<?php
declare(strict_types=1);

namespace Gatecraft;

use WP_User, WP_Error, WP_Session_Tokens, WP_CLI, RuntimeException, Throwable, Exception, DateTime, DateTimeImmutable, ZipArchive;

if (!defined('ABSPATH')) exit;

// RFC 6238 time-based one-time passwords (SHA1, 6 digits, 30 seconds), compatible with
// Google Authenticator, 1Password, Authy, Microsoft Authenticator.

function base32_encode_raw(string $bin): string
{
    $alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';
    $bits = '';
    foreach (str_split($bin) as $c) $bits .= str_pad(decbin(ord($c)), 8, '0', STR_PAD_LEFT);
    $out = '';
    foreach (str_split($bits, 5) as $chunk) $out .= $alpha[bindec(str_pad($chunk, 5, '0'))];
    return $out;
}

function base32_decode_raw(string $s): string
{
    $alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';
    $s = strtoupper(preg_replace('/[^A-Za-z2-7]/', '', $s));
    $bits = '';
    foreach (str_split($s) as $c) $bits .= str_pad(decbin(strpos($alpha, $c)), 5, '0', STR_PAD_LEFT);
    $out = '';
    foreach (str_split($bits, 8) as $byte) if (strlen($byte) === 8) $out .= chr(bindec($byte));
    return $out;
}

function totp_new_secret(): string
{
    return base32_encode_raw(random_bytes(20));
}

function totp_code(string $secretB32, int $step): string
{
    $key = base32_decode_raw($secretB32);
    $h = hash_hmac('sha1', pack('J', $step), $key, true);
    $o = ord($h[19]) & 0xf;
    $n = ((ord($h[$o]) & 0x7f) << 24) | (ord($h[$o + 1]) << 16) | (ord($h[$o + 2]) << 8) | ord($h[$o + 3]);
    return str_pad((string)($n % 1000000), 6, '0', STR_PAD_LEFT);
}

/** Returns the matched time step, or null. Accepts one step of clock drift either side. */
function totp_match(string $secretB32, string $code, ?int $lastStep): ?int
{
    $code = preg_replace('/\D/', '', $code);
    if (strlen($code) !== 6) return null;
    $now = intdiv(time(), 30);
    foreach ([0, -1, 1] as $d) {
        $step = $now + $d;
        if ($lastStep !== null && $step <= $lastStep) continue; // replay protection
        if (hash_equals(totp_code($secretB32, $step), $code)) return $step;
    }
    return null;
}

function totp_uri(string $secretB32, string $email): string
{
    $issuer = setting('brand_name');
    return 'otpauth://totp/' . rawurlencode($issuer . ':' . $email) . '?secret=' . $secretB32 . '&issuer=' . rawurlencode($issuer) . '&algorithm=SHA1&digits=6&period=30';
}


/* After 30 wrong codes in a day for one person, codes stop being checked for that day and the person is emailed once.
   Per-attempt limits already slow guessing; this caps it, however many addresses an attacker uses. */
const TOTP_DAILY_FAILURES = 30;

function totp_fail_key(int $userId): string
{
    return hash('sha256', 'totp-fail|' . $userId . '|' . intdiv(time(), 86400));
}

function totp_locked(int $userId): bool
{
    return (int)qv('SELECT hits FROM {rate_limits} WHERE k = ?', [totp_fail_key($userId)]) >= TOTP_DAILY_FAILURES;
}

function totp_note_failure(int $userId): void
{
    $k = totp_fail_key($userId);
    q('INSERT INTO {rate_limits} (k, hits, window_start) VALUES (?, 1, ?) ON DUPLICATE KEY UPDATE hits = hits + 1', [$k, time() + 86400]);
    if ((int)qv('SELECT hits FROM {rate_limits} WHERE k = ?', [$k]) === TOTP_DAILY_FAILURES) {
        audit('2fa.locked', 'user', $userId);
        gatecraft_notify_security_change($userId, 'Many wrong authenticator codes were entered for your account today, so codes are not accepted until tomorrow. If this was not you, change your password');
    }
}

/** Verify a user's code against their stored secret and record the step to stop replays. */
function totp_verify_user(int $userId, string $code): bool
{
    if (totp_locked($userId)) return false;
    $u = q1('SELECT totp_secret_enc, totp_last_step FROM {accounts} WHERE user_id = ?', [$userId]);
    $secret = decrypt_secret($u['totp_secret_enc'] ?? null);
    if (!$secret) {
        // The secret is there but cannot be read: the encryption key changed. Say so in the log, as no code can ever match.
        if (!empty($u['totp_secret_enc'])) log_debug('the authenticator secret of user ' . $userId . ' cannot be decrypted. The app key changed; reset this person\'s authenticator.');
        return false;
    }
    $step = totp_match($secret, $code, $u['totp_last_step'] !== null ? (int)$u['totp_last_step'] : null);
    if ($step === null) { totp_note_failure($userId); return false; }
    $upd = q('UPDATE {accounts} SET totp_last_step = ? WHERE user_id = ? AND (totp_last_step IS NULL OR totp_last_step < ?)', [$step, $userId, $step]);
    return $upd->rowCount() === 1;
}