import random

import string

from django.db import models

class MyWrapper:

    def __init__(self, value):

        self.value = value

    def __repr__(self):

        return "<%s: %s>" % (self.__class__.__name__, self.value)

    def __str__(self):

        return self.value

    def __eq__(self, other):

        if isinstance(other, self.__class__):

            return self.value == other.value

        return self.value == other

class MyWrapperField(models.CharField):

    def __init__(self, *args, **kwargs):

        kwargs["max_length"] = 10

        super().__init__(*args, **kwargs)

    def pre_save(self, instance, add):

        value = getattr(instance, self.attname, None)

        if not value:

            value = MyWrapper("".join(random.sample(string.ascii_lowercase, 10)))

            setattr(instance, self.attname, value)

        return value

    def to_python(self, value):

        if not value:

            return

        if not isinstance(value, MyWrapper):

            value = MyWrapper(value)

        return value

    def from_db_value(self, value, expression, connection):

        if not value:

            return

        return MyWrapper(value)

    def get_db_prep_save(self, value, connection):

        if not value:

            return

        if isinstance(value, MyWrapper):

            return str(value)

        return value

    def get_db_prep_value(self, value, connection, prepared=False):

        if not value:

            return

        if isinstance(value, MyWrapper):

            return str(value)

        return value

class MyAutoField(models.BigAutoField):

    def from_db_value(self, value, expression, connection):

        if value is None:

            return None

        return MyWrapper(value)

    def get_prep_value(self, value):

        if value is None:

            return None

        return int(value)