View source for Playground/MediaPlayer

Discussion here is easier than on the etherpad. Please ''watch'' the page to know when it is updated.

== Useful doc ==
* http://wiki.hydrogenaud.io/index.php?title=APE_key
* http://id3.org/id3v2.4.0-frames
* http://taglib.github.io/api

== Description of the interactions ==

We keep one collection that can morphed into different views (possibly a tree view, list, grid, whatever)
3 modules: database manager, collection manager, ui


=== Artists ===

Left panel: click on artists
Middle Pannel > ??? collection view sorts by artists(highest rated or alphabetically) 

=== Albums ===
Left panel: click on albums
Middle Pannel > ??   show album covers grid view, double clicking an album cover replaces Now Playing with all the tracks from that album

=== Genre ===
Left Panel click on Genre
Middle Panel > collection view sorts by Genre      


                                
=== Year ===
Left Panel click on Year
Middle Panel > collection view sorts by Year
....

== Database ==
 After some reflection and I think we should use a no-sql database, not to have to deal with other keys. See http://quodlibet.readthedocs.io/en/latest/development/faq.html#what-about-my-favourite-nosql-db-then.

'**' do we really need so much metadata, most of it is not directly editable by end users   => yes but they might want to see it, and it's faster to read the database than compute something on the file each time we want to show it.
foreign key relationships need to be defined properly before we implement in code
 => True for the foreing key relationship

All these tag should be tracked: http://taglib.github.io/api/classTagLib_1_1PropertyMap.html

QuodLibet does this and IIMO it's a great thing that most music players lack....

=== Tracks ===
* id
* title
* id_rootpath
* complementary_path   why do we need 2 path colums?? I based myself on Amarok: you have several folder, so you have a * relative path and a root path selected by the user.  ok 
* duration
* album_id
* ? artist_id ? it could be recovered with track->album->artist  by that logic track_artist_id can be recovered, so let's choose one  _artist_id and recover the others as necessary. !!There needs to be an album artist id tracked, it will greatly help with the organization of music libraries inside the player!!
* track_artist_id
* composer
* sample_rate**
* bitrate**
* bpm**
* creation_date**
* modification_date**
* file_size**
* file_type = format**
* user_rate

Do we do 3 tables Artist/Album artist/Composer or do we add a int in it to tell which type it is? For instance track artist = 1, album artist = 2, composer = 4 so that 3 means the two first (and so on)

=== Artists ===
* id
* name
* type (int: Composer/album artist/track artist) prefer the integer enum, no need to duplicate data

=== Albums ===
* id
* name
* artist_id
* year
* cover_path   this should be filepath to a local cache dir   << Why cache? isn't .local/share/MusicPlayer/covers good ? that's a fine. << I think it should be local, in order for the cover art to stay with the music in case of a library migration or something as simple as redoing a linux partition completely. cover art should be kept locally, and If I recall correctly, MP3s actually are embedded with cover art