hermes-agent/cron/scheduler_provider.py

"""CronScheduler provider interface (Axis B — the trigger).

⚠️ EXPERIMENTAL — this interface is validated by exactly ONE consumer (the
built-in) until an external provider (Chronos, Phase 4) shakes it out. Until
then the module path, method signatures, and start() kwargs MAY change without
a deprecation cycle. Once a second provider validates the shape it becomes
stable. Any growth MUST be additive (new optional method with a default), never
a changed signature on start() or a new abstractmethod.

A CronScheduler decides *when* a due job fires. It does NOT decide what firing
means: execution + delivery stay in cron.scheduler.run_job / _deliver_result,
shared by all providers. Providers must never reimplement agent construction or
delivery.

The built-in InProcessCronScheduler runs the historical 60s daemon-thread
ticker. Alternative providers (e.g. Chronos, a NAS-mediated managed-cron
provider for scale-to-zero deployments) live under plugins/cron/<name>/ and are
selected via the `cron.provider` config key (empty = built-in).
"""
from __future__ import annotations

import threading
from abc import ABC, abstractmethod
from typing import Any


class CronScheduler(ABC):
    """Axis-B trigger provider. Decides WHEN a due cron job fires.

    Required surface is intentionally minimal: ``name`` + ``start``. ``stop``
    and ``is_available`` carry safe defaults. The three Phase-4 hooks
    (``on_jobs_changed`` / ``fire_due`` / ``reconcile``) are added later as
    NON-abstract methods so the built-in keeps satisfying the ABC without
    overriding them — see ``test_abc_growth_stays_additive``.
    """

    @property
    @abstractmethod
    def name(self) -> str:
        """Short identifier, e.g. 'builtin', 'chronos'."""

    def is_available(self) -> bool:
        """Whether this provider can run in the current environment.

        MUST NOT make network calls. The built-in is always available; an
        external provider checks for configured endpoint/credentials. When a
        named provider returns False, the resolver falls back to the built-in.
        """
        return True

    @abstractmethod
    def start(
        self,
        stop_event: threading.Event,
        *,
        adapters: Any = None,
        loop: Any = None,
        interval: int = 60,
    ) -> None:
        """Begin firing due jobs.

        For the built-in this BLOCKS in the 60s loop until stop_event is set
        (it is run inside a daemon thread by the caller, exactly as today).
        An external provider may register a schedule/webhook and return
        immediately; in that case it must still honor stop_event for teardown.
        """

    def stop(self) -> None:
        """Optional eager teardown hook. Default no-op; setting the stop_event
        is the primary stop signal. Override for providers holding external
        resources (queue consumers, HTTP servers)."""
        return None


def resolve_cron_scheduler() -> "CronScheduler":
    """Return the active cron scheduler provider.

    Reads ``cron.provider`` from config. Empty/absent → built-in. A named
    provider that is missing, fails to load, or reports ``is_available() ==
    False`` falls back to the built-in with a warning — cron must never be left
    without a trigger.
    """
    import logging

    logger = logging.getLogger("cron.scheduler_provider")

    name = ""
    try:
        from hermes_cli.config import cfg_get, load_config
        name = (cfg_get(load_config(), "cron", "provider", default="") or "").strip()
    except Exception:
        pass

    if not name or name in ("builtin", "in-process", "inprocess"):
        return InProcessCronScheduler()

    try:
        from plugins.cron import load_cron_scheduler
        provider = load_cron_scheduler(name)
        if provider is None:
            logger.warning("cron.provider '%s' not found; using built-in ticker", name)
            return InProcessCronScheduler()
        if not provider.is_available():
            logger.warning("cron.provider '%s' not available; using built-in ticker", name)
            return InProcessCronScheduler()
        logger.info("Using cron scheduler provider: %s", provider.name)
        return provider
    except Exception as e:
        logger.warning(
            "Failed to load cron.provider '%s' (%s); using built-in ticker", name, e
        )
        return InProcessCronScheduler()


class InProcessCronScheduler(CronScheduler):
    """Default provider: the historical in-process 60s ticker.

    ``start()`` blocks in the tick loop until ``stop_event`` is set, identical
    to the pre-refactor ``_start_cron_ticker`` core loop. The caller runs it in
    a daemon thread.
    """

    @property
    def name(self) -> str:
        return "builtin"

    def start(self, stop_event, *, adapters=None, loop=None, interval=60):
        import logging
        from cron.scheduler import tick as cron_tick

        logger = logging.getLogger("cron.scheduler_provider")
        logger.info("In-process cron scheduler started (interval=%ds)", interval)
        while not stop_event.is_set():
            try:
                cron_tick(verbose=False, adapters=adapters, loop=loop, sync=False)
            except Exception as e:
                logger.debug("Cron tick error: %s", e)
            stop_event.wait(interval)