Improve upload limit calculation

[kittey]

After some high-volume dumps of garbage posts, a better way to calculate the upload limit for members is being discussed in topic #16499 in order to not reward idle uploaders and better reward good uploaders.

Since additional upload slots up to a maximum of 50 are awarded solely based on account age and garbage uploads only reduce that amount, simply waiting for a while can get a user all 50 slots, which can then be used to dump a large amount of garbage uploads at once. On the other hand, a new user with good uploads still needs to wait for five months to be able to use all 50 slots, getting no better treatment than a user who uploads nothing.

Based on the various ideas, I created this suggestion:

MinLimit = 10
MaxLimit = 50
ApprovalWeight = 0.1
BaseLimit = Min(MinLimit + ApprovedPostsOver60Days * ApprovalWeight, MaxLimit)
DeletionConfidence = WilsonScoreInterval(UploadsOver60Days, DeletionsOver60Days, 95%) 
EffectiveLimit = Max(BaseLimit * (1 - (DeletionConfidence / 15)), MinLimit)

ApprovedPostsOver60Days should not include pending/flagged posts. I assume the DeletionConfidence we currently have doesn’t go above 15.

Examples:
400 approved posts over the last 60 days, no deletions = 50 slots
100 approved posts over the last 60 days, no deletions = 20 slots
10 approved posts over the last 60 days, no deletions = 11 slots
400 approved posts plus ~60 deletions over 60 days = 10 slots (15% deletion confidence, the current maximum)
Not uploading anything for 60 days = 10 slots

This might look harsh, but a user who uploaded only 100 posts during 60 days doesn’t really need a limit above 20 unless they plan on uploading a whole doujinshi in one day or something, which is discouraged anyway.

Users who upload exactly their limit every day and have no deletions can reach 50 slots in 18 days, so this alternative would reward good uploaders about eight times as fast compared to the current system while not rewarding idle/garbage uploaders at all.

To sustain 50 slots, 50 uploads per week with no deletions are enough, so it’s possible for users to take care of their upload duty in just one day per week.

Drawbacks: Going on a long vacation will (temporarily) hurt a user’s upload limit. This calculation is a bit more complicated than the current one.

Contstants/factors might need some adjustment after a trial period.