-module(clock).

-export([start/1, stop/0, join/0, leave/0]).

start(Period) ->
  Pid    = spawn(fun () -> loop(Period, subscription:start()) end),
  register(clock, Pid),
  {ok, Pid}.

join() ->
  subscription:subscribe(get_pid()),
  ok.

leave() ->
  subscription:unsubscribe(get_pid()),
  ok.

stop() ->
  Pid = whereis(clock),
  unregister(clock),
  Pid ! {quit},
  ok.

get_pid() ->
  clock ! {manager, self()},
  receive
    {clock_manager, Manager} -> Manager
    after 500 -> exit({clock, manager_down})
  end.

loop(Period, SubMan) ->
  receive
    {quit} ->
      subscription:stop(SubMan);
    {manager, Whom} ->
      Whom ! {clock_manager, SubMan},
      loop(Period, SubMan)
    after Period ->
      subscription:send(SubMan, tick),
      loop(Period, SubMan)
  end.