Change API so it works when a midnight boundary is crossed.

Emakefile

@@ -1,4 +1,4 @@
-%% Erlang Makefile for the reminders app
+%% Erlang Makefile for the wake-app.
 
 {'src/*', [debug_info,
            {i, "src"},

README.md

@@ -12,9 +12,9 @@ I currently use it to start the radio playing for an hour each morning.
 
 ``` erlang
 % Start playing SBS Radio 2 at 8am every morning, until 9am.
-{ok, Pid} = daily_event:start_link("open 'radium://tune-in/?h=&b=sbs&c=2&'",
+{ok, Pid} = daily_task:start_link("open 'radium://tune-in/?h=&b=sbs&c=2&'",
                                    {8,0,0},
-                                   {9,0,0}).
+                                   3600).
 ```
 
 ## License & Copyright

src/daily_task.erl

@@ -0,0 +1,61 @@
+%% @doc Runs a command at the same time every day.
+
+-module(daily_task).
+
+-export([start/3,
+         start_link/3]).
+
+-record(task, {cmd,
+               start_at,
+               duration=60000,
+               state=wait}).
+
+%% -- public api
+
+%% @doc Start the task server standalone.
+%%
+%% @spec start(Cmd, {H,M,S}, Duration) -> {ok, Pid}.
+%% @spec start("say 'Wakey Wakey!'", {6,0,0}, 30) -> {ok, Pid}.
+start(Cmd, Start = {_, _, _}, Duration) ->
+  {ok, spawn(fun() -> loop(make_task(Cmd, Start, Duration)) end)}.
+
+%% @doc Start the task server.
+%%
+%% Cmd is the shell command to run.
+%% {H,M,S} represents the time at which it should run.
+%% Duration is the number of seconds the task should run for.
+%%
+%% @spec start_link(Cmd, {H,M,S}, Duration) -> {ok, Pid}.
+%% @spec start_link("say 'Wakey Wakey!'", {6,0,0}, 30) -> {ok, Pid}.
+start_link(Cmd, Start = {_, _, _}, Duration) ->
+  {ok, spawn_link(fun() -> loop(make_task(Cmd, Start, Duration)) end)}.
+
+%% -- private api
+
+loop(Task = #task{state=wait}) ->
+  case within_run_window(calendar:local_time(), Task) of
+    true ->
+      io:format("Running `~s'~n", [Task#task.cmd]),
+      os:cmd(Task#task.cmd),
+      loop(Task#task{state=running});
+    false ->
+      timer:sleep(1000),
+      loop(Task)
+  end;
+loop(Task = #task{state=running}) ->
+  case within_run_window(calendar:local_time(), Task) of
+    true ->
+      timer:sleep(1000),
+      loop(Task);
+    false ->
+      io:format("Stopping `~s'~n", [Task#task.cmd]),
+      loop(Task#task{state=wait})
+  end.
+
+make_task(Cmd, {H,M,S}, Duration) ->
+  #task{cmd=Cmd, state=wait, start_at={H,M,S}, duration=Duration}.
+
+within_run_window({Date, Time}, #task{start_at={H, M, S}, duration=Duration}) ->
+  Now   = calendar:datetime_to_gregorian_seconds({Date, Time}),
+  Start = calendar:datetime_to_gregorian_seconds({Date, {H, M, S}}),
+  Now >= Start andalso Now < Start + Duration.