from django.conf import settings
from django.db import models
from django.utils.translation import get_language


class MultilingualField(models.Field):
 SUPPORTED_FIELD_TYPES = [models.CharField, models.TextField]

 def __init__(self, verbose_name=None, **kwargs):
  self.localized_field_model = None
  for model in MultilingualField.SUPPORTED_FIELD_TYPES:
   if issubclass(self.__class__, model):
    self.localized_field_model = model
  self._blank = kwargs.get("blank", False)
  self._editable = kwargs.get("editable", True)
  super().__init__(verbose_name, **kwargs)

 @staticmethod
 def localized_field_name(name, lang_code):
  lang_code_safe = lang_code.replace("-", "_")
  return f"{name}_{lang_code_safe}"

 def get_localized_field(self, lang_code, lang_name):
  _blank = (self._blank
     if lang_code == settings.LANGUAGE_CODE
     else True)
  localized_field = self.localized_field_model(
   f"{self.verbose_name} ({lang_name})",
   name=self.name,
   primary_key=self.primary_key,
   max_length=self.max_length,
   unique=self.unique,
   blank=_blank,
   null=False, # we ignore the null argument!
   db_index=self.db_index,
   default=self.default or "",
   editable=self._editable,
   serialize=self.serialize,
   choices=self.choices,
   help_text=self.help_text,
   db_column=None,
   db_tablespace=self.db_tablespace)
  return localized_field

 def contribute_to_class(self, cls, name,
       private_only=False):
  def translated_value(self):
   language = get_language()
   val = self.__dict__.get(
    MultilingualField.localized_field_name(
      name, language))
   if not val:
    val = self.__dict__.get(
     MultilingualField.localized_field_name(
       name, settings.LANGUAGE_CODE))
   return val

  # generate language-specific fields dynamically
  if not cls._meta.abstract:
   if self.localized_field_model:
    for lang_code, lang_name in settings.LANGUAGES:
     localized_field = self.get_localized_field(
      lang_code, lang_name)
     localized_field.contribute_to_class(
       cls,
       MultilingualField.localized_field_name(
         name, lang_code))

    setattr(cls, name, property(translated_value))
   else:
    super().contribute_to_class(
     cls, name, private_only)


class MultilingualCharField(models.CharField, MultilingualField):
 pass


class MultilingualTextField(models.TextField, MultilingualField):
 pass

LANGUAGE_CODE = 'zh-hans'
TIME_ZONE = 'Asia/Shanghai'

LANGUAGES = (
 ('en-us', 'US English'),
 ('zh-hans', 'Asia/Shanghai')
)

from django.db import models
from django.utils.translation import ugettext_lazy as _

from utils.fields import (
 MultilingualCharField,
 MultilingualTextField
)

class Item(models.Model):
 title = MultilingualCharField(_('Title'), max_length=200)
 description = MultilingualTextField(_('Description'), blank=True)
 content = MultilingualTextField(_('Content'))

 def __str__(self):
  return self.title