# -*- coding: UTF-8 -*-
# -*- Mode: Python; py-indent-offset: 4 -*-
#
#  Copyright (c) 2005 Helmut Merz helmutm@cy55.de
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

"""
The relation package provides all you need for setting up dyadic and
triadic relations.

$Id$
"""

from persistent import Persistent
from zope.interface import implements
from interfaces import IPredicate
from interfaces import IRelation, IDyadicRelation, ITriadicRelation
from interfaces import IRelatable

class Relation(Persistent):

    implements(IPredicate, IRelation)

    order = 0
    relevance = 1.0

    @classmethod
    def getPredicateName(cls):
        return '%s.%s' % (cls.__module__, cls.__name__)

    def validate(self, registry=None):
        return True

    def checkRelatable(self, *objects):
        for obj in objects:
            if obj is not None and not IRelatable.providedBy(obj):
                raise(ValueError, 'Objects to be used in relations '
                        'must provide the IRelatable interface.')


class DyadicRelation(Relation):

    implements(IDyadicRelation)

    def __init__(self, first, second):
        self.first = first
        self.second = second
        self.checkRelatable(first, second)


class TriadicRelation(Relation):

    implements(ITriadicRelation)

    def __init__(self, first, second, third):
        self.first = first
        self.second = second
        self.third = third
        self.checkRelatable(first, second, third)