local function lock_is_older_than (creation_timestamp_milliseconds, duration_milliseconds)
	if (creation_timestamp_milliseconds + duration_milliseconds < get_current_time_milliseconds()) then
		return true
	end
	return false
end

local function keep_alive_locks ()
	local locks= redis.call("SMEMBERS", lock_owner_id)

	local extended= 0
	local removed= 0
	for _, member in ipairs(locks) do
		local lock= cjson.decode(member)
		if (lock_is_older_than(lock.creation_time_milliseconds, max_lock_lifetime_seconds*1000)) then
			errorLog("The lock with key '%s' (owned by '%s') was found to exist longer than %s seconds and its lifetime will not be extended. " ..
				"This is an indicator of a logic failure! Please report this issue.", lock.lock_key, lock_owner_id, max_lock_lifetime_seconds)
			remove_from_current_lock_owner_set(member)
			removed = removed + 1
		else
			-- extend lock's expiration
			local result = redis.call("EXPIRE", lock.lock_key, default_lock_lifetime_seconds)
			if (result == 1) then
				local warnThresholdSeconds= math.floor(default_lock_lifetime_seconds / 2)
				if (lock_is_older_than(lock.creation_time_milliseconds, warnThresholdSeconds*1000)) then
					warnLog("The lock with key '%s' (owned by '%s') was found to exist longer than %s seconds. " ..
                    	"This is an indicator of slow requests.", lock.lock_key, lock_owner_id, warnThresholdSeconds)
				end
				extended = extended + 1
			else
				-- remove lock entry from set as it no longer exists
				remove_from_current_lock_owner_set(member)
				removed = removed + 1
			end
		end
	end
	if (extended > 0 or removed > 0) then
		debugLog("Iteration through set of size %d for lock owner '%s' extended expiration of %d locks and removed %d entries.", #locks, lock_owner_id, extended, removed)
	end

	-- make sure an unused set is deleted after 'max_lock_lifetime_seconds'
	redis.call("EXPIRE", lock_owner_id, max_lock_lifetime_seconds)
	return { "ok" }
end

return scriptResult(keep_alive_locks())