from __future__ import annotations

import time
from dataclasses import dataclass, field


@dataclass
class PeriodicRefresh:
    """Small scheduler for optional CCU state-refresh frames."""

    frames: list[bytes] = field(default_factory=list)
    interval: float = 0.0
    _next_due: float | None = None
    _index: int = 0

    @property
    def enabled(self) -> bool:
        return bool(self.frames) and self.interval > 0

    def start(self, now: float | None = None) -> None:
        if not self.enabled:
            self._next_due = None
            return
        self._next_due = (time.monotonic() if now is None else now) + self.interval

    def due_frames(self, now: float | None = None) -> list[bytes]:
        if not self.enabled:
            return []
        current = time.monotonic() if now is None else now
        if self._next_due is None:
            self._next_due = current + self.interval
            return []
        if current < self._next_due:
            return []

        frame = self.frames[self._index % len(self.frames)]
        self._index += 1

        while self._next_due <= current:
            self._next_due += self.interval
        return [frame]