using Shouldly;
using TwinCAT.Ads.TypeSystem;
using TwinCAT.TypeSystem;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;

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

/// <summary>
///     Coverage for <see cref="AdsTwinCATClient.ResolveSymbolDataType"/> — the discovery
///     helper that maps a TwinCAT <see cref="IDataType"/> to a driver <see cref="TwinCATDataType"/>.
///     PR-1.5 added ENUM and ALIAS chain handling on top of the original primitive name match.
/// </summary>
[Trait("Category", "Unit")]
public sealed class TwinCATTypeResolutionTests
{
    [Fact]
    public void Primitive_resolves_directly()
    {
        var dt = new PrimitiveType("DINT", typeof(int));
        AdsTwinCATClient.ResolveSymbolDataType(dt).ShouldBe(TwinCATDataType.DInt);
    }

    [Fact]
    public void Null_data_type_returns_null()
    {
        AdsTwinCATClient.ResolveSymbolDataType(null).ShouldBeNull();
    }

    [Fact]
    public void Single_alias_resolves_to_underlying_atomic()
    {
        var primitive = new PrimitiveType("INT", typeof(short));
        var alias = new AliasType("DegreesC", primitive);

        AdsTwinCATClient.ResolveSymbolDataType(alias).ShouldBe(TwinCATDataType.Int);
    }

    [Fact]
    public void Chained_alias_resolves_through_multiple_links()
    {
        var primitive = new PrimitiveType("DINT", typeof(int));
        var inner = new AliasType("Inner", primitive);
        var outer = new AliasType("Outer", inner);

        AdsTwinCATClient.ResolveSymbolDataType(outer).ShouldBe(TwinCATDataType.DInt);
    }

    [Fact]
    public void Alias_to_unknown_primitive_returns_null()
    {
        // A primitive whose IEC name we don't recognise should drop through cleanly. Pick a CLR
        // type with a known marshal size so PrimitiveType's ctor accepts it; the name is what
        // exercises the unknown-type branch in MapSymbolTypeName.
        var primitive = new PrimitiveType("MYSTERY", typeof(int));
        var alias = new AliasType("Wrap", primitive);

        AdsTwinCATClient.ResolveSymbolDataType(alias).ShouldBeNull();
    }

    [Fact]
    public void Enum_resolves_to_underlying_integer_base_type()
    {
        var underlying = new PrimitiveType("INT", typeof(short));
        var enumType = new TestEnumType("EState", underlying);

        AdsTwinCATClient.ResolveSymbolDataType(enumType).ShouldBe(TwinCATDataType.Int);
    }

    [Fact]
    public void Enum_with_dint_base_resolves_to_DInt()
    {
        var underlying = new PrimitiveType("DINT", typeof(int));
        var enumType = new TestEnumType("EBigFlags", underlying);

        AdsTwinCATClient.ResolveSymbolDataType(enumType).ShouldBe(TwinCATDataType.DInt);
    }

    [Fact]
    public void Cyclic_alias_chain_terminates_at_depth_cap()
    {
        // Pathological: a self-referential alias. The resolver must give up rather than spin.
        var loop = new SelfReferentialAlias();
        AdsTwinCATClient.ResolveSymbolDataType(loop).ShouldBeNull();
    }

    /// <summary>
    ///     Minimal in-test stub for <see cref="IEnumType"/>. Only <c>Category</c> and
    ///     <c>BaseType</c> are exercised by <see cref="AdsTwinCATClient.ResolveSymbolDataType"/>;
    ///     the rest of the surface throws to flag any accidental dependence in future tests.
    /// </summary>
    private sealed class TestEnumType(string name, IDataType baseType) : IDataType, IAliasType
    {
        public string Name { get; } = name;
        public IDataType BaseType { get; } = baseType;
        public DataTypeCategory Category => DataTypeCategory.Enum;
        public string BaseTypeName => BaseType.Name;
        public string FullName => Name;
        public string Namespace => string.Empty;
        public int Id => 0;
        public string Comment => string.Empty;
        public ITypeAttributeCollection Attributes => throw new NotSupportedException();
        public bool IsContainer => false;
        public bool IsPointer => false;
        public bool IsReference => false;
        public bool IsPrimitive => false;
        public int Size => BaseType.Size;
        public int ByteSize => BaseType.ByteSize;
        public int BitSize => BaseType.BitSize;
        public bool IsBitType => false;
        public bool IsByteAligned => true;
    }

    /// <summary>Self-referential alias — exercises the depth cap.</summary>
    private sealed class SelfReferentialAlias : IDataType, IAliasType
    {
        public string Name => "Loop";
        public IDataType BaseType => this;
        public DataTypeCategory Category => DataTypeCategory.Alias;
        public string BaseTypeName => Name;
        public string FullName => Name;
        public string Namespace => string.Empty;
        public int Id => 0;
        public string Comment => string.Empty;
        public ITypeAttributeCollection Attributes => throw new NotSupportedException();
        public bool IsContainer => false;
        public bool IsPointer => false;
        public bool IsReference => false;
        public bool IsPrimitive => false;
        public int Size => 0;
        public int ByteSize => 0;
        public int BitSize => 0;
        public bool IsBitType => false;
        public bool IsByteAligned => true;
    }
}