Design: Update library information

I decided to put the library into a namespace to keep the code clean.  I
also added an update algorithm and made minor naming changes.

Signed-off-by: Bryan Schumaker <bjschuma@gmail.com>

design.txt

@@ -130,30 +130,34 @@ API:
 
 
 Library: (lib/library.cpp)
+	The library manages databases containing track information added by the
+	user.  Ocarina 6 splits the library into multiple database tables for
+	storing content.  The library will exist in a library namespace to
+	to make functions and classes more unique.
 
-	This file will manage and control access to the library.  The library
-	will be split into 5 database tables based on the content being stored,
-	and should be initialized before access attempts.
+	When a library : Track is created, it should be added to the "Library"
+	group if it is NOT a member of the banned songs group.
 
-	class Album : public DatabaseEntry {
+Structures:
+	class library :: Album : public DatabaseEntry {
 		string name;
 		short  year;
 	};
 
-	class Artist : public DatabaseEntry {
+	class library :: Artist : public DatabaseEntry {
 		string name;
 	};
 
-	class Genre : public DatabaseEntry {
+	class library :: Genre : public DatabaseEntry {
 		string name;
 	};
 
-	class Library : public DatabaseEntry {
-		string base_path;
+	class library :: Root : public DatabaseEntry {
+		string root_path;
 		bool enabled;
 	};
 
-	class Track : public DatabaseEntry {
+	class library :: Track : public DatabaseEntry {
 		unsigned int artist_id;
 		unsigned int album_id;
 		unsigned int genre_id;
@@ -170,11 +174,19 @@ Library: (lib/library.cpp)
 		string filepath;
 	};
 
-	Database album_db;
-	Database artist_db;
-	Database genre_db;
-	Database library_db;
-	Database track_db;
+	struct Track { /* Leave this outside of the namespace */
+		library :: Album   *album;
+		library :: Artist  *artist;
+		library :: Genre   *genre;
+		library :: Library *library;
+		library :: Track   *track;
+	};
+
+	Database<library :: Album>   album_db;
+	Database<library :: Artist>  artist_db;
+	Database<library :: Album>   genre_db;
+	Database<library :: Library> library_db;
+	Database<library :: Track>   track_db;
 
 File formats:
   Album:
@@ -187,30 +199,44 @@ File formats:
 	name
 
   Track:
-	artist_id album_id genre_id library_id track last_year last_month last_day play_count length
+	artist_id album_id genre_id library_id track last_year last_month last_day play_count length length_str
 	title
-	length_str
 	filepath
 
   Library:
 	enabled base_path;
 
+Updating algorithm:
+	set<pair<lib_id, track_path>> known_tracks;
+
+	1) For each track currently in the library, check if the track exists
+	   in the filesystem.
+	   1a) If the track does exist, add to the known_tracks map.
+	   1b) Else, mark track invalid.
+	2) For each file in the scan directory, check if (lib_id, track_path)
+	   exists in the known_tracks map.
+	   2a) If the file is in the map, do nothing.
+	   2b) Else, add track to the library.
+
+	The taglib library should be used for finding artist, album, etc. tags
+	for each track.
+
+	Use idle tasks for step 2 to break up tagging new files into chunks.
+	This way the user will still be able to use Ocarina and scanning can
+	happen while idle.
 
 - API
 	/* Path management */
-	add_path_to_library(dir);
+	library :: add_path(string dir);
 		Add new row to paths table, update
-	rm_path_from_library(dir);
-		Remove row from paths table
-	update_path(dir);
-		Scan tracks table, remove paths that don't exist
-		Scan dir, add new files to database
-		Consider having SQLite create an index on tracks.filepath
-	update_all();
-		Call update_path() for each paths.dirpath
-	list_paths(list<>);
-		Tell the caller basic information about library paths
-		(dir, enabled, size,...)
+	library :: del_path(unsigned int lib_id);
+		Invalidate a path row
+	library :: update_path(lib_id);
+		Update the given library path, if valid.
+	const Database<LibraryEntry> &library :: get_db();
+		Returns the database containing library information.
+	struct Track library :: resolve(track_id)
+		Fill out a Track structure for the provided track_id