#include <Windows.h>
#include <Psapi.h>
#include <string>

#if PSAPI_VERSION == 1
#pragma comment(lib, "Psapi.lib")
#endif

template <typename DestType, typename SrcType>
DestType* ByteOffset(SrcType* ptr, ptrdiff_t offset)
{
	return reinterpret_cast<DestType*>(reinterpret_cast<unsigned char*>(ptr) + offset);
}

bool eat_hook(void* old_function, void* new_function)
{
	HMODULE hModule;
	GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS, (LPCSTR)old_function, &hModule);

	PIMAGE_DOS_HEADER DosHeader = (PIMAGE_DOS_HEADER)hModule;
	PIMAGE_NT_HEADERS NtHeader = ByteOffset<IMAGE_NT_HEADERS>(DosHeader, DosHeader->e_lfanew);
	if (IMAGE_NT_SIGNATURE != NtHeader->Signature)
	{
		MessageBox(0, "Bad NT header signature", "Error", 0);
		return false;
	}

	PIMAGE_EXPORT_DIRECTORY ExportDirectory = ByteOffset<IMAGE_EXPORT_DIRECTORY>(DosHeader,
		NtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
	
	DWORD* functions = ByteOffset<DWORD>(DosHeader, ExportDirectory->AddressOfFunctions);
	for (size_t i = 0; i < ExportDirectory->NumberOfFunctions; ++i)
	{
		if (functions[i] == (DWORD)old_function - (DWORD)hModule)
		{
			DWORD oldProtection;
			if (!VirtualProtect(functions + i, sizeof(DWORD), PAGE_EXECUTE_READWRITE, &oldProtection))
			{
				MessageBox(0, "VirtualProtect failed", "Error", 0);
				return false;
			}

			functions[i] = reinterpret_cast<DWORD>(new_function) - reinterpret_cast<DWORD>(DosHeader);

			if (!VirtualProtect(functions + i, sizeof(DWORD), oldProtection, &oldProtection))
			{
				MessageBox(0, "VirtualProtect failed", "Error", 0);
				return false;
			}

			return true;
		}
	}

	return false;
}

bool iat_hook(void* old_function, void* new_function)
{
	HMODULE hModule;
	DWORD sizeNeeded;
	if (0 == EnumProcessModules(GetCurrentProcess(), &hModule, sizeof(hModule), &sizeNeeded))
	{
		MessageBox(0, "EnumProcessModules failed", "Error", 0);
		return false;
	}

	PIMAGE_DOS_HEADER DosHeader = (PIMAGE_DOS_HEADER)hModule;
	PIMAGE_NT_HEADERS NtHeader = ByteOffset<IMAGE_NT_HEADERS>(DosHeader, DosHeader->e_lfanew);
	if (IMAGE_NT_SIGNATURE != NtHeader->Signature)
	{
		MessageBox(0, "Bad NT header signature", "Error", 0);
		return false;
	}
	
	PIMAGE_IMPORT_DESCRIPTOR ImportDirectory = ByteOffset<IMAGE_IMPORT_DESCRIPTOR>(DosHeader,
		NtHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress);
	
	for (size_t i = 0; ImportDirectory[i].Characteristics; ++i)
	{
		PIMAGE_THUNK_DATA thunk = ByteOffset<IMAGE_THUNK_DATA>(hModule, ImportDirectory[i].FirstThunk);
		PIMAGE_THUNK_DATA origThunk = ByteOffset<IMAGE_THUNK_DATA>(hModule, ImportDirectory[i].OriginalFirstThunk);

		for (; origThunk->u1.Function; origThunk++, thunk++)
		{
			if (thunk->u1.Function == (DWORD)old_function)
			{
				DWORD oldProtection;
				if (!VirtualProtect(&thunk->u1.Function, sizeof(DWORD), PAGE_EXECUTE_READWRITE, &oldProtection))
				{
					MessageBox(0, "VirtualProtect failed", "Error", 0);
					return false;
				}

				thunk->u1.Function = reinterpret_cast<DWORD>(new_function);

				if (!VirtualProtect(&thunk->u1.Function, sizeof(DWORD), oldProtection, &oldProtection))
				{
					MessageBox(0, "VirtualProtect failed", "Error", 0);
					return false;
				}

				return true;
			}
		}
	}

	return false;
}

bool hook(void* old_function, void* new_function)
{
	return eat_hook(old_function, new_function) && iat_hook(old_function, new_function);
}