using System.Buffers.Binary;
using System.Text;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Wire;

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

/// <summary>
///     #740 / R07:H20 — <c>ParseAlarms</c> picked the 76-byte vendor layout whenever <c>Length % 76 == 0</c>, so a
///     legacy 80-byte reply of exactly 19 records (1,520 B = 20 × 76) decoded as 20 garbage vendor records. The
///     response block carries no record count, so the layout is now chosen from the two things that are known: the
///     count the REQUEST asked for (a reply never holds more) and each layout's own field invariants.
/// </summary>
[Trait("Category", "Unit")]
public sealed class FocasAlarmLayoutTests
{
    private static byte[] Legacy(params (int no, int type, int axis, string msg)[] records)
    {
        var buf = new byte[records.Length * 80];
        for (var i = 0; i < records.Length; i++)
        {
            var o = i * 80;
            var (no, type, axis, msg) = records[i];
            BinaryPrimitives.WriteInt32BigEndian(buf.AsSpan(o, 4), no);
            BinaryPrimitives.WriteInt32BigEndian(buf.AsSpan(o + 4, 4), type);
            BinaryPrimitives.WriteInt32BigEndian(buf.AsSpan(o + 8, 4), axis);
            BinaryPrimitives.WriteInt32BigEndian(buf.AsSpan(o + 12, 4), msg.Length);
            Encoding.ASCII.GetBytes(msg).CopyTo(buf.AsSpan(o + 16));
        }
        return buf;
    }

    private static byte[] Vendor(params (int no, short type, short axis, string msg)[] records)
    {
        var buf = new byte[records.Length * 76];
        for (var i = 0; i < records.Length; i++)
        {
            var o = i * 76;
            var (no, type, axis, msg) = records[i];
            BinaryPrimitives.WriteInt32BigEndian(buf.AsSpan(o, 4), no);
            BinaryPrimitives.WriteInt16BigEndian(buf.AsSpan(o + 4, 2), type);
            BinaryPrimitives.WriteInt16BigEndian(buf.AsSpan(o + 6, 2), axis);
            BinaryPrimitives.WriteInt16BigEndian(buf.AsSpan(o + 10, 2), (short)msg.Length);
            Encoding.ASCII.GetBytes(msg).CopyTo(buf.AsSpan(o + 12));
        }
        return buf;
    }

    private static (int, int, int, string)[] LegacySet(int n) =>
        [.. Enumerable.Range(0, n).Select(i => (400 + i, 2 + (i % 3), 1 + (i % 4), $"SERVO ALARM {400 + i}"))];

    private static (int, short, short, string)[] VendorSet(int n) =>
        [.. Enumerable.Range(0, n).Select(i => (1000 + i, (short)(4 + (i % 3)), (short)(i % 2), $"OVERTRAVEL +{i}"))];

    /// <summary>The ambiguous length: 19 legacy records decode as 19 legacy records, not 20 vendor ones.</summary>
    [Fact]
    public void Nineteen_legacy_records_decode_as_legacy()
    {
        var payload = Legacy(LegacySet(19));
        payload.Length.ShouldBe(1520);
        (payload.Length % 76).ShouldBe(0, "the length really is ambiguous");

        var alarms = FocasWireClient.ParseAlarms(payload, 32);

        alarms.Count.ShouldBe(19);
        alarms[0].AlarmNumber.ShouldBe(400);
        alarms[0].Message.ShouldBe("SERVO ALARM 400");
        alarms[18].AlarmNumber.ShouldBe(418);
        alarms[18].Axis.ShouldBe((short)(1 + (18 % 4)));
    }

    /// <summary>Positive control at the same length: 20 vendor records still decode as vendor.</summary>
    [Fact]
    public void Twenty_vendor_records_decode_as_vendor()
    {
        var payload = Vendor(VendorSet(20));
        payload.Length.ShouldBe(1520);

        var alarms = FocasWireClient.ParseAlarms(payload, 32);

        alarms.Count.ShouldBe(20);
        alarms[0].AlarmNumber.ShouldBe(1000);
        alarms[19].Message.ShouldBe("OVERTRAVEL +19");
    }

    /// <summary>
    ///     Review I2 edge: vendor records with type 0 and EMPTY messages also satisfy the legacy invariants (the
    ///     int32 read of <c>type&lt;&lt;16 | axis</c> is just the axis, and the "length" int32 is the empty message's
    ///     zero bytes) — both readings are plausible, so the vendor default must hold and the numbers decode.
    /// </summary>
    [Fact]
    public void Twenty_vendor_records_with_type_zero_and_empty_messages_stay_vendor()
    {
        var payload = Vendor([.. Enumerable.Range(0, 20).Select(i => (2000 + i, (short)0, (short)(i % 3), ""))]);
        payload.Length.ShouldBe(1520);

        var alarms = FocasWireClient.ParseAlarms(payload, 32);

        alarms.Count.ShouldBe(20);
        alarms.Select(a => a.AlarmNumber).ShouldBe(Enumerable.Range(2000, 20));
        alarms.ShouldAllBe(a => a.Type == 0 && a.Message == "");
    }

    /// <summary>The unambiguous lengths are unchanged.</summary>
    [Fact]
    public void Unambiguous_lengths_are_unchanged()
    {
        FocasWireClient.ParseAlarms(Vendor(VendorSet(3)), 32).Count.ShouldBe(3);
        FocasWireClient.ParseAlarms(Legacy(LegacySet(3)), 32).Count.ShouldBe(3);
        FocasWireClient.ParseAlarms([], 32).ShouldBeEmpty();
        Should.Throw<FocasWireException>(() => FocasWireClient.ParseAlarms(new byte[77], 32));
    }
}