"""Celery tasks for the QI Projects app."""

import logging
from datetime import datetime, time as datetime_time, timedelta

from celery import shared_task
from django.conf import settings
from django.utils import timezone

logger = logging.getLogger(__name__)

FIRST_REMINDER_HOURS_BEFORE = 24
SECOND_REMINDER_HOURS_BEFORE = 6


@shared_task
def send_qi_task_reminders():
    """Send deadline-approaching reminders for assigned QI tasks.

    Runs every 15 minutes via Celery Beat. Sends a first reminder 24h before the
    due date and a second reminder 6h before. Each reminder fires at most once per
    task (deduped via `reminder_sent_at` / `second_reminder_sent_at`). Tasks with
    no email-capable assignee or whose send fails are retried on subsequent runs.
    """
    from apps.notifications.services import NotificationService

    from .models import QIProjectTask

    now = timezone.now()
    tz = timezone.get_current_timezone()
    site_url = getattr(settings, "SITE_URL", "http://localhost:8000").rstrip("/")

    def _deadline(task):
        # Interpret due_date (a date) as end-of-day in the current tz.
        return timezone.make_aware(datetime.combine(task.due_date, datetime_time(23, 59, 59)), tz)

    def _send(task, hours_before, label):
        project_url = f"{site_url}/projects/{task.project.id}/"
        message = (
            f"Reminder ({label}): The task '{task.title}' in project "
            f"'{task.project.name}' is due on {task.due_date.strftime('%Y-%m-%d')} "
            f"({hours_before}h remaining)."
        )
        NotificationService.send_email(
            email=task.assigned_to.user.email,
            subject=f"QI Task Reminder: {task.title}",
            message=message,
            related_object=task,
            metadata={
                "notification_type": "qi_task_reminder",
                "task_id": str(task.id),
                "project_id": str(task.project.id),
                "reminder": label,
                "hours_before": hours_before,
            },
            notification_type="qi_task_reminder",
            user=task.assigned_to.user,
        )
        logger.info(
            f"QI task {label} reminder sent for task {task.id} "
            f"(assignee {task.assigned_to_id}, due {task.due_date})"
        )

    first_count = 0
    second_count = 0

    # First reminders: due within 24h, not yet reminded
    for task in QIProjectTask.objects.filter(
        assigned_to__isnull=False,
        status__in=["pending", "active"],
        due_date__isnull=False,
        reminder_sent_at__isnull=True,
        project__is_template=False,
    ).select_related("assigned_to__user", "project"):
        deadline = _deadline(task)
        if not (deadline - timedelta(hours=FIRST_REMINDER_HOURS_BEFORE) <= now < deadline):
            continue
        user = task.assigned_to.user
        if not user or not getattr(user, "email", None):
            logger.warning(f"QI task {task.id} assignee has no email; skipping first reminder.")
            continue
        try:
            _send(task, FIRST_REMINDER_HOURS_BEFORE, "first")
            task.reminder_sent_at = now
            task.save(update_fields=["reminder_sent_at"])
            first_count += 1
        except Exception as e:
            logger.warning(f"Failed to send first QI reminder for task {task.id}: {e}")

    # Second reminders: due within 6h, first sent >=1h ago, not yet second-reminded
    for task in QIProjectTask.objects.filter(
        assigned_to__isnull=False,
        status__in=["pending", "active"],
        due_date__isnull=False,
        second_reminder_sent_at__isnull=True,
        reminder_sent_at__isnull=False,
        reminder_sent_at__lt=now - timedelta(hours=1),
        project__is_template=False,
    ).select_related("assigned_to__user", "project"):
        deadline = _deadline(task)
        if not (deadline - timedelta(hours=SECOND_REMINDER_HOURS_BEFORE) <= now < deadline):
            continue
        user = task.assigned_to.user
        if not user or not getattr(user, "email", None):
            logger.warning(f"QI task {task.id} assignee has no email; skipping second reminder.")
            continue
        try:
            _send(task, SECOND_REMINDER_HOURS_BEFORE, "second")
            task.second_reminder_sent_at = now
            task.save(update_fields=["second_reminder_sent_at"])
            second_count += 1
        except Exception as e:
            logger.warning(f"Failed to send second QI reminder for task {task.id}: {e}")

    logger.info(f"QI task reminders: {first_count} first, {second_count} second")
    return {"first_reminder_count": first_count, "second_reminder_count": second_count}