(* Title:  MathEngine/step.sml

    Author: Walther Neuper 2019

    (c) due to copyright terms

 Unify function of structure Step_Specify and structure Step_Solve

 as well as of structure Specify_Step and structure Solve_Step.

 *)

 signature STEP =

 sig

   val do_next: Pos.pos' -> Calc.state_pre -> string * Calc.state_post

   val by_tactic: Tactic.input -> Calc.T -> string * Calc.state_post

 (*val by_term  = Step_Solve.by_term: Calc.T -> term -> string * Calc.state_post NOT for specify*)

   val check: Tactic.input -> Calc.T -> Applicable.T

   val add: Tactic.T -> Istate_Def.T * Proof.context -> Calc.T -> Test_Out.T

   val inconsistent: Subst.input option * ThmC.T -> term -> Istate_Def.T * Proof.context ->

     Pos.pos' -> Ctree.ctree -> Calc.T

 \<^isac_test>\<open>

   val specify_do_next: Calc.T -> string * Calc.state_post

   val switch_specify_solve: Pos.pos_ -> Calc.T -> string * Calc.state_post

 \<close>

 end

 (**)

 structure Step(**): STEP(**) =

 struct

 (**)

 (** check a tactic for applicability **)

 fun check tac (ctree, pos) =

   if Tactic.for_specify tac

   then Specify_Step.check tac (ctree, pos)

   else Solve_Step.check tac (ctree, pos);

 (** add a step to a calculation **)

 val add = Solve_Step.add_general;

 (* survey on results of by_tactic, find_next, by_term:

    * Step_Specify

      * by_tactic "ok", "ok", 

    * Step_Solve              

      * locate_input_tactic  : "ok", "unsafe-ok", "not-applicable", "end-of-calculation"

      * locate_input_term : "ok", "syntax error", "same-formula", "no derivation found",

         "error pattern #" ^ errpatID (the latter doesn't fit into the pattern of fixed string)

      * find_next_formula    : "ok", "helpless", "no-fmz-spec"(=helpless), "end-of-calculation"

  *)

 (** do a next step **)

 fun specify_do_next (ptp as (pt, (p, p_))) =

   let

     val (_, (p_', tac)) = Specify.find_next_step ptp

     val ist_ctxt =  Ctree.get_loc pt (p, p_)

   in

     case tac of

   	  Tactic.Apply_Method mI =>

   	    (*vvvvvvvvvv-------------------------------------------------------------- solve-phase *)

   	    LI.by_tactic (Tactic.Apply_Method' (mI, NONE, Istate.empty, ContextC.empty))

   	      ist_ctxt (pt, (p, p_'))

     | _ => Step_Specify.by_tactic_input  tac (pt, (p, p_'))

   end

 fun switch_specify_solve state_pos (pt, input_pos) =

   let

     val result =

       if Pos.on_specification ([], state_pos)

   	  then specify_do_next (pt, input_pos)

       else LI.do_next (pt, input_pos)

   in

     case result of

     (*unclean alternatives*)

       scs as ("ok", _) => scs

     | (_, cs as ([], _, _)) => ("helpless", cs)

     | _ => raise ERROR "switch_specify_solve: uncovered case in fun.def."

   end

 (* does a step forward; returns tactic used, ctree updated (i.e. with NEW term/calchead) *)

 fun do_next (ip as (_, p_)) (ptp as (pt, p), tacis) =

   if Pos.on_calc_end ip then

     ("end-of-calculation", (tacis, [], ptp): Calc.state_post) 

   else

     let

       val (_, probl_id, _) = Calc.references (pt, p);

     in

       case tacis of

         (_ :: _) => 

           if ip = p (*the request is done where ptp waits for*) then                 

             let     (*spurious -------------vvvvvvvvvvvvvv*)

               val (pt', c', p') = Solve_Step.s_add_general tacis (pt, [], p)

             in

              ("ok", (tacis, c', (pt', p')))

             end

          else

             switch_specify_solve p_ (pt, ip)

       | _ =>

         if probl_id = Problem.id_empty then

            ("no-fmz-spec", ([], [], ptp))

         else switch_specify_solve p_ (pt, ip)

     end;

 (** locate an input tactic **)

 (* LEGACY: report of tacs' applicability in tacis; pt is dropped in setNextTactic*)

 fun by_tactic _ (ptp as (_, ([], Pos.Res))) = ("end-of-calculation", ([], [], ptp))

   | by_tactic tac (ptp as (pt, p)) =

     case check tac (pt, p) of

 	    Applicable.No _ => ("not-applicable", ([],[],  ptp): Calc.state_post)

 	  | Applicable.Yes tac' =>

 	    if Tactic.for_specify' tac'

 	    then Step_Specify.by_tactic tac' ptp

 	    else Step_Solve.by_tactic tac' ptp

 (** add an inconsisten step **)

 fun inconsistent (subs_opt, thm') f' (is, ctxt) (pos as (p,_)) pt =

   let

     val f = Ctree.get_curr_formula (pt, pos)

     val pos' as (p', _) = (Pos.lev_on p, Pos.Res)

     val (pt, _) = case subs_opt of

       NONE => Ctree.cappend_atomic pt p' (is, ctxt) f

         (Tactic.Rewrite thm') (f', []) Ctree.Inconsistent

     | SOME subs => Ctree.cappend_atomic pt p' (is, ctxt) f

         (Tactic.Rewrite_Inst (subs, thm')) (f', []) Ctree.Inconsistent

     val pt = Ctree.update_branch pt p' Ctree.TransitiveB

   in (pt, pos') end

 (**)end(**)