//////////////////////////////////////////////////////////////////////////////
//
//  FPS limit removal patch for GothicMod.exe 1.08k_mod
//
//  UNSUPPORTED - USAGE AT YOUR OWN RISK
//
//////////////////////////////////////////////////////////////////////////////

#include <windows.h>

//////////////////////////////////////////////////////////////////////////////

// constants for the patch
const LPTSTR PATCH_CAPTION = TEXT("FPS patch");
const unsigned long PATCH_OFFSET = 0x001CE592;
const unsigned long PATCH_LENGTH = 0x00000007;
const BYTE PATCH_O[PATCH_LENGTH] = {0x51, 0xFF, 0x15, 0xF0, 0x00, 0x7D, 0x00};
const BYTE PATCH_N[PATCH_LENGTH] = {0x90, 0x90, 0x90, 0x90, 0x90, 0x90, 0x90};

//////////////////////////////////////////////////////////////////////////////

// show error/success messages
void ShowErrorMessage(LPTSTR Func, DWORD Code)
{
    TCHAR Message[1024];
    LPTSTR ErrorMsg;
    LPTSTR Caption;
    DWORD Flags;

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER |
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL, Code, 0, LPTSTR(&ErrorMsg), 0, NULL);
    wsprintf(Message, TEXT("%s: %s"), Func, ErrorMsg);
    if (Code == ERROR_SUCCESS)
    {
        Caption = PATCH_CAPTION;
        Flags = MB_OK | MB_ICONINFORMATION;
    }
    else
    {
        Caption = NULL;
        Flags = MB_OK | MB_ICONERROR;
    }
    MessageBox(NULL, Message, Caption, Flags);
    if (ErrorMsg) LocalFree((HLOCAL)ErrorMsg);
}

// open GUI dialog box to let the user choose the file
BOOL SelectFileToPatch(LPTSTR Filename, DWORD MaxFilename)
{
    OPENFILENAME ofn;

    ZeroMemory(&ofn, sizeof(OPENFILENAME));
    ofn.lStructSize = sizeof(OPENFILENAME);
    ofn.lpstrFilter = TEXT("GothicMod.exe\0GothicMod.exe\0");
    ofn.nFilterIndex = 1;
    ofn.lpstrFile = Filename;
    ofn.nMaxFile = MaxFilename;
    ofn.Flags = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST |
                OFN_NOREADONLYRETURN | OFN_NOTESTFILECREATE |
                OFN_HIDEREADONLY | OFN_ENABLESIZING;
    return GetOpenFileName(&ofn);
}

// get file handle with read/write access
BOOL OpenFileToPatch(LPTSTR Filename, HANDLE &Filehandle)
{
    Filehandle = CreateFile(Filename, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    if ( Filehandle == INVALID_HANDLE_VALUE )
    {
        ShowErrorMessage(TEXT("Open"), GetLastError());
        return FALSE;
    }
    return TRUE;
}

// close file handle
BOOL CloseFileToPatch(HANDLE &Filehandle)
{
    if ( (Filehandle != NULL) && (Filehandle != INVALID_HANDLE_VALUE) )
        CloseHandle(Filehandle);
    Filehandle = INVALID_HANDLE_VALUE;
    return TRUE;
}

// seek to the file offset where the patch starts
BOOL SeekFileToPatch(HANDLE Filehandle)
{
    if ( SetFilePointer(Filehandle, PATCH_OFFSET, NULL, FILE_BEGIN) == INVALID_SET_FILE_POINTER )
    {
        ShowErrorMessage(TEXT("Seek"), GetLastError());
        return FALSE;
    }
    return TRUE;
}

// verify if the source pattern matches the original which we want to patch
BOOL VerifyFileToPatch(HANDLE Filehandle)
{
    BYTE Buffer[PATCH_LENGTH];
    DWORD BytesRead;
    int Index;

    if ( !ReadFile(Filehandle, &Buffer, PATCH_LENGTH, &BytesRead, NULL) || (BytesRead != PATCH_LENGTH) )
    {
        ShowErrorMessage(TEXT("Read"), GetLastError());
        return FALSE;
    }
    else
    {
        for (Index = 0; Index < PATCH_LENGTH; Index++)
        if ( Buffer[Index] != PATCH_O[Index] )
        {
            MessageBox(NULL, TEXT("Wrong version or already patched!"), PATCH_CAPTION, MB_OK | MB_ICONERROR);
            return FALSE;
        }
        return TRUE;
    }
}

// try to make an backup (filename + '.org')
BOOL BackupFileToPatch(LPTSTR Filename)
{
    TCHAR NewFilename[MAX_PATH+4];

    lstrcpyn(NewFilename, Filename, MAX_PATH);
    lstrcat(NewFilename, TEXT(".org"));
    if ( !CopyFile(Filename, NewFilename, FALSE) )
    {
        ShowErrorMessage(TEXT("Backup"), GetLastError());
        return FALSE;
    }
    return TRUE;
}

// finally patch the file
BOOL WriteFileToPatch(HANDLE Filehandle)
{
    DWORD BytesWritten;

    if ( !WriteFile(Filehandle, &PATCH_N, PATCH_LENGTH, &BytesWritten, NULL) || (BytesWritten != PATCH_LENGTH) )
    {
        ShowErrorMessage(TEXT("Write"), GetLastError());
        return FALSE;
    }
    return TRUE;
}

//////////////////////////////////////////////////////////////////////////////

int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    UNREFERENCED_PARAMETER(hInstance);
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);
    UNREFERENCED_PARAMETER(nCmdShow);

    TCHAR Filename[MAX_PATH] = {0};
    HANDLE Filehandle;

    if ( SelectFileToPatch(Filename, sizeof(Filename) / sizeof(TCHAR)) )
    if ( OpenFileToPatch(Filename, Filehandle) )
    {
        if ( SeekFileToPatch(Filehandle) )
        if ( VerifyFileToPatch(Filehandle) )
        {
            CloseFileToPatch(Filehandle);
            if ( BackupFileToPatch(Filename) )
            if ( OpenFileToPatch(Filename, Filehandle) )
            if ( SeekFileToPatch(Filehandle) )
            if ( WriteFileToPatch(Filehandle) )
            {
                ShowErrorMessage(PATCH_CAPTION, ERROR_SUCCESS);
            }
        }
        CloseFileToPatch(Filehandle);
    }

    return 0;
}