class BackupBase(object):
    """Base class that describes the interface a backup command must implement.

    Attributes:
        command     the value used in the command line to invoke this command,
                    usually is the name of the database (e.g.: mongo, mysql)
    """
    command = ""

    def __init__(self, args, extra):
        """Initialize a backup command given the arguments passed to CLI"""
        self.args = args
        self.extra = extra

    @classmethod
    def parse_args(cls, subparsers):
        """Parse CLI arguments specific to this subcommand"""
        raise NotImplementedError("Base method not overriden.")

    def backup(self):
        """Backup a database given the arguments specified.

        All the values passed via the CLI are available at `self.args` and
        `self.extra`. The first object stores known arguments that have been
        explicitly parsed. The second object is a list of arguments that are
        unkown to the parser and can be useful for invoking other commands
        withouht having to re-define its parser's arguments.

        This method should raise exceptions in case of errors so any active
        notifier can hadle it.
        """
        raise NotImplementedError("Base method not overriden.")


class UploadBase(object):
    """Base class that describes the interface an upload command must implement.

    Attributes:
        command     the value used in the command line to invoke this command,
                    usually is the name of the service (e.g.: softlayer, s3)
    """
    command = ""

    def __init__(self, args, extra):
        """Initialize an upload command given the arguments passed to CLI"""
        self.args = args
        self.extra = extra

    @classmethod
    def parse_args(cls, subparsers):
        """Parse CLI arguments specific to this subcommand"""
        raise NotImplementedError("Base method not overriden.")

    def upload(self):
        """Upload a file to the remote service.

        All the values passed via the CLI are available at `self.args` and
        `self.extra`. The first object stores known arguments that have been
        explicitly parsed. The second object is a list of arguments that are
        unkown to the parser and can be useful for invoking other commands
        withouht having to re-define its parser's arguments.

        This method should raise exceptions in case of errors so any active
        notifier can hadle it.
        """
        raise NotImplementedError("Base method not overriden.")


class NotifierBase(object):
    """Base class for notifiers

    Notifiers are responsible for sending messages to external services to
    report relevant events that may happen during the execution of a command.

    Attributes:
        command     the value used to enable a notifier in the command line,
                    e.g.: `backwork -n {command}`
    """
    command = ""

    def __init__(self, args, extra):
        self.args = args
        self.extra = extra

    @classmethod
    def parse_args(cls, parser):
        """Add command line argument parsing rules relevant to the notifier.

        This method is not required to be implemented as it might not be
        necessary to add more arguments to the parser in some cases.
        """
        pass

    def notify(self, msg=""):
        """Handle an incoming message.

        The `msg` object could be either a `string` or an `Exception`. You may
        want to handle them differently with something like:

            if issubclass(msg.__class__, Exception):
              handle_exception(msg)
            else:
              handle_string(msg)

        If `msg` is an exception, the call to this method will be in the context
        of an `except`, meaning you will be able to access `sys.exc_info()`.
        """
        raise NotImplementedError("Base method not overriden.")

setup(
    ...
    entry_points={
        "backwork.backups": [
            "<COMMAND NAME>": "module:BackupClass"
        ],
        "backwork.restores": [
            "<COMMAND NAME>": "module:RestoreClass"
        ]
    },
    ...

setup(
    ...
    entry_points={
        "backwork.uploads": [
            "<COMMAND NAME>": "module:UploadClass"
        ],
        "backwork.shows": [
            "<COMMAND NAME>": "module:ShowClass"
        ]
        "backwork.downloads": [
            "<COMMAND NAME>": "module:DownloadClass"
        ]
    },
    ...

setup(
    ...
    entry_points={
        "backwork.notifiers": [
            "<COMMAND NAME>": "module:NotifierClass"
        ]
    },
    ...