/*! SPDX-License-Identifier: GPL-2.0
 *
 * Copyright (C) 2015-2020 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */
'use strict'

const crypto = require('crypto')

const gf = (init) => {
	let r = new Float64Array(16);
	if (init) {
		for (let i = 0; i < init.length; ++i)
			r[i] = init[i]
	}
	return r
}
const pack = (o, n) => {
	let b, m = gf(), t = gf()
	for (let i = 0; i < 16; ++i)
		t[i] = n[i]
	carry(t)
	carry(t)
	carry(t)
	for (let j = 0; j < 2; ++j) {
		m[0] = t[0] - 0xffed
		for (let i = 1; i < 15; ++i) {
			m[i] = t[i] - 0xffff - ((m[i - 1] >> 16) & 1)
			m[i - 1] &= 0xffff
		}
		m[15] = t[15] - 0x7fff - ((m[14] >> 16) & 1)
		b = (m[15] >> 16) & 1
		m[14] &= 0xffff
		cswap(t, m, 1 - b)
	}
	for (let i = 0; i < 16; ++i) {
		o[2 * i] = t[i] & 0xff
		o[2 * i + 1] = t[i] >> 8
	}
}
const carry = (o) => {
	for (let i = 0; i < 16; ++i) {
		o[(i + 1) % 16] += (i < 15 ? 1 : 38) * Math.floor(o[i] / 65536)
		o[i] &= 0xffff
	}
}
const cswap = (p, q, b) => {
	let t, c = ~(b - 1)
	for (let i = 0; i < 16; ++i) {
		t = c & (p[i] ^ q[i])
		p[i] ^= t
		q[i] ^= t
	}
}
const add = (o, a, b) => {
	for (let i = 0; i < 16; ++i)
		o[i] = (a[i] + b[i]) | 0
}
const subtract = (o, a, b) => {
	for (let i = 0; i < 16; ++i)
		o[i] = (a[i] - b[i]) | 0
}
const multmod = (o, a, b) => {
	let t = new Float64Array(31)
	for (let i = 0; i < 16; ++i) {
		for (let j = 0; j < 16; ++j)
			t[i + j] += a[i] * b[j]
	}
	for (let i = 0; i < 15; ++i)
		t[i] += 38 * t[i + 16]
	for (let i = 0; i < 16; ++i)
		o[i] = t[i]
	carry(o)
	carry(o)
}
const invert = (o, i) => {
	let c = gf()
	for (let a = 0; a < 16; ++a)
		c[a] = i[a]
	for (let a = 253; a >= 0; --a) {
		multmod(c, c, c)
		if (a !== 2 && a !== 4)
			multmod(c, c, i)
	}
	for (let a = 0; a < 16; ++a)
		o[a] = c[a]
}
const clamp = (z) => {
	z[31] = (z[31] & 127) | 64
	z[0] &= 248
}

const generatePublicKey = (privateKey) => {
	let r, z = new Uint8Array(32)
	let a = gf([1]),
		b = gf([9]),
		c = gf(),
		d = gf([1]),
		e = gf(),
		f = gf(),
		_121665 = gf([0xdb41, 1]),
		_9 = gf([9])
	for (let i = 0; i < 32; ++i)
		z[i] = privateKey[i]
	clamp(z)
	for (let i = 254; i >= 0; --i) {
		r = (z[i >>> 3] >>> (i & 7)) & 1
		cswap(a, b, r)
		cswap(c, d, r)
		add(e, a, c)
		subtract(a, a, c)
		add(c, b, d)
		subtract(b, b, d)
		multmod(d, e, e)
		multmod(f, a, a)
		multmod(a, c, a)
		multmod(c, b, e)
		add(e, a, c)
		subtract(a, a, c)
		multmod(b, a, a)
		subtract(c, d, f)
		multmod(a, c, _121665)
		add(a, a, d)
		multmod(c, c, a)
		multmod(a, d, f)
		multmod(d, b, _9)
		multmod(b, e, e)
		cswap(a, b, r)
		cswap(c, d, r)
	}
	invert(c, c)
	multmod(a, a, c)
	pack(z, a)
	return z
}
const generatePresharedKey = () => {
	let privateKey = new Uint8Array(32)
	crypto.webcrypto.getRandomValues(privateKey)
	return privateKey
}
const generatePrivateKey = () => {
	let privateKey = generatePresharedKey()
	clamp(privateKey)
	return privateKey
}

const encodeBase64 = (dest, src) => {
	let input = Uint8Array.from([(src[0] >> 2) & 63, ((src[0] << 4) | (src[1] >> 4)) & 63, ((src[1] << 2) | (src[2] >> 6)) & 63, src[2] & 63]);
	for (let i = 0; i < 4; ++i)
		dest[i] = input[i] + 65 +
		(((25 - input[i]) >> 8) & 6) -
		(((51 - input[i]) >> 8) & 75) -
		(((61 - input[i]) >> 8) & 15) +
		(((62 - input[i]) >> 8) & 3);
}
const keyToBase64 = (key) => {
	let i, base64 = new Uint8Array(44);
	for (i = 0; i < 32 / 3; ++i)
		encodeBase64(base64.subarray(i * 4), key.subarray(i * 3));
	encodeBase64(base64.subarray(i * 4), Uint8Array.from([key[i * 3 + 0], key[i * 3 + 1], 0]));
	base64[43] = 61;
	return String.fromCharCode.apply(null, base64);
}

module.exports = {
	generateKeypair: async () => {
		const privateKey = await generatePrivateKey()
		const publicKey = await generatePublicKey(privateKey)
		return [
			keyToBase64(publicKey),
			keyToBase64(privateKey),
		]
	},
	generatePSK: async () => {
		return keyToBase64(await generatePresharedKey())
	},
}