-module(fs_sup).

-behaviour(supervisor).

-export([start_link/4]).

-export([init/1]).

-define(CHILD(I, Type, Args),
        {I, {I, start_link, Args}, permanent, 5000, Type, [I]}).

start_link(SupName, EventHandler, FileHandler, Path) ->
    supervisor:start_link({local, SupName},
                          ?MODULE,
                          [EventHandler, FileHandler, Path]).

init([EventHandler, FileHandler, Path]) ->
    Backend = case os:type() of
                  {unix, darwin} -> fsevents;
                  {unix, linux} -> inotifywait;
                  {unix, sunos} -> undefined;
                  {unix, _} -> kqueue;
                  {win32, nt} -> inotifywait_win32;
                  _ -> undefined
              end,
    Children = case has_executable(Backend) of
                   false -> [];
                   true ->
                       [?CHILD(fs_server, worker,
                               [FileHandler, EventHandler, Backend, Path, Path])]
               end,
    {ok,
     {{one_for_one, 5, 10},
      Children ++
          [?CHILD(gen_event, worker, [{local, EventHandler}])]}}.

has_executable(undefined) ->
    os_not_supported(),
    false;
has_executable(Backend) ->
    case Backend:find_executable() of
        false ->
            backend_port_not_found(Backend),
            false;
        _ -> true
    end.

os_not_supported() ->
    logger:warning("fs does not support the current operating "
                   "system: auto-reloading might not work~n").

backend_port_not_found(Backend) ->
    logger:error("backend port not found: ~p~n", [Backend]).