# Copyright 2014 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.
"""Batch updates / deletes of storage buckets / blobs.

See: https://cloud.google.com/storage/docs/json_api/v1/how-tos/batch
"""
from email.encoders import encode_noop
from email.generator import Generator
from email.mime.application import MIMEApplication
from email.mime.multipart import MIMEMultipart
from email.parser import Parser
import io
import json

import httplib2
import six

from google.cloud.exceptions import make_exception
from google.cloud.storage._http import Connection


class MIMEApplicationHTTP(MIMEApplication):
    """MIME type for ``application/http``.

    Constructs payload from headers and body

    :type method: str
    :param method: HTTP method

    :type uri: str
    :param uri: URI for HTTP request

    :type headers:  dict
    :param headers: HTTP headers

    :type body: str
    :param body: (Optional) HTTP payload

    """
    def __init__(self, method, uri, headers, body):
        if isinstance(body, dict):
            body = json.dumps(body)
            headers['Content-Type'] = 'application/json'
            headers['Content-Length'] = len(body)
        if body is None:
            body = ''
        lines = ['%s %s HTTP/1.1' % (method, uri)]
        lines.extend(['%s: %s' % (key, value)
                      for key, value in sorted(headers.items())])
        lines.append('')
        lines.append(body)
        payload = '\r\n'.join(lines)
        if six.PY2:
            # email.message.Message is an old-style class, so we
            # cannot use 'super()'.
            MIMEApplication.__init__(self, payload, 'http', encode_noop)
        else:  # pragma: NO COVER  Python3
            super_init = super(MIMEApplicationHTTP, self).__init__
            super_init(payload, 'http', encode_noop)


class NoContent(object):
    """Emulate an HTTP '204 No Content' response."""
    status = 204


class _FutureDict(object):
    """Class to hold a future value for a deferred request.

    Used by for requests that get sent in a :class:`Batch`.
    """

    @staticmethod
    def get(key, default=None):
        """Stand-in for dict.get.

        :type key: object
        :param key: Hashable dictionary key.

        :type default: object
        :param default: Fallback value to dict.get.

        :raises: :class:`KeyError` always since the future is intended to fail
                 as a dictionary.
        """
        raise KeyError('Cannot get(%r, default=%r) on a future' % (
            key, default))

    def __getitem__(self, key):
        """Stand-in for dict[key].

        :type key: object
        :param key: Hashable dictionary key.

        :raises: :class:`KeyError` always since the future is intended to fail
                 as a dictionary.
        """
        raise KeyError('Cannot get item %r from a future' % (key,))

    def __setitem__(self, key, value):
        """Stand-in for dict[key] = value.

        :type key: object
        :param key: Hashable dictionary key.

        :type value: object
        :param value: Dictionary value.

        :raises: :class:`KeyError` always since the future is intended to fail
                 as a dictionary.
        """
        raise KeyError('Cannot set %r -> %r on a future' % (key, value))


class Batch(Connection):
    """Proxy an underlying connection, batching up change operations.

    :type client: :class:`google.cloud.storage.client.Client`
    :param client: The client to use for making connections.
    """
    _MAX_BATCH_SIZE = 1000

    def __init__(self, client):
        super(Batch, self).__init__(client)
        self._requests = []
        self._target_objects = []

    def _do_request(self, method, url, headers, data, target_object):
        """Override Connection:  defer actual HTTP request.

        Only allow up to ``_MAX_BATCH_SIZE`` requests to be deferred.

        :type method: str
        :param method: The HTTP method to use in the request.

        :type url: str
        :param url: The URL to send the request to.

        :type headers: dict
        :param headers: A dictionary of HTTP headers to send with the request.

        :type data: str
        :param data: The data to send as the body of the request.

        :type target_object: object
        :param target_object:
            (Optional) This allows us to enable custom behavior in our batch
            connection. Here we defer an HTTP request and complete
            initialization of the object at a later time.

        :rtype: tuple of ``response`` (a dictionary of sorts)
                and ``content`` (a string).
        :returns: The HTTP response object and the content of the response.
        """
        if len(self._requests) >= self._MAX_BATCH_SIZE:
            raise ValueError("Too many deferred requests (max %d)" %
                             self._MAX_BATCH_SIZE)
        self._requests.append((method, url, headers, data))
        result = _FutureDict()
        self._target_objects.append(target_object)
        if target_object is not None:
            target_object._properties = result
        return NoContent(), result

    def _prepare_batch_request(self):
        """Prepares headers and body for a batch request.

        :rtype: tuple (dict, str)
        :returns: The pair of headers and body of the batch request to be sent.
        :raises: :class:`ValueError` if no requests have been deferred.
        """
        if len(self._requests) == 0:
            raise ValueError("No deferred requests")

        multi = MIMEMultipart()

        for method, uri, headers, body in self._requests:
            subrequest = MIMEApplicationHTTP(method, uri, headers, body)
            multi.attach(subrequest)

        # The `email` package expects to deal with "native" strings
        if six.PY3:  # pragma: NO COVER  Python3
            buf = io.StringIO()
        else:
            buf = io.BytesIO()
        generator = Generator(buf, False, 0)
        generator.flatten(multi)
        payload = buf.getvalue()

        # Strip off redundant header text
        _, body = payload.split('\n\n', 1)
        return dict(multi._headers), body

    def _finish_futures(self, responses):
        """Apply all the batch responses to the futures created.

        :type responses: list of (headers, payload) tuples.
        :param responses: List of headers and payloads from each response in
                          the batch.

        :raises: :class:`ValueError` if no requests have been deferred.
        """
        # If a bad status occurs, we track it, but don't raise an exception
        # until all futures have been populated.
        exception_args = None

        if len(self._target_objects) != len(responses):
            raise ValueError('Expected a response for every request.')

        for target_object, sub_response in zip(self._target_objects,
                                               responses):
            resp_headers, sub_payload = sub_response
            if not 200 <= resp_headers.status < 300:
                exception_args = exception_args or (resp_headers,
                                                    sub_payload)
            elif target_object is not None:
                target_object._properties = sub_payload

        if exception_args is not None:
            raise make_exception(*exception_args)

    def finish(self):
        """Submit a single `multipart/mixed` request with deferred requests.

        :rtype: list of tuples
        :returns: one ``(headers, payload)`` tuple per deferred request.
        """
        headers, body = self._prepare_batch_request()

        url = '%s/batch' % self.API_BASE_URL

        # Use the private ``_base_connection`` rather than the property
        # ``_connection``, since the property may be this
        # current batch.
        response, content = self._client._base_connection._make_request(
            'POST', url, data=body, headers=headers)
        responses = list(_unpack_batch_response(response, content))
        self._finish_futures(responses)
        return responses

    def current(self):
        """Return the topmost batch, or None."""
        return self._client.current_batch

    def __enter__(self):
        self._client._push_batch(self)
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        try:
            if exc_type is None:
                self.finish()
        finally:
            self._client._pop_batch()


def _generate_faux_mime_message(parser, response, content):
    """Convert response, content -> (multipart) email.message.

    Helper for _unpack_batch_response.
    """
    # We coerce to bytes to get consistent concat across
    # Py2 and Py3. Percent formatting is insufficient since
    # it includes the b in Py3.
    if not isinstance(content, six.binary_type):
        content = content.encode('utf-8')
    content_type = response['content-type']
    if not isinstance(content_type, six.binary_type):
        content_type = content_type.encode('utf-8')
    faux_message = b''.join([
        b'Content-Type: ',
        content_type,
        b'\nMIME-Version: 1.0\n\n',
        content,
    ])

    if six.PY2:
        return parser.parsestr(faux_message)
    else:  # pragma: NO COVER  Python3
        return parser.parsestr(faux_message.decode('utf-8'))


def _unpack_batch_response(response, content):
    """Convert response, content -> [(headers, payload)].

    Creates a generator of tuples of emulating the responses to
    :meth:`httplib2.Http.request` (a pair of headers and payload).

    :type response: :class:`httplib2.Response`
    :param response: HTTP response / headers from a request.

    :type content: str
    :param content: Response payload with a batch response.
    """
    parser = Parser()
    message = _generate_faux_mime_message(parser, response, content)

    if not isinstance(message._payload, list):
        raise ValueError('Bad response:  not multi-part')

    for subrequest in message._payload:
        status_line, rest = subrequest._payload.split('\n', 1)
        _, status, _ = status_line.split(' ', 2)
        sub_message = parser.parsestr(rest)
        payload = sub_message._payload
        ctype = sub_message['Content-Type']
        msg_headers = dict(sub_message._headers)
        msg_headers['status'] = status
        headers = httplib2.Response(msg_headers)
        if ctype and ctype.startswith('application/json'):
            payload = json.loads(payload)
        yield headers, payload
