(* 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 UNION
 *)

(*
(*
 * 
 *)
let xres_fill_context hr h1 l1 =
 match l1 with
    [] -> []
 |   _ ->
     let hh = List.combine h1 l1
     in
      List.map
       (fun x ->
        if (List.mem_assoc x hh) then
	 List.assoc x hh
	else
	 ""
       )
       hr
;;

(*
 * implementazione del comando UNION
 *)
let union_ex alist1 alist2 =
 let head1 = List.hd alist1
 and tail1 = List.tl alist1
 and head2 = List.hd alist2
 and tail2 = List.tl alist2 (* e fin qui ... *)
 in
  match (head1, head2) with
     ([], _) -> assert false (* gli header non devono mai essere vuoti *)
  |  (_, []) -> assert false (* devono contenere almeno [retVal] *)
  |  (_,  _) -> let headr = (head2 @
                            (List.find_all
			     (function t -> not (List.mem t head2))
			     head1)
			    ) in (* header del risultato finale *)
      List.append (* il risultato finale e' la concatenazione ...*)
       [headr]             (* ... dell'header costruito prima ...*)
       (Sort.list
        (fun l m -> List.hd l < List.hd m)
        (match (tail1, tail2) with      (* e di una coda "unione" *)
            ([], _) -> tail2 (* va bene perche' l'altra lista e' vuota *)
         |  (_, []) -> tail1 (* va bene perche' l'altra lista e' vuota *)
         |  (_,  _) ->
	     let first = (* parte dell'unione che riguarda solo il primo set *)
	      List.map
	       (
	        fun l ->
	         [List.hd l] @
	         xres_fill_context (List.tl headr) (List.tl head1) (List.tl l)
	       )
	       tail1
             in
	      List.fold_left
	       (fun par x ->
	        let y = (* elemento candidato ad entrare *)
	         [List.hd x]
		 @
	         xres_fill_context
	          (List.tl headr) (List.tl head2) (List.tl x)
	        in
	         par @ if (List.find_all (fun t -> t = y) par) = [] then
		        [y]
		       else
		        []
	       )
	       first (* List.fold_left *)
	       tail2 (* List.fold_left *)
(*	     first @
	     List.map (fun l -> [List.hd l] @
	               xres_fill_context
	                (List.tl headr) (List.tl head2) (List.tl l)
		      ) tail2
*)
        ) (* match *)
       )
;;
*)

(* preserves order and gets rid of duplicates *)
let rec union_ex l1 l2 =
 let module S = Mathql_semantics in
  match (l1, l2) with
     [],l
   | l,[] -> l
   | ({S.uri = uri1} as entry1)::tl1,
     ({S.uri = uri2} as entry2)::_ when uri1 < uri2 ->
       entry1::(union_ex tl1 l2)
   | ({S.uri = uri1} as entry1)::_,
     ({S.uri = uri2} as entry2)::tl2 when uri2 < uri1 ->
       entry2::(union_ex l1 tl2)
   | entry1::tl1,entry2::tl2 -> (* same entry *)
      if entry1 = entry2 then (* same attributes *)
       entry1::(union_ex tl1 tl2)
      else
       assert false
;;

let union_ex l1 l2 =
 let before = Unix.time () in
 let res = union_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 ("UNION(" ^ ll1 ^ "," ^ ll2 ^ "): " ^ diff ^ "s") ;
  flush stdout ;
  res
;;