from typing import Optional, Sequence

from .monitor_maintenance_window_types import MaintenanceWindow


def active_maintenance(windows: Sequence[MaintenanceWindow], at: int) -> Optional[MaintenanceWindow]:
    """The window with start <= at < end. Half-open, so a window ending at
    02:00 and the next starting at 02:00 never both apply. When several
    overlap, the one that started first wins (ties: the first in the list),
    so the answer does not depend on how the caller sorted them. Every window
    is checked, not only the active ones: a backwards window is a config
    error that would otherwise silently never apply."""
    if not isinstance(at, int) or isinstance(at, bool):
        raise ValueError("at must be a whole second, received %r" % (at,))
    best: Optional[MaintenanceWindow] = None
    for w in windows:
        if w.end <= w.start:
            raise ValueError('maintenance window "%s" must end after it starts: start %d, end %d' % (w.name, w.start, w.end))
        if w.start <= at < w.end and (best is None or w.start < best.start):
            best = w
    return None if best is None else MaintenanceWindow(name=best.name, start=best.start, end=best.end)