Watch for changes in the docs and rebuild HTML docs when changed.

def doc_watch():
    """Watch for changes in the docs and rebuild HTML docs when changed."""
    try:
        from watchdog.events import FileSystemEventHandler
        from watchdog.observers import Observer
    except ImportError:
        print_failure_message('Install the watchdog package to use this task, '
                              "i.e., `pip install watchdog'.")
        raise SystemExit(1)

    class RebuildDocsEventHandler(FileSystemEventHandler):
        def __init__(self, base_paths):
            self.base_paths = base_paths

        def dispatch(self, event):
            """Dispatches events to the appropriate methods.
            :param event: The event object representing the file system event.
            :type event: :class:`watchdog.events.FileSystemEvent`
            """
            for base_path in self.base_paths:
                if event.src_path.endswith(base_path):
                    super(RebuildDocsEventHandler, self).dispatch(event)
                    # We found one that matches. We're done.
                    return

        def on_modified(self, event):
            print_failure_message('Modification detected. Rebuilding docs.')
            # # Strip off the path prefix.
            # import os
            # if event.src_path[len(os.getcwd()) + 1:].startswith(
            #         CODE_DIRECTORY):
            #     # sphinx-build doesn't always pick up changes on code files,
            #     # even though they are used to generate the documentation. As
            #     # a workaround, just clean before building.
            doc_html()
            print_success_message('Docs have been rebuilt.')

    print_success_message(
        'Watching for changes in project files, press Ctrl-C to cancel...')
    handler = RebuildDocsEventHandler(get_project_files())
    observer = Observer()
    observer.schedule(handler, path='.', recursive=True)
    observer.start()
    try:
        while True:
            time.sleep(1)
    except KeyboardInterrupt:
        observer.stop()
        observer.join()