"""Tests for PEM → fixed-width byte extraction."""

import pytest
from cryptography.hazmat.primitives.asymmetric import ec

from aliro_harness.personalizer.credentials import (
    P256_COORD_LEN,
    extract_priv_scalar,
    extract_pub_xy,
)


def test_extract_priv_scalar_is_32_bytes():
    key = ec.generate_private_key(ec.SECP256R1())
    s = extract_priv_scalar(key)
    assert len(s) == 32


def test_extract_priv_scalar_matches_private_value_be():
    key = ec.generate_private_key(ec.SECP256R1())
    expected = key.private_numbers().private_value.to_bytes(32, "big")
    assert extract_priv_scalar(key) == expected


def test_extract_priv_scalar_pads_short_value():
    """A scalar small enough to need leading zeros must be left-padded."""
    # Private value of 1 is the smallest possible; should pad with 31 zeros.
    pem = ec.derive_private_key(1, ec.SECP256R1()).private_numbers()
    key = ec.derive_private_key(1, ec.SECP256R1())
    s = extract_priv_scalar(key)
    assert s == bytes(31) + b"\x01"
    assert len(s) == P256_COORD_LEN


def test_extract_pub_xy_is_64_bytes_no_prefix():
    key = ec.generate_private_key(ec.SECP256R1())
    xy = extract_pub_xy(key.public_key())
    assert len(xy) == 64
    # The 0x04 uncompressed-point tag must NOT appear; the applet's
    # set_reader_pubk_apdu prepends nothing.
    nums = key.public_key().public_numbers()
    assert xy[:32] == nums.x.to_bytes(32, "big")
    assert xy[32:] == nums.y.to_bytes(32, "big")


def test_non_p256_priv_rejected():
    key = ec.generate_private_key(ec.SECP384R1())
    with pytest.raises(ValueError, match="P-256"):
        extract_priv_scalar(key)


def test_non_p256_pub_rejected():
    key = ec.generate_private_key(ec.SECP384R1())
    with pytest.raises(ValueError, match="P-256"):
        extract_pub_xy(key.public_key())