# Copyright 2015-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.

"""Tools for representing raw BSON documents.
"""

from bson import _raw_to_dict, _get_object_size
from bson.py3compat import abc, iteritems
from bson.codec_options import (
    DEFAULT_CODEC_OPTIONS as DEFAULT, _RAW_BSON_DOCUMENT_MARKER)
from bson.son import SON


class RawBSONDocument(abc.Mapping):
    """Representation for a MongoDB document that provides access to the raw
    BSON bytes that compose it.

    Only when a field is accessed or modified within the document does
    RawBSONDocument decode its bytes.
    """

    __slots__ = ('__raw', '__inflated_doc', '__codec_options')
    _type_marker = _RAW_BSON_DOCUMENT_MARKER

    def __init__(self, bson_bytes, codec_options=None):
        """Create a new :class:`RawBSONDocument`

        :class:`RawBSONDocument` is a representation of a BSON document that
        provides access to the underlying raw BSON bytes. Only when a field is
        accessed or modified within the document does RawBSONDocument decode
        its bytes.

        :class:`RawBSONDocument` implements the ``Mapping`` abstract base
        class from the standard library so it can be used like a read-only
        ``dict``::

            >>> from bson import encode
            >>> raw_doc = RawBSONDocument(encode({'_id': 'my_doc'}))
            >>> raw_doc.raw
            b'...'
            >>> raw_doc['_id']
            'my_doc'

        :Parameters:
          - `bson_bytes`: the BSON bytes that compose this document
          - `codec_options` (optional): An instance of
            :class:`~bson.codec_options.CodecOptions` whose ``document_class``
            must be :class:`RawBSONDocument`. The default is
            :attr:`DEFAULT_RAW_BSON_OPTIONS`.

        .. versionchanged:: 3.8
          :class:`RawBSONDocument` now validates that the ``bson_bytes``
          passed in represent a single bson document.

        .. versionchanged:: 3.5
          If a :class:`~bson.codec_options.CodecOptions` is passed in, its
          `document_class` must be :class:`RawBSONDocument`.
        """
        self.__raw = bson_bytes
        self.__inflated_doc = None
        # Can't default codec_options to DEFAULT_RAW_BSON_OPTIONS in signature,
        # it refers to this class RawBSONDocument.
        if codec_options is None:
            codec_options = DEFAULT_RAW_BSON_OPTIONS
        elif codec_options.document_class is not RawBSONDocument:
            raise TypeError(
                "RawBSONDocument cannot use CodecOptions with document "
                "class %s" % (codec_options.document_class, ))
        self.__codec_options = codec_options
        # Validate the bson object size.
        _get_object_size(bson_bytes, 0, len(bson_bytes))

    @property
    def raw(self):
        """The raw BSON bytes composing this document."""
        return self.__raw

    def items(self):
        """Lazily decode and iterate elements in this document."""
        return iteritems(self.__inflated)

    @property
    def __inflated(self):
        if self.__inflated_doc is None:
            # We already validated the object's size when this document was
            # created, so no need to do that again.
            # Use SON to preserve ordering of elements.
            self.__inflated_doc = _inflate_bson(
                self.__raw, self.__codec_options)
        return self.__inflated_doc

    def __getitem__(self, item):
        return self.__inflated[item]

    def __iter__(self):
        return iter(self.__inflated)

    def __len__(self):
        return len(self.__inflated)

    def __eq__(self, other):
        if isinstance(other, RawBSONDocument):
            return self.__raw == other.raw
        return NotImplemented

    def __repr__(self):
        return ("RawBSONDocument(%r, codec_options=%r)"
                % (self.raw, self.__codec_options))


def _inflate_bson(bson_bytes, codec_options):
    """Inflates the top level fields of a BSON document.

    :Parameters:
      - `bson_bytes`: the BSON bytes that compose this document
      - `codec_options`: An instance of
        :class:`~bson.codec_options.CodecOptions` whose ``document_class``
        must be :class:`RawBSONDocument`.
    """
    # Use SON to preserve ordering of elements.
    return _raw_to_dict(
        bson_bytes, 4, len(bson_bytes)-1, codec_options, SON())


DEFAULT_RAW_BSON_OPTIONS = DEFAULT.with_options(document_class=RawBSONDocument)
"""The default :class:`~bson.codec_options.CodecOptions` for
:class:`RawBSONDocument`.
"""
