function S32 os_main();
const SizeU page_size = 4096;

LRESULT CALLBACK 
WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
  return DefWindowProcW(hwnd, uMsg, wParam, lParam);;
}

int
WinMain(HINSTANCE hInstance, HINSTANCE a, LPSTR b, int nShowCmd){
  wchar_t *CLASS_NAME  = L"Cool window class";
  wchar_t *WINDOW_NAME = L"Have a good day!";
  
  WNDCLASSW wc = { };
  wc.lpfnWndProc   = WindowProc;
  wc.hInstance     = hInstance;
  wc.lpszClassName = CLASS_NAME;
  RegisterClassW(&wc);
  
  HWND window_handle = CreateWindowExW(0, CLASS_NAME, WINDOW_NAME, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, 0, 0, hInstance, 0);
  ShowWindow(window_handle, nShowCmd);
  return os_main();
}

function String
os_read_file(String name){
  String result = {};
  FILE *f = fopen((char *)name.str, "rb");
  fseek(f, 0, SEEK_END);
  result.len = ftell(f);
  fseek(f, 0, SEEK_SET);  /* same as rewind(f); */
  
  result.str = malloc(result.len + 1);
  fread(result.str, result.len, 1, f);
  fclose(f);
  
  result.str[result.len] = 0;
  return result;
}

function OS_Memory
os_reserve(SizeU size){
  OS_Memory result = {0};
  SizeU adjusted_size = align_up(size, page_size);
  result.data = VirtualAlloc(0, adjusted_size, MEM_RESERVE, PAGE_READWRITE);
  assert_msg(result.data, "Failed to reserve virtual memory");
  result.reserve = adjusted_size;
  return result;
}

function void
os_commit(OS_Memory *m, SizeU size){
  SizeU commit = align_up(size, page_size);
  void *p = VirtualAlloc((U8 *)m->data + m->commit, commit, MEM_COMMIT, PAGE_READWRITE);
  assert_msg(p, "Failed to commit more memory");
  m->commit += commit;
}