class DownloadCancelled(Exception):
    """Excepción para cancelar descargas en vuelo."""
    def __init__(self, message: str = "Descarga cancelada por solicitud del usuario"):
        super().__init__(message)


def unwrap_redirect_url(url: str, timeout: int = 6) -> str:
    """
    Desempaqueta URLs envueltas o enlaces cortos de redirección (ej. getsnap.link, thedylink.com)
    utilizando únicamente cabeceras HTTP nativas y análisis de parámetros estándar.
    NO utiliza ninguna API externa ni servicios de terceros.
    """
    if not url or not isinstance(url, str):
        return url
    curr = url.strip()
    if not curr.startswith(("http://", "https://")):
        return curr

    from urllib.parse import parse_qs, urljoin, urlparse
    try:
        parsed = urlparse(curr)
        host = (parsed.hostname or "").lower()
    except Exception:
        return curr

    wrapper_domains = ("getsnap.link", "thedylink.com", "snaptube", "bit.ly", "tinyurl.com", "t.co")
    if not any(d in host for d in wrapper_domains):
        return curr

    import requests
    session = requests.Session()
    session.headers.update({
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36"
    })
    try:
        for _ in range(5):
            parsed = urlparse(curr)
            host = (parsed.hostname or "").lower()

            qs = parse_qs(parsed.query)
            for key in ("url", "link", "target", "dest"):
                val = qs.get(key)
                if val and val[0].startswith(("http://", "https://")):
                    curr = val[0]
                    break

            if not any(d in host for d in wrapper_domains):
                break

            try:
                r = session.get(curr, allow_redirects=False, timeout=timeout)
                loc = r.headers.get("Location")
                if not loc:
                    break
                if loc.startswith("intent://"):
                    intent_p = urlparse(loc.replace("intent://", "http://", 1))
                    intent_qs = parse_qs(intent_p.query)
                    if intent_qs.get("url"):
                        curr = intent_qs["url"][0]
                        break
                elif loc.startswith(("http://", "https://")):
                    curr = loc
                else:
                    curr = urljoin(curr, loc)
            except Exception:
                break
    except Exception:
        pass
    finally:
        session.close()

    return curr