dialog.rb

require 'ffi'

# button constants
BUTTONS_OK = 0
BUTTONS_OKCANCEL = 1
BUTTONS_ABORTRETRYIGNORE = 2
BUTTONS_YESNO = 4

# return code constants
CLICKED_OK = 1
CLICKED_CANCEL = 2
CLICKED_ABORT = 3
CLICKED_RETRY = 4
CLICKED_IGNORE = 5
CLICKED_YES = 6
CLICKED_NO = 7

extend FFI::Library

ffi_lib 'user32'
ffi_convention :stdcall 

attach_function :msgbox, 'MessageBoxA', [:pointer, :string, :string, :uint], :int

def message_box(txt, title=APP_TITLE, buttons=BUTTONS_OK)
    r = msgbox(nil, txt, title, buttons)
    return r
end

response = message_box("Are you sure you want to proceed?",
"Proceed?", BUTTONS_YESNO)

if response == CLICKED_YES
    # insert your code here
end