from __future__ import annotations

from pathlib import Path
from uuid import uuid4

from flask import current_app, url_for
from werkzeug.datastructures import FileStorage
from werkzeug.utils import secure_filename


ALLOWED_AVATAR_EXTENSIONS = {".png", ".jpg", ".jpeg", ".webp", ".gif"}


def save_avatar_upload(file_storage: FileStorage | None) -> str | None:
    if file_storage is None or not file_storage.filename:
        return None

    original_name = secure_filename(file_storage.filename)
    suffix = Path(original_name).suffix.lower()
    if suffix not in ALLOWED_AVATAR_EXTENSIONS:
        raise ValueError("Bitte ein Bild als PNG, JPG, WEBP oder GIF hochladen.")

    upload_dir = Path(current_app.config["AVATAR_UPLOAD_DIR"])
    upload_dir.mkdir(parents=True, exist_ok=True)

    filename = f"{uuid4().hex}{suffix}"
    file_storage.save(upload_dir / filename)
    return url_for("main.uploaded_avatar", filename=filename)