(* 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/.
 *)

(******************************************************************************)
(*                                                                            *)
(*                               PROJECT HELM                                 *)
(*                                                                            *)
(*                Claudio Sacerdoti Coen <sacerdot@cs.unibo.it>               *)
(*                                 24/01/2000                                 *)
(*                                                                            *)
(* This module implements a trival cache system (an hash-table) for cic       *)
(* objects. Uses the getter (getter.ml) and the parser (cicParser.ml)         *)
(*                                                                            *)
(******************************************************************************)

let cleanup_tmp = true;;

let trust_obj = function uri -> true;;

type type_checked_obj =
   CheckedObj of Cic.obj     (* cooked obj *)
 | UncheckedObj of Cic.obj   (* uncooked obj to proof-check *)
;;


exception AlreadyCooked of string;;
exception CircularDependency of string;;
exception CouldNotFreeze of string;;
exception CouldNotUnfreeze of string;;

(* Cache that uses == instead of = for testing equality *)
(* Invariant: an object is always in at most one of the *)
(* following states: unchecked, frozen and cooked.      *)
module Cache :
  sig
   val find_or_add_unchecked :
    UriManager.uri -> get_object_to_add:(unit -> Cic.obj) -> Cic.obj
   val unchecked_to_frozen : UriManager.uri -> unit
   val frozen_to_cooked :
    uri:UriManager.uri -> unit
   val find_cooked : key:UriManager.uri -> Cic.obj
   val add_cooked : key:UriManager.uri -> Cic.obj -> unit
  end 
=
  struct
   module CacheOfCookedObjects :
    sig
     val mem  : UriManager.uri -> bool
     val find : UriManager.uri -> Cic.obj
     val add  : UriManager.uri -> Cic.obj -> unit
    end
   =
    struct
     module HashedType =
      struct
       type t = UriManager.uri
       let equal = UriManager.eq
       let hash = Hashtbl.hash
      end
     ;;
     module HT = Hashtbl.Make(HashedType);;
     let hashtable = HT.create 1009;;
     let mem uri =
      try
       HT.mem hashtable uri
      with
       Not_found -> false
     ;;
     let find uri = HT.find hashtable uri
     ;;
     let add uri obj =
      HT.add hashtable uri obj
     ;;
    end
   ;;
   let frozen_list = ref [];;
   let unchecked_list = ref [];;

   let find_or_add_unchecked uri ~get_object_to_add =
    try
     List.assq uri !unchecked_list
    with
     Not_found ->
      if List.mem_assq uri !frozen_list then
       raise (CircularDependency (UriManager.string_of_uri uri))
      else
       if CacheOfCookedObjects.mem uri then
        raise (AlreadyCooked (UriManager.string_of_uri uri))
       else
        (* OK, it is not already frozen nor cooked *)
        let obj = get_object_to_add () in
         unchecked_list := (uri,obj)::!unchecked_list ;
         obj
   ;;
   let unchecked_to_frozen uri =
    try
     let obj = List.assq uri !unchecked_list in
      unchecked_list := List.remove_assq uri !unchecked_list ;
      frozen_list := (uri,obj)::!frozen_list
    with
     Not_found -> raise (CouldNotFreeze (UriManager.string_of_uri uri))
   ;;
   let frozen_to_cooked ~uri =
    try
     let obj = List.assq uri !frozen_list in
      frozen_list := List.remove_assq uri !frozen_list ;
       CacheOfCookedObjects.add uri obj
    with
     Not_found -> raise (CouldNotUnfreeze (UriManager.string_of_uri uri))
   ;;
   let find_cooked ~key:uri = CacheOfCookedObjects.find uri;;
   let add_cooked ~key:uri obj = CacheOfCookedObjects.add uri obj;;
  end
;;

let find_or_add_unchecked_to_cache uri =
 Cache.find_or_add_unchecked uri
  ~get_object_to_add:
   (function () ->
     let filename = Getter.getxml uri in
     let bodyfilename =
      match UriManager.bodyuri_of_uri uri with
         None -> None
       | Some bodyuri ->
          try
           ignore (Getter.resolve bodyuri) ;
           (* The body exists ==> it is not an axiom *)
           Some (Getter.getxml bodyuri)
          with
           Getter.Unresolved ->
            (* The body does not exist ==> we consider it an axiom *)
            None
     in
      let obj = CicParser.obj_of_xml filename bodyfilename in
       if cleanup_tmp then
        begin
         Unix.unlink filename ;
         match bodyfilename with
            Some f -> Unix.unlink f
          | None -> ()
        end ;
       obj
   )
;;

(* set_type_checking_info uri                               *)
(* must be called once the type-checking of uri is finished *)
(* The object whose uri is uri is unfreezed                 *)
let set_type_checking_info uri =
 Cache.frozen_to_cooked uri
;;

(* is_type_checked uri                                                *)
(* CSC: commento falso ed obsoleto *)
(* returns a CheckedObj if the term has been type-checked             *)
(* otherwise it freezes the term for type-checking and returns
 it *)
(* set_type_checking_info must be called to unfreeze the term         *)
let is_type_checked ?(trust=true) uri =
 try
  CheckedObj (Cache.find_cooked uri)
 with
  Not_found ->
   let obj = find_or_add_unchecked_to_cache uri in
    Cache.unchecked_to_frozen uri ;
    if trust && trust_obj uri then
     begin
      Logger.log (`Trusting uri) ;
      set_type_checking_info uri ;
      CheckedObj (Cache.find_cooked uri)
     end
    else
     UncheckedObj obj
;;

(* get_cooked_obj ~trust uri *)
(* returns the object if it is already type-checked or if it can be *)
(* trusted (if [trust] = true and the trusting function accepts it) *)
(* Otherwise it raises Not_found                                    *)
let get_cooked_obj ?(trust=true) uri =
 try
  Cache.find_cooked uri
 with Not_found ->
  if trust && trust_obj uri then
   begin
    match is_type_checked uri with
       CheckedObj obj -> obj
     | _ -> assert false
   end
  else
   begin
    prerr_endline ("@@@ OOOOOOOPS: get_cooked_obj(" ^ UriManager.string_of_uri uri ^ ") raises Not_found since the object is not type-checked nor trusted.") ;
    raise Not_found
   end
;;

(* get_obj uri                                                                *)
(* returns the cic object whose uri is uri. If the term is not just in cache, *)
(* then it is parsed via CicParser.term_of_xml from the file whose name is    *)
(* the result of Getter.getxml uri                                            *)
let get_obj uri =
 try
  get_cooked_obj uri
 with
  Not_found ->
   find_or_add_unchecked_to_cache uri
;; 

exception OnlyPutOfInductiveDefinitionsIsAllowed

let put_inductive_definition uri obj =
 match obj with
    Cic.InductiveDefinition _ -> Cache.add_cooked uri obj
  | _ -> raise OnlyPutOfInductiveDefinitionsIsAllowed
;;