redis_ratelimit

--[[ 
 RATELIMIT LUA script does the following  :
	1. Increments counter for the supplied bucket.  
	2. Deletes the subsequent buckets.
	3. Renews  expiry time for the subjectKey

	KEYS[1]: subject's key
	ARGV[1]: bucket number
	ARGV[2]: subject expiry in seconds
	ARGV[3]: buckets to clear ahead
	ARGV[4]: bucket count
	RETURNS: nothing
]]


-- increment the bucket counter
redis.call('HINCRBY', KEYS[1], ARGV[1], 1)


-- clear the buckets ahead, create space separated bucket ids
local buckets = ARGV[3]
local ids = ''
for i=1, buckets do
    local id = (ARGV[1] + i) % ARGV[4]
    if (i == 1) then
        ids = id
    else
        ids = ids .. ' ' .. id
    end
end

redis.call('HDEL', KEYS[1], ids)

-- renew the key's expiry time
redis.call('EXPIRE',KEYS[1], ARGV[2])

return ids