Revise paste Advanced Django Model Techniques 1-3

# 1. Customer

def validator(value):
    for char in value:
        if not char.isalpha() or not char.isspace():
            raise ValidationError("Name can only contain letters and spaces")
            
def phone_validator(value):
    if not re.match(r'^\+359\d{9}$', value):
        raise ValidationError("Phone number must start with a '+359' followed by 9 digits")

class Customer(models.Model):
    name = models.CharField(max_length=100, validators=[validator])
    age = models.PositiveIntegerField(validators=[MinValueValidator(18), message="Age must be greater than 18"])
    email = models.EmailFiled(error_message = {'invalid': "Enter a valid email address"})
    phone_number = models.CharField(max_length=13, validatiors=[phone_validator])
    website_url = models.URLField(error_message = {'invalid': "Enter a valid URL"})
    
# 2.	Media

class BaseMedia(models.Model):
    title = models.CharField(max_length=100)
    description = models.TextField()
    genre = models.CharField(max_length=50)
    created_at = models.DateTimeField(auto_now_add=True)
    
    class Meta:
        abstract= True
        ordering = ["-created_at", "title"]
        
        
class Book(BaseMedia):
    author = models.CharField(max_length=100, validators=[MinLengthValidator(5, message="Author must be at least 5 characters long")])
    isbn = models.CharField(max_length=20, unique=True, validators=[MinLengthValidator(6, message="ISBN must be at least 6 characters long")])
    
    class Meta(BaseMedia.Meta):
        verbose_name = "Model Book"
        verbose_name_plural = "Models of type - Book"
    
class Movie(BaseMedia):
    director = models.CharField(max_length=100, validators=[MinLengthValidator(8, message="Director must be at least 8 characters long")])
    
    class Meta(BaseMedia.Meta):
        verbose_name = "Model Movie"
        verbose_name_plural = "Models of type - Movie"
    
    
class Music(BaseMedia):
    artist = models.CharField(max_length=100, validators=[MinLengthValidator(9, message="Artist must be at least 9 characters long")])
    
    class Meta(BaseMedia.Meta):
        verbose_name = "Model Music"
        verbose_name_plural = "Models of type - Music "
        
        
# 3.	Digital Products

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimaField(max_digits=10, decimal_places=2)
    
    def calculate_tax(self):
        return self.price * Decimal(0.08)
        # да проверя без Decimal дали минава
        
    def calculate_shipping_cost(weight: Decimal):
        return weight * Decimal(2.00)
        
    def format_product_name(self):
        return f"Product: {self.name}"
        
    
# когато моделът Child споделя същата таблица като Parent class-a предоставя допълнителна функционалност, то той е class Meta: е proxy

class DiscountedProduct(Product):
    class Meta:
        proxy = True
        
    def calculate_price_without_discount(self):
        return self.price  * Decimal(1.20)
        
    def calculate_tax(self):
        return self.price * Decimal(0.05)
        # да проверя без Decimal дали минава
        
    def calculate_shipping_cost(weight: Decimal):
        return weight * Decimal(1.50)
        
    def format_product_name(self):
        return f"Discounted Product: {self.name}"