gistfile1.txt

local ad     = tonumber(ARGV[1])
local BL     = 1
local weight = 0
-- bid price constant will be 50p : 500000 /1000 =  500
-- give up bid price constant will be 10p : 100000/1000 = 100
local give_up_bid  = 100
-- Check if there is a weight
if tonumber(redis.call('zscore', 'ad:weights', ad)) == nil then
  return nil
end

-- Retrieve attributes
local bid, bids, wins, stake = unpack(redis.call('hmget', "ad::" .. ad, "bid", "bids", "wins", "stake"))

-- Pure paranoia: ensure we get number back
bid   = tonumber(bid) or 0
bids  = tonumber(bids) or 0
wins  = tonumber(wins) or 0
stake = tonumber(stake) or 0
if stake < 0 then stake = 0 end

-- Calculate weight for pacing
if bid > give_up_bid then
  weight = math.floor( BL * stake/(bid) * bids/(wins+0.0001) + 0.5 )
end 

-- Store weight
redis.call('zadd', 'ad:weights', weight, ad)

return weight