# Sentinal value for nondeterministic dependencies
DISCORDIA = 'discordia'

class Dependencies(set):
    def add(self, d):
        assert d == DISCORDIA or len(d) == 4, d
        set.add(self, d)
    
    def addRawDep(self, ename, pname, id, version):
        self.add((ename, pname, id, version))
    def makeUncacheable(self):
        self.add(DISCORDIA)
    def addDep(self, propval):
        self.addRawDep(propval.element.ename, propval.prop.name,
                       propval.id, propval.version)
    # TODO(xavid): rename and make sure this makes sense
    def addExistsDep(self, ename):
        self.addRawDep(ename, '__exists', None, None)
    def addNoPropvalDep(self, ename, pname):
        self.addRawDep(ename, pname, None, None)
    def addPropvalDep(self, e, pname):
        if pname in e:
            self.addDep(e[pname])
        else:
            self.addNoPropvalDep(e.ename, pname)

    def addRawElementDep(self, e):
        self.addRawDep(e.ename, '__version', e.id, e.version)
    def addChildrenDep(self, e):
        self.addRawElementDep(e)
    def addParentDep(self, e):
        self.addRawElementDep(e)
    def addElementPropvalsDep(self, e):
        self.addRawElementDep(e)