using Shouldly;
using Xunit;

namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.DL205;

/// <summary>
///     Verifies DL205/DL260 CDAB word ordering for 32-bit floats against the
///     <c>dl205.json</c> pymodbus profile. DirectLOGIC stores IEEE-754 singles with the low
///     word at the lower register address (CDAB) rather than the high word (ABCD). Reading
///     <c>HR[1056..1057]</c> with <see cref="ModbusByteOrder.BigEndian"/> produces a tiny
///     denormal (~5.74e-41) instead of the intended 1.5f — a silent "value is 0" bug in the
///     field unless the caller opts into <see cref="ModbusByteOrder.WordSwap"/>.
/// </summary>
[Collection(ModbusSimulatorCollection.Name)]
[Trait("Category", "Integration")]
[Trait("Device", "DL205")]
public sealed class DL205FloatCdabQuirkTests(ModbusSimulatorFixture sim)
{
    [Fact]
    public async Task DL205_Float32_CDAB_decodes_1_5f_from_HR1056()
    {
        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
        if (!string.Equals(Environment.GetEnvironmentVariable("MODBUS_SIM_PROFILE"), "dl205",
                StringComparison.OrdinalIgnoreCase))
        {
            Assert.Skip("MODBUS_SIM_PROFILE != dl205 — skipping (standard profile does not seed HR[1056..1057]).");
        }

        var options = new ModbusDriverOptions
        {
            Host = sim.Host,
            Port = sim.Port,
            UnitId = 1,
            Timeout = TimeSpan.FromSeconds(2),
            Tags =
            [
                new ModbusTagDefinition("DL205_Float_CDAB",
                    ModbusRegion.HoldingRegisters, Address: 1056,
                    DataType: ModbusDataType.Float32, Writable: false,
                    ByteOrder: ModbusByteOrder.WordSwap),
                // Control: same address, BigEndian — proves the default decode produces garbage.
                new ModbusTagDefinition("DL205_Float_ABCD",
                    ModbusRegion.HoldingRegisters, Address: 1056,
                    DataType: ModbusDataType.Float32, Writable: false,
                    ByteOrder: ModbusByteOrder.BigEndian),
            ],
            Probe = new ModbusProbeOptions { Enabled = false },
        };
        await using var driver = new ModbusDriver(options, driverInstanceId: "dl205-cdab");
        await driver.InitializeAsync("{}", TestContext.Current.CancellationToken);

        var results = await driver.ReadAsync(["DL205_Float_CDAB", "DL205_Float_ABCD"],
            TestContext.Current.CancellationToken);

        results[0].StatusCode.ShouldBe(0u);
        results[0].Value.ShouldBe(1.5f, "DL205 Float32 with WordSwap (CDAB) must decode HR[1056..1057] as 1.5f");

        // The BigEndian read of the same wire bytes should differ — not asserting the exact
        // denormal value (that couples the test to IEEE-754 bit math) but the two decodes MUST
        // disagree, otherwise the word-order flag is a no-op.
        results[1].StatusCode.ShouldBe(0u);
        results[1].Value.ShouldNotBe(1.5f);
    }
}