Waiting for multiple tiers to load in an object graph

gistfile1.m

// Assume that there is a -(TCTask*)load method on these objects

-(void)fillTrackPool {
	
	[[SPSession sharedSession] load].then(^(SPSession *sess) {
	    return sess.userPlaylists.load;
	}).then(^(SPPlaylistContainer *container) ^{
		NSMutableArray *playlists = [NSMutableArray array];
		[playlists addObject:sess.starredPlaylist];
		[playlists addObject:sess.inboxPlaylist];
		[playlists addObjectsFromArray:container.flattenedPlaylists];
		return [TCTask waitAll:[playlists valueForKeyPath:@"load"]];
	}).then(^(NSArray *loadedPlaylists) {
		NSArray *playlistItems = [loadedPlaylists valueForKeyPath:@"@unionOfArrays.items"];
		NSArray *tracks = [self tracksFromPlaylistItems:playlistItems];
		return [TCTask waitAll:[tracks valueForKeyPath:@"load"]];
	}).then(^(NSArray *loadedTracks) {
		NSMutableArray *theTrackPool = [NSMutableArray arrayWithCapacity:loadedTracks.count];
		for (SPTrack *aTrack in loadedTracks) {
			if (aTrack.availability == SP_TRACK_AVAILABILITY_AVAILABLE && [aTrack.name length] > 0)
				[theTrackPool addObject:aTrack];
		}
	
		self.trackPool = [NSMutableArray arrayWithArray:[[NSSet setWithArray:theTrackPool] allObjects]];
		// ^ Thin out duplicates.
	
		[self startNewRound];
	})
}