriate for the specified service.method.
      global_params: Optional additional parameters to pass into
          method.PrepareHttpRequest.

    Returns:
      None
    """
    # Retrieve the configs for the desired method and service.
    method_config = service.GetMethodConfig(method)
    upload_config = service.GetUploadConfig(method)

    # Prepare the HTTP Request.
    http_request = service.PrepareHttpRequest(
        method_config, request, global_params=global_params,
        upload_config=upload_config)

    # Create the request and add it to our master list.
    api_request = self.ApiCall(
        http_request, self.retryable_codes, service, method_config)
    self.api_requests.append(api_request)

  def Execute(self, http, sleep_between_polls=5, max_retries=5):
    """Execute all of the requests in the batch.

    Args:
      http: httplib2.Http object for use in the request.
      sleep_between_polls: Integer number of seconds to sleep between polls.
      max_retries: Max retries. Any requests that have not succeeded by
          this number of retries simply report the last response or
          exception, whatever it happened to be.

    Returns:
      List of ApiCalls.
    """
    requests = [request for request in self.api_requests if not
                request.terminal_state]

    for attempt in range(max_retries):
      if attempt:
        time.sleep(sleep_between_polls)

      # Create a batch_http_request object and populate it with incomplete
      # requests.
      batch_http_request = BatchHttpRequest(batch_url=self.batch_url)
      for request in requests:
        batch_http_request.Add(request.http_request, request.HandleResponse)
      batch_http_request.Execute(http)

      # Collect retryable requests.
      requests = [request for request in self.api_requests if not
                  request.terminal_state]

      if (any(request.authorization_failed for request in requests)
          and hasattr(http.request, 'credentials')):
        http.request.credentials.refresh(http)

      if not requests:
        break

    return self.api_requests


class BatchHttpRequest(object):
  """Batches multiple http_wrapper.Request objects into a single request."""

  def __init__(self, batch_url, callback=None):
    """Constructor for a BatchHttpRequest.

    Args:
      batch_url: URL to send batch requests to.
      callback: A callback to be called for each response, of the
        form callback(response, exception). The first parameter is
        the deserialized Response object. The second is an
        apiclient.errors.HttpError exception object if an HTTP error
        occurred while processing the request, or None if no error occurred.
    """
    # Endpoint to which these requests are sent.
    self.__batch_url = batch_url

    # Global callback to be called for each individual response in the batch.
    self.__callback = callback

    # List of requests, responses and handlers.
    self.__request_response_handlers = {}

    # The last auto generated id.
    self.__last_auto_id = itertools.count()

    # Unique ID on which to base the Content-ID headers.
    self.__base_id = uuid.uuid4()

  def _ConvertIdToHeader(self, request_id):
    """Convert an id to a Content-ID header value.

    Args:
      request_id: String identifier for a individual request.

    Returns:
      A Content-ID header with the id_ encoded into it. A UUID is prepended to
      the value because Content-ID headers are supposed to be universally
      unique.
    """
    return '<%s+%s>' % (self.__base_id, urllib.quote(request_id))

  @staticmethod
  def _ConvertHeaderToId(header):
    """Convert a Content-ID header value to an id.

    Presumes the Content-ID header conforms to the format that
    _ConvertIdToHeader() returns.

    Args:
      header: A string indicating the Content-ID header value.

    Returns:
      The extracted id value.

    Raises:
      BatchError if the header is not in the expected format.
    """
    if not (header.startswith('<') or header.endswith('>')):
      raise exceptions.BatchError('Invalid value for Content-ID: %s' % header)
    if '+' not in header:
      raise exceptions.BatchError('Invalid value for Content-ID: %s' % header)
    _, request_id = header[1:-1].rsplit('+', 1)

    return urllib.unquote(request_id)

  def _SerializeRequest(self, request):
    """Convert a http_wrapper.Request object into a string.

    Args:
      request: A http_wrapper.Request to serialize.

    Returns:
      The request as a string in application/http format.
    """
    # Construct status line
    parsed = urlparse.urlsplit(request.url)
    request_line = urlparse.urlunsplit(
        (None, None, parsed.path, parsed.query, None))
    status_line = request.http_method + ' ' + request_line + ' HTTP/1.1\n'
    major, minor = request.headers.get(
        'content-type', 'application/json').split('/')
    msg = mime_nonmultipart.MIMENonMultipart(major, minor)

    # MIMENonMultipart adds its own Content-Type header.
    # Keep all of the other headers in `request.headers`.
    for key, value in request.headers.items():
      if key == 'content-type':
        continue
      msg[key] = value

    msg['Host'] = parsed.netloc
    msg.set_unixfrom(None)

    if request.body is not None:
      msg.set_payload(request.body)

    # Serialize the mime message.
    str_io = StringIO.StringIO()
    # maxheaderlen=0 means don't line wrap headers.
    gen = generator.Generator(str_io, maxheaderlen=0)
    gen.flatten(msg, unixfrom=False)
    body = str_io.getvalue()

    # Strip off the \n\n that the MIME lib tacks onto the end of the payload.
    if request.body is None:
      body = body[:-2]

    return status_line.encode('utf-8') + body

  def _DeserializeResponse(self, payload):
    """Convert string into Response and content.

    Args:
      payload: Header and body string to be deserialized.

    Returns:
      A Response object
    """
    # Strip off the status line.
    status_line, payload = payload.split('\n', 1)
    _, status, _ = status_line.split(' ', 2)

    # Parse the rest of the response.
    parser = email_parser.Parser()
    msg = parser.parsestr(payload)

    # Get the headers.
    info = dict(msg)
    info['status'] = status

    # Create Response from the parsed headers.
    content = msg.get_payload()

    return http_wrapper.Response(info, content, self.__batch_url)

  def _NewId(self):
    """Create a new id.

    Auto incrementing number that avoids conflicts with ids already used.

    Returns:
       A new unique id string.
    """
    return str(next(self.__last_auto_id))

  def Add(self, request, callback=None):
    """Add a new request.

    Args:
      request: A http_wrapper.Request to add to the batch.
      callback: A callback to be called for this response, of the
        form callback(response, exception). The first parameter is the
        deserialized response object. The second is an
        apiclient.errors.HttpError exception object if an HTTP error
        occurred while processing the request, or None if no errors occurred.

    Returns:
      None
    """
    self.__request_response_handlers[self._NewId()] = RequestResponseAndHandler(
        request, None, callback)

  def _Execute(self, http):
    """Serialize batch request, send to server, process response.

    Args:
      http: A httplib2.Http object to be used to make the request with.

    Raises:
      httplib2.HttpLib2Error if a transport error has occured.
      apiclient.errors.BatchError if the response is the wrong format.
    """
    message = mime_multipart.MIMEMultipart('mixed')
    # Message should not write out its own headers.
    setattr(message, '_write_headers', lambda self: None)

    # Add all the individual requests.
    for key in self.__request_response_handlers:
      msg = mime_nonmultipart.MIMENonMultipart('application', 'http')
      msg['Content-Transfer-Encoding'] = 'binary'
      msg['Content-ID'] = self._ConvertIdToHeader(key)

      body = self._SerializeRequest(
          self.__request_response_handlers[key].request)
      msg.set_payload(body)
      message.attach(msg)

    request = http_wrapper.Request(self.__batch_url, 'POST')
    request.body = message.as_string()
    request.headers['content-type'] = (
        'multipart/mixed; boundary="%s"') % message.get_boundary()

    response = http_wrapper.MakeRequest(http, request)

    if response.status_code >= 300:
      raise exceptions.HttpError.FromResponse(response)

    # Prepend with a content-type header so Parser can handle it.
    header = 'content-type: %s\r\n\r\n' % response.info['content-type']

    parser = email_parser.Parser()
    mime_response = parser.parsestr(header + response.content)

    if not mime_response.is_multipart():
      raise exceptions.BatchError('Response not in multipart/mixed format.')

    for part in mime_response.get_payload():
      request_id = self._ConvertHeaderToId(part['Content-ID'])
      response = self._DeserializeResponse(part.get_payload())

      # Disable protected access because namedtuple._replace(...)
      # is not actually meant to be protected.
      self.__request_response_handlers[request_id] = (
          self.__request_response_handlers[request_id]._replace(  # pylint: disable=protected-access
              response=response))

  def Execute(self, http):
    """Execute all the requests as a single batched HTTP request.

    Args:
      http: A httplib2.Http object to be used with the request.

    Returns:
      None

    Raises:
      BatchError if the response is the wrong format.
    """

    self._Execute(http)

    for key in self.__request_response_handlers:
      response = self.__request_response_handlers[key].response
      callback = self.__request_response_handlers[key].handler

      exception = None

      if response.status_code >= 300:
        exception = exceptions.HttpError.FromResponse(response)

      if callback is not None:
        callback(response, exception)
      if self.__callback is not None:
        self.__callback(response, exception)
