using Shouldly;
using Xunit;

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

/// <summary>
///     Regression coverage for Driver.Modbus-009: two configuration edge cases that previously
///     silently produced wrong wire behaviour.
///     (1) <c>StringLength = 0</c> for a <c>String</c>-typed tag — used to flow into an FC03
///     with quantity 0, a spec-illegal request the PLC rejects with exception 03. Now bind-time
///     validation in <c>ModbusDriverFactoryExtensions</c> rejects the misconfiguration with a
///     clear diagnostic.
///     (2) Sub-second <see cref="TimeSpan"/> values on <c>ModbusKeepAliveOptions.Time</c> /
///     <c>Interval</c> — the int-cast in <c>EnableKeepAlive</c> truncated <c>500&#160;ms</c> to
///     <c>0</c>, which most OSes interpret as "use the default", silently defeating the
///     configured timing. <c>ModbusTcpTransport.ClampToWholeSeconds</c> rounds up to a minimum
///     of 1&#160;second.
/// </summary>
[Trait("Category", "Unit")]
public sealed class ModbusEdgeCaseValidationTests
{
    /// <summary>Verifies that string tags with zero length are rejected during factory creation.</summary>
    [Fact]
    public void Factory_rejects_String_tag_with_StringLength_zero_via_structured_form()
    {
        const string json = """
        {
          "host": "10.0.0.10",
          "tags": [
            { "name": "Greeting", "region": "HoldingRegisters", "address": 100, "dataType": "String", "stringLength": 0 }
          ]
        }
        """;
        var ex = Should.Throw<InvalidOperationException>(
            () => ModbusDriverFactoryExtensions.CreateInstance("modbus-1", json));
        ex.Message.ShouldContain("StringLength");
        ex.Message.ShouldContain("Greeting");
    }

    /// <summary>Verifies that omitted string length defaults to zero and is rejected.</summary>
    [Fact]
    public void Factory_rejects_String_tag_with_StringLength_zero_via_missing_field()
    {
        // No stringLength → defaults to 0. Same misconfiguration via a different DTO shape.
        const string json = """
        {
          "host": "10.0.0.10",
          "tags": [
            { "name": "Greeting", "region": "HoldingRegisters", "address": 100, "dataType": "String" }
          ]
        }
        """;
        var ex = Should.Throw<InvalidOperationException>(
            () => ModbusDriverFactoryExtensions.CreateInstance("modbus-1", json));
        ex.Message.ShouldContain("StringLength");
    }

    /// <summary>Verifies that string tags with length one are accepted.</summary>
    [Fact]
    public void Factory_accepts_String_tag_with_StringLength_one()
    {
        const string json = """
        {
          "host": "10.0.0.10",
          "tags": [
            { "name": "Greeting", "region": "HoldingRegisters", "address": 100, "dataType": "String", "stringLength": 1 }
          ]
        }
        """;
        Should.NotThrow(() => ModbusDriverFactoryExtensions.CreateInstance("modbus-1", json));
    }

    /// <summary>Verifies that non-string tags are unaffected by string length zero.</summary>
    [Fact]
    public void Factory_accepts_non_String_tag_with_StringLength_zero()
    {
        // The validation only kicks in for String tags — Int16 tags with StringLength=0 are normal.
        const string json = """
        {
          "host": "10.0.0.10",
          "tags": [
            { "name": "Level", "region": "HoldingRegisters", "address": 100, "dataType": "Int16" }
          ]
        }
        """;
        Should.NotThrow(() => ModbusDriverFactoryExtensions.CreateInstance("modbus-1", json));
    }

    /// <summary>Verifies that sub-second time spans are rounded up to at least one second.</summary>
    /// <param name="ms">The input duration in milliseconds.</param>
    /// <param name="expected">The expected clamped value in whole seconds.</param>
    [Theory]
    [InlineData(0, 1)]       // zero clamps up to 1
    [InlineData(500, 1)]     // 500 ms rounds up to 1
    [InlineData(999, 1)]     // just under 1s rounds up to 1
    [InlineData(1_000, 1)]   // exactly 1s passes through
    [InlineData(1_500, 2)]   // 1.5s rounds up to 2
    [InlineData(30_000, 30)] // historical PR 53 default — unchanged
    [InlineData(60_000, 60)]
    public void ClampToWholeSeconds_rounds_up_to_at_least_one_second(int ms, int expected)
    {
        ModbusTcpTransport.ClampToWholeSeconds(TimeSpan.FromMilliseconds(ms)).ShouldBe(expected);
    }

    /// <summary>Verifies that negative time spans are treated as one second.</summary>
    [Fact]
    public void ClampToWholeSeconds_treats_negative_TimeSpan_as_one_second()
    {
        // Defensive — operators occasionally configure a negative TimeSpan thinking it disables
        // the feature. The OS would reject the negative int — clamping to 1 keeps the socket
        // valid until the operator fixes the config.
        ModbusTcpTransport.ClampToWholeSeconds(TimeSpan.FromSeconds(-5)).ShouldBe(1);
    }
}