from django.core.exceptions import FieldDoesNotExist
from django.db.models import Field


def ensure_field(model, name: str, field: Field):
    try:
        existing_field = model._meta.get_field(name)
    except FieldDoesNotExist:
        field.contribute_to_class(model, name)
    else:
        if not isinstance(existing_field, field.__class__):
            msg = (
                '{model} requires a field with name {name} of type {type}.'.format(
                    model=model, name=name, type=field.__class__.__name__
                )
            )
            raise TypeError(msg)
    return field