using System.Net;
using System.Net.Sockets;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Cip;

namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.Differential;

/// <summary>
///     Offline pins for the differential's press-safety rules (Task 18 review r1). No controller is touched:
///     the "endpoint" is a loopback listener that accepts and immediately hangs up.
/// </summary>
[Collection(DifferentialCollection.Name)]
public sealed class DifferentialSafetyTests
{
    [Fact]
    public async Task A_failing_endpoint_aborts_the_native_phase_after_exactly_one_connect()
    {
        await using var endpoint = HangUpListener.Start();
        var target = Target(endpoint.Port);
        IReadOnlyList<SelectedTag> selection =
        [
            new("A", AbCipDataType.DInt, 1, false, "scalar"),
            new("B", AbCipDataType.DInt, 1, false, "scalar"),
            new("C", AbCipDataType.DInt, 1, false, "scalar"),
        ];

        var ex = await Should.ThrowAsync<DifferentialAbortedException>(
            () => DifferentialRun.RunNativePhaseAsync(target, selection, TestContext.Current.CancellationToken));

        ex.Message.ShouldContain("native phase at browse");
        // Long enough for a throttled (≥ 1 s) reconnect to have reached the listener, had one been allowed.
        await Task.Delay(TimeSpan.FromSeconds(2.5), TestContext.Current.CancellationToken);
        endpoint.Connections.ShouldBe(1);
        Volatile.Read(ref CipConnection.OpenAttemptBudget).ShouldBe(-1, "the budget is restored after the phase");
    }

    [Fact]
    public async Task A_failing_endpoint_aborts_the_libplctag_phase_before_any_tag_is_read()
    {
        await using var endpoint = HangUpListener.Start();
        var target = Target(endpoint.Port);

        var ex = await Should.ThrowAsync<DifferentialAbortedException>(
            () => DifferentialRun.RunLibplctagPhaseAsync(target, TestContext.Current.CancellationToken));

        ex.Message.ShouldContain("libplctag phase at");
        await Task.Delay(TimeSpan.FromSeconds(1), TestContext.Current.CancellationToken);
        // libplctag's own session layer may redial inside its one anchor-create timeout; the harness cannot
        // reach below that. Recorded, and bounded: one anchor create, never one per tag.
        TestContext.Current.TestOutputHelper?.WriteLine($"libplctag connects before the abort: {endpoint.Connections}");
        endpoint.Connections.ShouldBeInRange(1, 2);
    }

    [Fact]
    public void The_default_selection_keeps_arrays_and_udt_members_at_any_cap()
    {
        var browsed = new TransportObservations();
        for (var i = 0; i < 300; i++) browsed.Browse.Add(new AbCipDiscoveredTag($"S{i}", null, AbCipDataType.DInt, false));
        for (var i = 0; i < 30; i++)
            browsed.Browse.Add(new AbCipDiscoveredTag($"A{i}", null, AbCipDataType.Real, false, ElementCount: 4, IsArray: true));
        browsed.Browse.Add(new AbCipDiscoveredTag("U", null, AbCipDataType.Structure, false, TemplateInstanceId: 7));
        browsed.Shapes[7] = new AbCipUdtShape("Udt", 400,
            [.. Enumerable.Range(0, 25).Select(i => new AbCipUdtMember($"M{i}", i * 4, AbCipDataType.DInt, 1))]);

        var at200 = DifferentialRun.Select(Target(1) with { MaxTags = 200 }, browsed);
        at200.Count.ShouldBe(200);
        at200.Count(t => t.Origin == "array").ShouldBe(20);
        at200.Count(t => t.Origin == "udt member").ShouldBe(20);
        at200.Count(t => t.Origin == "scalar").ShouldBe(160);

        var at25 = DifferentialRun.Select(Target(1) with { MaxTags = 25 }, browsed);
        at25.Count.ShouldBe(25);
        at25.ShouldContain(t => t.Origin == "array");
        at25.ShouldContain(t => t.Origin == "udt member");
        at25.ShouldContain(t => t.Origin == "scalar");
        DifferentialRun.SelectionCoverageProblems(Target(1) with { MaxTags = 25 }, browsed, at25).ShouldBeEmpty();

        // The coverage check is not vacuous: a selection of scalars only is flagged for both kinds.
        DifferentialRun.SelectionCoverageProblems(Target(1), browsed, [.. at200.Where(t => t.Origin == "scalar")])
            .Count.ShouldBe(2);
    }

    [Fact]
    public void Template_parity_fails_when_vacuous_or_undecodable()
    {
        var lib = new TransportObservations();
        var native = new TransportObservations();
        lib.Browse.Add(new AbCipDiscoveredTag("U", null, AbCipDataType.Structure, false, TemplateInstanceId: 7));
        DifferentialRun.TemplateProblems(lib, native).ShouldHaveSingleItem().ShouldContain("vacuous");

        lib.Shapes[7] = null;
        native.Shapes[7] = null;
        DifferentialRun.TemplateProblems(lib, native).ShouldHaveSingleItem().ShouldContain("undecodable");

        var shape = new AbCipUdtShape("Udt", 4, [new AbCipUdtMember("M", 0, AbCipDataType.DInt, 1)]);
        lib.Shapes[7] = shape;
        native.Shapes[7] = shape with { Members = [new AbCipUdtMember("M", 0, AbCipDataType.DInt, 1)] };
        DifferentialRun.TemplateProblems(lib, native).ShouldBeEmpty();
    }

    [Fact]
    public void Volume_knobs_fail_fast_above_the_ceiling_instead_of_clamping()
    {
        var saved = Snapshot(DifferentialTarget.EndpointVar, DifferentialTarget.MaxTagsVar, DifferentialTarget.MaxTemplatesVar, DifferentialTarget.PaceVar,
            DifferentialTarget.LatencyTagsVar, DifferentialTarget.LatencyPassesVar, DifferentialTarget.LatencyPassGapVar);
        try
        {
            Environment.SetEnvironmentVariable(DifferentialTarget.EndpointVar, "127.0.0.1:1");
            Environment.SetEnvironmentVariable(DifferentialTarget.MaxTagsVar, "501");
            Should.Throw<InvalidOperationException>(DifferentialTarget.FromEnvironment).Message.ShouldContain(DifferentialTarget.MaxTagsVar);

            Environment.SetEnvironmentVariable(DifferentialTarget.MaxTagsVar, "500");
            Environment.SetEnvironmentVariable(DifferentialTarget.MaxTemplatesVar, "9999");
            Should.Throw<InvalidOperationException>(DifferentialTarget.FromEnvironment).Message.ShouldContain(DifferentialTarget.MaxTemplatesVar);

            Environment.SetEnvironmentVariable(DifferentialTarget.MaxTemplatesVar, null);
            Environment.SetEnvironmentVariable(DifferentialTarget.PaceVar, null);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyTagsVar, null);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassesVar, null);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassGapVar, null);
            var t =DifferentialTarget.FromEnvironment()!;
            t.MaxTags.ShouldBe(500);
            t.MaxTemplates.ShouldBe(DifferentialTarget.DefaultMaxTemplates);
            t.PaceMs.ShouldBe(DifferentialTarget.DefaultPaceMs);
            t.LatencyTags.ShouldBe(100);
            t.LatencyPasses.ShouldBe(30);
            t.LatencyPassGapMs.ShouldBe(200);

            // Latency knobs (Task 21): the same fail-fast rule, with tighter ceilings.
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyTagsVar, "201");
            Should.Throw<InvalidOperationException>(DifferentialTarget.FromEnvironment).Message.ShouldContain(DifferentialTarget.LatencyTagsVar);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyTagsVar, "200");
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassesVar, "51");
            Should.Throw<InvalidOperationException>(DifferentialTarget.FromEnvironment).Message.ShouldContain(DifferentialTarget.LatencyPassesVar);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassesVar, "50");
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassGapVar, "10001");
            Should.Throw<InvalidOperationException>(DifferentialTarget.FromEnvironment).Message.ShouldContain(DifferentialTarget.LatencyPassGapVar);
            Environment.SetEnvironmentVariable(DifferentialTarget.LatencyPassGapVar, "0");
            var lat = DifferentialTarget.FromEnvironment()!;
            (lat.LatencyTags, lat.LatencyPasses, lat.LatencyPassGapMs).ShouldBe((200, 50, 0));
        }
        finally
        {
            foreach (var (k, v) in saved) Environment.SetEnvironmentVariable(k, v);
        }
    }

    private static DifferentialTarget Target(int port) =>
        new("127.0.0.1", port, "1,0", AbCipPlcFamily.CompactLogix, null, 200, CountOpens: false, MaxTemplates: 50, PaceMs: 0);

    private static (string, string?)[] Snapshot(params string[] names) =>
        [.. names.Select(n => (n, Environment.GetEnvironmentVariable(n)))];

    /// <summary>Accepts every connection and closes it at once, counting them.</summary>
    private sealed class HangUpListener : IAsyncDisposable
    {
        private readonly TcpListener _listener = new(IPAddress.Loopback, 0);
        private readonly CancellationTokenSource _stop = new();
        private readonly Task _loop;
        private int _connections;

        private HangUpListener()
        {
            _listener.Start();
            _loop = Task.Run(AcceptLoopAsync);
        }

        public static HangUpListener Start() => new();

        public int Port => ((IPEndPoint)_listener.LocalEndpoint).Port;

        public int Connections => Volatile.Read(ref _connections);

        private async Task AcceptLoopAsync()
        {
            try
            {
                while (!_stop.IsCancellationRequested)
                {
                    using var socket = await _listener.AcceptSocketAsync(_stop.Token);
                    Interlocked.Increment(ref _connections);
                    socket.Close();
                }
            }
            catch (OperationCanceledException) { }
            catch (SocketException) { }
            catch (ObjectDisposedException) { }
        }

        public async ValueTask DisposeAsync()
        {
            await _stop.CancelAsync();
            _listener.Stop();
            try { await _loop; } catch { /* stopped */ }
            _stop.Dispose();
        }
    }
}