from app.core.config import settings


class ReservedProxyPortError(ValueError):
    pass


def backend_port() -> int:
    return settings.API_PORT


def reserved_proxy_port_message(proxy_port: int) -> str:
    return (
        f"Proxy port {proxy_port} is reserved for the backend API "
        "and cannot be used by mitmdump."
    )


def ensure_proxy_port_not_reserved(proxy_port: int) -> None:
    if proxy_port == backend_port():
        raise ReservedProxyPortError(reserved_proxy_port_message(proxy_port))