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

from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
from os.path import exists, isdir

from tfw.networking.event_handlers.server_connector import ServerUplinkConnector
from tfw.components.decorators import RateLimiter
from tfw.event_handler_base import TriggerlessEventHandler

from tfw.config.logs import logging
log = logging.getLogger(__name__)


class WebideReloadEventHandler(FileSystemEventHandler):
    def __init__(self):
        super().__init__()
        self.uplink = ServerUplinkConnector()
        self._paused = False
        self.ignore = 0

    def pause(self):
        self._paused = True

    def resume(self):
        self._paused = False

    @RateLimiter(rate_per_second=5)
    def on_modified(self, event):
        if self._paused: return
        if self.ignore > 0:
            self.ignore = self.ignore - 1
            return
        log.debug(event)
        key = 'webide'
        self.uplink.send(key, {'data': {'command': 'reload'}})


class DirectoryMonitor:
    def __init__(self, directory):
        self.observer = Observer()
        self.eventhandler = WebideReloadEventHandler()
        self.observer.schedule(self.eventhandler, directory, recursive=True)
        self.pause, self.resume = self.eventhandler.pause, self.eventhandler.resume

    def watch(self):
        self.observer.start()

    def stop(self):
        self.observer.stop()
        self.observer.join()

    @property
    def ignore(self):
        return self.eventhandler.ignore

    @ignore.setter
    def ignore(self, value):
        self.ignore = value if value >= 0 else 0

    @property
    def pauser(self):
        return DirectoryMonitor.Pauser(self)

    class Pauser:
        def __init__(self, directory_monitor):
            self.directorymonitor = directory_monitor
        def __enter__(self):
            self.directorymonitor.pause()
        def __exit__(self, exc_type, exc_val, exc_tb):
            self.directorymonitor.resume()


class DirectoryMonitoringEventHandler(TriggerlessEventHandler):
    def __init__(self, key, directory):
        super().__init__(key)
        self._directory = directory
        self._monitor = None
        self.reload_monitor()
        self.commands = {'pause':     self.pause,
                         'resume':    self.resume,
                         'ignore':    self.ignore,
                         'selectdir': self.selectdir}

    @property
    def directory(self):
        return self._directory

    @directory.setter
    def directory(self, directory):
        if not exists(directory) or not isdir(directory): raise EnvironmentError('No such directory!')
        self._directory = directory

    @property
    def monitor(self):
        return self._monitor

    def reload_monitor(self):
        if self._monitor:
            try: self._monitor.stop()
            except KeyError: logging.debug('Working directory was removed – ignoring...')
        self._monitor = DirectoryMonitor(self._directory)
        self._monitor.watch()   # This runs on a separate thread

    def handle_event(self, key, message):
        try:
            message['data'] = self.commands[message['data']['command']](message['data'])
            return message
        except KeyError:
            log.error('IGNORING MESSAGE: Invalid message received: {}'.format(message))

    def pause(self, data):
        self.monitor.pause()
        return data

    def resume(self, data):
        self.monitor.resume()
        return data

    def ignore(self, data):
        self.monitor.ignore += data['ignore']
        return data

    def selectdir(self, data):
        try:
            self.directory = data['directory']
            self.reload_monitor()
            return data
        except EnvironmentError:
            log.error('DirManagingEH failed to switch directory!')

    def cleanup(self):
        self.monitor.stop()