namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;

/// <summary>
///     Optional driver capability: expose a small bag of operator-facing diagnostic key/value pairs
///     (e.g. S7's negotiated PDU size) that ride the driver-health snapshot to the AdminUI <c>/hosts</c>
///     page (Gitea #640).
/// </summary>
/// <remarks>
///     <para>
///         <b>Why a bag rather than fields on <see cref="DriverHealth"/>.</b> The facts worth showing are
///         driver-specific and do not change the driver's <i>state</i>; a typed field per driver would
///         widen the core record and the telemetry proto for every driver. Same additive-never-a-state-change
///         rule as <see cref="ISkippedTagReporter"/>.
///     </para>
///     <para>
///         Values are strings so the telemetry proto stays a plain <c>map&lt;string,string&gt;</c>. Keep the
///         bag small (<see cref="DriverDiagnostics.MaxEntries"/> entries, text truncated to
///         <see cref="DriverDiagnostics.MaxValueLength"/>): it is published on every state change.
///     </para>
/// </remarks>
public interface IDriverDiagnostics
{
    /// <summary>
    ///     Snapshot of the driver's diagnostics. Must be a pure in-memory read with no I/O — it is called on
    ///     the health-publish path, deliberately NOT through the resilience pipeline.
    /// </summary>
    /// <returns>The key/value pairs; empty when there is nothing to show yet.</returns>
    IReadOnlyDictionary<string, string> GetDiagnostics();
}

/// <summary>Bounds and helpers shared by every consumer of <see cref="IDriverDiagnostics"/>.</summary>
public static class DriverDiagnostics
{
    /// <summary>Maximum number of entries carried on a health snapshot; extras are dropped (ordinal key order).</summary>
    public const int MaxEntries = 16;

    /// <summary>Maximum length of a key or value carried on a health snapshot; longer text is truncated.</summary>
    public const int MaxValueLength = 200;

    /// <summary>
    ///     Normalises a driver's bag for publishing: ordinal key order, capped entry count, truncated text.
    ///     Deterministic so the same facts always produce the same fingerprint digest.
    /// </summary>
    /// <param name="raw">The bag the driver returned.</param>
    /// <returns>A bounded, ordered copy.</returns>
    public static IReadOnlyDictionary<string, string> Bound(IReadOnlyDictionary<string, string> raw)
    {
        var result = new SortedDictionary<string, string>(StringComparer.Ordinal);
        foreach (var kv in raw.OrderBy(k => k.Key, StringComparer.Ordinal))
        {
            if (result.Count >= MaxEntries) break;
            result[Truncate(kv.Key ?? "")] = Truncate(kv.Value ?? "");
        }
        return result;
    }

    private static string Truncate(string s) => s.Length <= MaxValueLength ? s : s[..MaxValueLength];
}