% main routine
schedule(Schedule, FinTime):-
  tasks(TDs),
  constrain(TDs, Schedule, FinTime),
  minimize(FinTime).

% add basic constraints
constrain([], [], _).
constrain([T/D | TDs], [T/Start/D | Rest], FinTime):-
  { Start >= 0, Start + D =< FinTime },
  constrain(TDs, Rest, FinTime),
  prec_constr(T/Start/D, Rest).

% add precedence constraints
prec_constr(_, []).
prec_constr(T/S/D, [T1/S1/D1 | Rest]):-
  ( prec(T, T1), !, { S + D =< S1 }
    ;
    prec(T1, T), !, { S1 + D1 =< S }
    ;
    true ),
  prec_constr(T/S/D, Rest).



% podaj problem (opisi taske in podaj precedence)
tasks([t1/5, t2/7, t3/10, t4/2, t5/9]).
prec(t1, t2).
prec(t1, t4).
prec(t2, t3).
prec(t4, t5).