BepInEx/Runtimes/Unity/BepInEx.Unity.IL2CPP/Hook/Funchook/FunchookDetour.cs

using System;
using System.Runtime.CompilerServices;

namespace BepInEx.Unity.IL2CPP.Hook.Funchook;

internal class FunchookDetour : BaseNativeDetour<FunchookDetour>
{
    private readonly nint funchookInstance;

    public FunchookDetour(nint originalMethodPtr, Delegate detourMethod) : base(originalMethodPtr, detourMethod)
    {
        funchookInstance = FunchookLib.Create();
    }

    protected override void ApplyImpl() => EnsureSuccess(FunchookLib.Install(funchookInstance, 0));

    protected override unsafe void PrepareImpl()
    {
        var trampolinePtr = OriginalMethodPtr;
        EnsureSuccess(FunchookLib.Prepare(funchookInstance, &trampolinePtr, DetourMethodPtr));
        TrampolinePtr = trampolinePtr;
    }

    protected override void UndoImpl() => EnsureSuccess(FunchookLib.Uninstall(funchookInstance, 0));

    protected override void FreeImpl() => EnsureSuccess(FunchookLib.Destroy(funchookInstance));

    private string GetErrorMessage()
        => FunchookLib.ErrorMessage(funchookInstance);

    private void EnsureSuccess(FunchookResult result, [CallerArgumentExpression("result")] string methodName = null)
    {
        if (result == FunchookResult.Success) return;
        var errorMsg = GetErrorMessage();
        if (result == FunchookResult.OutOfMemory) throw new OutOfMemoryException($"{methodName} failed: {errorMsg}");
        throw new Exception($"{methodName} failed with result {result}: {errorMsg}");
    }
}