baseimage-tutorial-framework/lib/tfw/components/history_monitor.py

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from watchdog.observers import Observer
from watchdog.events import PatternMatchingEventHandler
from os.path import dirname
class CallbackEventHandler(PatternMatchingEventHandler):
def __init__(self, files, *callbacks):
super().__init__(files)
self.callbacks = callbacks
def on_modified(self, event):
for callback in self.callbacks:
callback()
class HistoryMonitor:
def __init__(self, histfile):
self.histfile = histfile
self._history = []
self._last_length = len(self._history)
self._callbacks = []
self.observer = Observer()
self.observer.schedule(CallbackEventHandler([self.histfile],
self._fetch_history,
self._invoke_callbacks),
dirname(self.histfile))
@property
def history(self):
return self._history
@property
def callbacks(self):
return self._callbacks
def _fetch_history(self):
self._last_length = len(self._history)
with open(self.histfile, 'r') as ifile:
self._history = [line.rstrip() for line in ifile.readlines()]
def _invoke_callbacks(self):
if self._last_length < len(self._history):
for callback in self.callbacks:
callback(self.history)
def watch(self):
self.observer.start()
def stop(self):
self.observer.stop()
self.observer.join()