Redis track a user event

trackuserevent.lua

local utcDate     = KEYS[1]  -- because redis does not have os.time, we require a utc date expecting yyyy-mm-dd hh-mm-ss
local userId      = KEYS[2]  -- a username/email/unique identifier
local eventName   = KEYS[3]  -- event name to track
local siteId      = KEYS[4]  -- site id
local appPrefix   = ARGV[1]

if not utcDate then
  return "error: utcDate/keys[1] is required"
end

if not userId then
  return "error: userId/keys[2] is required"
end

if not eventName then
  return "error: eventName/keys[3] is required"
end

if not appPrefix then
  appPrefix = "trak"
end

local d = {}
local i = 0
local ukey        = appPrefix .. "::users::" .. userId
local uid         = redis.call("GET", ukey)
for word in string.gmatch(utcDate, "(%d+)") do
  i = i+1
  d[i] = word
end

if not uid then
  uid = redis.call("INCR", appPrefix .. "::identity::users") 
  redis.call("SET", ukey, uid)
end

local key1 = (appPrefix .. "::" .. eventName .. "::" .. string.format("%d-%d-%d-%d-%d", d[1], d[2], d[3], d[4], d[5]))

redis.call("SETBIT", key1, uid, 1)  -- minute
redis.call("SETBIT", string.sub(key1, 1, -3), uid, 1) -- hour
redis.call("SETBIT", string.sub(key1, 1, -6), uid, 1) -- day
redis.call("SETBIT", string.sub(key1, 1, -9), uid, 1) -- month
redis.call("SETBIT", string.sub(key1, 1, -12), uid, 1) -- yyyy

if siteId then
key1 =  (appPrefix .. "::site::" .. siteid .. "::" .. eventName .. "::" .. string.format("%d-%d-%d-%d-%d", d[1], d[2], d[3], d[4], d[5]))

redis.call("SETBIT", key1, uid, 1)  -- minute
redis.call("SETBIT", string.sub(key1, 1, -3), uid, 1) -- hour
redis.call("SETBIT", string.sub(key1, 1, -6), uid, 1) -- day
redis.call("SETBIT", string.sub(key1, 1, -9), uid, 1) -- month
redis.call("SETBIT", string.sub(key1, 1, -12), uid, 1) -- yyyy
end

return uid .. ""