(* 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/.
 *)

exception NotCompatible;;

(* intersect_attributes is successful iff there is no attribute with *)
(* two different values in the two lists. The returned list is the   *)
(* union of the two lists.                                           *)
let rec intersect_attributes (attr1, attr2) =
 match attr1, attr2 with
    [],_ -> attr2
  | _,[] -> attr1
  | (key1,value1)::tl1, (key2,_)::_ when key1 < key2 ->
      (key1,value1)::(intersect_attributes (tl1,attr2))
  | (key1,_)::_, (key2,value2)::tl2 when key2 < key1 ->
      (key2,value2)::(intersect_attributes (attr1,tl2))
  | entry1::tl1, entry2::tl2 when entry1 = entry2 ->
     entry1::(intersect_attributes (tl1,tl2))
  | _, _ -> raise NotCompatible  (* same keys, different values *)
;;

(* preserves order and gets rid of duplicates *)
let rec intersect_ex l1 l2 =
 let module S = Mathql_semantics in
  match (l1, l2) with
     [],_
   | _,[] -> []
   | {S.uri = uri1}::tl1,
     {S.uri = uri2}::_ when uri1 < uri2 -> intersect_ex tl1 l2
   | {S.uri = uri1}::_,
     {S.uri = uri2}::tl2 when uri2 < uri1 -> intersect_ex l1 tl2
   | {S.uri = uri1 ; S.attributes = attributes1}::tl1,
     {S.uri = uri2 ; S.attributes = attributes2}::tl2 ->
       try
        let attributes' = intersect_attributes (attributes1,attributes2) in
         {S.uri = uri1 ; S.attributes = attributes' ; S.extra = ""}::(intersect_ex tl1 tl2)
       with
        NotCompatible ->
         intersect_ex tl1 tl2
;;

let intersect_ex l1 l2 =
 (* PRE-CLAUDIO
 (*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*)
 let before = Unix.time () in
 let res = intersect_ex l1 l2 in
 let after = Unix.time () in
  let ll1 = string_of_int (List.length l1) in
  let ll2 = string_of_int (List.length l2) in
  let diff = string_of_float (after -. before) in
  print_endline
   ("INTERSECT(" ^ ll1 ^ "," ^ ll2 ^ ") = " ^ string_of_int (List.length res) ^
    ": " ^ diff ^ "s") ;
  flush stdout ;
  res
;;