namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;

/// <summary>
///     The ONE place an AbCip driver's effective transport is decided from its configured
///     <see cref="AbCipDriverOptions.Transport"/>. The driver constructor, the Test Connect probe and the
///     CLI (through the driver) all resolve through here, so they cannot disagree about what an absent
///     <c>transport</c> key means.
///     <para>Precedence (final review I1): an explicit per-driver <c>transport</c> key wins; otherwise the
///     node-level default (<c>Drivers:AbCip:DefaultTransport</c>, read in the Host composition root and passed
///     in as <c>nodeDefault</c>); otherwise the compiled <see cref="Default"/>.</para>
/// </summary>
public static class AbCipTransportResolver
{
    /// <summary>The compiled default: the transport an absent key selects when no node default is configured.</summary>
    public const AbCipTransport Default = AbCipTransport.Native;

    /// <summary>Returns the effective transport: an explicit value always wins; null means <paramref name="nodeDefault"/>.</summary>
    /// <param name="configured">The configured transport, or null for "use the default".</param>
    /// <param name="nodeDefault">The node-level default for drivers with no key (the compiled <see cref="Default"/> unless pinned).</param>
    /// <returns>The transport the driver runs on.</returns>
    public static AbCipTransport Resolve(AbCipTransport? configured, AbCipTransport nodeDefault = Default) =>
        configured ?? nodeDefault;

    /// <summary>Returns the effective transport for <paramref name="options"/>.</summary>
    /// <param name="options">The driver options.</param>
    /// <param name="nodeDefault">The node-level default for drivers with no key.</param>
    /// <returns>The transport the driver runs on.</returns>
    public static AbCipTransport Resolve(AbCipDriverOptions options, AbCipTransport nodeDefault = Default)
    {
        ArgumentNullException.ThrowIfNull(options);
        return Resolve(options.Transport, nodeDefault);
    }

    /// <summary>
    ///     Parses a transport name the way the driver-config <c>transport</c> key and the node-level default
    ///     are parsed: a defined enum NAME, case-insensitive. Numeric strings ("0", "7") and the flags form
    ///     ("Native,Libplctag") are rejected — <c>Enum.TryParse</c> alone accepts both.
    /// </summary>
    /// <param name="raw">The raw value.</param>
    /// <param name="transport">The parsed transport.</param>
    /// <returns>True when <paramref name="raw"/> names a transport.</returns>
    public static bool TryParse(string? raw, out AbCipTransport transport)
    {
        transport = Default;
        if (string.IsNullOrWhiteSpace(raw)) return false;
        // Exact name match only: Enum.TryParse would also accept "1" and the flags form "Native,Libplctag".
        var name = Enum.GetNames<AbCipTransport>()
            .FirstOrDefault(n => string.Equals(n, raw.Trim(), StringComparison.OrdinalIgnoreCase));
        return name is not null && Enum.TryParse(name, out transport);
    }

    /// <summary>
    ///     Operator-facing description of the configured-vs-effective transport for the init log line:
    ///     <c>Native (default)</c> when the key was absent and the compiled default applies,
    ///     <c>Libplctag (node default)</c> when the key was absent and the node pinned a different default,
    ///     <c>Native (configured)</c> when the key was explicit.
    /// </summary>
    /// <param name="configured">The configured transport, or null.</param>
    /// <param name="nodeDefault">The node-level default.</param>
    /// <returns>A short description.</returns>
    public static string Describe(AbCipTransport? configured, AbCipTransport nodeDefault = Default) =>
        configured is not null ? $"{configured} (configured)"
        : nodeDefault == Default ? $"{nodeDefault} (default)"
        : $"{nodeDefault} (node default)";
}