from Acquisition import aq_base
from Products.CMFCore.interfaces import IContentish
from Products.CMFCore.interfaces import IFolderish
from zope.component.hooks import getSite
try:
    from zope.globalrequest import getRequest
    getRequest  # pyflakes
except ImportError:
    # Fake it
    getRequest = object


def closest_content(context=None):
    """Try to find a usable context, with increasing agression"""
    # Normally, we should be given a useful context (e.g the page)
    c = context
    c = _valid_context(c)
    if c is not None:
        return c
    # Subforms (e.g. DataGridField) may not have a context set, find out
    # what page is being published
    c = getattr(getRequest(), 'PUBLISHED', None)
    c = _valid_context(c)
    if c is not None:
        return c
    # During widget traversal nothing is being published yet, use getSite()
    c = getSite()
    c = _valid_context(c)
    if c is not None:
        return c
    raise ValueError('Cannot find suitable context to bind to source')


def _valid_context(context):
    """Walk up until finding a content item."""
    # Avoid loops. The object id is used as context may not be hashable
    seen = set()
    while context is not None and id(aq_base(context)) not in seen:
        seen.add(id(aq_base(context)))
        if (IContentish.providedBy(context)
            or IFolderish.providedBy(context)):
            return context
        parent = getattr(context, '__parent__', None)
        if parent is None:
            parent = getattr(context, 'context', None)
        context = parent

    return None