LB-1742 Notify user if they're adding a duplicate to a playlist

[fettuccinae]

Problem

When a user adds a track which is already present in the playlist, there is no indication about it.
https://tickets.metabrainz.org/browse/LB-1742

Solution

Added logic to check if the track is already present in the playlist, and if it is then render DuplicateTrackModal.

[fettuccinae]

Duplicate model UI

[MonkeyDo]

Looks good!

If you want to make all users happy, adding a "don't ask me again until I close this page" checkbox to the modal would ensure you don't make it miserable for creative users that want the same track 30 times in a playlist (not that I know anyone who would do that...).

Than you can save that boolean into the playlist page state, and skip the confirmation or not accordingly. Probably ideally passing the saved state back to the modal component to allow users to change their mind by unticking the checkbox.

Another option, different from the solution you opted for, would be to show a toast message instead of a modal.
So it would require no extra interaction to confirm anything, but would instead give you the option (in the toast message) to remove the duplicate entry.
Make that toast message not self-closing, and you've got another working solution.

I leave it as an exercise to the reader to figure out which one they would like more themselves.