import datetime

from django.db import models
from django.utils import timezone
from django.utils.translation import gettext_lazy as _
from wagtail.models import Page

from vbv_lernwelt.core.models import User
from vbv_lernwelt.course.models import CourseSession


class DueDate(models.Model):
    start = models.DateTimeField(null=True, db_index=True)
    end = models.DateTimeField(null=True, blank=True, db_index=True)
    title = models.CharField(default="", max_length=1024)
    learning_content_description = models.CharField(
        default="", blank=True, max_length=1024
    )
    description = models.CharField(default="", blank=True, max_length=1024)
    url = models.CharField(default="", blank=True, max_length=1024)
    course_session = models.ForeignKey(
        "course.CourseSession",
        on_delete=models.CASCADE,
        blank=True,
    )

    page = models.ForeignKey(Page, on_delete=models.SET_NULL, null=True, blank=True)

    def Meta(self):
        ordering = ["start", "end"]
        verbose_name = _("Termin")
        help = "The start date is mandatory. You can set the end date if you want to have a deadline with a duration."

    def __str__(self):
        if self.is_undefined:
            return f"DueDate: {self.title} undefined"
        start_str = self.start.strftime("%Y-%m-%d %H:%M") if self.start else "-"
        result = f"DueDate: {self.title} {start_str}"

        if self.end:
            end_str = self.end.strftime("%Y-%m-%d %H:%M") if self.end else "-"
            result += f" - {end_str}"

        return result

    @property
    def is_undefined(self):
        return self.start is None

    @property
    def duration(self):
        if self.end is None:
            return datetime.timedelta(0)
        return self.end - self.start

    @classmethod
    def get_users_next_events_qs(
        cls, user: User, course_session: CourseSession = None, limit=10
    ):
        """
        Returns a queryset of all due dates that are relevant for the given user.
        If course_session is given, only due dates for that course_session are returned.
        The user is determined by via a course session user of a course_assignment.

        """
        qs = cls.get_next_due_dates_qs()

        if course_session:
            qs = qs.filter(
                course_session=course_session,
                course_session__course_assignment__user=user,
            )
        else:
            qs = qs.filter(course_session__course_assignment__user=user)

        qs = qs.order_by("start")[:limit]

        return qs

    @classmethod
    def get_next_due_dates_qs(cls):
        now = timezone.now()
        qs = cls.objects.filter(start__gte=now)
        return qs