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, GroupToolSubscription, GroupTaskSubscription


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

    def _active_task_subscriptions(self):
        for subscription in GroupTaskSubscription.objects.all():
            if subscription.should_remind:
                yield subscription

        for tool_subscription in GroupToolSubscription.objects.all():
            for subscription in tool_subscription.get_task_subscriptions():
                if subscription.should_remind:
                    yield subscription

    def _expand_group_subscriptions_to_users(self, subscriptions):
        out = {}
        for subscription in subscriptions:
            for user in subscription.group.user_set.all():
                if user not in out:
                    out[user] = []
                out[user].append(subscription)

        return {
            user: sorted(subscriptions, key=lambda r: r.task.next_recurrence)
            for user, subscriptions in out.items()
        }

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

        group_subscriptions = self._active_task_subscriptions()
        subscriptions_per_user = self._expand_group_subscriptions_to_users(
            group_subscriptions
        )

        for user, subscriptions in subscriptions_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(subscriptions)} task(s) to {user}"
                )
            )

            try:
                send_mail(
                    subject=f"[CMS Tool Maintenance] {len(subscriptions)} tasks are upcoming or overdue!",
                    message=template.render({"subscriptions": subscriptions}).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}"
                    )
                )