"""Injectable clock abstraction for testability."""

from __future__ import annotations

from datetime import UTC, datetime, timedelta
from typing import Protocol


class Clock(Protocol):
    """Clock protocol — provides current UTC time."""

    def now(self) -> datetime: ...


class SystemClock:
    """Real wall-clock implementation."""

    def now(self) -> datetime:
        """Return the current UTC time."""
        return datetime.now(UTC)


class FakeClock:
    """Deterministic clock for tests."""

    def __init__(self, start: datetime | None = None) -> None:
        self._now = start or datetime(2026, 1, 1, tzinfo=UTC)

    def now(self) -> datetime:
        """Return the fixed current time."""
        return self._now

    def advance(self, seconds: float) -> None:
        """Advance the clock by the given number of seconds."""
        self._now += timedelta(seconds=seconds)

    def set(self, dt: datetime) -> None:
        """Set the clock to an exact time."""
        self._now = dt