(* Copyright (C) 2000, HELM Team.
 * 
 * This file is part of HELM, an Hypertextual, Electronic
 * Library of Mathematics, developed at the Computer Science
 * Department, University of Bologna, Italy.
 * 
 * HELM 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.
 * 
 * HELM 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 HELM; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA  02111-1307, USA.
 * 
 * For details, see the HELM World-Wide-Web page,
 * http://cs.unibo.it/helm/.
 *)

(*
 * implementazione del comando INTERSECT
 *)

(*
 * eccezione sollevata quando il join dei contesti
 * deve essere vuoto
 *)
exception Join_must_be_empty;;

(*
 * join fra due contesti
 *)
let xres_join_context h1 l1 h2 l2 =
 match (l1, l2) with
    ([], _) -> l2
 |  (_, []) -> l1
 |  (_,  _) ->
     let hh = h2 @ (List.find_all (function t -> not (List.mem t h2)) h1)
     and m1 = List.combine h1 l1
     and m2 = List.combine h2 l2
     in
       List.map
        (fun elem ->
         let value1 = try (List.assoc elem m1) with Not_found -> List.assoc elem m2
         and value2 = try (List.assoc elem m2) with Not_found -> List.assoc elem m1
         in
          if value1 = value2 then value1 else raise Join_must_be_empty
        )
        hh
;;

(*
 *
 *)
let intersect_tails h1 t1 h2 t2 =
 let rec aux t1 t2 =
  match (t1, t2) with
     ([], _)
  |  (_, []) -> []
  |  ((l1::tl1)::tll1, (l2::tl2)::tll2) ->
       if l1 = l2 then
        try
         (*match xres_join_context h1 tl1 h2 tl2 with
            [] -> aux tll1 tll2
          | t  -> (l1::(xres_join_context h1 tl1 h2 tl2))::(aux tll1 tll2)*)
	  (l1::(tl1 @ tl2))::(aux tll1 tll2)
	with
	 Join_must_be_empty -> aux tll1 tll2
       else
        if l1 < l2 then
         aux tll1 t2
        else
         aux t1 tll2
   | _ -> assert false
 in
  aux t1 t2
;;

(*
 * implementazione del comando INTERSECT
 *)
let intersect_ex l1 l2 =
 let _ = print_string ("INTERSECT ")
 and t = Unix.time () in
  let result = 
 match (l1, l2) with
    ((head1::tail1), (head2::tail2)) ->
     (match (head1, head2) with
         ([], _) -> assert false (* gli header non devono mai essere vuoti *)
      |  (_, []) -> assert false (* devono contenere almeno [retVal] *)
      |  (_,  _) ->
          (match (tail1, tail2) with
              ([], _) -> [["retVal"]] (* se una delle due code e' vuota... *)
           |  (_, []) -> [["retVal"]] (* ... l'intersezione e' vuota *)
           |  (_,  _) ->
               [head2 @
                (List.find_all
     	         (function t -> not (List.mem t head2))
	         head1
	        )
	       ] (* header del risultato finale *)
	       @
	       intersect_tails (List.tl head1) tail1 (List.tl head2) tail2
	       (*
	       List.fold_left
                (fun par1 elem1 -> par1 @
                 List.map
	          (fun elem2 ->
	           [(List.hd elem1)] @
	           (xres_join_context (List.tl head1) (List.tl elem1)
	                              (List.tl head2) (List.tl elem2)
                   )
	          )
                  (List.find_all (* *)
                   (fun elem2 ->    (* trova tutti gli elementi della lista tail2 *)
	            ((List.hd elem1) = (List.hd elem2)) && (* che stanno in tail1 *)
	            not ((xres_join_context (List.tl head1) (List.tl elem1)
		                            (List.tl head2) (List.tl elem2)) = [])
	            (* e per i quali la xres_join_context non sia vuota *)
	           )
                   tail2 (* List.find_all *)
	          )
                 )
               []
               tail1 (* per ogni elemento di tail1 applica la List.fold_left *)
	       *)
          ) (* match *)
     )
 | _ -> []
  in
   let _ = print_endline (string_of_float (Unix.time () -. t)); flush stdout in
    result
;;