import re
from django import forms
class LinkFieldWidget(Widget):
    '''
    A TextField widget with previewing link, generated from field's value with special url mask
    '''
    def __init__(self, text, url='%s', *args, **kwargs):
        self.url = url
        self.text = text
        if not re.search('%', self.url):
            raise forms.ValidationError, u'Invalid URL mask'
        super(LinkFieldWidget, self).__init__(*args, **kwargs)

    def render(self, name, value, attrs=None):
        output = []
        output.append('''<input type="text" name="%s" value="%s" onkeyup="$('a#%s-link').attr('href', '%s'.replace('%s', this.value)).css({'display': (this.value ? 'inline' : 'none')})" />''' % (name, value or '', name, self.url, '%s'))
        if self.url and self.text:
            output.append('<span><a href="%s" id="%s-link" target="blank" style="display: %s;">%s</a></span>' % (value and self.url % value or '#', name, value and 'inline' or 'none', self.text))

        return mark_safe(u' '.join(output))