from wtforms import Form, ValidationError
from wtforms import StringField, PasswordField
from wtforms.validators import Length, InputRequired
from werkzeug.datastructures import MultiDict
import re

def is_proper_username(form, field):
    if not re.match(r"^\w+$", field.data):
        msg = 'Polje "{}" može imati samo slova i brojke'.format(field.name)
        raise ValidationError(msg)

class LoginForm(Form):
    username = StringField(u'Username:', [InputRequired(), is_proper_username,Length(min=3, max=40)])
    password = PasswordField(u'Password:', [InputRequired(), Length(min=5, max=12)])

    @staticmethod
    def validate_password(form, field):
        data = field.data
        if not re.findall('.*[a-z].*', data):
            msg = 'Polje "{}" mora imati barem jedno malo slovo'.format(field.name)
            raise ValidationError(msg)

        # has at least one uppercase character
        if not re.findall('.*[A-Z].*', data):
            msg = 'Polje "{}" mora imati barem jedno veliko slovo'.format(field.name)
            raise ValidationError(msg)

        # has at least one number
        if not re.findall('.*[0-9].*', data):
            msg = 'Polje "{}" mora imati barem jedan broj'.format(field.name)
            raise ValidationError(msg)

        # has at least one special character
        if not re.findall('.*[^ a-zA-Z0-9].*', data):
            msg = 'Polje "{}" mora imati barem jedan specijalan znak'.format(field.name)
            raise ValidationError(msg)

# testing our form
form = LoginForm(MultiDict([('username', 'nikovrdoljak'), ('password', 'lL2m@msbb')]))
print (form.validate())
print (form.errors)