from MiscUtils import AbstractError


class Task:
    """Abstract base class from which you have to derive your own tasks."""

    def __init__(self):
        """Subclasses should invoke super for this method."""
        # Nothing for now, but we might do something in the future.
        pass

    def run(self):
        """Override this method for you own tasks.

        Long running tasks can periodically use the proceed() method to check
        if a task should stop.

        """
        raise AbstractError, self.__class__


    ## Utility method ##

    def proceed(self):
        """Check whether this task should continue running.

        Should be called periodically by long tasks to check if the system
        wants them to exit. Returns True if its OK to continue, False if
        it's time to quit.

        """
        return self._handle._isRunning


    ## Attributes ##

    def handle(self):
        """Return the task handle.

        A task is scheduled by wrapping a handler around it. It knows
        everything about the scheduling (periodicity and the like).
        Under normal circumstances you should not need the handler,
        but if you want to write period modifying run() methods,
        it is useful to have access to the handler. Use it with care.

        """
        return self._handle

    def name(self):
        """Return the unique name under which the task was scheduled."""
        return self._name


    ## Private method ##

    def _run(self, handle):
        """This is the actual run method for the Task thread.

        It is a private method which should not be overriden.

        """
        self._name = handle.name()
        self._handle = handle
        try:
            self.run()
        except Exception:
            handle.notifyFailure()
        handle.notifyCompletion()