Lua/Redis round-robin increment set

zincr_roundrobin.lua

local numbers_list = redis.call('ZRANGE', KEYS[1], 0, -1, 'WITHSCORES')
local numbers = {}
--every other value is a key
for idx = 1, #numbers_list, 2 do
  numbers[numbers_list[idx]] = numbers_list[idx + 1]
end
--add missing numbers at '0' and immediately return first one
for _, f in pairs(ARGV) do
  if numbers[f] == nil then
    redis.call('ZADD', KEYS[1], 1, f)
    return { f, 1 }
  end
end
--increment lowest
local count = redis.call('ZINCRBY', KEYS[1], 1, numbers_list[1])
return { numbers_list[1], count }