using S7.Net;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using S7NetDataType = global::S7.Net.DataType;

namespace ZB.MOM.WW.OtOpcUa.Driver.S7.Tests;

/// <summary>
///     Unit tests for the S7 reconnect path (STAB-1). The <see cref="IS7PlcFactory"/> seam lets
///     these exercise the lazy <see cref="S7Driver"/> reconnect logic — dispose-dead-handle +
///     re-open on the next data call — without a live PLC, which was previously impossible (the
///     driver <c>new</c>-ed a concrete <c>S7.Net.Plc</c> inline and had no reopen path at all).
/// </summary>
[Trait("Category", "Unit")]
public sealed class S7DriverReconnectTests
{
    private static S7DriverOptions Options() => new()
    {
        Host = "192.0.2.1",
        Timeout = TimeSpan.FromMilliseconds(250),
        // Probe off — these tests drive reconnect through the read path deterministically; a
        // background probe would race the created-connection assertions.
        Probe = new S7ProbeOptions { Enabled = false },
        Tags = [new S7TagDefinition("W0", "DB1.DBW0", S7DataType.UInt16, Writable: false)],
    };

    /// <summary>
    ///     A connection-fatal fault on a read marks the handle dead; the NEXT read disposes it and
    ///     opens a fresh connection, and the tag recovers to Good with health Degraded→Healthy.
    /// </summary>
    [Fact]
    public async Task Read_reopens_a_fresh_connection_after_a_connection_fatal_fault()
    {
        var factory = new FakeS7PlcFactory();
        using var drv = new S7Driver(Options(), "s7-reconnect", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
        factory.Created.Count.ShouldBe(1);

        // Read #1 — good value, Healthy.
        var r1 = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        r1[0].StatusCode.ShouldBe(0u);
        drv.GetHealth().State.ShouldBe(DriverState.Healthy);

        // The live socket drops on its next read. IsConnected deliberately stays true (a stale
        // socket that hasn't noticed the drop) so the ONLY trigger for reopen is the driver's
        // own dead-handle flag set by the connection-fatal classification.
        factory.Created[0].NextReadThrows = new PlcException(ErrorCode.ConnectionError, "socket dropped");

        // Read #2 — connection-fatal fault → Degraded, handle marked dead, but no reopen yet.
        var r2 = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        r2[0].StatusCode.ShouldNotBe(0u);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);
        factory.Created.Count.ShouldBe(1);

        // Read #3 — EnsureConnectedAsync disposes the dead handle and opens a SECOND connection,
        // which reads Good; health recovers to Healthy.
        var r3 = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        factory.Created.Count.ShouldBe(2);
        r3[0].StatusCode.ShouldBe(0u);
        drv.GetHealth().State.ShouldBe(DriverState.Healthy);
        factory.Created[0].Disposed.ShouldBeTrue();
        factory.Created[1].Disposed.ShouldBeFalse();
    }

    /// <summary>
    ///     A protocol / data-address error (S7.Net <see cref="ErrorCode.ReadData"/>) is NOT a
    ///     connection loss — the driver keeps the same connection and does not churn a reopen.
    /// </summary>
    [Fact]
    public async Task Read_does_not_reopen_on_a_data_address_error()
    {
        var factory = new FakeS7PlcFactory();
        using var drv = new S7Driver(Options(), "s7-dataerr", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        // A data error — not a socket drop.
        factory.Created[0].NextReadThrows = new PlcException(ErrorCode.ReadData, "bad address");
        var bad = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        bad[0].StatusCode.ShouldNotBe(0u);

        // Next read reuses the SAME connection — no reopen for a data error.
        var ok = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        ok[0].StatusCode.ShouldBe(0u);
        factory.Created.Count.ShouldBe(1);
    }

    /// <summary>
    ///     A raw socket exception (no S7.Net wrapper) is also classified connection-fatal and
    ///     triggers a reopen — the driver doesn't depend on every drop arriving as a
    ///     <see cref="PlcException"/>.
    /// </summary>
    [Fact]
    public async Task Read_reopens_after_a_raw_socket_exception()
    {
        var factory = new FakeS7PlcFactory();
        using var drv = new S7Driver(Options(), "s7-socket", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        factory.Created[0].NextReadThrows = new System.Net.Sockets.SocketException();
        await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);

        var recovered = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        recovered[0].StatusCode.ShouldBe(0u);
        factory.Created.Count.ShouldBe(2);
    }

    /// <summary>
    ///     When the reopen itself fails (PLC still down), the batch degrades to a communication
    ///     error rather than throwing, and a later successful reopen recovers the tag.
    /// </summary>
    [Fact]
    public async Task Read_degrades_when_reopen_fails_then_recovers()
    {
        var factory = new FakeS7PlcFactory();
        using var drv = new S7Driver(Options(), "s7-reopen-fail", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        // Drop the live socket, and make the NEXT-created connection fail to open.
        factory.Created[0].NextReadThrows = new PlcException(ErrorCode.ConnectionError, "dropped");
        factory.NextOpenThrows = new PlcException(ErrorCode.ConnectionError, "still down");
        await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken); // marks dead

        // Reopen attempt #1 fails — whole batch is a comm error, no throw.
        var down = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        down[0].StatusCode.ShouldNotBe(0u);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);

        // PLC comes back; the next call reopens cleanly and the tag reads Good.
        var up = await drv.ReadAsync(["W0"], TestContext.Current.CancellationToken);
        up[0].StatusCode.ShouldBe(0u);
        drv.GetHealth().State.ShouldBe(DriverState.Healthy);
    }

    // ---- fakes ----

    private sealed class FakeS7PlcFactory : IS7PlcFactory
    {
        /// <summary>Every connection handed out, in creation order.</summary>
        public List<FakeS7Plc> Created { get; } = new();

        /// <summary>When set, the NEXT <see cref="Create"/>d connection throws this on OpenAsync (once).</summary>
        public Exception? NextOpenThrows { get; set; }

        public IS7Plc Create(S7CpuType cpuType, string host, int port, short rack, short slot, TimeSpan timeout)
        {
            var plc = new FakeS7Plc();
            if (NextOpenThrows is { } ex)
            {
                plc.OpenThrowsOnce = ex;
                NextOpenThrows = null;
            }
            Created.Add(plc);
            return plc;
        }
    }

    private sealed class FakeS7Plc : IS7Plc
    {
        public bool IsConnected { get; private set; }
        public bool Disposed { get; private set; }

        /// <summary>Thrown once by <see cref="OpenAsync"/>, then cleared.</summary>
        public Exception? OpenThrowsOnce { get; set; }

        /// <summary>Thrown once by the next <see cref="ReadAsync"/>, then cleared.</summary>
        public Exception? NextReadThrows { get; set; }

        /// <summary>Boxed value returned by a good read (UInt16 tag → ushort).</summary>
        public object? ReadValue { get; set; } = (ushort)42;

        public Task OpenAsync(CancellationToken cancellationToken)
        {
            if (OpenThrowsOnce is { } ex)
            {
                OpenThrowsOnce = null;
                return Task.FromException(ex);
            }
            IsConnected = true;
            return Task.CompletedTask;
        }

        public void Close() => IsConnected = false;

        public Task<object?> ReadAsync(string address, CancellationToken cancellationToken)
        {
            if (NextReadThrows is { } ex)
            {
                NextReadThrows = null;
                return Task.FromException<object?>(ex);
            }
            return Task.FromResult(ReadValue);
        }

        public Task<byte[]> ReadBytesAsync(S7NetDataType area, int db, int startByteAdr, int count, CancellationToken cancellationToken) =>
            throw new NotSupportedException("FakeS7Plc: block reads not needed for the reconnect tests");

        public Task WriteAsync(string address, object value, CancellationToken cancellationToken) =>
            Task.CompletedTask;

        public Task WriteBytesAsync(S7NetDataType area, int db, int startByteAdr, byte[] value, CancellationToken cancellationToken) =>
            Task.CompletedTask;

        public Task ReadStatusAsync(CancellationToken cancellationToken) => Task.CompletedTask;

        public void Dispose()
        {
            Disposed = true;
            IsConnected = false;
        }
    }
}