# Copyright 2014-present MongoDB, 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.

"""CommandCursor class to iterate over command results."""

from collections import deque

from bson import _convert_raw_document_lists_to_streams
from bson.py3compat import integer_types
from pymongo.cursor import _SocketManager, _CURSOR_CLOSED_ERRORS
from pymongo.errors import (ConnectionFailure,
                            InvalidOperation,
                            OperationFailure)
from pymongo.message import (_CursorAddress,
                             _GetMore,
                             _RawBatchGetMore)
from pymongo.response import PinnedResponse


class CommandCursor(object):
    """A cursor / iterator over command cursors."""
    _getmore_class = _GetMore

    def __init__(self, collection, cursor_info, address, retrieved=0,
                 batch_size=0, max_await_time_ms=None, session=None,
                 explicit_session=False):
        """Create a new command cursor.

        The parameter 'retrieved' is unused.
        """
        self.__sock_mgr = None
        self.__collection = collection
        self.__id = cursor_info['id']
        self.__data = deque(cursor_info['firstBatch'])
        self.__postbatchresumetoken = cursor_info.get('postBatchResumeToken')
        self.__address = address
        self.__batch_size = batch_size
        self.__max_await_time_ms = max_await_time_ms
        self.__session = session
        self.__explicit_session = explicit_session
        self.__killed = (self.__id == 0)
        if self.__killed:
            self.__end_session(True)

        if "ns" in cursor_info:
            self.__ns = cursor_info["ns"]
        else:
            self.__ns = collection.full_name

        self.batch_size(batch_size)

        if (not isinstance(max_await_time_ms, integer_types)
                and max_await_time_ms is not None):
            raise TypeError("max_await_time_ms must be an integer or None")

    def __del__(self):
        self.__die()

    def __die(self, synchronous=False):
        """Closes this cursor.
        """
        already_killed = self.__killed
        self.__killed = True
        if self.__id and not already_killed:
            cursor_id = self.__id
            address = _CursorAddress(
                self.__address, self.__ns)
        else:
            # Skip killCursors.
            cursor_id = 0
            address = None
        self.__collection.database.client._cleanup_cursor(
            synchronous,
            cursor_id,
            address,
            self.__sock_mgr,
            self.__session,
            self.__explicit_session)
        if not self.__explicit_session:
            self.__session = None
        self.__sock_mgr = None

    def __end_session(self, synchronous):
        if self.__session and not self.__explicit_session:
            self.__session._end_session(lock=synchronous)
            self.__session = None

    def close(self):
        """Explicitly close / kill this cursor.
        """
        self.__die(True)

    def batch_size(self, batch_size):
        """Limits the number of documents returned in one batch. Each batch
        requires a round trip to the server. It can be adjusted to optimize
        performance and limit data transfer.

        .. note:: batch_size can not override MongoDB's internal limits on the
           amount of data it will return to the client in a single batch (i.e
           if you set batch size to 1,000,000,000, MongoDB will currently only
           return 4-16MB of results per batch).

        Raises :exc:`TypeError` if `batch_size` is not an integer.
        Raises :exc:`ValueError` if `batch_size` is less than ``0``.

        :Parameters:
          - `batch_size`: The size of each batch of results requested.
        """
        if not isinstance(batch_size, integer_types):
            raise TypeError("batch_size must be an integer")
        if batch_size < 0:
            raise ValueError("batch_size must be >= 0")

        self.__batch_size = batch_size == 1 and 2 or batch_size
        return self

    def _has_next(self):
        """Returns `True` if the cursor has documents remaining from the
        previous batch."""
        return len(self.__data) > 0

    @property
    def _post_batch_resume_token(self):
        """Retrieve the postBatchResumeToken from the response to a
        changeStream aggregate or getMore."""
        return self.__postbatchresumetoken

    def _maybe_pin_connection(self, sock_info):
        client = self.__collection.database.client
        if not client._should_pin_cursor(self.__session):
            return
        if not self.__sock_mgr:
            sock_info.pin_cursor()
            sock_mgr = _SocketManager(sock_info, False)
            # Ensure the connection gets returned when the entire result is
            # returned in the first batch.
            if self.__id == 0:
                sock_mgr.close()
            else:
                self.__sock_mgr = sock_mgr

    def __send_message(self, operation):
        """Send a getmore message and handle the response.
        """
        client = self.__collection.database.client
        try:
            response = client._run_operation(
                operation, self._unpack_response, address=self.__address)
        except OperationFailure as exc:
            if exc.code in _CURSOR_CLOSED_ERRORS:
                # Don't send killCursors because the cursor is already closed.
                self.__killed = True
            # Return the session and pinned connection, if necessary.
            self.close()
            raise
        except ConnectionFailure:
            # Don't send killCursors because the cursor is already closed.
            self.__killed = True
            # Return the session and pinned connection, if necessary.
            self.close()
            raise
        except Exception:
            self.close()
            raise

        if isinstance(response, PinnedResponse):
            if not self.__sock_mgr:
                self.__sock_mgr = _SocketManager(response.socket_info,
                                                 response.more_to_come)
        if response.from_command:
            cursor = response.docs[0]['cursor']
            documents = cursor['nextBatch']
            self.__postbatchresumetoken = cursor.get('postBatchResumeToken')
            self.__id = cursor['id']
        else:
            documents = response.docs
            self.__id = response.data.cursor_id

        if self.__id == 0:
            self.close()
        self.__data = deque(documents)

    def _unpack_response(self, response, cursor_id, codec_options,
                         user_fields=None, legacy_response=False):
        return response.unpack_response(cursor_id, codec_options, user_fields,
                                        legacy_response)

    def _refresh(self):
        """Refreshes the cursor with more data from the server.

        Returns the length of self.__data after refresh. Will exit early if
        self.__data is already non-empty. Raises OperationFailure when the
        cursor cannot be refreshed due to an error on the query.
        """
        if len(self.__data) or self.__killed:
            return len(self.__data)

        if self.__id:  # Get More
            dbname, collname = self.__ns.split('.', 1)
            read_pref = self.__collection._read_preference_for(self.session)
            self.__send_message(
                self._getmore_class(dbname,
                                    collname,
                                    self.__batch_size,
                                    self.__id,
                                    self.__collection.codec_options,
                                    read_pref,
                                    self.__session,
                                    self.__collection.database.client,
                                    self.__max_await_time_ms,
                                    self.__sock_mgr, False))
        else:  # Cursor id is zero nothing else to return
            self.__die(True)

        return len(self.__data)

    @property
    def alive(self):
        """Does this cursor have the potential to return more data?

        Even if :attr:`alive` is ``True``, :meth:`next` can raise
        :exc:`StopIteration`. Best to use a for loop::

            for doc in collection.aggregate(pipeline):
                print(doc)

        .. note:: :attr:`alive` can be True while iterating a cursor from
          a failed server. In this case :attr:`alive` will return False after
          :meth:`next` fails to retrieve the next batch of results from the
          server.
        """
        return bool(len(self.__data) or (not self.__killed))

    @property
    def cursor_id(self):
        """Returns the id of the cursor."""
        return self.__id

    @property
    def address(self):
        """The (host, port) of the server used, or None.

        .. versionadded:: 3.0
        """
        return self.__address

    @property
    def session(self):
        """The cursor's :class:`~pymongo.client_session.ClientSession`, or None.

        .. versionadded:: 3.6
        """
        if self.__explicit_session:
            return self.__session

    def __iter__(self):
        return self

    def next(self):
        """Advance the cursor."""
        # Block until a document is returnable.
        while self.alive:
            doc = self._try_next(True)
            if doc is not None:
                return doc

        raise StopIteration

    __next__ = next

    def _try_next(self, get_more_allowed):
        """Advance the cursor blocking for at most one getMore command."""
        if not len(self.__data) and not self.__killed and get_more_allowed:
            self._refresh()
        if len(self.__data):
            coll = self.__collection
            return coll.database._fix_outgoing(self.__data.popleft(), coll)
        else:
            return None

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()


class RawBatchCommandCursor(CommandCursor):
    _getmore_class = _RawBatchGetMore

    def __init__(self, collection, cursor_info, address, retrieved=0,
                 batch_size=0, max_await_time_ms=None, session=None,
                 explicit_session=False):
        """Create a new cursor / iterator over raw batches of BSON data.

        Should not be called directly by application developers -
        see :meth:`~pymongo.collection.Collection.aggregate_raw_batches`
        instead.

        .. seealso:: The MongoDB documentation on `cursors <https://dochub.mongodb.org/core/cursors>`_.
        """
        assert not cursor_info.get('firstBatch')
        super(RawBatchCommandCursor, self).__init__(
            collection, cursor_info, address, retrieved, batch_size,
            max_await_time_ms, session, explicit_session)

    def _unpack_response(self, response, cursor_id, codec_options,
                         user_fields=None, legacy_response=False):
        raw_response = response.raw_response(
            cursor_id, user_fields=user_fields)
        if not legacy_response:
            # OP_MSG returns firstBatch/nextBatch documents as a BSON array
            # Re-assemble the array of documents into a document stream
            _convert_raw_document_lists_to_streams(raw_response[0])
        return raw_response

    def __getitem__(self, index):
        raise InvalidOperation("Cannot call __getitem__ on RawBatchCursor")