import typing
from email.message import EmailMessage


class BaseEmailBackend:
    """
    Base class for email backend implementations.
    Subclasses must at least overwrite send_messages().
    open() and close() can be called indirectly by using a backend object as a
    context manager:
       with backend as connection:
           # do something with connection
           pass
    """

    def __init__(self, fail_silently: bool = False, **kwargs: typing.Any) -> None:
        self.fail_silently = fail_silently

    def open(self):
        """
        Open a network connection.
        This method can be overwritten by backend implementations to open a network
        connection.
        It's up to the backend implementation to track the status of a network
        connection if it's needed by the backend.
        This method can be called by applications to force a single network connection
        to be used when sending mails. See the send_messages() method of the SMTP
        backend for a reference implementation.

        The default implementation does nothing.
        """

    def close(self):
        """Close a network connection."""

    def __enter__(self):
        try:
            self.open()
        except Exception:
            self.close()
            raise
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close()
        print("close", self)

    def send_messages(self, email_messages: typing.List[EmailMessage]) -> int:
        """
        Send one or more EmailMessage objects and return the number of email
        messages sent.
        """

        msg = "subclasses of BaseEmailBackend must override send_messages() method"
        raise NotImplementedError(msg)
