from __future__ import annotations

import base64
from typing import Tuple

from nacl import public, signing, bindings


def ed25519_to_x25519(ed_seed: bytes) -> Tuple[public.PrivateKey, public.PublicKey]:
    """Convert Ed25519 seed (32 bytes) to X25519 key pair using libsodium conversion."""
    if len(ed_seed) != 32:
        raise ValueError("ed25519 seed must be 32 bytes")
    sk_ed = signing.SigningKey(ed_seed)
    sk_ed_bytes = sk_ed._seed + sk_ed.verify_key._key  # 64-byte expanded sk (seed||pub)
    sk_x_bytes = bindings.crypto_sign_ed25519_sk_to_curve25519(sk_ed_bytes)
    pk_x_bytes = bindings.crypto_sign_ed25519_pk_to_curve25519(bytes(sk_ed.verify_key))
    sk_x = public.PrivateKey(sk_x_bytes)
    pk_x = public.PublicKey(pk_x_bytes)
    return sk_x, pk_x


def x25519_pub_b64_from_ed_seed(ed_seed: bytes) -> str:
    _, pk = ed25519_to_x25519(ed_seed)
    return base64.b64encode(bytes(pk)).decode()