using System.Net.Sockets;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;

/// <summary>
///     05/STAB-9 — the poll engine's <c>onError</c> sink must be wired to the driver health
///     surface: a poll-loop reader failure degrades health while preserving
///     <see cref="DriverHealth.LastSuccessfulRead"/>, and must never downgrade a pre-existing
///     <see cref="DriverState.Faulted"/> (the S7 nuance ported fleet-wide).
/// </summary>
[Trait("Category", "Unit")]
public sealed class ModbusPollErrorHealthTests
{
    private sealed class NoopTransport : IModbusTransport
    {
        public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
            => Task.FromResult(new byte[] { 0x03, 0x00 });
        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
    }

    /// <summary>A poll reader failure degrades health, preserving the last successful read timestamp.</summary>
    [Fact]
    public async Task PollReaderFailure_DegradesHealth_PreservesLastSuccessfulRead()
    {
        var opts = new ModbusDriverOptions { Host = "fake", Probe = new ModbusProbeOptions { Enabled = false } };
        var drv = new ModbusDriver(opts, "modbus-1", _ => new NoopTransport());
        await drv.InitializeAsync("{}", CancellationToken.None);

        var before = drv.GetHealth();
        before.State.ShouldBe(DriverState.Healthy);
        before.LastSuccessfulRead.ShouldNotBeNull();

        drv.HandlePollError(new InvalidOperationException("poll boom"));

        var after = drv.GetHealth();
        after.State.ShouldBe(DriverState.Degraded);
        after.LastSuccessfulRead.ShouldBe(before.LastSuccessfulRead);
        after.LastError.ShouldNotBeNull();
        after.LastError.ShouldContain("poll boom");
    }

    /// <summary>A poll reader failure never downgrades a pre-existing Faulted state.</summary>
    [Fact]
    public async Task PollReaderFailure_NeverDowngradesFaulted()
    {
        var opts = new ModbusDriverOptions { Host = "fake", Probe = new ModbusProbeOptions { Enabled = false } };
        var drv = new ModbusDriver(opts, "modbus-1", _ => throw new SocketException());

        // Init faults (the throwing factory) → Faulted, then rethrows.
        await Should.ThrowAsync<Exception>(() => drv.InitializeAsync("{}", CancellationToken.None));
        drv.GetHealth().State.ShouldBe(DriverState.Faulted);

        drv.HandlePollError(new InvalidOperationException("poll boom"));

        drv.GetHealth().State.ShouldBe(DriverState.Faulted);
    }
}