"""Extract the byte representations PersonalizationApplet expects from
PEM-encoded P-256 keys produced by ``aliro-trustgen init``.

The applet stores raw scalars / raw uncompressed-point coordinates with
fixed lengths (32 / 64 bytes), so we strip PEM/DER framing and BigInteger
sign-padding here.
"""

from cryptography.hazmat.primitives.asymmetric import ec

P256_COORD_LEN = 32


def extract_priv_scalar(private_key: ec.EllipticCurvePrivateKey) -> bytes:
    """Return the 32-byte big-endian P-256 private scalar."""
    if not isinstance(private_key.curve, ec.SECP256R1):
        raise ValueError(f"expected P-256 (secp256r1), got {private_key.curve.name}")
    return _to_fixed_be(private_key.private_numbers().private_value, P256_COORD_LEN)


def extract_pub_xy(public_key: ec.EllipticCurvePublicKey) -> bytes:
    """Return the 64-byte uncompressed point (x || y) without the 0x04 tag."""
    if not isinstance(public_key.curve, ec.SECP256R1):
        raise ValueError(f"expected P-256 (secp256r1), got {public_key.curve.name}")
    nums = public_key.public_numbers()
    return _to_fixed_be(nums.x, P256_COORD_LEN) + _to_fixed_be(nums.y, P256_COORD_LEN)


def _to_fixed_be(value: int, length: int) -> bytes:
    """Big-endian unsigned, zero-padded to exactly ``length`` bytes."""
    return value.to_bytes(length, "big")