1 files changed, 85 insertions, 0 deletions
diff --git a/src/xdg_pipe_menu_watcher.erl b/src/xdg_pipe_menu_watcher.erl
new file mode 100644
index 0000000..64fb2c6
--- /dev/null
+++ b/src/xdg_pipe_menu_watcher.erl
@@ -0,0 +1,85 @@
+%%%-------------------------------------------------------------------
+%% @doc Watches the XDG application directories for changes.
+%%
+%% Starts one `fs' (native inotify) watch per existing directory
+%% returned by `xdg_pipe_menu_scanner:data_dirs/0' and subscribes
+%% to its file events. On any event, a debounce timer is (re)started;
+%% once it fires with no further events in the window, the menu cache
+%% is invalidated so the next request gets a freshly rebuilt menu.
+%%
+%% `fs' watches recursively (it drives `inotifywait -r' on Linux), so
+%% changes in vendor subdirectories (e.g. `applications/kde4/*') are
+%% picked up without any extra handling here.
+%% @end
+%%%-------------------------------------------------------------------
+
+-module(xdg_pipe_menu_watcher).
+
+-behaviour(gen_server).
+
+-export([start_link/0]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+-define(DEFAULT_DEBOUNCE_MS, 500).
+
+-spec start_link() -> {ok, pid()}.
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+init([]) ->
+    warn_if_inotifywait_missing(),
+    Dirs = [D || D <- xdg_pipe_menu_scanner:data_dirs(), filelib:is_dir(D)],
+    lists:foreach(fun watch/1, lists:zip(lists:seq(1, length(Dirs)), Dirs)),
+    {ok, #{timer => undefined}}.
+
+watch({Index, Dir}) ->
+    Name = list_to_atom("xdg_pipe_menu_fs_" ++ integer_to_list(Index)),
+    case fs:start_link(Name, Dir) of
+        {ok, _Pid} -> fs:subscribe(Name);
+        {error, Reason} -> log_watch_failure(Dir, Reason)
+    end.
+
+%% `fs' on Linux shells out to the system `inotifywait' binary; if
+%% it's missing, `fs:start_link/2' still returns `{ok, _}' but simply
+%% never delivers events, which is otherwise silent.
+warn_if_inotifywait_missing() ->
+    case os:find_executable("inotifywait") of
+        false ->
+            error_logger:warning_msg(
+                "xdg_pipe_menu_watcher: 'inotifywait' not found on PATH "
+                "(install inotify-tools) -- desktop file changes won't be "
+                "picked up until the daemon is restarted~n",
+                []
+            );
+        _Path ->
+            ok
+    end.
+
+log_watch_failure(Dir, Reason) ->
+    error_logger:warning_msg(
+        "xdg_pipe_menu_watcher: failed to watch ~p: ~p~n", [Dir, Reason]
+    ).
+
+handle_call(_Request, _From, State) ->
+    {reply, ok, State}.
+
+handle_cast(_Msg, State) ->
+    {noreply, State}.
+
+handle_info({_Pid, {fs, file_event}, {_Path, _Events}}, State) ->
+    {noreply, reset_debounce(State)};
+handle_info(debounce_fire, State) ->
+    xdg_pipe_menu_cache:invalidate(),
+    {noreply, State#{timer => undefined}};
+handle_info(_Info, State) ->
+    {noreply, State}.
+
+reset_debounce(#{timer := Timer} = State) ->
+    case Timer of
+        undefined -> ok;
+        Ref -> erlang:cancel_timer(Ref)
+    end,
+    State#{timer => erlang:send_after(debounce_ms(), self(), debounce_fire)}.
+
+debounce_ms() ->
+    application:get_env(xdg_pipe_menu, debounce_ms, ?DEFAULT_DEBOUNCE_MS).