<?php
/**
 * Minimal SMTP sender (STARTTLS + AUTH LOGIN) without Composer.
 * Tested with Azure Communication Service SMTP: smtp.azurecomm.net:587
 * Author: www.sraga.cz
 */


// ---------------- Example usage ----------------
try {
    smtp_send([
        'host'      => 'smtp.azurecomm.net',
        'port'      => 587,
        'username'  => 'userName@domena.cz',
        'password'  => 'clientSecretValue',                 // ← store securely (env/secret)
        'from'      => 'mailFromAddress@domena.cz',
        'from_name' => 'mailFromAddress@domena.cz',
        'to'        => 'test@domena.cz',
        'subject'   => 'Test email from PHP',
        'body'      => "This is a test email sent from a pure-PHP SMTP client.",
        'debug'     => true,                 // set true to see SMTP I/O to STDERR
    ]);
    echo "Email sent OK\n";
} catch (Throwable $e) {
    // Print a clear error if something goes wrong
    fwrite(STDERR, "SMTP error: " . $e->getMessage() . "\n");
    exit(1);
}


// ---------------- Functions ----------------

function smtp_send(array $cfg): void
{
    $host        = $cfg['host'];          // e.g. smtp.azurecomm.net
    $port        = $cfg['port'] ?? 587;   // 587 for STARTTLS
    $username    = $cfg['username'];      // SMTP user (e.g. web@domain.cz)
    $password    = $cfg['password'];      // SMTP password
    $from        = $cfg['from'];          // RFC5322 From: email address
    $fromName    = $cfg['from_name'] ?? '';   // Display name (optional)
    $to          = $cfg['to'];            // recipient email
    $subject     = $cfg['subject'];       // subject (UTF-8 ok)
    $body        = $cfg['body'];          // plain text body
    $timeout     = $cfg['timeout'] ?? 30;
    $debug       = $cfg['debug'] ?? false;

    $peerName = $cfg['peer_name'] ?? $host; // SNI name for TLS

    $context = stream_context_create([
        'ssl' => [
            'crypto_method'        => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT | STREAM_CRYPTO_METHOD_TLSv1_3_CLIENT,
            'verify_peer'          => true,
            'verify_peer_name'     => true,
            'peer_name'            => $peerName,
            // If your OS trust store is standard, no need to set cafile/capath.
            // 'cafile'            => '/etc/ssl/certs/ca-certificates.crt',
            'SNI_enabled'          => true,
            'disable_compression'  => true,
        ],
    ]);

    $fp = stream_socket_client(
        "tcp://$host:$port",
        $errno,
        $errstr,
        $timeout,
        STREAM_CLIENT_CONNECT,
        $context
    );

    if (!$fp) {
        throw new RuntimeException("Connect failed: $errno $errstr");
    }
    stream_set_timeout($fp, $timeout);

    // --- Helpers -------------------------------------------------------------
    $read = function() use ($fp, $debug): array {
        $lines = [];
        while (($line = fgets($fp, 2048)) !== false) {
            $lines[] = rtrim($line, "\r\n");
            if ($debug) { fwrite(STDERR, "S: $line"); }
            // Multi-line replies have format "123-..." and end on "123 ..." (space)
            if (preg_match('/^\d{3} /', $line)) break;
        }
        if (empty($lines)) throw new RuntimeException("No response from server");
        $code = (int)substr($lines[count($lines)-1], 0, 3);
        return [$code, $lines];
    };

    $send = function(string $cmd) use ($fp, $debug) {
        if ($debug) { fwrite(STDERR, "C: $cmd\n"); }
        fwrite($fp, $cmd . "\r\n");
    };

    $expect = function(int $want) use ($read) {
        [$code, $lines] = $read();
        if ($code !== $want) {
            $msg = implode("\n", $lines);
            throw new RuntimeException("Expected $want, got $code\n$msg");
        }
        return $lines;
    };

    // --- SMTP dialogue -------------------------------------------------------
    $expect(220);                                // 220 greeting
    $ehloName = gethostname() ?: 'localhost';
    $send("EHLO $ehloName");
    $expect(250);

    // STARTTLS
    $send("STARTTLS");
    $expect(220);                                // Ready to start TLS
    if (!stream_socket_enable_crypto($fp, true, STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT | STREAM_CRYPTO_METHOD_TLSv1_3_CLIENT)) {
        throw new RuntimeException("TLS handshake failed");
    }

    // Re‑EHLO after STARTTLS
    $send("EHLO $ehloName");
    $expect(250);

    // AUTH LOGIN
    $send("AUTH LOGIN");
    $expect(334);                                // "VXNlcm5hbWU6" (Username:)
    $send(base64_encode($username));
    $expect(334);                                // "UGFzc3dvcmQ6" (Password:)
    $send(base64_encode($password));
    $expect(235);                                // Auth OK

    // MAIL/RCPT
    $send("MAIL FROM:<$from>");
    $expect(250);
    $send("RCPT TO:<$to>");
    $expect(250);

    // DATA – headers + body with dot‑stuffing
    $send("DATA");
    $expect(354);

    // Headers
    $headers = [];
    $fromHeader = $fromName !== ''
        ? sprintf('From: %s <%s>', encodeDisplayName($fromName), $from)
        : sprintf('From: <%s>', $from);
    $headers[] = $fromHeader;
    $headers[] = "To: <$to>";
    $headers[] = "Subject: " . encodeSubject($subject);
    $headers[] = "Date: " . date('r');
    $headers[] = "Message-ID: <" . bin2hex(random_bytes(16)) . '@' . (parse_url("https://$peerName", PHP_URL_HOST) ?: 'localhost') . ">";
    $headers[] = "MIME-Version: 1.0";
    $headers[] = "Content-Type: text/plain; charset=UTF-8";
    $headers[] = "Content-Transfer-Encoding: 8bit";
    $headers[] = "X-Mailer: PHP-SMTP/1.0";

    $data  = implode("\r\n", $headers) . "\r\n\r\n" . $body;

    // Dot‑stuffing per RFC5321 §4.5.2
    $data = preg_replace('/\r\n\./', "\r\n..", $data);
    // Ensure ends with CRLF.CRLF
    if (!str_ends_with($data, "\r\n")) $data .= "\r\n";

    fwrite($fp, $data . ".\r\n");
    $expect(250);                                // accepted

    // QUIT
    $send("QUIT");
    $read();                                     // 221
    fclose($fp);
}

/** Encode UTF‑8 display name safely for headers */
function encodeDisplayName(string $name): string {
    // Quote if contains specials; also provide RFC2047 when needed
    if (preg_match('/[^\x20-\x7E]/', $name)) {
        return '=?UTF-8?B?' . base64_encode($name) . '?=';
    }
    if (preg_match('/[",]/', $name)) {
        return '"' . addcslashes($name, '\\"') . '"';
    }
    return $name;
}

/** RFC2047 encode UTF‑8 Subject if needed */
function encodeSubject(string $subject): string {
    return preg_match('/[^\x20-\x7E]/', $subject)
        ? '=?UTF-8?B?' . base64_encode($subject) . '?='
        : $subject;
}