:- module test_hailstone.

:- interface.

:- import_module io.

:- pred main(io.state::di, io.state::uo) is det.

:- implementation.

:- import_module int, list.
:- import_module hailstone.

:- pred longest(int::in, int::out, int::out) is det.
:- pred longest(int::in, int::in, int::in, int::out, int::out) is det.

longest(M, N, L) :- longest(M, 0, 0, N, L).

longest(N, CN, CL, MN, ML) :-
  ( N > 1 ->
      L = list.length(hailstone(N)),
      ( L > CL -> longest(N - 1, N,  L,  MN, ML)
      ;           longest(N - 1, CN, CL, MN, ML) )
  ;   MN = CN, ML = CL ).


main(!IO) :-
  S = hailstone(27),
  ( list.length(S) = 112,
    list.append([27, 82, 41, 124], _, S),
    list.remove_suffix(S, [8, 4, 2, 1], _),
    longest(100000, 77031, 351) ->
      io.write_string("All tests succeeded.\n", !IO)
  ;   io.write_string("At least one test failed.\n", !IO) ).

:- end_module test_hailstone.