from itertools import groupby

from django.core.mail import send_mail
from django.core.management.base import BaseCommand, CommandError
from django.template import loader

from tasks.models import Tool, Task, Event, Reminder


class Command(BaseCommand):
    help = 'Sends any notifications for upcoming and overdue tasks'

    def _active_reminders(self):
        for reminder in Reminder.objects.all():
            if reminder.should_remind:
                yield reminder

    def handle(self, *args, **options):
        template = loader.get_template('tasks/notificationEmail.txt')

        reminders_per_user = {
            user: sorted(reminders, key=lambda r: r.task.next_recurrence)
            for user, reminders in groupby(self._active_reminders(), lambda r: r.user)
        }

        for user, reminders in reminders_per_user.items():
            if not user.email:
                self.stdout.write(self.style.ERROR(
                    f"Can't send email, user '{user}' is missing an email address"))
                continue

            self.stdout.write(self.style.SUCCESS(
                f'Sending notification for {len(reminders)} task(s) to {user}'))

            try:
                send_mail(
                    subject=f'[CMS Tool Maintenance] {len(reminders)} tasks are upcoming or overdue!',
                    message=template.render({'reminders': reminders}).strip(),
                    from_email='adam@adamgoldsmith.name',
                    recipient_list=[user.email],
                    fail_silently=False
                )

            except Exception as e:
                self.stdout.write(self.style.ERROR(
                    f"Failed to send mail for user '{user}': {type(e).__name__}: {e}"))