"""
The group-key envelope: round trip, and every refusal it owes.

`groupbox.seal`/`unseal` is what puts `index_sync`, `index_delta` and the
`handshake_ack` configuration under a key the hub does not hold. The structural
tests here matter less than `test_index_no_cleartext.py`, which asserts the
property on a real frame; these pin the primitive.
"""

import msgpack
import pytest
from cryptography.exceptions import InvalidTag
from meshbay_common.crypto import generate_gek
from meshbay_common.groupbox import (
    PURPOSE_ACK,
    PURPOSE_INDEX,
    group_key,
    seal,
    unseal,
)

PAYLOAD = {"version": 7, "entries": [{"name": "a.mkv", "size": 12}], "dirs": ["root"]}


@pytest.fixture
def gek():
    return generate_gek()


def test_round_trip(gek):
    for purpose in (PURPOSE_INDEX, PURPOSE_ACK):
        sealed = seal(gek, purpose, "index_sync", "g1", PAYLOAD)
        assert set(sealed) == {"nonce", "ct"}
        assert unseal(gek, purpose, "index_sync", "g1", sealed) == PAYLOAD


def test_a_wrong_key_does_not_open(gek):
    sealed = seal(gek, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)
    with pytest.raises(InvalidTag):
        unseal(generate_gek(), PURPOSE_INDEX, "index_sync", "g1", sealed)


def test_purposes_are_separate_key_spaces(gek):
    """
    The reason there are two info strings rather than one key reused.

    An ack sealed under the index subkey would otherwise be openable by anything
    holding the index subkey — the confusion that treating "the index as chunk 0 of
    a virtual index file" would create for chunk keys.
    """
    assert group_key(gek, PURPOSE_INDEX) != group_key(gek, PURPOSE_ACK)
    sealed = seal(gek, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)
    with pytest.raises(InvalidTag):
        unseal(gek, PURPOSE_ACK, "index_sync", "g1", sealed)


def test_a_body_cannot_be_replayed_as_another_message_type(gek):
    """The AAD's first half: an index_sync body is not an index_delta."""
    sealed = seal(gek, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)
    with pytest.raises(InvalidTag):
        unseal(gek, PURPOSE_INDEX, "index_delta", "g1", sealed)


def test_a_body_cannot_be_moved_between_groups(gek):
    """
    The AAD's second half. Two groups on one node share a GEK-holding process but
    not a GEK; this closes the case where they do share one (a rotation in flight,
    a test fixture, an operator reusing a key) as well.
    """
    sealed = seal(gek, PURPOSE_INDEX, "index_sync", "group-a", PAYLOAD)
    with pytest.raises(InvalidTag):
        unseal(gek, PURPOSE_INDEX, "index_sync", "group-b", sealed)


def test_a_tampered_ciphertext_does_not_open(gek):
    sealed = seal(gek, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)
    sealed["ct"] = bytes([sealed["ct"][0] ^ 1]) + sealed["ct"][1:]
    with pytest.raises(InvalidTag):
        unseal(gek, PURPOSE_INDEX, "index_sync", "g1", sealed)


def test_a_message_that_is_not_sealed_is_refused_as_such(gek):
    """
    Not an empty payload, and not a crash on a missing key — the two shapes a
    caller might otherwise paper over.
    """
    with pytest.raises(ValueError):
        unseal(gek, PURPOSE_INDEX, "index_sync", "g1", {"entries": []})


def test_a_fresh_nonce_per_message(gek):
    """
    Never derived from the payload: two identical payloads under one long-lived
    subkey would then reuse a nonce, which for GCM is a total break.
    """
    nonces = {seal(gek, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)["nonce"]
              for _ in range(50)}
    assert len(nonces) == 50


def test_no_key_is_an_error_not_a_plaintext_fallback(gek):
    with pytest.raises(ValueError):
        seal(None, PURPOSE_INDEX, "index_sync", "g1", PAYLOAD)


def test_an_unknown_purpose_is_refused(gek):
    with pytest.raises(ValueError):
        group_key(gek, "chat")


def test_the_envelope_carries_no_readable_payload(gek):
    """
    The property, at the level of the primitive: what `seal` returns holds nothing
    of what went in. `test_index_no_cleartext.py` asserts the same thing on the
    real frames.
    """
    payload = {"video_root": "holidays-2019-invoices", "entries": ["ledger.pdf"]}
    frame = msgpack.packb(seal(gek, PURPOSE_ACK, "handshake_ack", "g1", payload))
    for word in (b"holidays", b"invoices", b"ledger", b"video_root"):
        assert word not in frame