-module(media).
-export([init/0,insert/3, ask/2, all/0, play/3]).

% Since we are not willing to calculate and deliver all the id3 tags everytime they are requested,
% we try to get something persistent with mnesia.
% Concerning the parsing of id3tags we use the library id3v2 by Brendon Hogger. For detailed information take a
% look at the header of the library.

% What is an entry in our database made of? By the way the filepath includes the filename.

-record(track, {artist, title, votes, locked, filepath }).

% With which application do we play mp3s?

player(path) ->
    {ok, ["/usr/bin/env", "mplayer", "-quiet", path]}.

% Before this module becomes usable, we must initialize it with the following steps:
% 1. Initialize the mnesiadatabase and create the table within it.
% 2. Parse the mp3s in the working directory and add them to the database
% 3. Get into a loop so the database can be actually queried and files can be played.

init() ->
    mnesia:create_schema([node()]),
    mnesia:start(),
    mnesia:create_table(track, [{attributes, record_info(fields, track)}]),
    io:format("Initialisation of mnesia successful.\n").

% Basic insertion of entrys into the database. Some entries are left out because they are 0 or false.

insert(Artist, Title, Filepath) ->
    F = fun() ->
                mnesia:write(#track{artist = Artist, title = Title, votes = 0, locked = false, filepath = Filepath})
        end,
    mnesia:transaction(F).

% We want to query in order to simplify the next calls.
ask(Artist, Title) ->
    F = fun() ->
		mnesia:match_object({track, Artist, Title, '_', '_', '_'})
	end,
    {atomic, Results} = mnesia:transaction(F),
    Results.

% Just in case the client is interested in everything we got.

all() ->
    F = fun() ->
                mnesia:match({track, '_','_','_','_','_'})
        end,
    {atomic, Results} = mnesia:transaction(F),
    Results.

% We want to play mp3s from our database.

play(Artist, Title, Callback) ->
    [Head|_] = ask(Artist, Title),
    {_, _, _, _, _, Fp} = Head,
%    Port = erlang:open_port({spawn, Cmd}, [exit_status]).
    Port = erlang:open_port({spawn_executable, "/usr/bin/mplayer"}, [{args, [Fp]}]).
% We want to execute commands locally