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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(dataset, 
      [  dataset/5 
      ,  dataset_size/2
      ,  dataset_query/2
      ,  dataset_query_dv/3
      ,  dataset_item/2
      ,  dataset_items/2
      ,  dataset_query_id/3
      ,  random_subset/4
      ]).

/** <module> Definition and memoising of datasets */

:- use_module(library(memo)).
:- use_module(library(semweb/rdf_db)).
:- use_module(library(sandbox)).
:- use_module(library(typedef)).

:- type natural == nonneg.
:- persistent_memo dataset(+class:ground,+dbv:ground,-id:ground,-size:natural, -items:list).
:- persistent_memo term_hash_id(+object:any, +hash:atom, -id:atom).
:- persistent_memo random_subset( +domain:nonneg, +size:nonneg, +index:nonneg, -set:list(nonneg)).

random_subset(N,K,_,Indices) :- randset(K,N,Indices).


:- initialization memo_attach(memo(datasets),[]).

:- meta_predicate dataset(1,+,-,-,-), dataset_query_id(1,+,-).

sandbox:safe_meta(dataset(G,_,_,_,_),[G]).
sandbox:safe_meta(dataset_query_id(G,_,_),[G]).

%% dataset( +Generator:pred(A), +DBVersion, -ID:atom, -Size:natural, -Items:list(A)) is det.
%
%  Note: Generator must be ground.
dataset(Generator,_,ID,Size,Items) :-
   setof(X, call(Generator,X), Items),
   length(Items,Size),
   variant_sha1(Items,Hash),
   term_hash_id(Items,Hash,ID).

term_hash_id(X,Hash,ID) :-
   (  browse(term_hash_id(X,Hash,ID)) -> true % makes it safe to call in compute mode
   ;  (ID=Hash; between(1,100,I), variant_sha1(Hash-I,ID)),
      \+browse(term_hash_id(_,_,ID))
   ;  throw(unable_to_unique_id(X))
   ).
   


%% dataset_query_id(+Query:class,+DBVersion:ground,-ID:ground) is det.
%  Get ID for given query and database version. If this query has been
%  requested before, the previously generated ID will be unified with ID.
%  Otherwise, a new ID will be created and the list of items stored in
%  the persistent Prolog database. An empty dataset results in an
%  exception.
dataset_query_id(Q,V,ID) :- 
   dif(Status,fail),
   memo(dataset(Q,V,ID,_,_),_-Status).

%% dataset_size(-ID:ground,-Size:natural) is nondet.
%% dataset_size(+ID:ground,-Size:natural) is semidet.
%  True when Size is the number of items in existing dataset with id ID.  
dataset_size(ID,Size) :- distinct(current_dataset(ID,Size,_)).

%% dataset_items(-ID,-Items:list) is nondet.
%% dataset_items(+ID,-Items:list) is semidet.
%  True when Items is the list of items in existing dataset with id ID.  
dataset_items(ID,Items) :- distinct(current_dataset(ID,_,Items)).

%% dataset_item(-ID,-Item) is nondet.
%% dataset_item(+ID,-Item) is nondet.
%  True when dataset ID contains Item.
dataset_item(ID,Item) :- dataset_items(ID,Items), member(Item,Items).

%% dataset_query(-ID,-Query) is nondet.
%% dataset_query(+ID,-Query) is nondet.
%  True when dataset ID contains Item.
dataset_query(ID,Q) :- browse(dataset(Q,_,ID,_,_)).

%% dataset_query_dv(-ID,-Query,-DV) is nondet.
%% dataset_query_dv(+ID,-Query,-DV) is nondet.
%  True when dataset ID contains Item.
dataset_query_dv(ID,Q,DV) :- browse(dataset(Q,DV,ID,_,_)).

current_dataset(ID,Size,Items) :- browse(dataset(_,_,ID,Size,Items)).