Non-secure nanoid implemented in Luau

nanoid.luau

-- This alphabet uses `A-Za-z0-9_-` symbols.
-- The order of characters is optimized for better gzip and brotli compression.
-- Same as in non-secure/index.js
local URL_ALPHABET = "useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict"
local DEFAULT_SIZE = 21

export type NanoIdFn = (size: number?) -> string

local function makeGenerator(alphabet: string, defaultSize: number?, rng: Random?): NanoIdFn
	assert(type(alphabet) == "string" and #alphabet > 0, "alphabet must be a non-empty string")

	local alphaLen = #alphabet
	local sizeDefault = defaultSize or DEFAULT_SIZE
	local r = rng or Random.new()

	return function(size: number?): string
		local n = math.floor(size or sizeDefault)
		if n <= 0 then
			return ""
		end

		-- build with a table to avoid repeated string concatenation
		local out = table.create(n)
		for i = 1, n do
			local idx = r:NextInteger(1, alphaLen)
			out[i] = string.sub(alphabet, idx, idx)
		end
		return table.concat(out)
	end
end

local Nanoid = {}

function Nanoid.customAlphabet(alphabet: string, defaultSize: number?): NanoIdFn
	return makeGenerator(alphabet, defaultSize, nil)
end

local defaultNanoid = makeGenerator(URL_ALPHABET, DEFAULT_SIZE, nil)

function Nanoid.nanoid(size: number?): string
	return defaultNanoid(size)
end

-- Export the alphabet as well, like the JS package does
Nanoid.urlAlphabet = URL_ALPHABET

return Nanoid

nanoid.test.luau

local Packages = script.Parent.Parent

local RegExp = require(Packages.Dev.RegExp)

local LuauPolyfill = require(Packages.Dev.LuauPolyfill)
local Object = LuauPolyfill.Object

local JestGlobals = require(Packages.Dev.JestGlobals)
local describe = JestGlobals.describe
local it = JestGlobals.it
local expect = JestGlobals.expect

local NonSecure = require(script.Parent.NonSecure)
local nanoid = NonSecure.nanoid
local customAlphabet = NonSecure.customAlphabet
local urlAlphabet = NonSecure.urlAlphabet

describe("non secure", function()
	it("generates URL-friendly IDs", function()
		for _ = 1, 10 do
			local id = nanoid()
			expect(#id).toBe(21)
			for _, char in string.split(id, "") do
				expect(char).toMatch(RegExp(char))
			end
		end
	end)

	it("changes ID length", function()
		expect(#nanoid(10)).toBe(10)
	end)

	it("has no collisions", function()
		local used = {}
		for _ = 1, 100 * 1000 do
			local id = nanoid()
			expect(used[id]).toBe(nil)
			used[id] = true
		end
	end)

	it("has flat distribution", function()
		local COUNT = 100 * 1000
		local LENGTH = #nanoid()

		local chars = {}
		for _ = 1, COUNT do
			local id = nanoid()
			for _, char in string.split(id, "") do
				if not chars[char] then
					chars[char] = 0
				end
				chars[char] += 1
			end
		end

		expect(#Object.keys(chars)).toBe(#urlAlphabet)

		local max = 0
		local min = math.huge
		for _, v in chars do
			local distribution = (v * #urlAlphabet) / (COUNT * LENGTH)
			if distribution > max then
				max = distribution
			end
			if distribution < min then
				min = distribution
			end
		end
		expect(max - min).toBeLessThanOrEqual(0.05)
	end)

	it("nanoid / avoids pool pollution, infinite loop", function()
		nanoid(2.1)
		local second = nanoid()
		local third = nanoid()
		expect(second).never.toBe(third)
	end)

	it("customAlphabet / has options", function()
		local nanoidA = customAlphabet("a", 5)
		expect(nanoidA()).toBe("aaaaa")
	end)

	it("customAlphabet / has flat distribution", function()
		local COUNT = 100 * 1000
		local LENGTH = 5
		local ALPHABET = "abcdefghijklmnopqrstuvwxyz"
		local nanoid2 = customAlphabet(ALPHABET, LENGTH)

		local chars = {}
		for _ = 1, COUNT do
			local id = nanoid2()
			for _, char in string.split(id, "") do
				if not chars[char] then
					chars[char] = 0
				end
				chars[char] += 1
			end
		end

		expect(#Object.keys(chars)).toBe(#ALPHABET)

		local max = 0
		local min = math.huge
		for _, v in chars do
			local distribution = (v * #ALPHABET) / (COUNT * LENGTH)
			if distribution > max then
				max = distribution
			end
			if distribution < min then
				min = distribution
			end
		end
		expect(max - min).toBeLessThanOrEqual(0.05)
	end)

	it("customAlphabet / avoids pool pollution, infinite loop", function()
		local ALPHABET = "abcdefghijklmnopqrstuvwxyz"
		local nanoid2 = customAlphabet(ALPHABET)
		nanoid2(2.1)
		local second = nanoid2()
		local third = nanoid2()
		expect(second).never.toBe(third)
	end)
end)