:- dynamic task/2.
:- dynamic requires/2.
:- dynamic idx/2.
:- discontiguous load/0.

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

print_task(X):-
    task(X,ISDONE), 
    write(ISDONE),
    write(': '), 
    write(X). 
print_task_list([],_).
print_task_list([H|T],N) :- 
    M is N+1,
    retractall(idx(N, _)),
    asserta(idx(N, H)),
    write(N),
    write(". "),
    print_task(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).
list :- all_tasks(L, todo), print_task_list(L,1).
list_done :- all_tasks(L, done), print_task_list(L,1).

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

new(X) :- 
    task(X, todo), 
    write("task already exist"),
    !.
new(X) :- 
    asserta(task(X, todo)), 
    write("added task "), 
    write(X).
new(X,Y) :- idx(Y, Task), new(X, Task).
new(X,Y) :- 
    asserta(task(X, todo)), 
    asserta(requires(X, Y)),
    uncheck(X), 
    write("added task "), 
    write(X),
    write(" as a subtask for "), 
    write(X).

delete(X):- idx(X,Y), delete(Y).
delete(X):-
    retractall(task(X,_)),
    retractall(requires(X,_)),
    retractall(requires(_,X)).
delete(X,Y):- idx(X,T), delete(T,Y).
delete(X,Y):- idx(Y,T), delete(X,T).
delete(X,Y):- retractall(requires(X,Y)).


depend(X,Y) :- idx(X, Task), depend(Task, Y).
depend(X,Y) :- idx(Y, Task), depend(X, Task).
depend(X,Y) :- 
    task(X, todo),
    task(Y, _),
    asserta(requires(X, Y)).
depend(X,Y) :- 
    task(X, done),
    task(Y, todo),
    uncheck(X).
depend(X,Y) :- 
    task(X, done),
    task(Y, done).

check(X) :- idx(X, Task), check(Task).
check(X) :- 
    task(X, todo), 
    \+ (requires(Y, X), task(Y,todo)),
    asserta(task(X, done)), 
    retractall(task(X, todo)), 
    write("marked "), 
    write(X), 
    write(" as done"),
    !.
check(X) :- 
    task(X, todo), 
    (requires(Y, X), task(Y,todo)),
    write("you need to do "), 
    write(Y), 
    write(" before doing "),
    write(X), 
    !.
check(X) :- 
    task(X, done),
    write("the task is already done "),
    !.
check(X) :- 
    \+ task(X, todo),
    write("no such task as "),
    write(X).

indent(0).
indent(N):- 
    write("   "),
    M is N-1,
    indent(M).

tree_branch([],_).
tree_branch([X|T],N):-
    indent(N),
    print_task(X),
    nl,
    findall(Y, requires(Y,X), L),
    M is N+1,
    tree_branch(L,M),
    tree_branch(T,N).
tree(X):- task(X,_), tree_branch([X],0).
tree(X):- idx(X,Y), tree(Y).

uncheck(X) :- idx(X, Task), uncheck(Task).
uncheck(X):-
    task(X, done),
    retractall(task(X, done)),
    asserta(task(X, todo)), 
    write("unchecked task: "),
    write(X),
    nl,
    findall(Parent, requires(X, Parent), L),
    uncheck_list(L).
uncheck_list([]).
uncheck_list([H|T]):-
    task(H, todo),
    uncheck_list(T).
uncheck_list([H|T]):-
    uncheck(H),
    uncheck_list(T).

save_requirement(T1, T2, Stream) :-
    requires(T1, T2),
    write_canonical(Stream, requires(T1,T2)),
    write(Stream, '.\n').
save_requirement_list(T2, [T1], Stream) :- 
    save_requirement(T1, T2, Stream).
save_requirement_list(T2,[H|T], Stream) :- 
    save_requirement(H, T2, Stream),
    save_requirement_list(T2, T, Stream).
save_task_requirements(Task, Stream) :- 
    findall(X, requires(X, Task), L),
    save_requirement_list(Task, L, Stream).
save_task_requirements(Task, _) :- \+ requires(_, Task).


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

save_task_list([Task], Stream) :- 
    save_task(Task, Stream).
save_task_list([H|T], Stream) :- 
    save_task(H, Stream),
    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,
%    write("reading: "),
%    write(Task),
%    nl,
    asserta(Task),
    load_task(Stream).

load_task(Stream) :- 
    read(Stream, Task),
    Task = end_of_file,
%    write("reading last: "),
%    write(Task),
    close(Stream).

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

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

load.