-module(media).
-export([init/0,insert/3, ask/2, all/0, play/2, vote/2, devote/2, lock_process/2]).
-define(TESTPATTERN, "../ac/*.mp3").
-define(TIMEOUT, 100000000).
%This module is responsible for the management of the music database.
%It keeps track of playlist items with their current voting and locked/unlocked status
%and automatically selects the next song with the highest vote count to play back.
% 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, {title, artist, votes, locked, filepath }).
% Before this module becomes usable, we must initialize it with the following steps:
% 1. Initialize the mnesia database 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 queried and files can be played.
init() ->
mnesia:create_schema([node()]),
mnesia:start(),
mnesia:create_table(track, [{attributes, record_info(fields, track)}]),
read_files(filelib:wildcard(?TESTPATTERN),0,0),
io:format("Initialisation of mnesia successful.~n"),
io:format("Starting to play music~n"),
start_playing().
% uses the algorithm of Brendon Hogger to split the id3-tags and
% inserts the songs into the Database
read_files([FN|Rest],Total,Fail) ->
case id3v2:read_file(FN) of
{ok, Props} -> % insert entry into mnesia DB
Artist = proplists:get_value(tpe1, Props),
Title = proplists:get_value(tit2, Props),
insert(bitstring_to_list(Artist), bitstring_to_list(Title), FN),
read_files(Rest, Total+1, Fail);
not_found -> read_files(Rest, Total+1, Fail+1)
end;
read_files([],Total,Fail) -> io:format("Total: ~w, Failed: ~w~n", [Total, Fail]).
% Our loop to play music all the time, play waits on exit_status
start_playing() ->
{Artist, Title} = search_best(media:all(), 0,0),
play(Artist, Title).
% Basic insertion of entries 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).
% Of course we need a query to find out whats actually the most wished for track.
% We will do it by requesting all the records from the database and then iteramte over just taking a look at the vote
% variable, so it is like list of integers. In case no tracks were voted for we just take the first track we find and play it.
% Of course it is locked afterwards so another will be choosen.
search_best([Head|Rest], Max_Votes, Track) ->
if
((Max_Votes =< Head#track.votes) and (Head#track.locked == false)) ->
search_best(Rest, Head#track.votes, Head);
true -> search_best(Rest, Max_Votes, Track)
end;
search_best([], 0, 0) -> reset_all(all());
search_best([], _, Track) -> {Track#track.artist, Track#track.title}.
% if nothing is playable anymore (because all songs are locked) just reset all songs and start playing again...
reset_all([Head|Rest]) ->
unlock(Head#track.artist, Head#track.title),
reset_all(Rest);
reset_all([]) -> ok.
% We want to query in order to simplify the next calls.
ask(Artist, Title) ->
F = fun() ->
mnesia:match_object({track, Title, Artist, '_', '_', '_'})
end,
{atomic, Results} = mnesia:transaction(F),
Results.
% Just in case the client is interested in everything we have.
all() ->
F = fun() ->
mnesia:match_object({track, '_','_','_','_','_'})
end,
{atomic, Results} = mnesia:transaction(F),
Results.
% We want to play mp3s from our database. After we play them they will be locked.
% In practice we are going to set their locked variable to true and spawn a process which will unlock them after a certain time.
% Well this could be considered abuse.
play(Artist, Title) ->
[Head|_] = ask(Artist, Title),
{_, Title, Artist, _, _, Fp} = Head,
Port = erlang:open_port({spawn_executable, "/usr/bin/mplayer"}, [{args, [Fp]}, exit_status]),
reset_votes(Artist, Title),
spawn(media, lock_process, [Artist, Title]),
io:format("playing: ~s, Artist: ~s~n", [Title, Artist]),
receive
{Port, {exit_status, 0}} -> cldb:update_votes(), start_playing();
{Port, {exit_status, S}} -> throw({commandfailed, S})
end.
% Of course we need a query to find out what the highest voted track is.
% We accomplish this by requesting all the records from the database and then iterate over them, just taking a look at the vote
% variable, so it is like a list of integers. In case no tracks were voted for we just take the first track we found and play it. Of course this song is locked afterwards so a different one will be chosen.
%votes for a track, i.e. increases its vote count by one.
vote(Artist, Title) ->
F = fun() ->
[Head|_] = ask(Artist, Title),
Votes = Head#track.votes + 1,
New = Head#track{votes = Votes},
mnesia:write(New)
end,
mnesia:transaction(F).
%votes against a track, i.e. decreases its vote count by one.
devote(Artist, Title) ->
F = fun() ->
[Head|_] = ask(Artist, Title),
Votes = Head#track.votes - 1,
New = Head#track{votes = Votes},
mnesia:write(New)
end,
mnesia:transaction(F).
%resets the vote count of selected track to 0 (this is called when the song is played).
reset_votes(Artist, Title) ->
F = fun() ->
[Head|_] = ask(Artist, Title),
New = Head#track{votes = 0},
mnesia:write(New)
end,
mnesia:transaction(F).
%locks a song so it can't be played again or voted for for that time.
lock(Artist, Title) ->
F = fun() ->
[Head|_] = ask(Artist, Title),
New = Head#track{locked = true},
mnesia:write(New)
end,
mnesia:transaction(F).
%unlocks a song so it can be played and voted for again.
unlock(Artist, Title) ->
F = fun() ->
[Head|_] = ask(Artist, Title),
New = Head#track{locked = false},
mnesia:write(New)
end,
mnesia:transaction(F).
% Lock a song if it was just played, after a Timeout it will be unlocked automaticly
% If all songs are locked, all will be unlocked.
lock_process(Artist, Title) ->
lock(Artist, Title),
receive
after ?TIMEOUT ->
unlock(Artist, Title) end.
