class Subject(models.Model):
    SUBJECT_CHOICES = (
        ('tech', 'Technical'),
        ('bus', 'Business'),
        ('lead', 'Leadership'),
    )
    name = models.CharField(max_length=20,choices=SUBJECT_CHOICES, unique=True)

    def __str__(self):
        return self.name

class Skill_level(models.Model):
    SKILL_LEVEL_CHOICES = (
        ('Begin', 'Beginner'),
        ('Interm', 'Intermediate'),
        ('Adv', 'Advanced'),
    )
    name = models.CharField(max_length=20,choices=SKILL_LEVEL_CHOICES, unique=True)

    def __str__(self):
        return self.name

class Course(models.Model):
    slug = models.SlugField()
    title = models.CharField(max_length=120)
    description = models.TextField()
    allowed_memberships = models.ManyToManyField(Membership)
    created_at = models.DateTimeField(auto_now_add=True)
    subjects = models.ManyToManyField(Subject)
    skill_level = models.ManyToManyField(Skill_level)
    visited_times = models.IntegerField(default=0)

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('courses:detail', kwargs={'slug': self.slug})

    @property
    def lessons(self):
        return self.lesson_set.all().order_by('position')