-module(cribbage).
 
-export([points/1]).
 
points([]) -> 0;
points(L) ->
    Hand = lists:sort(L),
    fifteens(Hand, 0) + runs(Hand, 0, 0) + pairs(Hand, 1, 0).

cardval(C) when C > 9 ->
    10;
cardval(C) ->
    C.

fifteens(_L, Total) when Total > 15 ->
    0;
fifteens(_Hand, Total) when Total =:= 15 ->
    2;
fifteens([], _Total) ->
    0;
fifteens([H | T], Total) when Total < 15 ->
    fifteens(T, Total) + fifteens(T, Total + cardval(H)).

run(3) ->
    3;
run(4) ->
    6;
run(5) ->
    12;
run(_Length) ->
    0.

%% two cases for runs
%%   1. A straight run - 4,5,6,7
%%   2. A run with a double in the sequence - 4,4,5,6 or 4,5,5,6
runs([], _Curr, Len) ->
    run(Len);
runs([H | T], Curr, Len) when H =:= (Curr+1) ->
    runs(T, H, Len + 1);
runs([H | T], Curr, Len) when H =:= Curr ->
    runs(T, Curr, Len, {H, 2});
runs([H | T], _Curr, Len) ->
    run(Len) + runs(T, H, 1).

runs([], _Curr, Len, {_Card, Mult}) ->
    Mult * run(Len);
runs([H | T], Curr, Len, {Card, Mult}) when H =:= (Curr+1) ->
    runs(T, H, (Len+1), {Card, Mult});
%% needed for special cases where multiple cards are doubled up
%% like 3,4,4,5,5
runs([H | T], Curr, Len, {Card, Mult}) when H =:= Curr, H > Card ->
    runs(T, Curr, Len, {H, (Mult*2)});
%% handles a triple carding, like 2,2,2,3,4
runs([H | T], Curr, Len, {Card, Mult}) when H =:= Curr ->
    runs(T, Curr, Len, {Card, (Mult+1)});
runs([H | T], _Curr, Len, {_Card, Mult}) ->
    (Mult * run(Len)) + runs(T, H, 1).

pairs([], Pairs, _Curr) ->
    pair(Pairs);
pairs([H | T], Pairs, Curr) when H =:= Curr ->
    pairs(T, Pairs+1, Curr);
pairs([H | T], Pairs, _Curr) ->
    pair(Pairs) + pairs(T, 1, H).
 
pair(2) ->
    2;
pair(3) ->
    6;
pair(4) ->
    12;
pair(_Length) ->
    0.