"""Various tools.

.. warning::

    This module should be considered as internal implementation details. Use

    with caution, as the API may change without notice.

"""

#: A short-term cache for user clones.

#: used by cached_build_user to speed-up repetitive calls to build_user

#: The expiration is handled in a dumb and brutal way: the whole cache is

#: cleared every 5 minutes.

_user_cache = {}

def clone_user(repo, user):

    """Clone a CWUser instance.

    .. warning::

        The returned clone is detached from any cnx.

        Before using it in any way, it should be attached to a cnx that has not

        this user already loaded.

    """

    CWUser = repo.vreg['etypes'].etype_class('CWUser')

    clone = CWUser(

        None,

        rset=user.cw_rset.copy(),

        row=user.cw_row,

        col=user.cw_col,

        groups=set(user._groups) if hasattr(user, '_groups') else None,

        properties=dict(user._properties)

        if hasattr(user, '_properties') else None)

    clone.cw_attr_cache = dict(user.cw_attr_cache)

    return clone

def cnx_attach_entity(cnx, entity):

    """Attach an entity to a cnx."""

    entity._cw = cnx

    if entity.cw_rset:

        entity.cw_rset.req = cnx

def cached_build_user(repo, eid):

    """Cached version of

    :meth:`cubicweb.server.repository.Repository._build_user`

    """

    with repo.internal_cnx() as cnx:

        if eid in _user_cache:

            entity = clone_user(repo, _user_cache[eid])

            # XXX the cnx is needed here so that the CWUser instance has an

            # access to the vreg, which it needs when its 'prefered_language'

            # property is accessed.

            # If this property did not need a cnx to access a vreg, we could

            # avoid the internal_cnx() and save more time.

            cnx_attach_entity(cnx, entity)

            return entity

        user = repo._build_user(cnx, eid)

        user.cw_clear_relation_cache()

        _user_cache[eid] = clone_user(repo, user)

        return user

def clear_cache():

    """Clear the user cache"""

    _user_cache.clear()

def includeme(config):

    """Start the cache maintenance loop task.

    """

    repo = config.registry['cubicweb.repository']

    interval = int(config.registry.settings.get(

        'cubicweb.usercache.expiration_time', 60*5))

    repo.looping_task(interval, clear_cache)