"""
Celery tasks for notifications.
"""

import json
import logging
from celery import shared_task
from django.utils import timezone
from django.core.mail import send_mail
from django.template.loader import render_to_string
from django.conf import settings
from django.db.models import Q
from datetime import timedelta
from zoneinfo import ZoneInfo

logger = logging.getLogger(__name__)


def notify_user(user, title, body, notification_type, task=None, url='/'):
    """
    Send a notification to a user via whichever of email/push they have
    enabled, and record it in the Notification log. Returns True if it went
    out on at least one channel.
    """
    from .models import Notification

    notified = False

    if user.email_notifications and user.email_verified:
        try:
            send_mail(
                subject=title,
                message=body,
                from_email=settings.DEFAULT_FROM_EMAIL,
                recipient_list=[user.email],
                fail_silently=False,
            )
            notified = True
        except Exception as e:
            logger.error(f"Failed to email {user.email}: {e}")

    if user.push_notifications:
        send_web_push_to_user(user, title=title, body=body, url=url)
        notified = True

    if notified:
        Notification.objects.create(
            user=user,
            notification_type=notification_type,
            title=title,
            message=body,
            task=task,
        )

    return notified


def send_web_push_to_user(user, title, body, url='/'):
    """Send a Web Push notification to all of a user's registered web devices."""
    if not settings.VAPID_PRIVATE_KEY:
        return

    from pywebpush import webpush, WebPushException
    from users.models import DeviceToken

    devices = DeviceToken.objects.filter(user=user, platform='web', is_active=True)

    for device in devices:
        try:
            subscription_info = json.loads(device.token)
        except (ValueError, TypeError):
            continue

        try:
            webpush(
                subscription_info=subscription_info,
                data=json.dumps({'title': title, 'body': body, 'url': url}),
                vapid_private_key=settings.VAPID_PRIVATE_KEY,
                vapid_claims={'sub': f'mailto:{settings.VAPID_ADMIN_EMAIL}'},
            )
        except WebPushException as e:
            status_code = e.response.status_code if e.response is not None else None
            if status_code in (404, 410):
                device.is_active = False
                device.save(update_fields=['is_active'])
            logger.warning(f"Web push failed for {user.email}: {e}")


@shared_task
def send_daily_task_email():
    """
    Send daily email to users with their tasks due today.
    Runs once per day and sends to users in their local morning time.
    """
    from django.contrib.auth import get_user_model
    from tasks.models import Task

    User = get_user_model()

    # Get all users who have email and/or push notifications enabled
    users = User.objects.filter(
        Q(email_notifications=True) | Q(push_notifications=True),
        is_active=True
    ).distinct()

    notifications_sent = 0
    current_utc_hour = timezone.now().hour

    for user in users:
        # Convert current UTC time to user's local time
        try:
            user_tz = ZoneInfo(user.timezone)
        except Exception:
            user_tz = ZoneInfo('UTC')

        user_local_time = timezone.now().astimezone(user_tz)
        user_local_hour = user_local_time.hour

        # Only send if it's between 6-7 AM in the user's timezone
        # (gives 1 hour window, task runs every hour)
        if not (6 <= user_local_hour < 7):
            continue

        # Get today's date in user's timezone
        today = user_local_time.date()

        # Check if we already sent an email today
        from .models import Notification
        already_sent_today = Notification.objects.filter(
            user=user,
            notification_type='daily_email',
            created_at__date=today
        ).exists()

        if already_sent_today:
            continue

        # Get tasks due today
        tasks_due_today = Task.objects.filter(
            user=user,
            due_date=today,
            status__in=['pending', 'in_progress']
        ).order_by('due_time', 'priority', 'title')

        # Get overdue tasks
        overdue_tasks = Task.objects.filter(
            user=user,
            due_date__lt=today,
            status__in=['pending', 'in_progress']
        ).order_by('due_date', 'due_time', 'priority', 'title')

        # Only send email if there are tasks
        if not tasks_due_today.exists() and not overdue_tasks.exists():
            continue

        # Prepare email content
        subject = f"Your tasks for {today.strftime('%A, %B %d, %Y')}"

        # Create plain text message
        message_lines = [
            f"Good morning! Here are your tasks for today:\n"
        ]

        if overdue_tasks.exists():
            message_lines.append(f"\n⚠️  OVERDUE TASKS ({overdue_tasks.count()}):")
            for task in overdue_tasks[:10]:  # Limit to 10
                due_str = task.due_date.strftime('%b %d')
                message_lines.append(f"  • {task.title} (due {due_str})")
            if overdue_tasks.count() > 10:
                message_lines.append(f"  ... and {overdue_tasks.count() - 10} more")

        if tasks_due_today.exists():
            message_lines.append(f"\n📅 DUE TODAY ({tasks_due_today.count()}):")
            for task in tasks_due_today:
                time_str = task.due_time.strftime('%I:%M %p') if task.due_time else ''
                priority_icon = {'high': '🔴', 'medium': '🟡', 'low': '🟢'}.get(task.priority, '')
                message_lines.append(f"  • {priority_icon} {task.title} {time_str}".strip())

        message_lines.append(f"\n\nView all tasks: https://{settings.SITE_DOMAIN}")
        message_lines.append("\nYou can change your email preferences in your profile settings.")

        message = '\n'.join(message_lines)

        notified = False

        # Send email
        if user.email_notifications and user.email_verified:
            try:
                send_mail(
                    subject=subject,
                    message=message,
                    from_email=settings.DEFAULT_FROM_EMAIL,
                    recipient_list=[user.email],
                    fail_silently=False,
                )
                notified = True
                logger.info(f"Sent daily task email to {user.email}")
            except Exception as e:
                logger.error(f"Failed to send daily email to {user.email}: {e}")

        # Send push
        if user.push_notifications:
            send_web_push_to_user(
                user,
                title=subject,
                body=f"{tasks_due_today.count()} due today, {overdue_tasks.count()} overdue",
                url='/',
            )
            notified = True

        if notified:
            # Record that we notified the user today (prevents duplicates)
            Notification.objects.create(
                user=user,
                notification_type='daily_email',
                title=subject,
                message=f"Daily notification sent with {tasks_due_today.count()} tasks due today and {overdue_tasks.count()} overdue tasks"
            )
            notifications_sent += 1

    logger.info(f"Daily task notification job completed. Notified {notifications_sent} users.")
    return notifications_sent


REMINDER_MESSAGES = {
    'reminder': lambda task: (f'Upcoming: {task.title}', f'"{task.title}" is due soon.'),
    'due_soon': lambda task: (f'Due now: {task.title}', f'"{task.title}" is due now.'),
    'overdue': lambda task: (f'Overdue: {task.title}', f'"{task.title}" is overdue.'),
}


@shared_task
def send_scheduled_reminders():
    """
    Send "before due", "due now", and "overdue" notifications from
    ScheduledReminder rows created by Task.reschedule_reminders(). Runs
    frequently (every few minutes) since these are time-sensitive, unlike
    the once-a-day digest above.
    """
    from .models import ScheduledReminder

    due_reminders = ScheduledReminder.objects.filter(
        is_sent=False, remind_at__lte=timezone.now()
    ).select_related('task', 'task__user')

    sent_count = 0
    for reminder in due_reminders:
        task = reminder.task
        if not task.is_deleted and task.status not in ('completed', 'cancelled'):
            title, body = REMINDER_MESSAGES[reminder.reminder_type](task)
            if notify_user(task.user, title, body, reminder.reminder_type, task=task, url=f'/tasks/{task.id}/'):
                sent_count += 1

        reminder.is_sent = True
        reminder.sent_at = timezone.now()
        reminder.save(update_fields=['is_sent', 'sent_at'])

    return sent_count


@shared_task
def process_recurring_tasks():
    """
    Process completed recurring tasks and create next instances.
    This runs daily as a safety net to catch any tasks that weren't
    automatically handled when marked as completed.
    """
    from tasks.models import Task

    # Find completed recurring tasks from the last 48 hours
    yesterday = timezone.now() - timedelta(days=2)

    completed_recurring_tasks = Task.objects.filter(
        status='completed',
        recurrence__in=['daily', 'weekly', 'biweekly', 'monthly', 'yearly', 'custom'],
        completed_at__gte=yesterday
    ).exclude(recurrence='none')

    tasks_created = 0
    for task in completed_recurring_tasks:
        # Check if a next recurrence already exists
        next_due_date = task.calculate_next_due_date()
        if next_due_date:
            # Check if we already created this recurrence
            # Check for any task (pending OR completed) to avoid duplicates
            existing = Task.objects.filter(
                user=task.user,
                title=task.title,
                due_date=next_due_date,
                recurrence=task.recurrence
            ).exists()

            if not existing:
                # Create the next recurrence
                new_task = task.create_next_recurrence()
                if new_task:
                    tasks_created += 1
                    logger.info(f"Created recurring task: {new_task.title} (due: {new_task.due_date})")

    if tasks_created > 0:
        logger.info(f"Created {tasks_created} recurring task instances")

    return tasks_created