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>
///     Guards for retiring the bespoke S7 poll fork onto the shared <c>PollGroupEngine</c>
///     (CONV-1). The engine brings two fixes the fork lacked — structural array diffing (PERF-3)
///     and drain-before-CTS-dispose on unsubscribe (STAB-6-S7) — and keeps failure→health parity.
/// </summary>
[Trait("Category", "Unit")]
public sealed class S7PollEngineMigrationTests
{
    // A fake that opens cleanly and serves a CONSTANT 6-byte block for array reads (three
    // big-endian UInt16 words) — every ReadArrayAsync decodes a fresh ushort[3] with identical
    // contents, so a reference-equality diff (the fork) refires every tick while a structural
    // diff (the engine) fires only once.
    private sealed class ConstantArrayFactory : IS7PlcFactory
    {
        public bool ReadThrows { get; set; }
        public IS7Plc Create(S7CpuType cpuType, string host, int port, short rack, short slot, TimeSpan timeout)
            => new ConstantArrayPlc(this);
    }

    private sealed class ConstantArrayPlc(ConstantArrayFactory owner) : IS7Plc
    {
        public bool IsConnected { get; private set; }
        public Task OpenAsync(CancellationToken ct) { IsConnected = true; return Task.CompletedTask; }
        public void Close() => IsConnected = false;

        public Task<object?> ReadAsync(string address, CancellationToken ct)
        {
            if (owner.ReadThrows) throw new PlcException(ErrorCode.ConnectionError, "poll failure");
            return Task.FromResult<object?>((ushort)42);
        }

        public Task<byte[]> ReadBytesAsync(S7NetDataType area, int db, int startByteAdr, int count, CancellationToken ct)
        {
            if (owner.ReadThrows) throw new PlcException(ErrorCode.ConnectionError, "poll failure");
            // Fresh array instance each call, identical contents: BE words 1, 2, 3.
            var block = new byte[count];
            for (var i = 0; i + 1 < block.Length; i += 2)
                block[i + 1] = (byte)(i / 2 + 1);
            return Task.FromResult(block);
        }

        public Task WriteAsync(string address, object value, CancellationToken ct) => Task.CompletedTask;
        public Task WriteBytesAsync(S7NetDataType area, int db, int startByteAdr, byte[] value, CancellationToken ct) => Task.CompletedTask;
        public Task ReadStatusAsync(CancellationToken ct) => Task.CompletedTask;
        public void Dispose() => IsConnected = false;
    }

    private static S7DriverOptions ArrayOptions() => new()
    {
        Host = "192.0.2.1",
        Timeout = TimeSpan.FromMilliseconds(250),
        Probe = new S7ProbeOptions { Enabled = false },
        Tags = [new S7TagDefinition("Arr", "DB1.DBW0", S7DataType.UInt16, Writable: false, ArrayCount: 3)],
    };

    /// <summary>
    ///     PERF-3 regression: a subscribed array tag whose contents are identical across polls
    ///     (fresh instance each read) must fire only the initial change, not on every tick. The
    ///     fork's reference-equality diff refires every poll.
    /// </summary>
    [Fact]
    public async Task ArrayTag_UnchangedBetweenPolls_DoesNotRefire()
    {
        var factory = new ConstantArrayFactory();
        using var drv = new S7Driver(ArrayOptions(), "s7-arr-perf3", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        var events = new System.Collections.Concurrent.ConcurrentQueue<DataChangeEventArgs>();
        drv.OnDataChange += (_, e) => events.Enqueue(e);

        var h = await drv.SubscribeAsync(["Arr"], TimeSpan.FromMilliseconds(100), TestContext.Current.CancellationToken);
        await Task.Delay(500, TestContext.Current.CancellationToken); // several poll cycles
        await drv.UnsubscribeAsync(h, TestContext.Current.CancellationToken);

        events.Count.ShouldBe(1); // only the initial-data push
    }

    /// <summary>
    ///     STAB-6-S7 regression: rapidly subscribing + unsubscribing must not fault a poll loop by
    ///     disposing its CTS out from under an in-flight <c>Task.Delay</c>. Post-migration the engine
    ///     drains each loop before disposing its CTS. Asserts the whole churn completes cleanly and
    ///     the driver still serves reads afterward.
    /// </summary>
    [Fact]
    public async Task RapidSubscribeUnsubscribe_NoObjectDisposedException()
    {
        var factory = new ConstantArrayFactory();
        using var drv = new S7Driver(ArrayOptions(), "s7-rapid", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        for (var i = 0; i < 50; i++)
        {
            var h = await drv.SubscribeAsync(["Arr"], TimeSpan.FromMilliseconds(20), TestContext.Current.CancellationToken);
            await drv.UnsubscribeAsync(h, TestContext.Current.CancellationToken);
        }

        // Driver still works after the churn — no wedged state.
        var read = await drv.ReadAsync(["Arr"], TestContext.Current.CancellationToken);
        read[0].StatusCode.ShouldBe(0u);
    }

    /// <summary>
    ///     Failure→health parity: a subscription polling a persistently-failing device degrades the
    ///     driver health (the fork's HandlePollFailure behaviour, now delivered by the engine's
    ///     onError→HandlePollError wiring + the read path's own status mapping).
    /// </summary>
    [Fact]
    public async Task SustainedPollFailure_DegradesHealth()
    {
        var factory = new ConstantArrayFactory { ReadThrows = true };
        using var drv = new S7Driver(ArrayOptions(), "s7-pollfail", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);

        await drv.SubscribeAsync(["Arr"], TimeSpan.FromMilliseconds(50), TestContext.Current.CancellationToken);

        var deadline = DateTime.UtcNow + TimeSpan.FromSeconds(3);
        while (drv.GetHealth().State == DriverState.Healthy && DateTime.UtcNow < deadline)
            await Task.Delay(25, TestContext.Current.CancellationToken);

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