from terms import URI, Variable, Fact
from interpreter import Interpreter
from sets import Set
import sys
sys.path += ['/home/katz/semweb/cwm/2000/10/']  #TEMPORARY
from swap.formula import Formula

class CWMFormula(Formula):
    """Our implementation of CWM's Formula object."""
    def __init__(self):
        # We're reusing the interpreter's representation of facts rather than
        # recreating an indexed store here.
        self.interp = Interpreter([])  #empty interpreter (no rules)

    def getStatements(self):
        """Retrieve the statements from the interpreter"""
        return self.interp.totalFacts()

    def setStatements(self, facts):
        """Reset the knowledge base to whatever facts (Set) are given to us :: Since we
        have no actual truth maintenance, this operation is dorky; there could be a
        case where a fact X is inferred (and is in the set 'inferredFacts',
        waiting to be added) but is asked to be removed by 'removeStatement'.  If we
        remove X from our knowledge base (i.e. 'initialFacts') it will simply be added in
        the next round again since it is a member of 'inferredFacts'.  We just remove it
        from the knowledge base carelessly.  Horrible."""
        # check inferredFacts, set appropriately
        self.interp.initialFacts = self.interp.inferredFacts.difference(facts)
        # same for totalFacts
        self.interp.totalFacts = self.interp.totalFacts.difference(facts)
        
    statements = property(getStatements, setStatements, None, "Statements in formula")

    
    def add(self, subj, pred, obj, why=None):
	"""Add a triple to the formula :: We ignore 'why' always"""
        self.interp.addFacts(Set([Fact(subj, pred, obj)]))
        return 1  # signal success -- although it seems like CWM ignores this return value
    
    def removeStatement(self, stmt):
	"""Removes a statement :: This makes no (semantic) sense,
        we implement it regardless.  `stmt' is of CWM type StoredStatement."""
        fact = Fact(stmt.subject(), stmt.predicate(), stmt.objecT())
        self.statements = Set([fact])

    def infer(self):
        """Put the current facts through the Rete"""
        self.interp.run()