from __future__ import annotations

import re
from urllib.parse import urlsplit, urlunsplit

from django.conf import settings


def normalize_set_language_next(value: str | None) -> str:
    """
    Normalize the `next` path used by Django's set_language view.

    Removes any leading language prefix from the path so switching from one
    locale to another cannot produce duplicated prefixes like `/de/en/...`.
    """
    if not value:
        return "/"

    parsed = urlsplit(str(value))
    path = parsed.path or "/"
    if not path.startswith("/"):
        path = f"/{path}"

    configured_codes = {
        str(code).lower().replace("_", "-") for code, _ in settings.LANGUAGES
    }
    first_segment, _, remainder = path.lstrip("/").partition("/")
    normalized_segment = first_segment.lower().replace("_", "-")
    looks_like_language_code = bool(
        re.fullmatch(r"[a-z]{2}(?:-[a-z]{2})?", normalized_segment)
    )
    should_strip = normalized_segment in configured_codes or looks_like_language_code

    if should_strip:
        path = f"/{remainder}" if remainder else "/"

    return urlunsplit(("", "", path, parsed.query, ""))