from django.contrib.sites.models import Site
from django.template import TemplateDoesNotExist

from dbtemplates.conf import settings
from dbtemplates.models import Template
from dbtemplates.utils.cache import cache, get_cache_key, set_and_return
from django.template.loader import BaseLoader


class Loader(BaseLoader):
    """
    A custom template loader to load templates from the database.

    Tries to load the template from the dbtemplates cache backend specified
    by the DBTEMPLATES_CACHE_BACKEND setting. If it does not find a template
    it falls back to query the database field ``name`` with the template path
    and ``sites`` with the current site.
    """
    is_usable = True

    def load_template_source(self, template_name, template_dirs=None):
        site = Site.objects.get_current()
        display_name = 'dbtemplates:%s:%s:%s' % (settings.DATABASE_ENGINE,
                                                 template_name, site.domain)
        cache_key = get_cache_key(template_name)
        if cache:
            try:
                backend_template = cache.get(cache_key)
                if backend_template:
                    return backend_template, template_name
            except:
                pass
        try:
            template = Template.objects.get(name__exact=template_name)
            return set_and_return(cache_key, template.content, display_name)
        except (Template.MultipleObjectsReturned, Template.DoesNotExist):
            try:
                template = Template.objects.get(
                    name__exact=template_name, sites__in=[site.id])
                return set_and_return(
                    cache_key, template.content, display_name)
            except Template.DoesNotExist:
                pass
        raise TemplateDoesNotExist(template_name)