using System;
using System.Runtime.InteropServices;
using WhiteMagic;
using WhiteMagic.Execution;
using Xunit;

namespace WhiteMagicTest.Execution;

/// <summary>
/// Tests for <see cref="InProcessInvoker"/> operating in-process.
/// </summary>
public class InProcessInvokerTests
{
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int AddDelegate(int a, int b);

    private static int NativeAdd(int a, int b) => a + b;

    [Fact]
    public void CreateFunction_calls_known_in_process_function()
    {
        using var reader = new InProcessReader();
        var invoker = new InProcessInvoker(reader);

        var native = new AddDelegate(NativeAdd);
        IntPtr functionPointer = Marshal.GetFunctionPointerForDelegate(native);

        AddDelegate callable = invoker.CreateFunction<AddDelegate>(functionPointer);
        int result = callable(5, 7);

        Assert.Equal(12, result);
        GC.KeepAlive(native);
    }

    [Fact]
    public void CreateFunction_rejects_zero_address()
    {
        using var reader = new InProcessReader();
        var invoker = new InProcessInvoker(reader);

        ArgumentException ex = Assert.Throws<ArgumentException>(() => invoker.CreateFunction<AddDelegate>(IntPtr.Zero));
        Assert.Equal("address", ex.ParamName);
    }

    [Fact]
    public void Vtable_helper_reads_function_pointer_slot()
    {
        using var reader = new InProcessReader();
        var invoker = new InProcessInvoker(reader);

        // Build a tiny fake vtable in a pinned buffer: two slots holding known pointers.
        IntPtr slot0 = Marshal.GetFunctionPointerForDelegate(new AddDelegate(NativeAdd));
        IntPtr slot1 = new IntPtr(0x12345678);

        IntPtr[] vtable;
        if (reader.Is64Bit)
        {
            vtable = [slot0, slot1];
        }
        else
        {
            vtable = [slot0, slot1];
        }

        GCHandle pin = GCHandle.Alloc(vtable, GCHandleType.Pinned);
        try
        {
            IntPtr vTableAddress = pin.AddrOfPinnedObject();
            Assert.Equal(slot0, invoker.ReadVTableFunction(vTableAddress, 0));
            Assert.Equal(slot1, invoker.ReadVTableFunction(vTableAddress, 1));
        }
        finally
        {
            pin.Free();
        }
    }
}