-module(rps5).
-export([
    get_rules/0,
    beats/1, test_beats/0,
    loses/1, test_loses/0,
    winning_hand/1, test_winning_hand/0]).
get_rules() -> [rock, paper, scissors, spock, lizard].
beats(rock) ->
    [scissors, lizard];
beats(paper) ->
    [spock, rock];
beats(scissors) ->
    [lizard, paper];
beats(spock) ->
    [rock, scissors];
beats(lizard) ->
    [paper, spock].
loses(lizard) ->
    [scissors, rock];
loses(spock) ->
    [paper, lizard];
loses(scissors) ->
    [rock, spock];
loses(paper) ->
    [lizard, scissors];
loses(rock) ->
    [spock, paper].
test_beats() ->
    lists:foreach(
        fun(H) ->
            io:format("~w beats ~w.~n", [H, beats(H)])
        end,
        get_rules()).
test_loses() ->
    lists:foreach(
        fun(H) ->
            io:format("~w loses to ~w.~n", [H, loses(H)])
        end,
        get_rules()).
% winner for 3 hands is:
% rock, rock, rock      -> rock
% rock, paper, scissors -> undefined
% rock, paper, paper    -> paper
% rock, rock, paper     -> paper
winning_hand(Hands) ->
    HSet = sets:from_list(Hands),
    sets:fold(
        fun(Hand, Acc) ->
            Loses = loses(Hand),
            case sets:is_disjoint(sets:from_list(Loses), HSet) of
                true -> Hand;
                false -> Acc
            end
        end, undefined, HSet).
test_winning_hand() ->
    Exclude = fun(Hand) -> lists:delete(Hand, get_rules()) end,
    Cases = [
             [rock, rock, rock],
             [rock, paper, scissors],
             [rock, paper, paper],
             [rock, rock, paper]
             |lists:map(Exclude, get_rules())
            ],
    lists:foreach(
        fun(Hands) ->
            Winner = winning_hand(Hands),
            io:format("~w wins in ~w.~n", [Winner, Hands])
        end,
        Cases).