``revisions``

            list of all available revisions' ids, in ascending order

        ``changesets``

            storage dict caching returned changesets

        ``path``

            absolute path to the repository

        ``branches``

            branches as list of changesets

        ``tags``

            tags as list of changesets

    """

    scm = None

    DEFAULT_BRANCH_NAME = None

    EMPTY_CHANGESET = '0' * 40

    def __init__(self, repo_path, create=False, **kwargs):

        """

        Initializes repository. Raises RepositoryError if repository could

        not be find at the given ``repo_path`` or directory at ``repo_path``

        exists and ``create`` is set to True.

        :param repo_path: local path of the repository

        :param create=False: if set to True, would try to craete repository.

        :param src_url=None: if set, should be proper url from which repository

          would be cloned; requires ``create`` parameter to be set to True -

          raises RepositoryError if src_url is set and create evaluates to

          False

        """

        raise NotImplementedError

    def __str__(self):

        return '<%s at %s>' % (self.__class__.__name__, self.path)

    def __repr__(self):

        return self.__str__()

    def __len__(self):

        return self.count()

    def __eq__(self, other):

        same_instance = isinstance(other, self.__class__)

        return same_instance and getattr(other, 'path', None) == self.path

    @LazyProperty

    def alias(self):

        for k, v in settings.BACKENDS.items():

            if v.split('.')[-1] == str(self.__class__.__name__):

                return k

    @LazyProperty

    def name(self):

        raise NotImplementedError

    @LazyProperty

    def owner(self):

        raise NotImplementedError

    @LazyProperty

    def description(self):

        raise NotImplementedError

    @LazyProperty

    def size(self):

        """

        Returns combined size in bytes for all repository files

        """

        size = 0

        try:

            tip = self.get_changeset()

            for topnode, dirs, files in tip.walk('/'):

                for f in files:

                    size += tip.get_file_size(f.path)

                for dir in dirs:

                    for f in files:

                        size += tip.get_file_size(f.path)

        except RepositoryError, e:

            pass

        return size

    def is_valid(self):

        """

        Validates repository.

        """

        raise NotImplementedError

    def get_last_change(self):

        self.get_changesets()

    #==========================================================================