Cater for polls that can have multiple votes per user.
This fixes an older UserMerge and migration which was intended to
de-duplicate poll votes but did not account for "multiple" type polls.
When merging users, polls may error out if the source and target users have both voted on the same poll before. 😢
There is no constraint on the `poll_votes` table either to support this. Ideally a composite primary key can be used `(poll_id, user_id)`, but alas there is no support yet, which is probably why it wasn't created in the first place.
This fix ensures that merging is successful by only keeping the target poll votes if duplicates exist.
This fix also runs a migration on older poll votes where failed merges would have caused a single user to have voted twice on a single poll. e.g. this weird edge case
* DEV: Remove spec that we no longer need.
As far as we know, the migration has been successful for a number of
years.
* FIX: Validate number of votes allowed per poll per user.
They can use the remove vote button or select the same option again for
single choice polls.
This commit refactor the plugin to properly organize code and make it
easier to follow.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
