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%% @author Matthew Dempsky <matthew@mochimedia.com>

%% @copyright 2007 Mochi Media, Inc.

%%

%% Permission is hereby granted, free of charge, to any person obtaining a

%% copy of this software and associated documentation files (the "Software"),

%% to deal in the Software without restriction, including without limitation

%% the rights to use, copy, modify, merge, publish, distribute, sublicense,

%% and/or sell copies of the Software, and to permit persons to whom the

%% Software is furnished to do so, subject to the following conditions:

%%

%% The above copyright notice and this permission notice shall be included in

%% all copies or substantial portions of the Software.

%%

%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

%% THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

%% FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

%% DEALINGS IN THE SOFTWARE.

%% @doc Erlang module for automatically reloading modified modules

%% during development.

-module(reloader).

-author("Matthew Dempsky <matthew@mochimedia.com>").

-include_lib("kernel/include/file.hrl").

-behaviour(gen_server).

-export([start/0, start_link/0]).

-export([stop/0]).

-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

-export([all_changed/0]).

-export([is_changed/1]).

-export([reload_modules/1]).

-record(state, {last, tref}).

%% External API

%% @spec start() -> ServerRet

%% @doc Start the reloader.

start() ->

    gen_server:start({local, ?MODULE}, ?MODULE, [], []).

%% @spec start_link() -> ServerRet

%% @doc Start the reloader.

start_link() ->

    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

%% @spec stop() -> ok

%% @doc Stop the reloader.

stop() ->

    gen_server:call(?MODULE, stop).

%% gen_server callbacks

%% @spec init([]) -> {ok, State}

%% @doc gen_server init, opens the server in an initial state.

init([]) ->

    {ok, TRef} = timer:send_interval(timer:seconds(1), doit),

    {ok, #state{last = stamp(), tref = TRef}}.

%% @spec handle_call(Args, From, State) -> tuple()

%% @doc gen_server callback.

handle_call(stop, _From, State) ->

    {stop, shutdown, stopped, State};

handle_call(_Req, _From, State) ->

    {reply, {error, badrequest}, State}.

%% @spec handle_cast(Cast, State) -> tuple()

%% @doc gen_server callback.

handle_cast(_Req, State) ->

    {noreply, State}.

%% @spec handle_info(Info, State) -> tuple()

%% @doc gen_server callback.

handle_info(doit, State) ->

    Now = stamp(),

    _ = doit(State#state.last, Now),

    {noreply, State#state{last = Now}};

handle_info(_Info, State) ->

    {noreply, State}.

%% @spec terminate(Reason, State) -> ok

%% @doc gen_server termination callback.

terminate(_Reason, State) ->

    {ok, cancel} = timer:cancel(State#state.tref),

    ok.

%% @spec code_change(_OldVsn, State, _Extra) -> State

%% @doc gen_server code_change callback (trivial).

code_change(_Vsn, State, _Extra) ->

    {ok, State}.

%% @spec reload_modules([atom()]) -> [{module, atom()} | {error, term()}]

%% @doc code:purge/1 and code:load_file/1 the given list of modules in order,

%%      return the results of code:load_file/1.

reload_modules(Modules) ->

    [begin code:purge(M), code:load_file(M) end || M <- Modules].

%% @spec all_changed() -> [atom()]

%% @doc Return a list of beam modules that have changed.

all_changed() ->

    [M || {M, Fn} <- code:all_loaded(), is_list(Fn), is_changed(M)].

%% @spec is_changed(atom()) -> boolean()

%% @doc true if the loaded module is a beam with a vsn attribute

%%      and does not match the on-disk beam file, returns false otherwise.

is_changed(M) ->

    try

        module_vsn(M:module_info()) =/= module_vsn(code:get_object_code(M))

    catch _:_ ->

            false

    end.

%% Internal API

module_vsn({M, Beam, _Fn}) ->

    {ok, {M, Vsn}} = beam_lib:version(Beam),

    Vsn;

module_vsn(L) when is_list(L) ->

    {_, Attrs} = lists:keyfind(attributes, 1, L),

    {_, Vsn} = lists:keyfind(vsn, 1, Attrs),

    Vsn.

doit(From, To) ->

    [case file:read_file_info(Filename) of

         {ok, #file_info{mtime = Mtime}} when Mtime >= From, Mtime < To ->

             reload(Module);

         {ok, _} ->

             unmodified;

         {error, enoent} ->

             %% The Erlang compiler deletes existing .beam files if

             %% recompiling fails.  Maybe it's worth spitting out a

             %% warning here, but I'd want to limit it to just once.

             gone;

         {error, Reason} ->

             io:format("Error reading ~s's file info: ~p~n",

                       [Filename, Reason]),

             error

     end || {Module, Filename} <- code:all_loaded(), is_list(Filename)].

reload(Module) ->

    io:format("Reloading ~p ...", [Module]),

    code:purge(Module),

    case code:load_file(Module) of

        {module, Module} ->

            io:format(" ok.~n"),

            case erlang:function_exported(Module, test, 0) of

                true ->

                    io:format(" - Calling ~p:test() ...", [Module]),

                    case catch Module:test() of

                        ok ->

                            io:format(" ok.~n"),

                            reload;

                        Reason ->

                            io:format(" fail: ~p.~n", [Reason]),

                            reload_but_test_failed

                    end;

                false ->

                    reload

            end;

        {error, Reason} ->

            io:format(" fail: ~p.~n", [Reason]),

            error

    end.

stamp() ->

    erlang:localtime().

%%

%% Tests

%%

-ifdef(TEST).

-include_lib("eunit/include/eunit.hrl").

-endif.