<?php
declare(strict_types=1);

const CONNECT_TIMEOUT = 12; // seconds
const EHLO_NAME = 'tool.medowar.de';

/**
 * Connects to a mail server, negotiates STARTTLS (or implicit TLS), and reports
 * on the TLS handshake and the server certificate: trust chain, hostname match,
 * validity window, issuer/subject and SANs.
 */
class MailTlsChecker
{
    /**
     * @return array TLS/certificate report for the given host:port and protocol.
     */
    public function check(string $host, int $port, string $protocol): array
    {
        $report = [
            'host'        => $host,
            'port'        => $port,
            'protocol'    => $protocol,
            'mode'        => in_array($protocol, ['smtps', 'imaps', 'pop3s'], true) ? 'implicit' : 'starttls',
            'connected'   => false,
            'starttls'    => null,   // negotiation transcript lines (starttls only)
            'tls_ok'      => false,  // handshake succeeded *and* peer verified
            'trusted'     => false,  // chain verified against CA bundle
            'hostname_ok' => false,  // certificate valid for the requested host
            'errors'      => [],
            'cert'        => null,
            'tls_version' => null,
            'cipher'      => null,
        ];

        // 1) Handshake with full verification to learn whether the chain is trusted.
        $verified = $this->handshake($host, $port, $protocol, true, $vErr, $transcript);
        $report['starttls'] = $transcript;
        if ($verified === null) {
            // Could not even reach the TLS stage — connection/protocol error.
            $report['errors'][] = $vErr;
            return $report;
        }
        $report['connected'] = true;
        $report['trusted']   = ($vErr === null);
        if ($vErr !== null) {
            $report['errors'][] = 'Certificate chain not trusted: ' . $vErr;
        }

        // 2) Handshake again without verification so we can always inspect the cert,
        //    even when it is self-signed, expired, or for the wrong hostname.
        $stream = $this->handshake($host, $port, $protocol, false, $rErr, $t2);
        if (!is_resource($stream)) {
            if ($rErr !== null) {
                $report['errors'][] = $rErr;
            }
            return $report;
        }

        $params  = stream_context_get_params($stream);
        $meta    = stream_get_meta_data($stream);
        $certRes = $params['options']['ssl']['peer_certificate'] ?? null;

        // Negotiated protocol version / cipher (from the crypto meta, when exposed).
        foreach (($meta['crypto'] ?? []) as $k => $v) {
            if ($k === 'protocol') { $report['tls_version'] = $v; }
            if ($k === 'cipher_name') { $report['cipher'] = $v; }
        }

        if ($certRes) {
            $report['cert'] = $this->describeCert($certRes, $host, $report);
            $report['hostname_ok'] = $report['cert']['hostname_ok'];
        } else {
            $report['errors'][] = 'TLS handshake completed but no peer certificate was presented.';
        }

        fclose($stream);

        $report['tls_ok'] = $report['trusted']
            && $report['hostname_ok']
            && ($report['cert']['time_ok'] ?? false);

        return $report;
    }

    /**
     * Opens a TCP connection, runs the STARTTLS dance if required, then enables
     * crypto. Returns the stream resource on success. On verification failure
     * with $verify=true, returns false-y stream but populates $err. On connection
     * failure returns null. $transcript receives the plaintext protocol lines.
     *
     * @return resource|false|null
     */
    private function handshake(string $host, int $port, string $protocol, bool $verify, ?string &$err, ?array &$transcript)
    {
        $err = null;
        $transcript = [];

        $ctx = stream_context_create(['ssl' => [
            'verify_peer'       => $verify,
            'verify_peer_name'  => $verify,
            'allow_self_signed' => !$verify,
            'capture_peer_cert' => true,
            'SNI_enabled'       => true,
            'peer_name'         => $host,
        ]]);

        // Always connect over plain TCP and drive the crypto switch ourselves.
        // For implicit-TLS ports that simply means enabling crypto immediately,
        // with no plaintext exchange — this keeps a single code path and gives us
        // reliable error reporting via the OpenSSL error queue.
        $errno = 0; $errstr = '';
        $stream = @stream_socket_client(
            sprintf('tcp://%s:%d', $host, $port),
            $errno,
            $errstr,
            CONNECT_TIMEOUT,
            STREAM_CLIENT_CONNECT,
            $ctx
        );

        if (!is_resource($stream)) {
            $err = $errstr !== '' ? "Connection failed: $errstr (errno $errno)" : 'Connection failed.';
            return null;
        }

        stream_set_timeout($stream, CONNECT_TIMEOUT);

        // STARTTLS protocols exchange a few plaintext commands before the switch.
        if (!in_array($protocol, ['smtps', 'imaps', 'pop3s'], true)) {
            try {
                $this->negotiateStartTls($stream, $protocol, $transcript);
            } catch (\RuntimeException $e) {
                fclose($stream);
                $err = $e->getMessage();
                return null;
            }
        }

        openssl_error_string(); // clear any stale queue entries
        error_clear_last();
        $ok = @stream_socket_enable_crypto(
            $stream,
            true,
            STREAM_CRYPTO_METHOD_TLS_CLIENT
        );

        if ($ok !== true) {
            $sslErr = $this->drainSslErrors();
            $last = error_get_last()['message'] ?? '';
            fclose($stream);
            // Trim PHP's noisy function prefix and collapse multi-line OpenSSL blurb.
            $detail = trim(preg_replace('/\s+/', ' ', str_replace('stream_socket_enable_crypto():', '', $sslErr ?: $last)));
            if ($verify) {
                // The handshake was reached; the certificate simply did not verify.
                $err = $detail ?: 'Certificate verification failed.';
                return false;
            }
            $err = $detail ?: 'TLS handshake failed.';
            return null;
        }

        return $stream;
    }

    /**
     * Speaks the protocol-specific STARTTLS handshake up to (not including) the
     * crypto switch. Throws RuntimeException if the server refuses.
     * @param resource $stream
     */
    private function negotiateStartTls($stream, string $protocol, array &$transcript): void
    {
        switch ($protocol) {
            case 'smtp':   // submission, port 587
            case 'smtp25': // MX / server-to-server, port 25
                $this->expect($stream, '220', $transcript);
                $this->send($stream, 'EHLO ' . EHLO_NAME, $transcript);
                $ehlo = $this->readSmtp($stream, $transcript);
                if (stripos($ehlo, 'STARTTLS') === false) {
                    throw new \RuntimeException('Server did not advertise STARTTLS in its EHLO response.');
                }
                $this->send($stream, 'STARTTLS', $transcript);
                $this->expect($stream, '220', $transcript);
                break;

            case 'imap':
                $this->expect($stream, '* OK', $transcript, true);
                $this->send($stream, 'a1 STARTTLS', $transcript);
                $resp = $this->readLine($stream, $transcript);
                if (stripos($resp, 'a1 OK') === false) {
                    throw new \RuntimeException('IMAP server refused STARTTLS: ' . trim($resp));
                }
                break;

            case 'pop3':
                $this->expect($stream, '+OK', $transcript, true);
                $this->send($stream, 'STLS', $transcript);
                $resp = $this->readLine($stream, $transcript);
                if (stripos($resp, '+OK') !== 0) {
                    throw new \RuntimeException('POP3 server refused STLS: ' . trim($resp));
                }
                break;

            default:
                throw new \RuntimeException('Unsupported protocol: ' . $protocol);
        }
    }

    /** @param resource $stream */
    private function send($stream, string $line, array &$transcript): void
    {
        $transcript[] = 'C: ' . $line;
        fwrite($stream, $line . "\r\n");
    }

    /**
     * Reads one line and asserts it starts with $code (or contains it, when $contains).
     * @param resource $stream
     */
    private function expect($stream, string $code, array &$transcript, bool $contains = false): void
    {
        $line = $this->readLine($stream, $transcript);
        $hit = $contains ? (stripos($line, $code) !== false) : (strpos(ltrim($line), $code) === 0);
        if (!$hit) {
            throw new \RuntimeException(sprintf('Expected "%s" but got: %s', $code, trim($line)));
        }
    }

    /**
     * Reads a full multiline SMTP reply (lines like "250-..." until "250 ...").
     * @param resource $stream
     */
    private function readSmtp($stream, array &$transcript): string
    {
        $all = '';
        while (($line = $this->readLine($stream, $transcript)) !== '') {
            $all .= $line;
            // Continuation lines have a hyphen as the 4th character.
            if (strlen($line) < 4 || $line[3] !== '-') {
                break;
            }
        }
        return $all;
    }

    /** @param resource $stream */
    private function readLine($stream, array &$transcript): string
    {
        $line = fgets($stream, 4096);
        if ($line === false) {
            $meta = stream_get_meta_data($stream);
            if (!empty($meta['timed_out'])) {
                throw new \RuntimeException('Timed out waiting for the server to respond.');
            }
            throw new \RuntimeException('Connection closed by server before a reply was received.');
        }
        $transcript[] = 'S: ' . rtrim($line, "\r\n");
        return $line;
    }

    /** Collects any pending messages from the OpenSSL error queue. */
    private function drainSslErrors(): string
    {
        $msgs = [];
        while ($e = openssl_error_string()) {
            $msgs[] = $e;
        }
        return implode('; ', $msgs);
    }

    /**
     * Parses the peer certificate and evaluates validity window + hostname match.
     * @param \OpenSSLCertificate|resource $certRes
     */
    private function describeCert($certRes, string $host, array $report): array
    {
        $info = openssl_x509_parse($certRes) ?: [];
        $now  = time();
        $from = $info['validFrom_time_t'] ?? 0;
        $to   = $info['validTo_time_t'] ?? 0;

        $sans = [];
        $altName = $info['extensions']['subjectAltName'] ?? '';
        foreach (array_filter(array_map('trim', explode(',', $altName))) as $entry) {
            if (stripos($entry, 'DNS:') === 0) {
                $sans[] = substr($entry, 4);
            } elseif (stripos($entry, 'IP Address:') === 0) {
                $sans[] = substr($entry, 11);
            } else {
                $sans[] = $entry;
            }
        }
        // Fall back to CN if there are no SANs (legacy certs).
        $cn = $info['subject']['CN'] ?? null;
        $names = $sans ?: ($cn !== null ? [$cn] : []);

        $pem = '';
        openssl_x509_export($certRes, $pem);

        return [
            'subject'      => $this->dn($info['subject'] ?? []),
            'issuer'       => $this->dn($info['issuer'] ?? []),
            'cn'           => $cn,
            'sans'         => $sans,
            'valid_from'   => $from,
            'valid_to'     => $to,
            'time_ok'      => $from && $to && $now >= $from && $now <= $to,
            'expired'      => $to && $now > $to,
            'not_yet'      => $from && $now < $from,
            'days_left'    => $to ? (int) floor(($to - $now) / 86400) : null,
            'hostname_ok'  => $this->matchesHost($host, $names),
            'self_signed'  => ($this->dn($info['subject'] ?? []) === $this->dn($info['issuer'] ?? [])),
            'serial'       => $info['serialNumberHex'] ?? ($info['serialNumber'] ?? ''),
            'sig_type'     => $info['signatureTypeSN'] ?? '',
            'fingerprint'  => openssl_x509_fingerprint($certRes, 'sha256') ?: '',
        ];
    }

    /** @param array<string,mixed> $dn */
    private function dn(array $dn): string
    {
        $parts = [];
        foreach ($dn as $k => $v) {
            $v = is_array($v) ? implode(' + ', $v) : $v;
            $parts[] = "$k=$v";
        }
        return implode(', ', $parts);
    }

    /**
     * RFC 6125 style match: exact or single leftmost wildcard.
     * @param string[] $names
     */
    private function matchesHost(string $host, array $names): bool
    {
        $host = strtolower(rtrim($host, '.'));
        foreach ($names as $name) {
            $name = strtolower(rtrim($name, '.'));
            if ($name === $host) {
                return true;
            }
            if (str_starts_with($name, '*.')) {
                $suffix = substr($name, 1); // ".example.com"
                // Wildcard matches exactly one leftmost label.
                if (str_ends_with($host, $suffix)
                    && substr_count($host, '.') === substr_count($name, '.')) {
                    return true;
                }
            }
        }
        return false;
    }
}

/** Default port for each protocol, used when the user leaves the port blank. */
const DEFAULT_PORTS = [
    'smtp25' => 25,
    'smtp'   => 587,
    'smtps'  => 465,
    'imap'   => 143,
    'imaps'  => 993,
    'pop3'   => 110,
    'pop3s'  => 995,
];

const PROTOCOL_LABELS = [
    'smtp25' => 'SMTP + STARTTLS — MX / server-to-server (25)',
    'smtp'   => 'SMTP + STARTTLS — submission (587)',
    'smtps'  => 'SMTPS — implicit TLS (465)',
    'imap'   => 'IMAP + STARTTLS (143)',
    'imaps'  => 'IMAPS — implicit TLS (993)',
    'pop3'   => 'POP3 + STLS (110)',
    'pop3s'  => 'POP3S — implicit TLS (995)',
];

$host     = trim((string) ($_GET['host'] ?? ''));
$protocol = (string) ($_GET['protocol'] ?? 'smtp');
$portRaw  = trim((string) ($_GET['port'] ?? ''));
$report   = null;
$inputError = null;

if (!isset(DEFAULT_PORTS[$protocol])) {
    $protocol = 'smtp';
}
$port = $portRaw !== '' ? (int) $portRaw : DEFAULT_PORTS[$protocol];

if ($host !== '') {
    // Accept a bare hostname; strip scheme/path/port if a URL was pasted.
    $host = preg_replace('#^\w+://#', '', $host);
    $host = explode('/', $host)[0];
    $host = strtolower(trim($host));
    if (str_contains($host, ':')) {
        $host = explode(':', $host)[0];
    }

    if (!preg_match('/^(?=.{1,253}$)([a-z0-9](-?[a-z0-9])*\.)+[a-z]{2,}$/', $host)) {
        $inputError = 'Please enter a valid mail server hostname (e.g. mail.example.com).';
    } elseif ($port < 1 || $port > 65535) {
        $inputError = 'Please enter a valid port between 1 and 65535.';
    } else {
        $report = (new MailTlsChecker())->check($host, $port, $protocol);
    }
}

function fmtDate(?int $ts): string
{
    return $ts ? gmdate('Y-m-d H:i:s', $ts) . ' UTC' : '—';
}
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Mail TLS Checker</title>
    <style>
        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
            max-width: 1000px;
            margin: 40px auto;
            padding: 0 20px;
            background: #f5f5f5;
            color: #333;
        }
        h1 { color: #333; }
        .info { background: #e3f2fd; padding: 15px; border-radius: 5px; margin-bottom: 20px; }
        form.lookup { margin-bottom: 20px; display: flex; gap: 10px; flex-wrap: wrap; align-items: stretch; }
        input[type=text], select {
            padding: 10px; font-size: 15px; border: 1px solid #ccc; border-radius: 5px; background: white;
        }
        input[name=host] { flex: 1; min-width: 220px; }
        input[name=port] { width: 90px; }
        .btn {
            display: inline-block; padding: 10px 20px; background: #2196F3; color: white;
            text-decoration: none; border-radius: 5px; border: none; cursor: pointer; font-size: 15px;
        }
        .btn:hover { background: #1976D2; }
        .error { background: #ffebee; color: #c62828; padding: 10px; border-radius: 5px; margin: 10px 0; }
        .verdict {
            display: flex; align-items: center; gap: 12px; padding: 16px 20px; border-radius: 6px;
            font-size: 18px; font-weight: 600; margin: 16px 0;
        }
        .verdict.ok   { background: #e8f5e9; color: #2e7d32; border-left: 6px solid #43a047; }
        .verdict.fail { background: #ffebee; color: #c62828; border-left: 6px solid #e53935; }
        .checks { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 10px; margin: 16px 0; }
        .check {
            display: flex; align-items: center; gap: 8px; padding: 12px 14px; border-radius: 5px;
            background: white; box-shadow: 0 1px 3px rgba(0,0,0,0.1); font-size: 14px;
        }
        .check .ic { font-size: 18px; }
        .check.pass { border-left: 4px solid #43a047; }
        .check.warn { border-left: 4px solid #fb8c00; }
        .check.crit { border-left: 4px solid #e53935; }
        .errlist { margin: 10px 0; }
        .errlist .error { margin: 6px 0; }
        h2 { color: #333; margin-top: 30px; }
        table { width: 100%; border-collapse: collapse; background: white; box-shadow: 0 1px 3px rgba(0,0,0,0.1); margin-top: 10px; }
        th, td { padding: 10px 12px; text-align: left; border-bottom: 1px solid #eee; font-size: 13px; vertical-align: top; }
        th { width: 180px; color: #555; background: #fafafa; font-weight: 600; }
        td.mono, .mono { font-family: monospace; word-break: break-all; }
        ul.sans { margin: 0; padding-left: 18px; }
        ul.sans li { font-family: monospace; font-size: 13px; }
        .pill { display: inline-block; padding: 2px 8px; border-radius: 10px; font-size: 12px; font-weight: 600; }
        .pill.g { background: #e8f5e9; color: #2e7d32; }
        .pill.r { background: #ffebee; color: #c62828; }
        .pill.o { background: #fff3e0; color: #e65100; }
        details.transcript { margin-top: 20px; }
        details.transcript pre {
            background: #263238; color: #cfd8dc; padding: 12px 14px; border-radius: 5px;
            font-size: 12px; overflow-x: auto; line-height: 1.5;
        }
        summary { cursor: pointer; font-weight: 600; color: #1976D2; }
    </style>
</head>
<body>
    <h1>🔐 Mail TLS Checker</h1>

    <div class="info">
        Connects to a mail server, negotiates <strong>STARTTLS</strong> (or implicit TLS) and reports on the
        <strong>TLS handshake</strong> and <strong>server certificate</strong>: trust chain, hostname match,
        validity window, issuer and SANs. Nothing is sent beyond the TLS negotiation — no login, no mail.
    </div>

    <form class="lookup" method="GET">
        <input type="text" name="host" placeholder="mail.example.com"
               value="<?= htmlspecialchars($host) ?>" autofocus>
        <select name="protocol">
            <?php foreach (PROTOCOL_LABELS as $key => $label): ?>
                <option value="<?= $key ?>" <?= $protocol === $key ? 'selected' : '' ?>>
                    <?= htmlspecialchars($label) ?>
                </option>
            <?php endforeach; ?>
        </select>
        <input type="text" name="port" placeholder="port"
               value="<?= htmlspecialchars($portRaw) ?>">
        <button type="submit" class="btn">🔍 Test TLS</button>
    </form>
    <p style="color:#888;font-size:12px;margin-top:-10px;">
        Leave the port blank to use the protocol default
        (<?= implode(', ', array_map(fn($p, $n) => "$p=$n", array_keys(DEFAULT_PORTS), DEFAULT_PORTS)) ?>).
    </p>

    <?php if ($inputError): ?>
        <div class="error"><?= htmlspecialchars($inputError) ?></div>
    <?php endif; ?>

    <?php if ($report !== null): ?>
        <?php $cert = $report['cert']; ?>

        <?php if ($report['tls_ok']): ?>
            <div class="verdict ok">✅ TLS is valid — trusted chain, correct hostname and within its validity period.</div>
        <?php else: ?>
            <div class="verdict fail">❌ TLS check failed — see the details below.</div>
        <?php endif; ?>

        <?php if (!empty($report['errors'])): ?>
            <div class="errlist">
                <?php foreach ($report['errors'] as $e): ?>
                    <div class="error">⚠️ <?= htmlspecialchars($e) ?></div>
                <?php endforeach; ?>
            </div>
        <?php endif; ?>

        <?php if ($report['connected']): ?>
        <div class="checks">
            <?php
            $timeOk = $cert['time_ok'] ?? false;
            $renderCheck = function (bool $pass, string $label, string $detail, bool $criticalIfFail = true) {
                $cls = $pass ? 'pass' : ($criticalIfFail ? 'crit' : 'warn');
                $ic  = $pass ? '✔️' : ($criticalIfFail ? '❌' : '⚠️');
                printf(
                    '<div class="check %s"><span class="ic">%s</span><div><strong>%s</strong><br>%s</div></div>',
                    $cls, $ic, htmlspecialchars($label), htmlspecialchars($detail)
                );
            };
            $renderCheck($report['trusted'], 'Trusted chain',
                $report['trusted'] ? 'Verified against system CA bundle' : 'Not verifiable / self-signed');
            $renderCheck($report['hostname_ok'], 'Hostname match',
                $report['hostname_ok'] ? $report['host'] . ' is covered' : 'Certificate not valid for ' . $report['host']);
            $renderCheck((bool) $timeOk, 'Validity period',
                $timeOk
                    ? ($cert['days_left'] !== null ? $cert['days_left'] . ' day(s) until expiry' : 'Currently valid')
                    : (($cert['expired'] ?? false) ? 'Certificate has expired' : 'Certificate not yet valid'));
            if ($cert && ($cert['days_left'] ?? null) !== null && $cert['days_left'] >= 0 && $cert['days_left'] <= 21) {
                $renderCheck(false, 'Expiry warning', 'Expires in ' . $cert['days_left'] . ' day(s)', false);
            }
            ?>
        </div>
        <?php endif; ?>

        <h2>Connection</h2>
        <table>
            <tr><th>Server</th><td class="mono"><?= htmlspecialchars($report['host'] . ':' . $report['port']) ?></td></tr>
            <tr><th>Protocol</th><td><?= htmlspecialchars(PROTOCOL_LABELS[$report['protocol']] ?? $report['protocol']) ?> — <?= htmlspecialchars($report['mode']) ?></td></tr>
            <tr><th>TLS version</th><td class="mono"><?= htmlspecialchars($report['tls_version'] ?: '—') ?></td></tr>
            <tr><th>Cipher</th><td class="mono"><?= htmlspecialchars($report['cipher'] ?: '—') ?></td></tr>
        </table>

        <?php if ($cert): ?>
        <h2>Certificate</h2>
        <table>
            <tr><th>Subject</th><td class="mono"><?= htmlspecialchars($cert['subject']) ?></td></tr>
            <tr><th>Common name</th><td class="mono"><?= htmlspecialchars($cert['cn'] ?? '—') ?></td></tr>
            <tr><th>Issuer</th><td class="mono"><?= htmlspecialchars($cert['issuer']) ?></td></tr>
            <tr>
                <th>Self-signed</th>
                <td><?= $cert['self_signed']
                    ? '<span class="pill o">yes</span>'
                    : '<span class="pill g">no</span>' ?></td>
            </tr>
            <tr>
                <th>Valid from</th>
                <td class="mono"><?= htmlspecialchars(fmtDate($cert['valid_from'])) ?>
                    <?= ($cert['not_yet'] ?? false) ? ' <span class="pill r">not yet valid</span>' : '' ?></td>
            </tr>
            <tr>
                <th>Valid to</th>
                <td class="mono"><?= htmlspecialchars(fmtDate($cert['valid_to'])) ?>
                    <?php if ($cert['expired'] ?? false): ?>
                        <span class="pill r">expired</span>
                    <?php elseif (($cert['days_left'] ?? 99) <= 21): ?>
                        <span class="pill o"><?= (int) $cert['days_left'] ?> day(s) left</span>
                    <?php else: ?>
                        <span class="pill g"><?= (int) $cert['days_left'] ?> day(s) left</span>
                    <?php endif; ?>
                </td>
            </tr>
            <tr>
                <th>Subject Alt Names</th>
                <td>
                    <?php if (!empty($cert['sans'])): ?>
                        <ul class="sans">
                            <?php foreach ($cert['sans'] as $s): ?>
                                <li><?= htmlspecialchars($s) ?></li>
                            <?php endforeach; ?>
                        </ul>
                    <?php else: ?>—<?php endif; ?>
                </td>
            </tr>
            <tr><th>Signature</th><td class="mono"><?= htmlspecialchars($cert['sig_type'] ?: '—') ?></td></tr>
            <tr><th>Serial</th><td class="mono"><?= htmlspecialchars((string) $cert['serial']) ?></td></tr>
            <tr><th>SHA-256 fingerprint</th><td class="mono"><?= htmlspecialchars(trim(chunk_split($cert['fingerprint'], 2, ':'), ':')) ?></td></tr>
        </table>
        <?php endif; ?>

        <?php if (!empty($report['starttls'])): ?>
        <details class="transcript">
            <summary>STARTTLS negotiation transcript</summary>
            <pre><?= htmlspecialchars(implode("\n", $report['starttls'])) ?></pre>
        </details>
        <?php endif; ?>
    <?php endif; ?>
</body>
</html>