import json
import logging

from django.conf import settings
from django.utils import timezone
from pywebpush import WebPushException, webpush

from accounts.models import PushSubscription

logger = logging.getLogger(__name__)


def push_is_configured() -> bool:
    return bool(settings.VAPID_PUBLIC_KEY and settings.VAPID_PRIVATE_KEY)


def send_to_subscription(subscription: PushSubscription, payload: dict) -> bool:
    """Push one message. Returns whether it was delivered.

    A 404 or 410 from the push service means the browser threw the subscription
    away (app uninstalled, notifications revoked); the row is then useless, so we
    delete it rather than retrying it forever.
    """
    if not push_is_configured():
        logger.warning("Push not configured: set VAPID_PUBLIC_KEY / VAPID_PRIVATE_KEY.")
        return False

    try:
        webpush(
            subscription_info=subscription.as_subscription_info(),
            data=json.dumps(payload),
            vapid_private_key=settings.VAPID_PRIVATE_KEY,
            vapid_claims={"sub": f"mailto:{settings.VAPID_CLAIM_EMAIL}"},
            timeout=10,
        )
    except WebPushException as exc:
        status = getattr(exc.response, "status_code", None)
        if status in (404, 410):
            logger.info("Dropping expired push subscription %s", subscription.pk)
            subscription.delete()
        else:
            logger.error("Push to %s failed: %s", subscription.pk, exc)
        return False

    subscription.last_success_at = timezone.now()
    subscription.save(update_fields=["last_success_at"])
    return True


def notify_user(user, payload: dict) -> int:
    """Push to every device the user has enabled. Returns the number delivered."""
    return sum(
        send_to_subscription(subscription, payload)
        for subscription in user.push_subscriptions.all()
    )