using Opc.Ua;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Server.OpcUa;

namespace ZB.MOM.WW.OtOpcUa.Server.Tests;

/// <summary>
///     Regression for Server-006 — synchronous OnReadValue / OnWriteValue stack hooks must
///     derive a <see cref="CancellationToken"/> from the operation deadline so a stalled
///     driver call doesn't pin a request thread for the full pipeline timeout. The shared
///     helper <see cref="DriverNodeManager.DeriveOperationCancellation"/> turns the
///     <see cref="ISystemContext"/>'s <c>OperationDeadline</c> into a linked CTS.
/// </summary>
[Trait("Category", "Unit")]
public sealed class DriverNodeManagerCancellationTests
{
    /// <summary>
    ///     Build a SystemContext bound to the supplied IOperationContext. SystemContext's
    ///     OperationContext setter is protected, so we use the public <c>Copy</c> method
    ///     which clones the context onto the supplied operation context.
    /// </summary>
    private static ISystemContext ContextWithDeadline(DateTime deadline)
        => new SystemContext().Copy(new StubOperationContext(deadline));

    [Fact]
    public void Future_deadline_produces_uncancelled_token()
    {
        var ctx = ContextWithDeadline(DateTime.UtcNow.AddSeconds(30));

        using var cts = DriverNodeManager.DeriveOperationCancellation(ctx, fallback: TimeSpan.FromSeconds(10));

        cts.Token.IsCancellationRequested.ShouldBeFalse();
    }

    [Fact]
    public void Past_deadline_produces_already_cancelled_token()
    {
        var ctx = ContextWithDeadline(DateTime.UtcNow.AddSeconds(-5));

        using var cts = DriverNodeManager.DeriveOperationCancellation(ctx, fallback: TimeSpan.FromSeconds(10));

        cts.Token.IsCancellationRequested.ShouldBeTrue(
            "an expired OperationDeadline must surface as an immediately-cancelled token so the "
            + "stalled driver call returns without burning a request thread");
    }

    [Fact]
    public void Missing_deadline_uses_fallback_timeout()
    {
        // No OperationContext attached → no deadline plumbed; helper falls back to the
        // supplied timeout so an OnReadValue hook into a stalled driver can't hang the
        // request thread indefinitely.
        var ctx = new SystemContext();

        using var cts = DriverNodeManager.DeriveOperationCancellation(ctx, fallback: TimeSpan.FromMilliseconds(20));

        cts.Token.WaitHandle.WaitOne(TimeSpan.FromMilliseconds(500)).ShouldBeTrue(
            "fallback timeout must fire so a missing deadline cannot hang the request thread");
        cts.Token.IsCancellationRequested.ShouldBeTrue();
    }

    [Fact]
    public void DateTime_MinValue_deadline_uses_fallback_timeout()
    {
        // IOperationContext.OperationDeadline is `DateTime.MinValue` when the stack hasn't
        // plumbed a deadline through. The helper treats that as "no deadline" and falls
        // back to the supplied timeout, otherwise an MinValue would surface as
        // already-cancelled and short-circuit every read.
        var ctx = ContextWithDeadline(DateTime.MinValue);

        using var cts = DriverNodeManager.DeriveOperationCancellation(ctx, fallback: TimeSpan.FromMilliseconds(20));

        cts.Token.WaitHandle.WaitOne(TimeSpan.FromMilliseconds(500)).ShouldBeTrue();
        cts.Token.IsCancellationRequested.ShouldBeTrue();
    }

    [Fact]
    public void DateTime_MaxValue_deadline_uses_fallback_timeout_not_overflow()
    {
        // OperationContext sets OperationDeadline = DateTime.MaxValue when the client's
        // RequestHeader.TimeoutHint is zero (the default). DateTime.MaxValue - UtcNow
        // overflows CancellationTokenSource(TimeSpan)'s Int32.MaxValue-ms cap, so the
        // helper must collapse it to the fallback — otherwise the read throws
        // ArgumentOutOfRangeException from inside DeriveOperationCancellation and surfaces
        // as BadInternalError on every read (regression that broke OpcUaServerIntegrationTests).
        var ctx = ContextWithDeadline(DateTime.MaxValue);

        using var cts = DriverNodeManager.DeriveOperationCancellation(ctx, fallback: TimeSpan.FromSeconds(30));

        cts.Token.IsCancellationRequested.ShouldBeFalse("MaxValue deadline + 30 s fallback must produce a live token");
    }

    [Fact]
    public void Null_context_returns_uncancelled_token_with_fallback()
    {
        // Defensive — OnReadValue receives an ISystemContext from the stack so the helper
        // shouldn't NRE if a future override passes through a null context.
        using var cts = DriverNodeManager.DeriveOperationCancellation(context: null!, fallback: TimeSpan.FromSeconds(30));

        cts.Token.IsCancellationRequested.ShouldBeFalse();
    }

    /// <summary>Minimal IOperationContext for deadline testing.</summary>
    private sealed class StubOperationContext(DateTime deadline) : IOperationContext
    {
        public DateTime OperationDeadline { get; } = deadline;
        public NodeId? SessionId => null;
        public IUserIdentity? UserIdentity => null;
        public IList<string>? PreferredLocales => null;
        public DiagnosticsMasks DiagnosticsMask => DiagnosticsMasks.None;
        public StringTable StringTable { get; } = new StringTable();
        public StatusCode OperationStatus => StatusCodes.Good;
        public string? AuditEntryId => null;
    }
}