VMT Interface

#pragma once

#include <map>
#include <Windows.h>

class VMT
{
public:
	explicit VMT( void*** pClass );
	~VMT( );

	void* Hook( size_t Index, void* pFunction );
	void Unhook( size_t Index );
	void UnhookTable( ) const;

	template <typename T>
	static T CallVirtual( void* pInstance, size_t Index)
	{
		auto VTable = *static_cast< void*** >( pInstance );
		return T( VTable[ Index ] );
	}

private:
	size_t Count( ) const;
	size_t CountFunctions;

	void*** ppClassInstance;
	void** pVTable;
	void** pSwapTable;

	std::map<size_t, void*> mapHooks;
};

#include "VMT.h"

VMT::VMT( void*** pClass )
{
	ppClassInstance = pClass;
	pVTable = *pClass;

	CountFunctions = Count( );

	pSwapTable = static_cast< void** >( VirtualAlloc( nullptr, sizeof( void* ) * CountFunctions, MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE ) );
	memcpy( pSwapTable, pVTable, sizeof( void* ) * CountFunctions );
	*ppClassInstance = pSwapTable;
}

VMT::~VMT( )
{
	if ( *ppClassInstance != pVTable && pSwapTable )
		UnhookTable( );
}

size_t VMT::Count( ) const
{
	if ( !ppClassInstance || !pVTable )
		return 0;

	size_t it = 0;
	while ( pVTable[ it ] )
		++it;

	return it;
}

void* VMT::Hook( size_t Index, void* pFunction )
{
	if ( !ppClassInstance || !pVTable )
		return nullptr;

	auto OriginalFunction = pVTable[ Index ];
	mapHooks[ Index ] = OriginalFunction;

	pSwapTable[ Index ] = pFunction;

	return OriginalFunction;
}

void VMT::Unhook( size_t Index )
{
	pSwapTable[ Index ] = mapHooks[ Index ];
}

void VMT::UnhookTable( ) const
{
	*ppClassInstance = pVTable;
	VirtualFree( pSwapTable, 0, MEM_RELEASE );
}