foerderbarometer/input/utils/mail/attachments.py

import os
import posixpath
import time
import mimetypes

from os import PathLike
from pathlib import Path
from urllib.parse import urlparse
from urllib.request import urlretrieve

from django.conf import settings
from django.core.mail import EmailMultiAlternatives

from foerderbarometer.constants import *

PathList = list[Path]


def ensure_dir(directory: PathLike) -> Path:
    """
    Ensure that the given directory exists.
    Creates it recursively if it doesn't.
    """

    directory = Path(directory)

    directory.mkdir(parents=True, exist_ok=True)

    return directory


def is_fresh(path: Path, ttl_seconds: int) -> bool:
    """
    Check if the cached file exists and is still fresh within TTL.
    """

    try:
        mtime = path.stat().st_mtime
    except FileNotFoundError:
        return False
    else:
        return time.time() - mtime < ttl_seconds


def get_attachment(url: str) -> Path:
    filepath = urlparse(url).path
    filename = posixpath.basename(filepath)
    destination = ensure_dir(settings.MAIL_ATTACHMENT_CACHE_DIR) / filename

    if is_fresh(destination, settings.MAIL_ATTACHMENT_TTL_SECONDS):
        return destination

    return download_attachment(url, destination)


def download_attachment(url: str, destination: Path) -> Path:
    filepath = destination.with_suffix('.tmp')

    try:
        urlretrieve(url, filepath)
        os.replace(filepath, destination)
    finally:
        filepath.unlink(missing_ok=True)

    return destination


def collect_attachment_paths(recipient: str, type_code: str) -> PathList:
    assert recipient in RECIPIENTS
    assert type_code in TYPES

    config = settings.MAIL_ATTACHMENT_URLS[recipient]
    urls = [*config[TYPE_ALL], *config.get(type_code, [])]

    return [get_attachment(url) for url in urls]


def get_mime_type(path: Path) -> str:
    mime_type, encoding = mimetypes.guess_type(path)

    return mime_type or 'application/octet-stream'


def attach_files(message: EmailMultiAlternatives, files: list[Path]):
    """
    Attach files to the EmailMultiAlternatives message.
    MIME type is guessed from path; falls back to application/octet-stream.
    """

    for path in files:
        mime_type = get_mime_type(path)

        with open(path, 'rb') as fp:
            message.attach(path.name, fp.read(), mime_type)