:- module day4.
:- interface.
:- import_module basics.

:- pred run(part::in, lines::in, answer::out) is cc_multi.

:- pred number(int::out, chars::in, chars::out) is semidet.

:- implementation.
:- import_module int.
:- import_module char.
:- import_module string.
:- import_module list.

:- type ranges ---> r(int, int, int, int).

number(N) --> digits(S), {to_int(from_char_list(S), N)}.

:- pred digits(chars::out, chars::in, chars::out) is semidet.
digits([C | Cs]) -->
  [C], {is_digit(C)},
  (if digits(Cs2) then {Cs = Cs2} else {Cs = []}).


:- pred int_pair(int::out, int::out, chars::in, chars::out) is semidet.
int_pair(A, B) --> number(A), ['-'], number(B).

:- pred ranges(ranges::out, chars::in, chars::out) is semidet.
ranges(r(A, B, C, D)) --> int_pair(A, B), [','], int_pair(C, D).

:- pred ranges(string::in, ranges::out) is det.
ranges(Str, R) :-
  if ranges(R2, to_char_list(Str), []) then R = R2
  else die("invalid line: ""%s""", [s(Str)]).


:- pred all_overlap(ranges::in) is semidet.
all_overlap(r(A, B, C, D)) :- C >= A, D =< B ; D >= B, C =< A.

:- pred any_overlap(ranges::in) is semidet.
any_overlap(r(A, B, C, D)) :- A =< C, B >= C ; C =< A, D >= A.


:- pred go(pred(ranges)::(pred(in) is semidet), lines::in, int::out) is det.
go(P, Lines, Out) :-
  map(ranges, Lines, Ranges),
  filter(P, Ranges, Overlaps),
  length(Overlaps, Out).


:- pragma no_determinism_warning(run/3).
run(one, Lines, int(Out)) :- go(all_overlap, Lines, Out).
run(two, Lines, int(Out)) :- go(any_overlap, Lines, Out).