-- Prosody IM

-- Copyright (C) 2008-2017 Matthew Wild

-- Copyright (C) 2008-2017 Waqas Hussain

-- Copyright (C) 2008-2017 Kim Alvefur

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

local s_gsub = string.gsub;

local random_bytes = require "util.random".bytes;

local base64_encode = require "util.encodings".base64.encode;

local b64url = { ["+"] = "-", ["/"] = "_", ["="] = "" };

local function b64url_random(len)

	return (s_gsub(base64_encode(random_bytes(len)), "[+/=]", b64url));

end

return {

	-- sizes divisible by 3 fit nicely into base64 without padding==

	-- for short lived things with low risk of collisions

	tiny = function() return b64url_random(3); end;

	-- close to 8 bytes, should be good enough for relatively short lived or uses

	-- scoped by host or users, half the size of an uuid

	short = function() return b64url_random(9); end;

	-- more entropy than uuid at 2/3 the size

	-- should be okay for globally scoped ids or security token

	medium = function() return b64url_random(18); end;

	-- as long as an uuid but MOAR entropy

	long = function() return b64url_random(27); end;

	-- pick your own adventure

	custom = function (size)

		return function () return b64url_random(size); end;

	end;

}