# Copyright (c) 2004 Divmod.
# See LICENSE for details.

from twisted.internet import defer
from twisted.python.context import get as getCtx
from nevow.util import Deferred

from nevow import flat

def deferflatten(stan, ctx, writer):
    finished = Deferred()

    iterable = flat.iterflatten(
        stan, ctx, writer, lambda D: isinstance(D, Deferred))

    def drive():
        try:
            deferred, returner = iterable.next()
            def cb(result):
                returner(result)
                drive()
                return result
            def eb(failure):
                finished.errback(failure)
                return failure
            cfac = getCtx('CursorFactory')
            if cfac:
                deferred.addCallback(cfac.store.transback, cb).addErrback(cfac.store.transback, eb)
            else:
                deferred.addCallback(cb).addErrback(eb)
        except StopIteration:
            finished.callback('')

    drive()
    return finished