from django.core.exceptions import ValidationError
from django.db import models


class UpperCaseCharField(models.CharField):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def get_prep_value(self, value):
        value = super().get_prep_value(value)
        if value is not None:
            return value.upper()
        return value


class ContainerNumberField(UpperCaseCharField):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def get_prep_value(self, value):
        value = super().get_prep_value(value)
        if value is not None:
            return value.upper()
        return value

    def validate(self, value, model_instance):
        super().validate(value, model_instance)
        if value and len(value) != 11:
            raise ValidationError('Container number must be exactly 11 characters long.')