Added pre-emptive batch artist update on playlist change (#32)

CHANGELOG.md

@@ -10,6 +10,9 @@
 ___
 
 ## [Unreleased][]
+### Changed
+- Better Web API handling in attempt to avoid 429 errors:
+  - Pre-emptive batch artist update on playlist import ([#32](https://github.com/TheQwertiest/foo_spotify/issues/32)).
 
 ## [1.1.0][] - 2020-10-26
 ### Added

foo_spotify/fb2k/playlist.cpp

@@ -116,7 +116,7 @@ void PlaylistCallbackSpotify::on_playlist_activate( t_size p_old, t_size p_new )
         {
             auto& waBackend = SpotifyInstance::Get().GetWebApi_Backend();
 
-            // cache tracks
+            // pre-cache tracks
             qwr::TimedAbortCallback tac1;
             const auto tracks = waBackend.GetTracks( trackIds, tac1 );
 
@@ -125,7 +125,7 @@ void PlaylistCallbackSpotify::on_playlist_activate( t_size p_old, t_size p_new )
                 | ranges::views::transform( []( const auto& pTrack ) -> std::string { return pTrack->artists[0]->id; } )
                 | ranges::to_vector;
 
-            // cache artists
+            // pre-cache artists
             qwr::TimedAbortCallback tac2;
             waBackend.RefreshCacheForArtists( artistIds, tac2 );
         }

foo_spotify/fb2k/playlist_loader.cpp

@@ -119,6 +119,15 @@ GetTracks( const SpotifyObject spotifyObject, abort_callback& p_abort )
     else if ( spotifyObject.type == "playlist" )
     {
         auto [tracks, localTracks] = waBackend.GetTracksFromPlaylist( spotifyObject.id, p_abort );
+
+        const auto artistIds =
+            tracks
+            | ranges::views::transform( []( const auto& pTrack ) -> std::string { return pTrack->artists[0]->id; } )
+            | ranges::to_vector;
+
+        // pre-cache artists
+        waBackend.RefreshCacheForArtists( artistIds, p_abort );
+
         // ??? Dunno why this is required. Smth to do with structureed bindings and RVO.
         return { std::move( tracks ), TransformToSkippedTracks( localTracks ) };
     }