namespace ScadaLink.NotificationService;

/// <summary>
/// NS-005: The three TLS modes the design doc defines for SMTP connections.
/// A single boolean cannot represent the requirement, so the configured
/// <c>SmtpConfiguration.TlsMode</c> string is parsed into this three-state enum.
/// </summary>
public enum SmtpTlsMode
{
    /// <summary>No transport security — plain SMTP. Maps to <c>SecureSocketOptions.None</c>.</summary>
    None,

    /// <summary>Opportunistic STARTTLS upgrade (typically port 587). Maps to <c>SecureSocketOptions.StartTls</c>.</summary>
    StartTls,

    /// <summary>Implicit TLS / SSL-on-connect (typically port 465). Maps to <c>SecureSocketOptions.SslOnConnect</c>.</summary>
    Ssl,
}

/// <summary>
/// NS-005: Parses the free-text <c>SmtpConfiguration.TlsMode</c> value into a
/// <see cref="SmtpTlsMode"/>, rejecting unknown values rather than silently
/// falling back to opportunistic negotiation.
/// </summary>
public static class SmtpTlsModeParser
{
    /// <summary>
    /// Parses a configured TLS mode string. A null or empty value defaults to
    /// <see cref="SmtpTlsMode.StartTls"/> (the design-doc default for port 587).
    /// </summary>
    /// <exception cref="ArgumentException">The value is not one of None/StartTLS/SSL.</exception>
    public static SmtpTlsMode Parse(string? tlsMode)
    {
        if (string.IsNullOrWhiteSpace(tlsMode))
        {
            return SmtpTlsMode.StartTls;
        }

        return tlsMode.Trim().ToLowerInvariant() switch
        {
            "none" => SmtpTlsMode.None,
            "starttls" => SmtpTlsMode.StartTls,
            "ssl" => SmtpTlsMode.Ssl,
            _ => throw new ArgumentException(
                $"Unknown SMTP TLS mode '{tlsMode}'. Expected one of: None, StartTLS, SSL.",
                nameof(tlsMode)),
        };
    }
}