from django.core.exceptions import FieldError

from django.db import models

from django.utils import simplejson as json

from django.utils.encoding import force_unicode

class Small(object):

    """

    A simple class to show that non-trivial Python objects can be used as

    attributes.

    """

    def __init__(self, first, second):

        self.first, self.second = first, second

    def __unicode__(self):

        return u'%s%s' % (force_unicode(self.first), force_unicode(self.second))

    def __str__(self):

        return unicode(self).encode('utf-8')

class SmallField(models.Field):

    """

    Turns the "Small" class into a Django field. Because of the similarities

    with normal character fields and the fact that Small.__unicode__ does

    something sensible, we don't need to implement a lot here.

    """

    __metaclass__ = models.SubfieldBase

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

        kwargs['max_length'] = 2

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

    def get_internal_type(self):

        return 'CharField'

    def to_python(self, value):

        if isinstance(value, Small):

            return value

        return Small(value[0], value[1])

    def get_db_prep_save(self, value):

        return unicode(value)

    def get_prep_lookup(self, lookup_type, value):

        if lookup_type == 'exact':

            return force_unicode(value)

        if lookup_type == 'in':

            return [force_unicode(v) for v in value]

        if lookup_type == 'isnull':

            return []

        raise TypeError('Invalid lookup type: %r' % lookup_type)

class SmallerField(SmallField):

    pass

class JSONField(models.TextField):

    __metaclass__ = models.SubfieldBase

    description = ("JSONField automatically serializes and desializes values to "

        "and from JSON.")

    def to_python(self, value):

        if not value:

            return None

        if isinstance(value, basestring):

            value = json.loads(value)

        return value

    def get_db_prep_save(self, value):

        if value is None:

            return None

        return json.dumps(value)