Versions

Versions are a method for us marking charts as being available in a certain "version" of the game.

The predominant use for this is for arcade games, where new versions of the game generally come out and add/remove charts.

It's useful for us to know what charts are available in what version for two purposes.

The first allows us to create folders - users playing on a certain version of a game don't want to see charts they can't play!

The second is more complex.

Disambiguation and isPrimary

Sadly, the real world isn't easy to deal with. It's possible for a chart to exist in version A of a game, get removed in version B, and then come back in version C with new, completely different charts.

Worse still, it's possible for that song to use the exact same in game ID it used before. If we use inGameID to identify things, now we've got a critical ambiguity!

Does inGameID: 1, difficulty: ANOTHER refer to the version A chart, or the version C one? For games where metrics are chart-dependent, this could be lethal to the leaderboards.

It's much easier to get a good score in IIDX if the chart thinks it has less notes than it actually has!

To fix this, we also use versions as an identifer for disambiguation. If a score comes in, it MAY pass what version the score was attained on.

This allows us to immediately disambiguate the previous case.

If a version is not passed in, we assume that the score is for the chart marked as isPrimary: true. Furthermore, seeds tests enforce that duplicates on certain IDs expected-to-be-unique cannot be true unless all-but-one-of-them is marked as isPrimary: false.