# based on http://www.djangosnippets.org/snippets/417/



from django.newforms.util import ValidationError

from django.utils.translation import ugettext as _

from time import time

from django.conf import settings

from Crypto.Cipher import Blowfish

from base64 import b64encode, b64decode

from django import newforms as forms





def get_key():

    cobj = Blowfish.new(settings.SECRET_KEY)

    text = unicode(time())

    text += "".join(["_" for i in xrange(8-len(text)%8)])

    return b64encode(cobj.encrypt(text))



class FormWithKeyField(forms.Form):

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

        self.base_fields['key'] = forms.CharField(max_length=100,

                                                  widget=forms.widgets.HiddenInput(),

                                                  initial=get_key())

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

    

    def clean_key(self):

        def validation_error():

            self.data['key'] = get_key()

            raise ValidationError(_('Incorrect key.'))

        

        cobj = Blowfish.new(settings.SECRET_KEY)

        text = cobj.decrypt(b64decode(self.cleaned_data['key'])).rstrip('_')

        try:

            key = float(text)

        except:

            validation_error()

        now = time()

        if now - key < 10 or now - key > 60*60*6: # valid for 6 hours

            validation_error()

        return