from django.db import models
from django.utils.translation import gettext_lazy as _


class Course(models.Model):

    LICENSE_FREE = 0
    LICENSE_VIP = 1

    title = models.CharField(max_length=128)
    description = models.TextField(default='')
    objectives = models.TextField(default='')
    propaedeutics = models.TextField(default='')
    references = models.TextField(default='')
    slug = models.SlugField(unique=True, blank=False, null=False, allow_unicode=True)
    category = models.ForeignKey(
        'university.Category', on_delete=models.PROTECT, null=True, blank=True)
    cover_image = models.ForeignKey('university.Upload', on_delete=models.PROTECT)
    online_exam = models.ForeignKey(
        'university.OnlineExam', on_delete=models.PROTECT, blank=True, null=True)
    visable_when_no_perm = models.BooleanField(default=True)
    license = models.SmallIntegerField(
        choices=(
            (LICENSE_FREE, _('free')),
            (LICENSE_VIP, _('vip'))
        ), default=LICENSE_FREE)

    class Meta:
        db_table = 'courses'

    def __str__(self):
        return self.title

    @property
    def speakers(self):
        speakers = self.chapter_set.all().values_list('lesson__speaker', flat=True)
        # exclude some `None` value
        # when chapter has no lessons, it returns `None` but not empty list
        speakers = list(set(filter(lambda i: i, speakers)))
        if speakers:
            return ','.join(list(speakers)[:3]) + '...'
        else:
            return ''