Community ads for redditors

community_ads.rb

# community ads ranking for subreddit
# see https://medium.com/product-dot-io/reddit-empowering-the-community-5c0ce2c266e2

def user_ad_ranking(ad, ups, downs)
    # difference between upvotes and downvotes for user-submitted ad
    # coeff is a business constant to be determined
    s = ups + coeff * Math.log10(ad.budget * 10) - downs
    order = Math.log10([s.abs, 1].max)
    sign = if s > 0
        1
    elsif s < 0
        -1
    else
        0
    end
    
    # Time.now.to_i converts ruby timestamp to seconds in Epoch
    seconds = Time.now.to_i - 1134028003
    
    # rating function, very similar to stories rating
    return Math.round(sign * order + seconds / 45000, 7)
end

# returns current ad to show for subreddit. Only one ad is shown per subreddit
def current_subreddit_ad(user_ads)
  return user_ads.map {|a| user_ad_ranking(a, a.ups, a.down )}.max
end

# returns pricing for user
def ad_price(subreddit, ups, downs)
   s = downs + subreddit.current_ads.size - ups
   # ad_coeff is a business constant to be determined
   return ad_coeff * Math.exp(s)
end