window change listener.py

#
# BSD 2-Clause License
#
# Copyright (c) 2018, Dane Finlay
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice, this
#    list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright notice,
#    this list of conditions and the following disclaimer in the documentation
#    and/or other materials provided with the distribution.

# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

"""
Script using the Windows API to register for window focus changes and print the
titles of newly focused windows.
"""

import sys
import time
import ctypes
import ctypes.wintypes
import threading
import six


class ObservableWindowChange(object):
    def __init__(self):
        self.__observers = []

    def register_observer(self, observer):
        self.__observers.append(observer)

    def notify_observers(self, *args, **kwargs):
        win_title = ''.join(args)
        if win_title == '':
            return ''
        for observer in self.__observers:
            observer.notify(win_title)

    def start_event_listener(self):
        # Create a WindowChangeEventListener object with this instance of
        # ObservableWindowChange as a parameter (self)
        listener = WindowChangeEventListener(self)
        listener.listen_forever()


class IWindowChangeObserver(object):
    """
    Base class for observing window changes
    """
    def __init__(self, observable):
        observable.register_observer(self)

    def notify(self, win_title):
        raise NotImplementedError


class WindowChangeEventListener(object):
    """
    WindowChangeEventListener
    """
    def __init__(self, observable):
        self.observable = observable

    def listen_forever(self):        
        # This is to fix a problem with ascii encoding (windows with Unicode in
        # their titles)
        if six.PY2:
            reload(sys)
            sys.setdefaultencoding('utf8')

        # Look here for DWORD event constants:
        # http://stackoverflow.com/questions/15927262/convert-dword-event-constant-from-wineventproc-to-name-in-c-sharp
        # Don't worry, they work for python too.
        EVENT_SYSTEM_DIALOGSTART = 0x0010
        WINEVENT_OUTOFCONTEXT = 0x0000
        EVENT_SYSTEM_FOREGROUND = 0x0003
        WINEVENT_SKIPOWNPROCESS = 0x0002

        user32 = ctypes.windll.user32
        ole32 = ctypes.windll.ole32
        EnumWindows = ctypes.windll.user32.EnumWindows
        EnumWindowsProc = ctypes.WINFUNCTYPE(ctypes.c_bool,
                                             ctypes.POINTER(ctypes.c_int),
                                             ctypes.POINTER(ctypes.c_int))
        GetWindowText = ctypes.windll.user32.GetWindowTextW
        GetWindowTextLength = ctypes.windll.user32.GetWindowTextLengthW
        IsWindowVisible = ctypes.windll.user32.IsWindowVisible

        ole32.CoInitialize(0)

        WinEventProcType = ctypes.WINFUNCTYPE(
            None,
            ctypes.wintypes.HANDLE,
            ctypes.wintypes.DWORD,
            ctypes.wintypes.HWND,
            ctypes.wintypes.LONG,
            ctypes.wintypes.LONG,
            ctypes.wintypes.DWORD,
            ctypes.wintypes.DWORD
        )

        def callback(hWinEventHook, event, hwnd, idObject, idChild, dwEventThread,
                     dwmsEventTime):
            length = GetWindowTextLength(hwnd)
            buff = ctypes.create_unicode_buffer(length + 1)
            GetWindowText(hwnd, buff, length + 1)

            # Notify observers
            self.observable.notify_observers(buff.value)

        WinEventProc = WinEventProcType(callback)

        user32.SetWinEventHook.restype = ctypes.wintypes.HANDLE
        hook = user32.SetWinEventHook(
            EVENT_SYSTEM_FOREGROUND,
            EVENT_SYSTEM_FOREGROUND,
            0,
            WinEventProc,
            0,
            0,
            WINEVENT_OUTOFCONTEXT | WINEVENT_SKIPOWNPROCESS
        )
        if hook == 0:
            print('SetWinEventHook failed')
            exit(1)

        msg = ctypes.wintypes.MSG()
        while user32.GetMessageW(ctypes.byref(msg), 0, 0, 0) != 0:
            user32.TranslateMessageW(msg)
            user32.DispatchMessageW(msg)

        # Stopped receiving events, so clear up the winevent hook and uninitialise.
        print('Stopped receiving new window change events. Exiting...')
        user32.UnhookWinEvent(hook)
        ole32.CoUninitialize()


class WindowObserver(IWindowChangeObserver):
    def notify(self, win_title):
        print("Window '%s' focused" % win_title)


if __name__ == '__main__':

    def run():
        # Create an observable and an observer observing it
        subject = ObservableWindowChange()
        observer = WindowObserver(subject)

        # Listen for window changes
        subject.start_event_listener()

    # Start the 'run' method in a daemonized thread.
    t = threading.Thread(target=run)
    t.setDaemon(True)
    t.start()

    # Keep the main thread running in a sleep loop until ctrl+c (SIGINT) is caught.
    # Once the main thread terminates, all daemon threads will automatically
    # terminate.
    while True:
        try:
            time.sleep(0.1)
        except KeyboardInterrupt:
            break