from django.contrib.admin import ModelAdmin
from django.conf.urls.defaults import patterns, url
from django.core.urlresolvers import reverse, NoReverseMatch
from django.shortcuts import render_to_response
from django.utils.safestring import mark_safe

import logging
logger = logging.getLogger('preview_admin')

class PreviewAdmin(ModelAdmin):
    preview_fields = {}
    def get_urls(self):
        info = self.model._meta.app_label, self.model._meta.module_name

        urls = super(PreviewAdmin, self).get_urls()
        myurls = patterns('',
                url(r'^preview/(.+)/$', self.admin_site.admin_view(self.preview),
                    name='%s_%s_preview' % info),
        )
        return myurls + urls

    def add_preview(self, formfield):
        render = formfield.widget.render

        def preview_render(name, *args, **kwargs):
            rendered = render(name, *args, **kwargs)

            info = self.model._meta.app_label, self.model._meta.module_name
            preview_url = reverse('admin:%s_%s_preview' % info,
                        args=[name], current_app=self.admin_site.name)

            rendered += '<p><a href="%s">Preview</a></p>' % preview_url
            return mark_safe(rendered)

        formfield.widget.render = preview_render

    def formfield_for_dbfield(self, db_field, **kwargs):
        formfield = super(PreviewAdmin, self).formfield_for_dbfield(db_field, **kwargs)

        if db_field.name in self.preview_fields:
            self.add_preview(formfield)

        return formfield

    def preview(self, request, field):
        return render_to_response('404.html')