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

function gf(init: number[] | undefined = undefined) {
    var r = new Float64Array(16);
    if (init) {
        for (var i = 0; i < init.length; ++i)
            r[i] = init[i];
    }
    return r;
}

function pack(o: Uint8Array, n: Float64Array) {
    var b, m = gf(), t = gf();
    for (var i = 0; i < 16; ++i)
        t[i] = n[i];
    carry(t);
    carry(t);
    carry(t);
    for (var j = 0; j < 2; ++j) {
        m[0] = t[0] - 0xffed;
        for (var 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 (var i = 0; i < 16; ++i) {
        o[2 * i] = t[i] & 0xff;
        o[2 * i + 1] = t[i] >> 8;
    }
}

function carry(o: Float64Array) {
    var c;
    for (var i = 0; i < 16; ++i) {
        o[(i + 1) % 16] += (i < 15 ? 1 : 38) * Math.floor(o[i] / 65536);
        o[i] &= 0xffff;
    }
}

function cswap(p: Float64Array, q: Float64Array, b: number) {
    var t, c = ~(b - 1);
    for (var i = 0; i < 16; ++i) {
        t = c & (p[i] ^ q[i]);
        p[i] ^= t;
        q[i] ^= t;
    }
}

function add(o: Float64Array, a: Float64Array, b: Float64Array) {
    for (var i = 0; i < 16; ++i)
        o[i] = (a[i] + b[i]) | 0;
}

function subtract(o: Float64Array, a: Float64Array, b: Float64Array) {
    for (var i = 0; i < 16; ++i)
        o[i] = (a[i] - b[i]) | 0;
}

function multmod(o: Float64Array, a: Float64Array, b: Float64Array) {
    var t = new Float64Array(31);
    for (var i = 0; i < 16; ++i) {
        for (var j = 0; j < 16; ++j)
            t[i + j] += a[i] * b[j];
    }
    for (var i = 0; i < 15; ++i)
        t[i] += 38 * t[i + 16];
    for (var i = 0; i < 16; ++i)
        o[i] = t[i];
    carry(o);
    carry(o);
}

function invert(o: Float64Array, i: Float64Array) {
    var c = gf();
    for (var a = 0; a < 16; ++a)
        c[a] = i[a];
    for (var a = 253; a >= 0; --a) {
        multmod(c, c, c);
        if (a !== 2 && a !== 4)
            multmod(c, c, i);
    }
    for (var a = 0; a < 16; ++a)
        o[a] = c[a];
}

function clamp(z: Uint8Array) {
    z[31] = (z[31] & 127) | 64;
    z[0] &= 248;
}

function generatePublicKey(privateKey: Uint8Array) {
    var r, z = new Uint8Array(32);
    var a = gf([1]),
        b = gf([9]),
        c = gf(),
        d = gf([1]),
        e = gf(),
        f = gf(),
        _121665 = gf([0xdb41, 1]),
        _9 = gf([9]);
    for (var i = 0; i < 32; ++i)
        z[i] = privateKey[i];
    clamp(z);
    for (var 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;
}

function generatePresharedKey() {
    var privateKey = new Uint8Array(32);
    crypto.getRandomValues(privateKey);
    return privateKey;
}

function generatePrivateKey() {
    var privateKey = generatePresharedKey();
    clamp(privateKey);
    return privateKey;
}

function encodeBase64(dest: Uint8Array, src: Uint8Array) {
    var 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 (var 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);
}

function keyToBase64(key: Uint8Array) {
    var 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 as any);
}

export function generateKeypair() {
    var privateKey = generatePrivateKey();
    var publicKey = generatePublicKey(privateKey);
    return {
        publicKey: keyToBase64(publicKey),
        privateKey: keyToBase64(privateKey)
    };
}