"""System event log message."""

from auditlogger.event import Event


class SystemEvent(Event):
    """Represent a system event."""

    SYSTEM_EVENTS = ["starting", "stopping"]
    ES_INDEX = "system-event"

    def __init__(
            self, system_name, version, event_name, instance_details=None):
        """Return the event.

        Args:
            system_name (str): The name of the system.
            version (str): The version of the running system.
            event_name (str): One of the known system events.
            instance_details (dict): Additional aspects worth logging.
        """
        if event_name not in self.SYSTEM_EVENTS:
            raise Exception("unexpected system event: {}".format(event_name))
        super().__init__()
        self.data["system_name"] = system_name
        self.data["version"] = version
        self.data["event_name"] = event_name
        self.data["instance_details"] = instance_details or []