--------------------------------------------------------------------------------
--  $Id: LabelClass.hs,v 1.1 2004/07/01 15:25:36 graham Exp $
--
--  Copyright (c) 2003, G. KLYNE.  All rights reserved.
--  See end of this file for licence information.
--------------------------------------------------------------------------------
-- |
--  Module      :  LabelClass
--  Copyright   :  (c) 2003, Graham Klyne
--  License     :  GPL V2
--
--  Maintainer  :  Graham Klyne
--  Stability   :  provisional
--  Portability :  H98
--
--  This module defines a Label class and the Arc datatype.
--
--------------------------------------------------------------------------------

------------------------------------------------------------
-- Define LDGraph, arc and related classes and types
------------------------------------------------------------

module RDF.Label.LabelClass
    ( Label(..)
    , Arc(..), arcSubj, arcPred, arcObj, arc, arcToTriple, arcFromTriple
    , Selector
    , hasLabel, arcLabels, arcNodes
    )
where

import ListHelpers
    ( subset )

import FunctorM
    ( FunctorM(..) )

import List
    ( nub, union, (\\) )

---------------
--  Label class
---------------
--
--  A label may have a fixed binding, which means that the label identifies (is) a
--  particular graph node, and different such labels are always distinct nodes.
--  Alternatively, a label may be unbound (variable), which means that it is a
--  placeholder for an unknown node label.  Unbound node labels are used as
--  graph-local identifiers for indicating when the same node appears in
--  several arcs.
--
--  For the purposes of graph-isomorphism testing, fixed labels are matched when they
--  are the same.  Variable labels may be matched with any other variable label.
--  Our definition of isomorphism (for RDF graphs) does not match variable labels
--  with fixed labels.

class (Eq lb, Show lb, Ord lb) => Label lb where
    labelIsVar  :: lb -> Bool           -- does this node have a variable binding?
    labelHash   :: Int -> lb -> Int     -- calculate hash of label using supplied seed
    getLocal    :: lb -> String         -- extract local id from variable node
    makeLabel   :: String -> lb         -- make label value given local id

------------
--  Arc type
------------

data Arc lb = Arc { asubj, apred, aobj :: lb }
    deriving Eq

arcSubj :: Arc lb -> lb
arcSubj = asubj

arcPred :: Arc lb -> lb
arcPred = apred

arcObj :: Arc lb -> lb
arcObj = aobj

arc :: lb -> lb -> lb -> Arc lb
arc s p o = Arc s p o

arcToTriple :: Arc lb -> (lb,lb,lb)
arcToTriple a = (asubj a,apred a,aobj a)

arcFromTriple :: (lb,lb,lb) -> Arc lb
arcFromTriple (s,p,o) = Arc s p o

instance Ord lb => Ord (Arc lb) where
    compare (Arc s1 p1 o1) (Arc s2 p2 o2) =
        if cs /= EQ then cs else
        if cp /= EQ then cp else co
        where
            cs = compare s1 s2
            cp = compare p1 p2
            co = compare o1 o2
    (Arc s1 p1 o1) <= (Arc s2 p2 o2) =
        if (s1 /= s2) then (s1 <= s2) else
        if (p1 /= p2) then (p1 <= p2) else (o1 <= o2)

instance Functor Arc where
    -- fmap :: (lb -> l2) -> Arc lb -> Arc l2
    fmap f (Arc s p o) = Arc (f s) (f p) (f o)

instance FunctorM Arc where
    -- fmapM :: (lb -> m l2) -> Arc lb -> m (Arc l2)
    fmapM f (Arc s p o) =
        do  { s' <- f s
            ; p' <- f p
            ; o' <- f o
            ; return $ Arc s' p' o'
            }

instance (Show lb) => Show (Arc lb) where
    show (Arc lb1 lb2 lb3) =
        "("++(show lb1)++","++(show lb2)++","++(show lb3)++")"

type Selector lb = Arc lb -> Bool

hasLabel :: (Eq lb) => lb -> Arc lb -> Bool
hasLabel lbv (Arc lb1 lb2 lb3) = (lbv==lb1) || (lbv==lb2) || (lbv==lb3)

arcLabels :: Arc lb -> [lb]
arcLabels (Arc lb1 lb2 lb3) = [lb1,lb2,lb3]

arcNodes :: Arc lb -> [lb]
arcNodes (Arc lb1 _ lb3) = [lb1,lb3]

--------------------------------------------------------------------------------
--
--  Copyright (c) 2003, G. KLYNE.  All rights reserved.
--
--  This file is part of Swish.
--
--  Swish 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.
--
--  Swish 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 Swish; if not, write to:
--    The Free Software Foundation, Inc.,
--    59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
--
--------------------------------------------------------------------------------
-- $Source: /file/cvsdev/HaskellRDF/RDF/Label/LabelClass.hs,v $
-- $Author: graham $
-- $Revision: 1.1 $
-- $Log: LabelClass.hs,v $
-- Revision 1.1  2004/07/01 15:25:36  graham
-- Moved Lavel and Vocabulary modules to separate directory
--
-- Revision 1.1  2004/07/01 11:10:11  graham
-- Separate RDFLabel from RDFGraph, and LabelClass from GraphClass,
-- in preparation for implementing an RDF/XML parser that operates
-- independently of the graph structure.
--