"""Claim 4: crypto-erasure makes both the original and an exfiltrated copy
permanently undecryptable."""

import copy
import os

import pytest

from capability_licensing import (
    KeyDestroyedError,
    UnsealError,
    generate_wrapping_key,
    seal,
    unseal,
)


def test_exfiltrated_copy_decrypts_before_erasure(sealed_setup):
    exfiltrated = copy.deepcopy(sealed_setup.sealed)
    plaintext = sealed_setup.keys.request_decrypt(
        exfiltrated, sealed_setup.chain.capability
    )
    assert plaintext == sealed_setup.payload


def test_after_erasure_both_copies_are_undecryptable(sealed_setup):
    exfiltrated = copy.deepcopy(sealed_setup.sealed)

    # Honest baseline: the copy is decryptable before erasure.
    assert (
        sealed_setup.keys.request_decrypt(exfiltrated, sealed_setup.chain.capability)
        == sealed_setup.payload
    )

    sealed_setup.keys.destroy(sealed_setup.sealed.unit_id)

    with pytest.raises(KeyDestroyedError):
        sealed_setup.keys.request_decrypt(
            sealed_setup.sealed, sealed_setup.chain.capability
        )
    with pytest.raises(KeyDestroyedError):
        sealed_setup.keys.request_decrypt(
            exfiltrated, sealed_setup.chain.capability
        )


def test_ciphertext_is_useless_without_the_exact_wrapping_key():
    wrapping_key = generate_wrapping_key()
    payload = b"STAND-IN CAPABILITY UNIT (not a real model)\n" + os.urandom(2048)
    sealed = seal("unit-raw-001", payload, wrapping_key, "CERT-example")

    # The exact key decrypts.
    assert unseal(sealed, wrapping_key) == payload

    # Any other key fails AES-256-GCM authentication: no partial decryption,
    # no garbage plaintext, a hard failure.
    with pytest.raises(UnsealError):
        unseal(sealed, os.urandom(32))

    # A single flipped bit in the key also fails: recovery requires the
    # destroyed key exactly, not something close to it.
    near_miss = bytearray(wrapping_key)
    near_miss[0] ^= 0x01
    with pytest.raises(UnsealError):
        unseal(sealed, bytes(near_miss))


def test_tampered_ciphertext_fails_authentication():
    import dataclasses

    wrapping_key = generate_wrapping_key()
    payload = b"STAND-IN CAPABILITY UNIT (not a real model)\n" + os.urandom(2048)
    sealed = seal("unit-raw-002", payload, wrapping_key, "CERT-example")

    tampered_hex = bytearray(sealed.payload_ciphertext_hex.encode())
    tampered_hex[0] = ord("f") if tampered_hex[0] != ord("f") else ord("0")
    tampered = dataclasses.replace(
        sealed, payload_ciphertext_hex=tampered_hex.decode()
    )
    with pytest.raises(UnsealError):
        unseal(tampered, wrapping_key)


def test_sealed_unit_reports_payload_digest(sealed_setup):
    import hashlib

    assert (
        sealed_setup.sealed.payload_sha256
        == hashlib.sha256(sealed_setup.payload).hexdigest()
    )