-module(conway).
-export([mochiweb_request/1, start/1, handle_request/2]).

start(PortString) ->
    %{Port, _} = string:to_integer(PortString),
    Port = 3001,
    mochiweb_http:start([{port, Port}, {loop, {?MODULE, mochiweb_request}}]), receive stop -> stop end.

% http://www.trapexit.org/String_join_with
string_join(Items, Sep)               -> lists:flatten(lists:reverse(string_join1(Items, Sep, []))).
string_join1([Head | []], _Sep, Acc)  -> [Head | Acc];
string_join1([Head | Tail], Sep, Acc) -> string_join1(Tail, Sep, [Sep, Head | Acc]).

random_matrix(XSize, YSize) ->
    array:from_list([random:uniform(2)-1 ||  _ <- lists:seq(1, XSize*YSize)]).

neighbor_count(CellPos, Matrix, SX, SY) ->
    X = CellPos rem SX,
    Y = erlang:trunc(CellPos/SX),

    % http://ejohn.org/apps/processing.js/examples/topics/conway.html
    lists:sum(
      [
       array:get((X + 1) rem SX      + (Y)*SX,                   Matrix),
       array:get((X)                 + ((Y + 1) rem SY)*SX,      Matrix),
       array:get((X + SX - 1) rem SX + (Y)*SX,                   Matrix),
       array:get((X)                 + ((Y + SY - 1) rem SY)*SX, Matrix),
       array:get((X + 1) rem SX      + ((Y + 1) rem SY)*SX,      Matrix),
       array:get((X + SX - 1) rem SX + ((Y + 1) rem SY)*SX,      Matrix),
       array:get((X + SX - 1) rem SX + ((Y + SY - 1) rem SY)*SX, Matrix),
       array:get((X + 1) rem SX      + ((Y + SY - 1) rem SY)*SX, Matrix)
    ]).

cell_status(2, S) -> S;
cell_status(3, _) -> 1;
cell_status(_, _) -> 0.

next_cell(CellPos, CellState, Matrix, SX, SY) ->
    Neighbors = neighbor_count(CellPos, Matrix, SX, SY),
    cell_status(Neighbors, CellState).

next_iteration(Matrix, SX, SY) ->
    array:map(fun (N, Z) -> next_cell(N, Z, Matrix, SX, SY) end, Matrix).

state_to_symbol(0) -> " ";
state_to_symbol(1) -> "#";
state_to_symbol(2) -> " \n";
state_to_symbol(3) -> "#\n".

handle_request(Req, Path) ->
     SX = 80, % size x of conway grid
     SY = 40, % size y of conway grid
     case Path of
         "/_reset" ->
             Matrix = random_matrix(SX, SY),
             put(matrix, Matrix),
             Req:ok({"text/plain", "Reset OK."});
         _ ->
             OldMatrix = get(matrix),
             Matrix = case OldMatrix of
                 undefined ->
                     random_matrix(SX, SY);
                 _ ->
                     next_iteration(OldMatrix, SX, SY)
             end,
             put(matrix, Matrix),
             % print newlines when we're at a right-edge
             PrettyGrid = array:to_list(array:map(
                                            fun (N, Cell) when N rem SX == 0, N =/= 0 -> state_to_symbol(Cell+2);
                                                (N, Cell) -> state_to_symbol(Cell) end, Matrix)
                                         ),
             Req:ok({"text/plain", PrettyGrid ++ "\n"})
     end.

mochiweb_request(Req) ->
     {Path, _, _} = mochiweb_util:urlsplit_path(Req:get(raw_path)),
     handle_request(Req, Path).