"""Per-slot watchdog store for safety-sell (REQ-034 / BAT-010).

WatchdogStore tracks the last time a snapshot RPC response included each
holding slot. BAT-011 trigger loops use is_expired() to decide whether a
slot is unmonitored (strategy module absent) and therefore eligible for
autonomous safety-sell actions.

Thread-safety: dict reads and writes in CPython are GIL-atomic for simple
assignments, which is sufficient here — one writer (snapshot-rpc thread)
and one or more readers (BAT-011 trigger-loop threads). No explicit lock
is needed.
"""
from __future__ import annotations

from datetime import datetime, timezone
from typing import Optional


class WatchdogStore:
    """In-memory per-slot last_seen_at tracker (REQ-034)."""

    def __init__(self) -> None:
        self._store: dict[str, datetime] = {}
        self._started_at: datetime = datetime.now(tz=timezone.utc)

    def update(self, slot_id: str) -> None:
        """Record that slot_id appeared in a snapshot RPC response."""
        self._store[slot_id] = datetime.now(tz=timezone.utc)

    def last_seen(self, slot_id: str) -> Optional[datetime]:
        """Return the last time slot_id was seen, or None if never (dcy-017).

        Read-only accessor for watchdog-ownership visibility (REQ-034)."""
        return self._store.get(slot_id)

    def is_expired(self, slot_id: str, timeout_sec: int) -> bool:
        """Return True if slot_id has not been seen for longer than timeout_sec.

        A slot that has never been seen is treated as expired (returns True)
        unless in_grace_period() is True — callers must check grace period
        before calling this method when they want to suppress false positives.
        """
        last = self._store.get(slot_id)
        if last is None:
            return True
        elapsed = (datetime.now(tz=timezone.utc) - last).total_seconds()
        return elapsed > timeout_sec

    def in_grace_period(self, grace_sec: int) -> bool:
        """Return True if the daemon started less than grace_sec seconds ago.

        During the grace period ALL expiry judgements must be deferred —
        no slot should be treated as watchdog-expired (REQ-034 AC-4).
        """
        elapsed = (datetime.now(tz=timezone.utc) - self._started_at).total_seconds()
        return elapsed < grace_sec