event_queue.py

"""
A priority queue for events.
"""
from events import Event


class EventQueue:
    """A priority queue of events.

    Events are dequeued in timestamp order (earlier timestamp = higher priority).
    """
    def is_empty(self) -> bool:
        """Return whether this event queue contains no items."""
        raise NotImplementedError

    def enqueue(self, event: Event) -> None:
        """Add event to this event queue, sorted by its timestamp."""
        raise NotImplementedError

    def dequeue(self) -> Event:
        """Remove and return the earliest event in this event queue.

        Preconditions:
        - not self.is_empty()
        """
        raise NotImplementedError


class EventQueueList(EventQueue):
    """A queue of events that can be dequeued in timestamp order.

    Note: this is related to the "PriorityQueueSorted" class
    we discussed last week.
    """
    # Private Instance Attributes:
    #   _events: a list of the events in this queue

    _events: list[Event]

    def __init__(self) -> None:
        """Initialize a new and empty event queue."""
        self._events = []

    def is_empty(self) -> bool:
        """Return whether this event queue contains no items."""
        return self._events == []

    def enqueue(self, event: Event) -> None:
        """Add event to this event queue."""
        index = 0
        while index < len(self._events) and \
                self._events[index].timestamp > event.timestamp:
            index = index + 1

        self._events.insert(index, event)

    def dequeue(self) -> Event:
        """Remove and return the earliest event in this event queue.

        Preconditions:
        - not self.is_empty()
        """
        return self._events.pop()