"""

Wrapper class that takes a list of template loaders as an argument and attempts

to load templates from them in order, caching the result.

"""

from django.template import TemplateDoesNotExist

from django.template.loader import BaseLoader, get_template_from_string, find_template_loader, make_origin

from django.utils.importlib import import_module

from django.core.exceptions import ImproperlyConfigured

class Loader(BaseLoader):

    is_usable = True

    def __init__(self, loaders):

        self.template_cache = {}

        self._loaders = loaders

        self._cached_loaders = []

    @property

    def loaders(self):

        # Resolve loaders on demand to avoid circular imports

        if not self._cached_loaders:

            for loader in self._loaders:

                self._cached_loaders.append(find_template_loader(loader))

        return self._cached_loaders

    def find_template(self, name, dirs=None):

        for loader in self.loaders:

            try:

                template, display_name = loader(name, dirs)

                return (template, make_origin(display_name, loader, name, dirs))

            except TemplateDoesNotExist:

                pass

        raise TemplateDoesNotExist(name)

    def load_template(self, template_name, template_dirs=None):

        if template_name not in self.template_cache:

            template, origin = self.find_template(template_name, template_dirs)

            if not hasattr(template, 'render'):

                try:

                    template = get_template_from_string(template, origin, template_name)

                except TemplateDoesNotExist:

                    # If compiling the template we found raises TemplateDoesNotExist, 

                    # back off to returning the source and display name for the template 

                    # we were asked to load. This allows for correct identification (later) 

                    # of the actual template that does not exist.

                    return template, origin

            self.template_cache[template_name] = template

        return self.template_cache[template_name], None

    def reset(self):

        "Empty the template cache."

        self.template_cache.clear()