using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using WhiteMagic;

namespace WhiteMagicTest;

/// <summary>
/// Tests for <see cref="MarshalCache{T}"/>: blittable size, marshal-required flag,
/// and computed-once behavior.
/// </summary>
public class MarshalCacheTests
{
    [Fact]
    public void Size_for_int_is_4()
    {
        Assert.Equal(4, MarshalCache<int>.Size);
    }

    [Fact]
    public void Size_for_byte_is_1()
    {
        Assert.Equal(1, MarshalCache<byte>.Size);
    }

    [Fact]
    public void Size_for_IntPtr_matches_native_pointer_size()
    {
        Assert.Equal(IntPtr.Size, MarshalCache<IntPtr>.Size);
    }

    [Fact]
    public void Size_for_bool_is_1()
    {
        Assert.Equal(1, MarshalCache<bool>.Size);
    }

    [Fact]
    public void Size_for_enum_matches_underlying_type()
    {
        Assert.Equal(4, MarshalCache<DayOfWeek>.Size);
    }

    [Fact]
    public void Size_for_blittable_struct_is_accurate()
    {
        Assert.Equal(8, MarshalCache<BlittableStruct>.Size);
    }

    [Fact]
    public void Size_for_struct_with_bool_is_managed_layout_width()
    {
        // Regression for the Marshal.SizeOf / Unsafe.SizeOf disagreement on a struct
        // whose only field is `bool`: Marshal reports 4 bytes (Win32 BOOL default marshaling),
        // but the blittable path (MemoryMarshal.Read<T>) actually lays out a bool as 1 byte.
        // MarshalCache.Size must match what the reader actually touches.
        Assert.Equal(Unsafe.SizeOf<SingleBoolStruct>(), MarshalCache<SingleBoolStruct>.Size);
        Assert.Equal(1, MarshalCache<SingleBoolStruct>.Size);
    }

    [Fact]
    public void Size_for_struct_with_bools_in_sequence_matches_managed_layout()
    {
        // Sequential struct { bool, bool } — managed width is 2, Marshal width is 8 (two BOOLs).
        // The blittable path uses 1 byte per bool, so Size must equal the managed width.
        Assert.Equal(Unsafe.SizeOf<SequentialBoolStruct>(), MarshalCache<SequentialBoolStruct>.Size);
        Assert.Equal(2, MarshalCache<SequentialBoolStruct>.Size);
    }

    [Fact]
    public void TypeRequiresMarshal_is_false_for_blittable_types()
    {
        Assert.False(MarshalCache<int>.TypeRequiresMarshal);
        Assert.False(MarshalCache<byte>.TypeRequiresMarshal);
        Assert.False(MarshalCache<IntPtr>.TypeRequiresMarshal);
        Assert.False(MarshalCache<IntPtr>.TypeRequiresMarshal);
    }

    [Fact]
    public void TypeRequiresMarshal_is_true_for_types_with_MarshalAs_field()
    {
        Assert.True(MarshalCache<MarshalAsStruct>.TypeRequiresMarshal);
    }

    [Fact]
    public void TypeRequiresMarshal_is_true_for_reference_containing_types()
    {
        Assert.True(MarshalCache<string>.TypeRequiresMarshal);
        Assert.True(MarshalCache<ClassWithInt>.TypeRequiresMarshal);
    }

    [Fact]
    public void Properties_are_computed_once_and_cached()
    {
        int size1 = MarshalCache<int>.Size;
        bool marshal1 = MarshalCache<int>.TypeRequiresMarshal;

        int size2 = MarshalCache<int>.Size;
        bool marshal2 = MarshalCache<int>.TypeRequiresMarshal;

        Assert.Equal(size1, size2);
        Assert.Equal(marshal1, marshal2);
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct BlittableStruct
    {
        public int X;
        public int Y;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct MarshalAsStruct
    {
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
        public byte[] Data;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct SingleBoolStruct
    {
        public bool Flag;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct SequentialBoolStruct
    {
        public bool A;
        public bool B;
    }

    private class ClassWithInt
    {
        public int Value = 0;
    }
}