import pymongo
import gridfs
from gridfs.errors import NoFile

from xmodule.contentstore.content import XASSET_LOCATION_TAG

import logging

from .content import StaticContent, ContentStore, StaticContentStream
from xmodule.exceptions import NotFoundError
from fs.osfs import OSFS
import os
import json
from bson.son import SON
from opaque_keys.edx.keys import AssetKey
from xmodule.modulestore.django import ASSET_IGNORE_REGEX


class MongoContentStore(ContentStore):

    # pylint: disable=W0613
    def __init__(self, host, db, port=27017, user=None, password=None, bucket='fs', collection=None, **kwargs):
        """
        Establish the connection with the mongo backend and connect to the collections

        :param collection: ignores but provided for consistency w/ other doc_store_config patterns
        """
        logging.debug('Using MongoDB for static content serving at host={0} db={1}'.format(host, db))
        _db = pymongo.database.Database(
            pymongo.MongoClient(
                host=host,
                port=port,
                document_class=dict,
                **kwargs
            ),
            db
        )

        if user is not None and password is not None:
            _db.authenticate(user, password)

        self.fs = gridfs.GridFS(_db, bucket)

        self.fs_files = _db[bucket + ".files"]  # the underlying collection GridFS uses

    def close_connections(self):
        """
        Closes any open connections to the underlying databases
        """
        self.fs_files.database.connection.close()

    def _drop_database(self):
        """
        A destructive operation to drop the underlying database and close all connections.
        Intended to be used by test code for cleanup.
        """
        self.close_connections()
        self.fs_files.database.connection.drop_database(self.fs_files.database)

    def save(self, content):
        content_id, content_son = self.asset_db_key(content.location)

        # The way to version files in gridFS is to not use the file id as the _id but just as the filename.
        # Then you can upload as many versions as you like and access by date or version. Because we use
        # the location as the _id, we must delete before adding (there's no replace method in gridFS)
        self.delete(content_id)  # delete is a noop if the entry doesn't exist; so, don't waste time checking

        thumbnail_location = content.thumbnail_location.to_deprecated_list_repr() if content.thumbnail_location else None
        with self.fs.new_file(_id=content_id, filename=content.get_url_path(), content_type=content.content_type,
                              displayname=content.name, content_son=content_son,
                              thumbnail_location=thumbnail_location,
                              import_path=content.import_path,
                              # getattr b/c caching may mean some pickled instances don't have attr
                              locked=getattr(content, 'locked', False)) as fp:
            if hasattr(content.data, '__iter__'):
                for chunk in content.data:
                    fp.write(chunk)
            else:
                fp.write(content.data)

        return content

    def delete(self, location_or_id):
        if isinstance(location_or_id, AssetKey):
            location_or_id, _ = self.asset_db_key(location_or_id)
        # Deletes of non-existent files are considered successful
        self.fs.delete(location_or_id)

    def find(self, location, throw_on_not_found=True, as_stream=False):
        content_id, __ = self.asset_db_key(location)

        try:
            if as_stream:
                fp = self.fs.get(content_id)
                thumbnail_location = getattr(fp, 'thumbnail_location', None)
                if thumbnail_location:
                    thumbnail_location = location.course_key.make_asset_key(
                        'thumbnail', thumbnail_location[4]
                    )
                return StaticContentStream(
                    location, fp.displayname, fp.content_type, fp, last_modified_at=fp.uploadDate,
                    thumbnail_location=thumbnail_location,
                    import_path=getattr(fp, 'import_path', None),
                    length=fp.length, locked=getattr(fp, 'locked', False)
                )
            else:
                with self.fs.get(content_id) as fp:
                    thumbnail_location = getattr(fp, 'thumbnail_location', None)
                    if thumbnail_location:
                        thumbnail_location = location.course_key.make_asset_key(
                            'thumbnail', thumbnail_location[4]
                        )
                    return StaticContent(
                        location, fp.displayname, fp.content_type, fp.read(), last_modified_at=fp.uploadDate,
                        thumbnail_location=thumbnail_location,
                        import_path=getattr(fp, 'import_path', None),
                        length=fp.length, locked=getattr(fp, 'locked', False)
                    )
        except NoFile:
            if throw_on_not_found:
                raise NotFoundError(content_id)
            else:
                return None

    def export(self, location, output_directory):
        content = self.find(location)

        if content.import_path is not None:
            output_directory = output_directory + '/' + os.path.dirname(content.import_path)

        if not os.path.exists(output_directory):
            os.makedirs(output_directory)

        disk_fs = OSFS(output_directory)

        with disk_fs.open(content.name, 'wb') as asset_file:
            asset_file.write(content.data)

    def export_all_for_course(self, course_key, output_directory, assets_policy_file):
        """
        Export all of this course's assets to the output_directory. Export all of the assets'
        attributes to the policy file.

        Args:
            course_key (CourseKey): the :class:`CourseKey` identifying the course
            output_directory: the directory under which to put all the asset files
            assets_policy_file: the filename for the policy file which should be in the same
                directory as the other policy files.
        """
        policy = {}
        assets, __ = self.get_all_content_for_course(course_key)

        for asset in assets:
            # TODO: On 6/19/14, I had to put a try/except around this
            # to export a course. The course failed on JSON files in
            # the /static/ directory placed in it with an import.
            #
            # If this hasn't been looked at in a while, remove this comment.
            #
            # When debugging course exports, this might be a good place
            # to look. -- pmitros
            self.export(asset['asset_key'], output_directory)
            for attr, value in asset.iteritems():
                if attr not in ['_id', 'md5', 'uploadDate', 'length', 'chunkSize', 'asset_key']:
                    policy.setdefault(asset['asset_key'].name, {})[attr] = value

        with open(assets_policy_file, 'w') as f:
            json.dump(policy, f)

    def get_all_content_thumbnails_for_course(self, course_key):
        return self._get_all_content_for_course(course_key, get_thumbnails=True)[0]

    def get_all_content_for_course(self, course_key, start=0, maxresults=-1, sort=None):
        return self._get_all_content_for_course(
            course_key, start=start, maxresults=maxresults, get_thumbnails=False, sort=sort
        )

    def remove_redundant_content_for_courses(self):
        """
        Finds and removes all redundant files (Mac OS metadata files with filename ".DS_Store"
        or filename starts with "._") for all courses
        """
        assets_to_delete = 0
        for prefix in ['_id', 'content_son']:
            query = SON([
                ('{}.tag'.format(prefix), XASSET_LOCATION_TAG),
                ('{}.category'.format(prefix), 'asset'),
                ('{}.name'.format(prefix), {'$regex': ASSET_IGNORE_REGEX}),
            ])
            items = self.fs_files.find(query)
            assets_to_delete = assets_to_delete + items.count()
            for asset in items:
                self.fs.delete(asset[prefix])

            self.fs_files.remove(query)
        return assets_to_delete

    def _get_all_content_for_course(self, course_key, get_thumbnails=False, start=0, maxresults=-1, sort=None):
        '''
        Returns a list of all static assets for a course. The return format is a list of asset data dictionary elements.

        The asset data dictionaries have the following keys:
            asset_key (:class:`opaque_keys.edx.AssetKey`): The key of the asset
            displayname: The human-readable name of the asset
            uploadDate (datetime.datetime): The date and time that the file was uploadDate
            contentType: The mimetype string of the asset
            md5: An md5 hash of the asset content
        '''
        if maxresults > 0:
            items = self.fs_files.find(
                query_for_course(course_key, "asset" if not get_thumbnails else "thumbnail"),
                skip=start, limit=maxresults, sort=sort
            )
        else:
            items = self.fs_files.find(
                query_for_course(course_key, "asset" if not get_thumbnails else "thumbnail"), sort=sort
            )
        count = items.count()
        assets = list(items)

        # We're constructing the asset key immediately after retrieval from the database so that
        # callers are insulated from knowing how our identifiers are stored.
        for asset in assets:
            asset_id = asset.get('content_son', asset['_id'])
            asset['asset_key'] = course_key.make_asset_key(asset_id['category'], asset_id['name'])
        return assets, count

    def set_attr(self, asset_key, attr, value=True):
        """
        Add/set the given attr on the asset at the given location. Does not allow overwriting gridFS built in
        attrs such as _id, md5, uploadDate, length. Value can be any type which pymongo accepts.

        Returns nothing

        Raises NotFoundError if no such item exists
        Raises AttributeError is attr is one of the build in attrs.

        :param asset_key: an AssetKey
        :param attr: which attribute to set
        :param value: the value to set it to (any type pymongo accepts such as datetime, number, string)
        """
        self.set_attrs(asset_key, {attr: value})

    def get_attr(self, location, attr, default=None):
        """
        Get the value of attr set on location. If attr is unset, it returns default. Unlike set, this accessor
        does allow getting the value of reserved keywords.
        :param location: a c4x asset location
        """
        return self.get_attrs(location).get(attr, default)

    def set_attrs(self, location, attr_dict):
        """
        Like set_attr but sets multiple key value pairs.

        Returns nothing.

        Raises NotFoundError if no such item exists
        Raises AttributeError is attr_dict has any attrs which are one of the build in attrs.

        :param location:  a c4x asset location
        """
        for attr in attr_dict.iterkeys():
            if attr in ['_id', 'md5', 'uploadDate', 'length']:
                raise AttributeError("{} is a protected attribute.".format(attr))
        asset_db_key, __ = self.asset_db_key(location)
        # catch upsert error and raise NotFoundError if asset doesn't exist
        result = self.fs_files.update({'_id': asset_db_key}, {"$set": attr_dict}, upsert=False)
        if not result.get('updatedExisting', True):
            raise NotFoundError(asset_db_key)

    def get_attrs(self, location):
        """
        Gets all of the attributes associated with the given asset. Note, returns even built in attrs
        such as md5 which you cannot resubmit in an update; so, don't call set_attrs with the result of this
        but only with the set of attrs you want to explicitly update.

        The attrs will be a superset of _id, contentType, chunkSize, filename, uploadDate, & md5

        :param location: a c4x asset location
        """
        asset_db_key, __ = self.asset_db_key(location)
        item = self.fs_files.find_one({'_id': asset_db_key})
        if item is None:
            raise NotFoundError(asset_db_key)
        return item

    def copy_all_course_assets(self, source_course_key, dest_course_key):
        """
        See :meth:`.ContentStore.copy_all_course_assets`

        This implementation fairly expensively copies all of the data
        """
        source_query = query_for_course(source_course_key)
        # it'd be great to figure out how to do all of this on the db server and not pull the bits over
        for asset in self.fs_files.find(source_query):
            asset_key = self.make_id_son(asset)
            # don't convert from string until fs access
            source_content = self.fs.get(asset_key)
            if isinstance(asset_key, basestring):
                asset_key = AssetKey.from_string(asset_key)
                __, asset_key = self.asset_db_key(asset_key)
            asset_key['org'] = dest_course_key.org
            asset_key['course'] = dest_course_key.course
            if getattr(dest_course_key, 'deprecated', False):  # remove the run if exists
                if 'run' in asset_key:
                    del asset_key['run']
                asset_id = asset_key
            else:  # add the run, since it's the last field, we're golden
                asset_key['run'] = dest_course_key.run
                asset_id = unicode(
                    dest_course_key.make_asset_key(asset_key['category'], asset_key['name']).for_branch(None)
                )

            self.fs.put(
                source_content.read(),
                _id=asset_id, filename=asset['filename'], content_type=asset['contentType'],
                displayname=asset['displayname'], content_son=asset_key,
                # thumbnail is not technically correct but will be functionally correct as the code
                # only looks at the name which is not course relative.
                thumbnail_location=asset['thumbnail_location'],
                import_path=asset['import_path'],
                # getattr b/c caching may mean some pickled instances don't have attr
                locked=asset.get('locked', False)
            )

    def delete_all_course_assets(self, course_key):
        """
        Delete all assets identified via this course_key. Dangerous operation which may remove assets
        referenced by other runs or other courses.
        :param course_key:
        """
        course_query = query_for_course(course_key)
        matching_assets = self.fs_files.find(course_query)
        for asset in matching_assets:
            asset_key = self.make_id_son(asset)
            self.fs.delete(asset_key)

    # codifying the original order which pymongo used for the dicts coming out of location_to_dict
    # stability of order is more important than sanity of order as any changes to order make things
    # unfindable
    ordered_key_fields = ['category', 'name', 'course', 'tag', 'org', 'revision']

    @classmethod
    def asset_db_key(cls, location):
        """
        Returns the database _id and son structured lookup to find the given asset location.
        """
        dbkey = SON((field_name, getattr(location, field_name)) for field_name in cls.ordered_key_fields)
        if getattr(location, 'deprecated', False):
            content_id = dbkey
        else:
            # NOTE, there's no need to state that run doesn't exist in the negative case b/c access via
            # SON requires equivalence (same keys and values in exact same order)
            dbkey['run'] = location.run
            content_id = unicode(location.for_branch(None))
        return content_id, dbkey

    def make_id_son(self, fs_entry):
        """
        Change the _id field in fs_entry into the properly ordered SON or string
        Args:
            fs_entry: the element returned by self.fs_files.find
        """
        _id_field = fs_entry.get('_id', fs_entry)
        if isinstance(_id_field, basestring):
            return _id_field
        dbkey = SON((field_name, _id_field.get(field_name)) for field_name in self.ordered_key_fields)
        if 'run' in _id_field:
            # NOTE, there's no need to state that run doesn't exist in the negative case b/c access via
            # SON requires equivalence (same keys and values in exact same order)
            dbkey['run'] = _id_field['run']
        fs_entry['_id'] = dbkey
        return dbkey


def query_for_course(course_key, category=None):
    """
    Construct a SON object that will query for all assets possibly limited to the given type
    (thumbnail v assets) in the course using the index in mongo_indexes.md
    """
    if getattr(course_key, 'deprecated', False):
        prefix = '_id'
    else:
        prefix = 'content_son'
    dbkey = SON([
        ('{}.tag'.format(prefix), XASSET_LOCATION_TAG),
        ('{}.org'.format(prefix), course_key.org),
        ('{}.course'.format(prefix), course_key.course),
    ])
    if category:
        dbkey['{}.category'.format(prefix)] = category
    if getattr(course_key, 'deprecated', False):
        dbkey['{}.run'.format(prefix)] = {'$exists': False}
    else:
        dbkey['{}.run'.format(prefix)] = course_key.run
    return dbkey
