"""

Wrapper for loading templates from "template" directories in INSTALLED_APPS

packages.

"""

import os

from django.conf import settings

from django.core.exceptions import ImproperlyConfigured

from django.template import TemplateDoesNotExist

from django.utils._os import safe_join

# At compile time, cache the directories to search.

app_template_dirs = []

for app in settings.INSTALLED_APPS:

    i = app.rfind('.')

    if i == -1:

        m, a = app, None

    else:

        m, a = app[:i], app[i+1:]

    try:

        if a is None:

            mod = __import__(m, {}, {}, [])

        else:

            mod = getattr(__import__(m, {}, {}, [a]), a)

    except ImportError, e:

        raise ImproperlyConfigured, 'ImportError %s: %s' % (app, e.args[0])

    template_dir = os.path.join(os.path.dirname(mod.__file__), 'templates')

    if os.path.isdir(template_dir):

        app_template_dirs.append(template_dir)

# It won't change, so convert it to a tuple to save memory.

app_template_dirs = tuple(app_template_dirs)

def get_template_sources(template_name, template_dirs=None):

    """

    Returns the absolute paths to "template_name", when appended to each

    directory in "template_dirs". Any paths that don't lie inside one of the

    template dirs are excluded from the result set, for security reasons.

    """

    if not template_dirs:

        template_dirs = app_template_dirs

    for template_dir in template_dirs:

        try:

            yield safe_join(template_dir, template_name)

        except UnicodeDecodeError:

            # The template dir name was a bytestring that wasn't valid UTF-8.

            raise

        except ValueError:

            # The joined path was located outside of template_dir.

            pass

def load_template_source(template_name, template_dirs=None):

    for filepath in get_template_sources(template_name, template_dirs):

        try:

            return (open(filepath).read().decode(settings.FILE_CHARSET), filepath)

        except IOError:

            pass

    raise TemplateDoesNotExist, template_name

load_template_source.is_usable = True