#  $Id$
#
#  Copyright (C) 2003 Rational Discovery LLC
#     All Rights Reserved
#
import sys

from VLib.Node import VLibNode

class TransformNode(VLibNode):
  """ base class for nodes which filter their input

  Assumptions:

    - transform function takes a number of arguments equal to the
      number of inputs we have.  We return whatever it returns

    - inputs (parents) can be stepped through in lockstep

  Usage Example:
    >>> from VLib.Supply import SupplyNode
    >>> def func(a,b):
    ...   return a+b
    >>> tform = TransformNode(func)
    >>> suppl1 = SupplyNode(contents=[1,2,3,3])
    >>> suppl2 = SupplyNode(contents=[1,2,3,1])
    >>> tform.AddParent(suppl1)
    >>> tform.AddParent(suppl2)
    >>> v = [x for x in tform]
    >>> v
    [2, 4, 6, 4]
    >>> tform.reset()
    >>> v = [x for x in tform]
    >>> v
    [2, 4, 6, 4]

    If we don't provide a function, just return the inputs:
    >>> tform = TransformNode()
    >>> suppl1 = SupplyNode(contents=[1,2,3,3])
    >>> suppl2 = SupplyNode(contents=[1,2,3,1])
    >>> tform.AddParent(suppl1)
    >>> tform.AddParent(suppl2)
    >>> v = [x for x in tform]
    >>> v
    [(1, 1), (2, 2), (3, 3), (3, 1)]

  """
  def __init__(self,func=None,**kwargs):
    VLibNode.__init__(self,**kwargs)
    self._func = func

  def next(self):
    done = 0
    parent = self.GetParents()[0]
    args = []
    try:
      for parent in self.GetParents():
        args.append(parent.next())
    except StopIteration:
      raise StopIteration
    args = tuple(args)
    if self._func is not None:
      res = apply(self._func,args)
    else:
      res = args
    return res  


  
#------------------------------------
#
#  doctest boilerplate
#
def _test():
  import doctest,sys
  return doctest.testmod(sys.modules["__main__"])

if __name__ == '__main__':
  import sys
  failed,tried = _test()
  sys.exit(failed)