import io
from os.path import join, abspath
from typing import Generator

from django.apps import apps
from django.template import TemplateDoesNotExist, Origin
from django.template.loaders.base import Loader as BaseLoader


class SpecificAppTemplateLoader(BaseLoader):

    def get_template_sources(self, app_template_name: str) -> Generator[Origin, None, None]:
        template_parts = app_template_name.split(':', 1)
        if len(template_parts) != 2:
            raise TemplateDoesNotExist(app_template_name)
        app_name, template_name = template_parts

        app_dir = apps.get_app_config(app_name).path
        template_dir = abspath(join(app_dir, 'templates'))
        template_path = join(template_dir, template_name)

        yield Origin(
            name=template_path,
            template_name=template_name,
            loader=self,
        )

    def get_contents(self, origin: Origin) -> str:
        try:
            with io.open(origin.name, encoding=self.engine.file_charset) as fp:
                return fp.read()
        except IOError:
            pass
        raise TemplateDoesNotExist(f'Could not read template content: {origin}')