using System.Buffers.Binary;
using System.Diagnostics;
using System.Globalization;
using System.Net.Sockets;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Cip;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Logix;
using ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.Differential;

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

/// <summary>
///     Gitea #566 hardware evidence (hw5): what a real Logix does with a class-3 connection that has been left idle
///     past its connection timeout. READ-ONLY: three Read Tag requests of one tag on one private pool, nothing else.
///     <list type="bullet">
///         <item>Opt-in: <c>AB_DIFF_ENDPOINT</c> (the target, see <see cref="DifferentialTarget"/>) AND
///             <c>AB_EVID_IDLE=1</c>.</item>
///         <item><c>AB_EVID_IDLE_TAG</c> — the tag read, default <c>test2</c> (a DINT).</item>
///         <item><c>AB_EVID_IDLE_SECONDS</c> — idle time, default 60, in [1, 300]. It must exceed the expiry the
///             controller grants (logged from the Forward Open reply), or the read just succeeds.</item>
///     </list>
///     The keep-alive is pushed out to one hour on this private pool so nothing touches the connection while it is
///     idle (in production it fires every half expiry, which is why this case only arises after a controller
///     restart / re-download or a network gap). The open-attempt budget is 2: the first open and one reconnect.
/// </summary>
[Trait("Category", "LiveIntegration")]
public sealed class IdleConnectionEvidenceTests
{
    private const string DefaultTag = "test2";

    [Fact]
    public async Task An_idle_connection_past_its_timeout_reports_what_the_controller_does_and_recovers()
    {
        var target = DifferentialTarget.FromEnvironment();
        if (target is null) Assert.Skip(DifferentialTarget.SkipReason);
        if (Environment.GetEnvironmentVariable("AB_EVID_IDLE") != "1") Assert.Skip("AB_EVID_IDLE=1 not set.");
        var tag = Environment.GetEnvironmentVariable("AB_EVID_IDLE_TAG") is { Length: > 0 } t ? t.Trim() : DefaultTag;
        var idleSeconds = 60;
        if (Environment.GetEnvironmentVariable("AB_EVID_IDLE_SECONDS") is { Length: > 0 } rawIdle
            && (!int.TryParse(rawIdle, NumberStyles.None, CultureInfo.InvariantCulture, out idleSeconds) || idleSeconds is < 1 or > 300))
            throw new InvalidOperationException($"AB_EVID_IDLE_SECONDS='{rawIdle}' must be an integer in [1, 300].");

        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(idleSeconds + 120));
        var ct = cts.Token;
        var pool = new DeviceSessionPool();
        var diagnostics = pool.Diagnostics;
        var p = target.Params(tag);
        var key = NativeAbCipDevice.Key(p);
        var options = NativeAbCipDevice.Options(p) with { KeepAliveInterval = TimeSpan.FromHours(1) };
        var clock = Stopwatch.StartNew();
        var log = new List<string>();
        void Note(string line)
        {
            var stamped = $"[{clock.Elapsed.TotalSeconds,7:F2} s] {line}";
            log.Add(stamped);
            TestContext.Current.TestOutputHelper?.WriteLine(stamped);
        }

        diagnostics.ExchangeObserver = (req, rep) => Note(DescribeExchange(req.Span, rep.Span));
        using var budget = diagnostics.LimitOpenAttempts(key, 2);
        var request = LogixServices.ReadTag(CipPath.EncodeSymbolic(tag), 1);
        Note($"Target {target}; tag '{tag}'; requested RPI {options.RpiMicros} us both ways, timeout multiplier " +
             $"{options.TimeoutMultiplier} (x{4 << options.TimeoutMultiplier}) => expiry {options.ConnectionExpiry.TotalSeconds:F1} s; " +
             $"keep-alive pushed to {options.KeepAliveInterval}; idle {idleSeconds} s");

        var lease = pool.Acquire(key, options);
        try
        {
            var first = await ReadAsync("read 1 (opens)", lease.Channel, request, Note, ct);
            first.ShouldBeTrue("the first read must succeed, or there is no connection to idle");
            Note($"Forward Opens {diagnostics.ForwardOpens}; now idle for {idleSeconds} s with no traffic");
            await Task.Delay(TimeSpan.FromSeconds(idleSeconds), ct);

            var opensBefore = diagnostics.ForwardOpens;
            var second = await ReadAsync("read 2 (after idle)", lease.Channel, request, Note, ct);
            Note($"After read 2: Forward Opens {diagnostics.ForwardOpens} (delta {diagnostics.ForwardOpens - opensBefore}), " +
                 $"closed-by-target {diagnostics.ConnectionsClosedByTarget}, success={second}");

            await Task.Delay(TimeSpan.FromSeconds(2), ct);   // past the 1 s Forward Open interval
            var third = await ReadAsync("read 3 (recovery)", lease.Channel, request, Note, ct);
            Note($"After read 3: Forward Opens {diagnostics.ForwardOpens}, closed-by-target " +
                 $"{diagnostics.ConnectionsClosedByTarget}, open attempts used {budget.Attempts}/{budget.Budget}, success={third}");
            third.ShouldBeTrue("the transport must recover on the request after the failed one");
        }
        finally
        {
            await lease.DisposeAsync();
            diagnostics.ExchangeObserver = null;
            Note($"Lease released: Forward Closes sent/acked {diagnostics.ForwardClosesSent}/{diagnostics.ForwardClosesAcked}");
        }
    }

    private static async Task<bool> ReadAsync(string label, ICipChannel channel, byte[] request, Action<string> note,
        CancellationToken ct)
    {
        var sw = Stopwatch.StartNew();
        try
        {
            var reply = CipReply.Parse(await channel.SendAsync(request, ct));
            note($"{label}: reply in {sw.ElapsedMilliseconds} ms, general 0x{reply.GeneralStatus:X2}" +
                 $"{(reply.ExtendedStatus.Length > 0 ? $" extended {string.Join(",", reply.ExtendedStatus.Select(e => $"0x{e:X4}"))}" : "")}");
            return reply.GeneralStatus == 0;
        }
        catch (AbTransportException ex)
        {
            note($"{label}: THREW after {sw.ElapsedMilliseconds} ms: AbTransportException status={ex.Status} " +
                 $"(OPC UA 0x{AbOpcUaStatusMap.MapStatus(ex.Status):X8}) message='{ex.Message}' inner={Inner(ex)}");
            return false;
        }
    }

    private static string Inner(Exception ex)
    {
        var parts = new List<string>();
        for (var e = ex.InnerException; e is not null; e = e.InnerException)
            parts.Add(e is SocketException se ? $"SocketException({se.SocketErrorCode})" : $"{e.GetType().Name}('{e.Message}')");
        return parts.Count == 0 ? "none" : string.Join(" <- ", parts);
    }

    private static string DescribeExchange(ReadOnlySpan<byte> request, ReadOnlySpan<byte> reply)
    {
        var service = request.Length > 0 ? request[0] : (byte)0;
        var hex = Convert.ToHexString(reply[..Math.Min(reply.Length, 48)]);
        if (service is 0x54 or 0x5B && reply.Length >= 4 && reply[2] == 0)
        {
            // Forward Open reply data: O->T id, T->O id, serial, vendor, originator serial, O->T API, T->O API.
            var d = reply[(4 + 2 * reply[3])..];
            if (d.Length >= 24)
                return $"Forward Open 0x{service:X2} granted: O->T id 0x{BinaryPrimitives.ReadUInt32LittleEndian(d):X8}, " +
                       $"O->T API {BinaryPrimitives.ReadUInt32LittleEndian(d[16..])} us, T->O API {BinaryPrimitives.ReadUInt32LittleEndian(d[20..])} us; raw {hex}";
        }
        return $"exchange: request service 0x{service:X2} ({request.Length} B) -> reply {reply.Length} B: {hex}";
    }
}