Lua basic UUID function (UUIDv1, UUIDv4, UUIDv7)

uuid.lua

local uuid = {}
assert(1<<60 ~= 0, "Requires at least 64-bit lua_Integer")

local nominal_unix_epoch = {year = 1970, month = 1, day = 1, hour = 0, min = 0, sec = 0}
local unix_epoch = os.time(os.date("!*t", os.difftime(os.time(nominal_unix_epoch), os.time(os.date("!*t", os.time(nominal_unix_epoch))))))
local unix_time_sec
if unix_epoch == 0 then
	-- Lua's "some epoch" is just the Unix epoch
	unix_time_sec = os.time
else
	function unix_time_sec()
		return os.difftime(os.time(), unix_epoch)
	end
end

local function math_round(x)
	return math.floor(x + 0.5)
end

local function time_ms()
	-- FIXME: this is not QUITE correct. It helps uniqueness,
	-- and will make sub-tick ordering MUCH MORE LIKELY to be correct in most cases,
	-- i.e., this still does better than an all-random or all-zero sub-tick component,
	-- but it still does not 100% GUARANTEE correct sub-tick ordering.
	-- https://stackoverflow.com/posts/comments/140974268
	return math_round(select(2, math.modf(os.clock())) * 1000.0)
end

local function random_node()
	return math.random(0, 0xffffffffffff) | 0x010000000000
end

uuid.node = random_node() -- FIXME, looking up MAC is complex and extremely platform-dependent

uuid.uuid1 = function(node, us, clock_seq)
	if node == nil then node = uuid.node end
	local ver = 1
	local var = 2
	local unix_ts_ms = math.tointeger(unix_time_sec() * 1000 + time_ms())
	local timestamp = (unix_ts_ms + 12219292800000) * 10000
	if us == nil then
		-- default: just random
		timestamp = timestamp + math.random(0, 9999)
	else
		-- caller-provided precision or counter
		timestamp = timestamp + math_round(us * 10)
	end
	if clock_seq == nil then
		-- default: just random
		clock_seq = math.random(0, 0x3fff)
	end

	return ("%08x-%04x-%04x-%04x-%012x"):format(
		timestamp & 0xffffffff,
		(timestamp >> 32) & 0xffff,
		(ver << 12) | ((timestamp >> 48) & 0x0fff),
		(var << 14) | (clock_seq & 0x3fff),
		node
	)
end

uuid.uuid4 = function()
	local ver = 4
	local var = 2
	local timestamp = math.random(0, 0x0fffffffffffffff)
	local clock_seq = math.random(0, 0x3fff)
	local node = math.random(0, 0xffffffffffff)

	return ("%08x-%04x-%04x-%04x-%012x"):format(
		timestamp & 0xffffffff,
		(timestamp >> 32) & 0xffff,
		(ver << 12) | ((timestamp >> 48) & 0x0fff),
		(var << 14) | (clock_seq & 0x3fff),
		node
	)
end

uuid.uuid7 = function()
	local ver = 7
	local var = 2
	local unix_ts_ms = math.tointeger(unix_time_sec() * 1000 + time_ms())
	local rand_a = math.random(0, 0x0fff)
	local rand_b = math.random(0, 0x3fffffffffffffff)

	return ("%08x-%04x-%04x-%04x-%012x"):format(
		(unix_ts_ms >> 16) & 0xffffffff,
		unix_ts_ms & 0xffff,
		(ver << 12) | (rand_a & 0x0fff),
		(var << 14) | ((rand_b >> 48) & 0x3fff),
		rand_b & 0xffffffffffff
	)
end

return uuid