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/* Part of DML (Digital Music Laboratory)
	Copyright 2014-2015 Samer Abdallah, University of London
	 
	This program 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.

	This program 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 this library; if not, write to the Free Software
	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

:- module(jpath, [ jpath/2, op(600,xfy,#) ]).
:- use_module(library(dcg_core)).
:- use_module(library(insist)).

% :- op(600,fx,#).
:- op(600,xfy,#).

% harvest(M,Tree) :- harvest(M,just(Tree),nothing).
% harvest(\X,just(X),nothing).
% harvest(@F,just(X),just(Y)) :- Y=X.F.
% harvest(#N,just(X),just(Y)) :- nth1(N,X,Y).
% harvest(F*G) --> harvest(F), harvest(G).
% harvest((F//G)) --> harvest(F) // harvest(G).

% dec(id,X,X).
% dec([],_,[]).
% dec([D|Ds],X,[Y|Ys]) :- dec(D,X,Y), dec(Ds,X,Ys).
% dec(@F,X,Y) :- Y=X.F.
% dec(F*G,X,Z) :- dec(F,X,Y), dec(G,Y,Z).
% dec(swap,(X,Y),(Y,X)).
% dec(dup,X,(X,X)).
% dec(fst(F),(X,Y),(Z,Y)) :- dec(F,X,Z).
% dec((F,G),X,(Y,Z)) :- dec(F,X,Y), dec(G,X,Z).
% dec(item,X,Y) :- member(Y,X).

% decode(F, R, X) :- atomic(F), X=R.F.
% decode(item(D), R, X) :- decode(D,R,Y), member(X,Y).
% decode(F/G, R, X) :- decode(F,R,Y), decode(G,Y,X).

jpath(Y,X) :- 
   (complex(X) -> (match(Y,X); Y=(_,_), multi_match(Y,[],X)) ; Y=X).

complex(X) :- is_list(X).
complex(X) :- is_dict(X).

match(\X,X).
match(Y,X) :- var(Y), !, 
   (  is_dict(X) -> match_dict(Y,X)
   ;  is_list(X) -> match_list(Y,X)
   ).
match(dict(X),X) :- must_be(dict,X).
match(list(X),X) :- must_be(list,X).
match(N#Y,X) :- must_be(list,X), match_member(N,Y,X).
match(F:Y,X) :- must_be(dict,X), match_field(F,Y,X).

match_dict(dict(X),X).
match_dict(F:V,X) :- match_field(F,V,X).

match_list(list(X),X).
match_list(N#Y,X) :- match_member(N,Y,X).

match_field(F,Y,X) :- 
   (  var(F) -> get_dict(F,X,Z)
   ;  insist(get_dict(F,X,Z),field_not_present(F,X))
   ), 
   jpath(Y,Z).

match_member(N,Y,X) :- 
   (  var(N) -> nth1(N,X,Z)
   ;  nth1(N,X,Z) % insist(...),index_out_of_range(N,X))
   ),
   jpath(Y,Z).

% multi_match([],_,_).
% multi_match([S|Ss],Prev,X) :- match1(S,X), \+member(S,Prev), multi_match(Ss,[S|Prev],X).
multi_match(S,Prev,X) :- match(S,X), \+member(S,Prev).
multi_match((S,Ss),Prev,X) :- match(S,X), \+member(S,Prev), multi_match(Ss,[S|Prev],X).