(*
    ||M||  This file is part of HELM, an Hypertextual, Electronic        
    ||A||  Library of Mathematics, developed at the Computer Science     
    ||T||  Department, University of Bologna, Italy.                     
    ||I||                                                                
    ||T||  HELM is free software; you can redistribute it and/or         
    ||A||  modify it under the terms of the GNU General Public License   
    \   /  version 2 or (at your option) any later version.      
     \ /   This software is distributed as is, NO WARRANTY.     
      V_______________________________________________________________ *)

(* $Id: nCicRefiner.mli 9227 2008-11-21 16:00:06Z tassi $ *)

module COT : Set.OrderedType with type t = NCic.term = 
  struct
        type t = NCic.term
        let compare = Pervasives.compare
  end

module HintSet = Set.Make(COT)

module DB = 
  Discrimination_tree.Make(NDiscriminationTree.NCicIndexable)(HintSet)

type db = DB.t

let dummy = NCic.Const (NReference.reference_of_string "cic:/dummy_conv.dec");;
let pair t1 t2 = (NCic.Appl [dummy;t1;t2]) ;;

let index_hint hdb context t1 t2 =
  assert (
    (match t1 with
    | NCic.Meta _ | NCic.Appl (NCic.Meta _ :: _) -> false | _ -> true)
    &&
    (match t2 with
    | NCic.Meta _ | NCic.Appl (NCic.Meta _ :: _) -> false | _ -> true)
  );
  let pair' = pair t1 t2 in
  let data = 
    List.fold_left 
     (fun t (n,e) -> 
        match e with
        | NCic.Decl ty -> NCic.Prod (n,ty,t)
        | _ -> assert false) 
      pair' context in
  let src = 
    List.fold_left 
     (fun t (_,e) -> 
        match e with
        | NCic.Decl _ -> 
            NCicSubstitution.subst (NCic.Meta (-1,(0,NCic.Irl 0))) t
        | _ -> assert false) 
     pair' context in
  DB.index hdb src data
;;

let empty_db = DB.empty ;;

let db () = 
  let _,_,_,x,_,_ = NCicEnvironment.get_checked_def
    (NReference.reference_of_string "cic:/matita/tests/pullback/xxx.def(0)")
  in
  let rec decontextualize ctx = function
    | NCic.Prod (n,s,t) -> decontextualize ((n,NCic.Decl s)::ctx) t
    | t -> ctx, t
  in
    match (decontextualize [] x) with
    | ctx, NCic.Appl [_;_;a;b] -> index_hint empty_db ctx a b
    | _ -> assert false
;;


let look_for_hint hdb metasenv subst context t1 t2 =
(*
  prerr_endline ("KEY1: "^NCicPp.ppterm ~metasenv ~subst ~context (pair t1 t2));
  prerr_endline ("KEY2: "^NCicPp.ppterm ~metasenv ~subst ~context (pair t2 t1));
  DB.iter hdb
   (fun p ds ->
      prerr_endline ("ENTRY: " ^
      NDiscriminationTree.NCicIndexable.string_of_path p ^ " |--> " ^
      String.concat "|" (List.map (NCicPp.ppterm ~metasenv:[] ~subst:[]
      ~context:[]) (HintSet.elements ds))));
*)
  let candidates1 = DB.retrieve_unifiables hdb (pair t1 t2) in
  let candidates2 = DB.retrieve_unifiables hdb (pair t2 t1) in
  let candidates1 = 
    List.map (fun ty -> 
       true,NCicMetaSubst.saturate ~delta:max_int metasenv subst context ty 0) 
    (HintSet.elements candidates1) 
  in
  let candidates2 = 
    List.map (fun ty -> 
       false,NCicMetaSubst.saturate ~delta:max_int metasenv subst context ty 0) 
    (HintSet.elements candidates2) 
  in
  List.map
   (function 
    | (true,(NCic.Appl [_; t1; t2],metasenv,_)) -> metasenv, t1, t2
    | (false,(NCic.Appl [_; t1; t2],metasenv,_)) -> metasenv, t2, t1
    | _ -> assert false)
   (candidates1 @ candidates2)
;;