local crypto = require "util.crypto";

local json = require "util.json";

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

local base64_decode = require "util.encodings".base64.decode;

local secure_equals = require "util.hashes".equals;

local bit = require "util.bitcompat";

local s_pack = require "util.struct".pack;

local s_gsub = string.gsub;

local v4_public = {};

local b64url_rep = { ["+"] = "-", ["/"] = "_", ["="] = "", ["-"] = "+", ["_"] = "/" };

local function b64url(data)

	return (s_gsub(base64_encode(data), "[+/=]", b64url_rep));

end

local function unb64url(data)

	return base64_decode(s_gsub(data, "[-_]", b64url_rep).."==");

end

local function le64(n)

	return s_pack("<I8", bit.band(n, 0x7F));

end

local function pae(parts)

	if type(parts) ~= "table" then

		error("bad argument #1 to 'pae' (table expected, got "..type(parts)..")");

	end

	local o = { le64(#parts) };

	for _, part in ipairs(parts) do

		table.insert(o, le64(#part)..part);

	end

	return table.concat(o);

end

function v4_public.sign(m, sk, f, i)

	if type(m) ~= "table" then

		return nil, "PASETO payloads must be a table";

	end

	m = json.encode(m);

	local h = "v4.public.";

	local m2 = pae({ h, m, f or "", i or "" });

	local sig = crypto.ed25519_sign(sk, m2);

	if not f or f == "" then

		return h..b64url(m..sig);

	else

		return h..b64url(m..sig).."."..b64url(f);

	end

end

function v4_public.verify(tok, pk, expected_f, i)

	local h, sm, f = tok:match("^(v4%.public%.)([^%.]+)%.?(.*)$");

	if not h then

		return nil, "invalid-token-format";

	end

	f = f and unb64url(f) or nil;

	if expected_f then

		if not f or not secure_equals(expected_f, f) then

			return nil, "invalid-footer";

		end

	end

	local raw_sm = unb64url(sm);

	if not raw_sm or #raw_sm <= 64 then

		return nil, "invalid-token-format";

	end

	local s, m = raw_sm:sub(-64), raw_sm:sub(1, -65);

	local m2 = pae({ h, m, f or "", i or "" });

	local ok = crypto.ed25519_verify(pk, m2, s);

	if not ok then

		return nil, "invalid-token";

	end

	local payload, err = json.decode(m);

	if err ~= nil or type(payload) ~= "table" then

		return nil, "json-decode-error";

	end

	return payload;

end

v4_public.import_private_key = crypto.import_private_pem;

v4_public.import_public_key = crypto.import_public_pem;

function v4_public.new_keypair()

	return crypto.generate_ed25519_keypair();

end

function v4_public.init(private_key_pem, public_key_pem, options)

	local sign, verify = v4_public.sign, v4_public.verify;

	local public_key = public_key_pem and v4_public.import_public_key(public_key_pem);

	local private_key = private_key_pem and v4_public.import_private_key(private_key_pem);

	local default_footer = options and options.default_footer;

	local default_assertion = options and options.default_implicit_assertion;

	return private_key and function (token, token_footer, token_assertion)

		return sign(token, private_key, token_footer or default_footer, token_assertion or default_assertion);

	end, public_key and function (token, expected_footer, token_assertion)

		return verify(token, public_key, expected_footer or default_footer, token_assertion or default_assertion);

	end;

end

function v4_public.new_signer(private_key_pem, options)

	return (v4_public.init(private_key_pem, nil, options));

end

function v4_public.new_verifier(public_key_pem, options)

	return (select(2, v4_public.init(public_key_pem, options)));

end

return {

	pae = pae;

	v4_public = v4_public;

};