import hashlib

import pytest

from quantumpipe.kdf import kdf


def test_matches_reference_construction():
    items = [b"info", b"\x01\x02", b""]
    h = hashlib.sha512(len(items).to_bytes(8, "little"))
    for it in items:
        h.update(len(it).to_bytes(8, "little"))
        h.update(it)
    assert kdf(*items) == h.digest()[:32]


def test_str_args_are_encoded():
    assert kdf("info", b"data") == kdf(b"info", b"data")
    # length counted after encoding: "é" is 2 bytes
    assert kdf("é") == kdf("é".encode())


def test_length_framing_prevents_concat_ambiguity():
    assert kdf("i", b"ab", b"c") != kdf("i", b"a", b"bc")
    assert kdf("i", b"") != kdf("i")


def test_length_limits():
    assert len(kdf("x", length=64)) == 64
    assert len(kdf("x", length=1)) == 1
    with pytest.raises(ValueError):
        kdf("x", length=65)
    with pytest.raises(ValueError):
        kdf("x", length=0)