:- dynamic task/2.
:- dynamic requires/2.
:- dynamic idx/2.
:- discontiguous load/0.
    
task_input(X, Y) :- task(X, Y).
task_input(X, Y) :- idx(X, Task), task(Task, Y).

all_tasks(L):- findall(X, task(X, _), L).
all_tasks(L, STATE):- findall(X, task(X, STATE), L).


print_task_list([],_).
print_task_list([H|T],N) :- 
    M is N+1,
    retractall(idx(N, _)),
    asserta(idx(N, H)),
    write(N),
    write(". "),
    task(H,ISDONE), 
    write(ISDONE),
    write(': '), 
    write(H),nl, 
    print_task_list(T, M).

list_all :- all_tasks(L), print_task_list(L,1).
list_all :- all_tasks(L), print_task_list(L,1).

print_list([]).
print_list([H|T]) :- write(H),nl, print_list(T).

new(X) :- asserta(task(X, todo)), write("added task "), 
write(X).
check(X) :- task(X, todo), asserta(task(X, done)), retractall(task(X, todo)), 
write("marked task "), write(X), write(" as done").


save_task(Task, Stream) :-
    task(Task, State),
    write_canonical(Stream, task(Task, State)),
    write(Stream, '.').

save_task_list([Task], Stream) :- 
    save_task(Task, Stream).

save_task_list([H|T], Stream) :- 
    save_task(H, Stream),
    write(Stream, '\n'),
    save_task_list(T, Stream).

save :-
    all_tasks(L), 
    open('data.pl', write, Stream), 
    save_task_list(L, Stream),
    close(Stream).


load_task(Stream) :- 
    read(Stream, Task),
    Task = end_of_file,
    close(Stream).

load_task(Stream) :- 
    read(Stream, Task),
    write("reading: "),
    write(Task),
    nl,
    asserta(Task),
    load_task(Stream).

load :-
    open('data.pl', read, Stream),
    load_task(Stream).

clear :- retractall(task(_, _)).

consult(data).