from mercurial import util

import weakref

def tolist(val):

    """

    a convenience method to return an empty list instead of None

    """

    if val is None:

        return []

    else:

        return [val]

class namespaces(object):

    """

    provides an interface to register a generic many-to-many mapping between

    some (namespaced) names and nodes. The goal here is to control the

    pollution of jamming things into tags or bookmarks (in extension-land) and

    to simplify internal bits of mercurial: log output, tab completion, etc.

    More precisely, we define a list of names (the namespace) and  a mapping of

    names to nodes. This name mapping returns a list of nodes.

    Furthermore, each name mapping will be passed a name to lookup which might

    not be in its domain. In this case, each method should return an empty list

    and not raise an error.

    We'll have a dictionary '_names' where each key is a namespace and

    its value is a dictionary of functions:

      'namemap': function that takes a name and returns a list of nodes

    """

    _names_version = 0

    def __init__(self, repo):

        self._names = util.sortdict()

        self._repo = weakref.ref(repo)

    def addnamespace(self, namespace, namemap, order=None):

        """

        register a namespace

        namespace: the name to be registered (in plural form)

        namemap: function that inputs a node, output name(s)

        order: optional argument to specify the order of namespaces

               (e.g. 'branches' should be listed before 'bookmarks')

        """

        val = {'namemap': namemap}

        if order is not None:

            self._names.insert(order, namespace, val)

        else:

            self._names[namespace] = val