# coding: utf-8

import asyncio
import datetime
import enum
import logging
from dataclasses import dataclass
from typing import Dict, FrozenSet, Iterable, List, Optional, Set

from asn1crypto import algos, cms, core, x509
from asn1crypto.x509 import Validity
from cryptography.exceptions import InvalidSignature

from ._state import ValProcState
from .asn1_types import AAControls, Target
from .authority import AuthorityWithCert, TrustAnchor
from .context import ACTargetDescription, ValidationContext
from .errors import (
    CRLFetchError,
    CRLNoMatchesError,
    CRLValidationIndeterminateError,
    DisallowedAlgorithmError,
    ExpiredError,
    InsufficientRevinfoError,
    InvalidAttrCertificateError,
    InvalidCertificateError,
    NotYetValidError,
    OCSPFetchError,
    OCSPNoMatchesError,
    OCSPValidationError,
    OCSPValidationIndeterminateError,
    PathBuildingError,
    PathValidationError,
    PSSParameterMismatch,
    StaleRevinfoError,
    ValidationError,
)
from .name_trees import (
    ExcludedSubtrees,
    PermittedSubtrees,
    default_excluded_subtrees,
    default_permitted_subtrees,
    process_general_subtrees,
)
from .path import QualifiedPolicy, ValidationPath
from .policy_decl import (
    AlgorithmUsagePolicy,
    PKIXValidationParams,
    RevocationCheckingRule,
    intersect_policy_sets,
)
from .policy_tree import (
    PolicyTreeNode,
    PolicyTreeRoot,
    apply_policy_mapping,
    enumerate_policy_mappings,
    prune_unacceptable_policies,
    update_policy_tree,
)
from .registry import CertificateCollection
from .revinfo.validate_crl import verify_crl
from .revinfo.validate_ocsp import verify_ocsp_response
from .sig_validate import SignatureValidator
from .util import (
    ConsList,
    extract_dir_name,
    get_ac_extension_value,
    get_declared_revinfo,
)

logger = logging.getLogger(__name__)


def validate_path(
    validation_context, path, parameters: Optional[PKIXValidationParams] = None
):
    """
    Validates the path using the algorithm from
    https://tools.ietf.org/html/rfc5280#section-6.1.

    Critical extensions on the end-entity certificate are not validated
    and are left up to the consuming application to process and/or fail on.

    .. note::
        This is a synchronous equivalent of :func:`.async_validate_path` that
        calls the latter in a new event loop. As such, it can't be used
        from within asynchronous code.

    :param validation_context:
        A pyhanko_certvalidator.context.ValidationContext object to use for
        configuring validation behavior

    :param path:
        A pyhanko_certvalidator.path.ValidationPath object of the path to validate

    :param parameters:
        Additional input parameters to the PKIX validation algorithm.
        These are not used when validating CRLs and OCSP responses.

    :raises:
        pyhanko_certvalidator.errors.PathValidationError - when an error occurs validating the path
        pyhanko_certvalidator.errors.RevokedError - when the certificate or another certificate in its path has been revoked

    :return:
        The final certificate in the path - an instance of
        asn1crypto.x509.Certificate
    """

    result = asyncio.run(
        async_validate_path(validation_context, path, parameters=parameters)
    )
    return result


async def async_validate_path(
    validation_context: ValidationContext,
    path: ValidationPath,
    parameters: Optional[PKIXValidationParams] = None,
):
    """
    Validates the path using the algorithm from
    https://tools.ietf.org/html/rfc5280#section-6.1.

    Critical extensions on the end-entity certificate are not validated
    and are left up to the consuming application to process and/or fail on.

    :param validation_context:
        A pyhanko_certvalidator.context.ValidationContext object to use for
        configuring validation behavior

    :param path:
        A pyhanko_certvalidator.path.ValidationPath object of the path to validate

    :param parameters:
        Additional input parameters to the PKIX validation algorithm.
        These are not used when validating CRLs and OCSP responses.

    :raises:
        pyhanko_certvalidator.errors.PathValidationError - when an error occurs validating the path
        pyhanko_certvalidator.errors.RevokedError - when the certificate or another certificate in its path has been revoked

    :return:
        The final certificate in the path - an instance of
        asn1crypto.x509.Certificate
    """

    proc_state = ValProcState(cert_path_stack=ConsList.sing(path))
    return await intl_validate_path(
        validation_context, path, parameters=parameters, proc_state=proc_state
    )


def validate_tls_hostname(
    validation_context: ValidationContext, cert: x509.Certificate, hostname: str
):
    """
    Validates the end-entity certificate from a
    pyhanko_certvalidator.path.ValidationPath object to ensure that the certificate
    is valid for the hostname provided and that the certificate is valid for
    the purpose of a TLS connection.

    THE CERTIFICATE PATH MUST BE VALIDATED SEPARATELY VIA validate_path()!

    :param validation_context:
        A pyhanko_certvalidator.context.ValidationContext object to use for
        configuring validation behavior

    :param cert:
        An asn1crypto.x509.Certificate object returned from validate_path()

    :param hostname:
        A unicode string of the TLS server hostname

    :raises:
        pyhanko_certvalidator.errors.InvalidCertificateError - when the certificate is not valid for TLS or the hostname
    """

    if validation_context.is_whitelisted(cert):
        return

    if not cert.is_valid_domain_ip(hostname):
        raise InvalidCertificateError(
            f"The X.509 certificate provided is not valid for {hostname}. "
            f"Valid hostnames include: {', '.join(cert.valid_domains)}."
        )

    bad_key_usage = (
        cert.key_usage_value
        and 'digital_signature' not in cert.key_usage_value.native
    )
    bad_ext_key_usage = (
        cert.extended_key_usage_value
        and 'server_auth' not in cert.extended_key_usage_value.native
    )

    if bad_key_usage or bad_ext_key_usage:
        raise InvalidCertificateError(
            "The X.509 certificate provided is not valid for securing TLS "
            "connections"
        )


def validate_usage(
    validation_context: ValidationContext,
    cert: x509.Certificate,
    key_usage: Set[str],
    extended_key_usage: Set[str],
    extended_optional: bool,
):
    """
    Validates the end-entity certificate from a
    pyhanko_certvalidator.path.ValidationPath object to ensure that the
    certificate is valid for the key usage and extended key usage purposes
    specified.

    THE CERTIFICATE PATH MUST BE VALIDATED SEPARATELY VIA validate_path()!

    :param validation_context:
        A pyhanko_certvalidator.context.ValidationContext object to use for
        configuring validation behavior

    :param cert:
        An asn1crypto.x509.Certificate object returned from validate_path()

    :param key_usage:
        A set of unicode strings of the required key usage purposes

    :param extended_key_usage:
        A set of unicode strings of the required extended key usage purposes

    :param extended_optional:
        A bool - if the extended_key_usage extension may be omitted and still
        considered valid

    :raises:
        pyhanko_certvalidator.errors.InvalidCertificateError - when the certificate is not valid for the usages specified
    """

    if validation_context.is_whitelisted(cert):
        return

    if key_usage is None:
        key_usage = set()

    if extended_key_usage is None:
        extended_key_usage = set()

    missing_key_usage = key_usage
    if cert.key_usage_value:
        missing_key_usage = key_usage - cert.key_usage_value.native

    missing_extended_key_usage = set()
    if extended_optional is False and not cert.extended_key_usage_value:
        missing_extended_key_usage = extended_key_usage
    elif cert.extended_key_usage_value is not None:
        missing_extended_key_usage = extended_key_usage - set(
            cert.extended_key_usage_value.native
        )

    if missing_key_usage or missing_extended_key_usage:
        plural = (
            's'
            if len(missing_key_usage | missing_extended_key_usage) > 1
            else ''
        )
        friendly_purposes = []
        for purpose in sorted(missing_key_usage | missing_extended_key_usage):
            friendly_purposes.append(purpose.replace('_', ' '))
        raise InvalidCertificateError(
            f"The X.509 certificate provided is not valid for the "
            f"purpose{plural} of {', '.join(friendly_purposes)}"
        )


def validate_aa_usage(
    validation_context: ValidationContext,
    cert: x509.Certificate,
    extended_key_usage: Optional[Set[str]] = None,
):
    """
    Validate AA certificate profile conditions in RFC 5755 § 4.5

    :param validation_context:
    :param cert:
    :param extended_key_usage:
    :return:
    """
    if validation_context.is_whitelisted(cert):
        return

    # Check key usage requirements
    validate_usage(
        validation_context,
        cert,
        key_usage={'digital_signature'},
        extended_key_usage=extended_key_usage or set(),
        extended_optional=extended_key_usage is not None,
    )

    # Check basic constraints: AA must not be a CA
    bc = cert.basic_constraints_value
    if bc is not None and bool(bc['ca']):
        raise InvalidCertificateError(
            "The X.509 certificate provided is a CA certificate, so "
            "it cannot be used to validate attribute certificates."
        )


def _validate_ac_targeting(
    attr_cert: cms.AttributeCertificateV2,
    acceptable_targets: ACTargetDescription,
):
    target_info = get_ac_extension_value(attr_cert, 'target_information')
    if target_info is None:
        return

    target: Target
    gen_name: x509.GeneralName
    for targets in target_info:
        for target in targets:
            if target.name == 'target_name':
                gen_name = target.chosen
                valid_names = acceptable_targets.validator_names
            elif target.name == 'target_group':
                gen_name = target.chosen
                valid_names = acceptable_targets.group_memberships
            else:
                logger.info(
                    f"'{target.name}' is not supported as a targeting mode; "
                    f"ignoring."
                )
                continue
            try:
                target_ok = gen_name in valid_names
            except ValueError:
                # fall back to binary comparison in case the name type is not
                # supported by asn1crypto's comparison logic for GeneralName
                #  (we could be more efficient here, but this is probably
                #   rare, so let's follow YAGNI)
                target_ok = gen_name.dump() in {n.dump() for n in valid_names}
            if target_ok:
                return

    # TODO log audit identity
    raise InvalidAttrCertificateError("AC targeting check failed")


SUPPORTED_AC_EXTENSIONS = frozenset(
    [
        'authority_information_access',
        'authority_key_identifier',
        'crl_distribution_points',
        'freshest_crl',
        'key_identifier',
        'no_rev_avail',
        'target_information',
        # NOTE: we don't actively process this extension, but we never log holder
        # identifying information, so the purpose of the audit identity
        # extension is still satisfied.
        # TODO actually use audit_identity for logging purposes, falling back
        #  to holder info if audit_identity is not available.
        'audit_identity',
    ]
)


def _parse_iss_serial(
    iss_serial: cms.IssuerSerial, err_msg_prefix: str
) -> bytes:
    """
    Render a cms.IssuerSerial value into something that matches
    x509.Certificate.issuer_serial output.
    """
    issuer_names = iss_serial['issuer']
    issuer_dirname = extract_dir_name(issuer_names, err_msg_prefix)
    result_bytes = b'%s:%d' % (
        issuer_dirname.sha256,
        iss_serial['serial'].native,
    )
    return result_bytes


def _process_aki_ext(aki_ext: x509.AuthorityKeyIdentifier):
    aki = aki_ext['key_identifier'].native  # could be None
    auth_iss_ser = auth_iss_dirname = None
    if not isinstance(aki_ext['authority_cert_issuer'], core.Void):
        auth_iss_dirname = extract_dir_name(
            aki_ext['authority_cert_issuer'],
            "Could not decode authority issuer in AKI extension",
        )
        auth_ser = aki_ext['authority_cert_serial_number'].native
        if auth_ser is not None:
            auth_iss_ser = b'%s:%d' % (auth_iss_dirname.sha256, auth_ser)

    return aki, auth_iss_dirname, auth_iss_ser


def _candidate_ac_issuers(
    attr_cert: cms.AttributeCertificateV2, registry: CertificateCollection
):
    # TODO support matching against subjectAltName?
    #  Outside the scope of RFC 5755, but it might make sense

    issuer_rec = attr_cert['ac_info']['issuer']
    aa_names: Optional[x509.GeneralNames] = None
    aa_iss_serial: Optional[bytes] = None
    if issuer_rec.name == 'v1_form':
        aa_names = issuer_rec.chosen
    else:
        issuerv2: cms.V2Form = issuer_rec.chosen
        if not isinstance(issuerv2['issuer_name'], core.Void):
            aa_names = issuerv2['issuer_name']
        if not isinstance(issuerv2['base_certificate_id'], core.Void):
            # not allowed by RFC 5755, but let's parse it anyway if
            # we encounter it
            aa_iss_serial = _parse_iss_serial(
                issuerv2['base_certificate_id'],
                "Could not identify AA issuer in base_certificate_id",
            )
        if not isinstance(issuerv2['object_digest_info'], core.Void):
            # TODO support objectdigestinfo? Also not allowed by RFC 5755
            raise NotImplementedError(
                "Could not identify AA; objectDigestInfo is not supported."
            )

    # Process the AKI extension if there is one
    aki_ext = get_ac_extension_value(attr_cert, 'authority_key_identifier')
    if aki_ext is not None:
        aki, aa_issuer, aki_aa_iss_serial = _process_aki_ext(aki_ext)
        if aki_aa_iss_serial is not None:
            if aa_iss_serial is not None and aa_iss_serial != aki_aa_iss_serial:
                raise InvalidAttrCertificateError(
                    "AC's AKI extension and issuer include conflicting "
                    "identifying information for the issuing AA"
                )
            else:
                aa_iss_serial = aki_aa_iss_serial
    else:
        aki = None

    candidates: Iterable[x509.Certificate] = ()
    aa_name = None
    if aa_names is not None:
        aa_name = extract_dir_name(aa_names, "Could not identify AA by name")
    if aa_iss_serial is not None:
        exact_cert = registry.retrieve_by_issuer_serial(aa_iss_serial)
        if exact_cert is not None:
            candidates = (exact_cert,)
    elif aa_name is not None:
        candidates = registry.retrieve_by_name(aa_name)

    for aa_candidate in candidates:
        if aa_name is not None and aa_candidate.subject != aa_name:
            continue
        if aki is not None and aa_candidate.key_identifier != aki:
            # AC's AKI doesn't match candidate's SKI
            continue
        yield aa_candidate


def _check_ac_signature(
    attr_cert: cms.AttributeCertificateV2,
    aa_cert: x509.Certificate,
    validation_context: ValidationContext,
):
    sd_algo = attr_cert['signature_algorithm']
    embedded_sd_algo = attr_cert['ac_info']['signature']
    use_time = validation_context.best_signature_time
    digest_allowed = (
        validation_context.algorithm_policy.signature_algorithm_allowed(
            sd_algo, use_time, public_key=aa_cert.public_key
        )
    )
    if sd_algo.native != embedded_sd_algo.native:
        raise InvalidAttrCertificateError(
            "Signature algorithm declaration in signed portion of AC does not "
            "match the signature algorithm declaration on the envelope."
        )
    elif not digest_allowed:
        raise DisallowedAlgorithmError(
            "The attribute certificate could not be validated because "
            f"the signature uses the disallowed signature algorithm "
            f"{sd_algo['algorithm'].native}. ",
            is_ee_cert=True,
            is_side_validation=False,
            banned_since=digest_allowed.not_allowed_after,
        )

    try:
        validation_context.sig_validator.validate_signature(
            signature=attr_cert['signature'].native,
            signed_data=attr_cert['ac_info'].dump(),
            # TODO support PK parameter inheritance?
            #  (would have to remember the working public key from the
            #  validation algo)
            # low-priority since this only affects DSA in practice
            public_key_info=aa_cert.public_key,
            signature_algorithm=sd_algo,
        )
    except PSSParameterMismatch:
        raise InvalidAttrCertificateError(
            "The signature parameters for the attribute certificate "
            "do not match the constraints on the public key. "
        )
    except InvalidSignature:
        raise InvalidAttrCertificateError(
            "The attribute certificate could not be validated because the "
            "signature could not be verified."
        )


def check_ac_holder_match(holder_cert: x509.Certificate, holder: cms.Holder):
    """
    Match a candidate holder certificate against the holder entry of an
    attribute certificate.

    :param holder_cert:
        Candidate holder certificate.
    :param holder:
        Holder value to match against.
    :return:
        Return the parts of the holder entry that mismatched as a set.
        Possible values are `'base_certificate_id'`, `'entity_name'` and
        `'object_digest_info'`.
        If the returned set is empty, all entries in the holder entry
        matched the information in the certificate.
    """

    base_cert_id = holder['base_certificate_id']
    mismatches = set()
    # TODO what about subjectAltName matches?

    if not isinstance(base_cert_id, core.Void):
        # repurpose _parse_iss_serial since RFC 5755 restricts
        # baseCertificateID.issuer to a single DN
        designated_iss_serial = _parse_iss_serial(
            base_cert_id, "Could not identify holder certificate issuer"
        )
        if designated_iss_serial != holder_cert.issuer_serial:
            mismatches.add('base_certificate_id')

    entity_name = holder['entity_name']
    # TODO what about subjectAltName matches?
    if not isinstance(entity_name, core.Void):
        holder_dn = extract_dir_name(
            entity_name, "Could not identify AC holder DN"
        )
        if holder_dn != holder_cert.subject:
            mismatches.add('entity_name')

    # TODO implement objectDigestInfo support
    obj_digest_info = holder['object_digest_info']
    if not isinstance(obj_digest_info, core.Void):
        raise NotImplementedError(
            "Object digest info is currently not supported"
        )
    return mismatches


@dataclass(frozen=True)
class ACValidationResult:
    """
    The result of a successful attribute certificate validation.
    """

    attr_cert: cms.AttributeCertificateV2
    """
    The attribute certificate that was validated.
    """

    aa_cert: x509.Certificate
    """
    The attribute authority that issued the certificate.
    """

    aa_path: ValidationPath
    """
    The validation path of the attribute authority's certificate.
    """

    approved_attributes: Dict[str, cms.AttCertAttribute]
    """
    Approved attributes in the attribute certificate, possibly filtered by
    AA controls.
    """


async def async_validate_ac(
    attr_cert: cms.AttributeCertificateV2,
    validation_context: ValidationContext,
    aa_pkix_params: PKIXValidationParams = PKIXValidationParams(),
    holder_cert: Optional[x509.Certificate] = None,
) -> ACValidationResult:
    """
    Validate an attribute certificate with respect to a given validation
    context.

    :param attr_cert:
        The attribute certificate to validate.
    :param validation_context:
        The validation context to validate against.
    :param aa_pkix_params:
        PKIX validation parameters to supply to the path validation algorithm
        applied to the attribute authority's certificate.
    :param holder_cert:
        Certificate of the presumed holder to match against the AC's holder
        entry. If not provided, the holder check is left to the caller to
        perform.

        .. note::
            This is a convenience option in case there's only one reasonable
            candidate holder certificate (e.g. when the attribute certificates
            are part of a CMS SignedData value with only a single signer).
    :return:
        An :class:`.ACValidationResult` detailing the validation result,
        if successful.
    """

    # Process extensions
    # We do this first because all later steps may involve potentially slow
    #  network IO, so this allows quicker failure.
    extensions_present = {
        ext['extn_id'].native: bool(ext['critical'])
        for ext in attr_cert['ac_info']['extensions']
    }
    unsupported_critical_extensions = {
        ext
        for ext, crit in extensions_present.items()
        if crit and ext not in SUPPORTED_AC_EXTENSIONS
    }
    if unsupported_critical_extensions:
        raise InvalidCertificateError(
            "The AC could not be validated because it contains the "
            f"following unsupported critical extension"
            f"{'s' if len(unsupported_critical_extensions) != 1 else ''}: "
            f"{', '.join(sorted(unsupported_critical_extensions))}."
        )
    if 'target_information' in extensions_present:
        targ_desc = validation_context.acceptable_ac_targets
        if targ_desc is None:
            raise InvalidAttrCertificateError(
                "The attribute certificate is targeted, but no targeting "
                "information is available in the validation context."
            )
        _validate_ac_targeting(attr_cert, targ_desc)

    ac_holder = attr_cert['ac_info']['holder']
    if len(ac_holder) == 0:
        raise InvalidAttrCertificateError("AC holder entry is empty")

    if holder_cert is not None:
        mismatches = check_ac_holder_match(holder_cert, ac_holder)
        if mismatches:
            raise InvalidAttrCertificateError(
                f"Could not match AC holder entry against supplied holder "
                f"certificate; mismatched entries: {', '.join(mismatches)}"
            )

    path_builder = validation_context.path_builder
    aa_candidates = _candidate_ac_issuers(
        attr_cert, validation_context.certificate_registry
    )

    exceptions: List[Exception] = []
    aa_path: Optional[ValidationPath] = None
    for aa_candidate in aa_candidates:
        try:
            validate_aa_usage(validation_context, aa_candidate)
        except InvalidAttrCertificateError as e:
            exceptions.append(e)
            continue
        try:
            paths = await path_builder.async_build_paths(aa_candidate)
        except PathBuildingError as e:
            exceptions.append(e)
            continue

        for candidate_path in paths:
            try:
                await intl_validate_path(
                    validation_context,
                    candidate_path,
                    parameters=aa_pkix_params,
                    proc_state=ValProcState(
                        cert_path_stack=ConsList.sing(candidate_path),
                        ee_name_override="AA certificate",
                    ),
                    cert_profile=EECertProfile.ATTRIBUTE_AUTHORITY,
                )
                aa_path = candidate_path
                break
            except ValidationError as e:
                exceptions.append(e)

    if aa_path is None:
        # TODO log audit identifier
        if not exceptions:
            raise PathBuildingError(
                "Could not find a suitable AA for the attribute certificate"
            )
        else:
            raise exceptions[0]

    # check the signature
    aa_cert = aa_path.last
    _check_ac_signature(attr_cert, aa_cert, validation_context)

    validity = attr_cert['ac_info']['att_cert_validity_period']
    # NOTE: this is a bit of a hack, and the path in question is only used
    #  for error reporting
    # TODO make paths with ACs at the end easier to handle
    ac_path = aa_path.copy_and_append(attr_cert)
    proc_state = ValProcState(
        cert_path_stack=ConsList.sing(ac_path),
        is_side_validation=False,
        ee_name_override="attribute certificate",
        init_index=len(ac_path),
    )
    _check_validity(
        validity=Validity(
            {
                'not_before': validity['not_before_time'],
                'not_after': validity['not_after_time'],
            }
        ),
        moment=validation_context.moment,
        tolerance=validation_context.time_tolerance,
        proc_state=proc_state,
    )
    if 'no_rev_avail' not in extensions_present:
        await _check_revocation(
            attr_cert, validation_context, ac_path, proc_state=proc_state
        )

    ok_attrs = {
        attr['type'].native: attr
        for attr in attr_cert['ac_info']['attributes']
        if aa_path.aa_attr_in_scope(attr['type'])
    }

    return ACValidationResult(
        attr_cert=attr_cert,
        aa_cert=aa_cert,
        aa_path=aa_path,
        approved_attributes=ok_attrs,
    )


@dataclass
class _PathValidationState:
    """
    State variables that need to be maintained while traversing a certification
    path
    """

    valid_policy_tree: Optional['PolicyTreeRoot']
    explicit_policy: int
    inhibit_any_policy: int
    policy_mapping: int
    max_path_length: int
    max_aa_path_length: int
    working_public_key: x509.PublicKeyInfo
    working_issuer_name: x509.Name
    permitted_subtrees: PermittedSubtrees
    excluded_subtrees: ExcludedSubtrees
    aa_controls_used: bool = False

    @staticmethod
    def init_pkix_validation_state(
        path_length,
        trust_anchor: TrustAnchor,
        parameters: Optional[PKIXValidationParams],
    ):
        trust_anchor_quals = trust_anchor.trust_qualifiers
        max_path_length = max_aa_path_length = path_length
        if trust_anchor_quals.max_path_length is not None:
            max_path_length = trust_anchor_quals.max_path_length
        if trust_anchor_quals.max_path_length is not None:
            max_aa_path_length = trust_anchor_quals.max_aa_path_length
        trust_anchor_params = trust_anchor_quals.standard_parameters

        if parameters is not None and trust_anchor_params is not None:
            # need to make sure both sets of parameters are respected
            acceptable_policies = intersect_policy_sets(
                parameters.user_initial_policy_set,
                trust_anchor_params.user_initial_policy_set,
            )
            initial_any_policy_inhibit = (
                parameters.initial_any_policy_inhibit
                and parameters.initial_any_policy_inhibit
            )

            initial_explicit_policy = (
                parameters.initial_explicit_policy
                and parameters.initial_explicit_policy
            )

            initial_policy_mapping_inhibit = (
                parameters.initial_policy_mapping_inhibit
                and parameters.initial_policy_mapping_inhibit
            )
            initial_permitted_subtrees = PermittedSubtrees(
                parameters.initial_permitted_subtrees
                or default_permitted_subtrees()
            )
            if trust_anchor_params.initial_permitted_subtrees is not None:
                initial_permitted_subtrees.intersect_with(
                    trust_anchor_params.initial_permitted_subtrees
                )
            initial_excluded_subtrees = ExcludedSubtrees(
                parameters.initial_excluded_subtrees
                or default_excluded_subtrees()
            )
            if trust_anchor_params.initial_excluded_subtrees is not None:
                initial_excluded_subtrees.union_with(
                    trust_anchor_params.initial_excluded_subtrees
                )
        else:
            parameters = (
                parameters or trust_anchor_params or PKIXValidationParams()
            )
            acceptable_policies = parameters.user_initial_policy_set
            initial_explicit_policy = parameters.initial_explicit_policy
            initial_any_policy_inhibit = parameters.initial_any_policy_inhibit
            initial_policy_mapping_inhibit = (
                parameters.initial_policy_mapping_inhibit
            )
            initial_permitted_subtrees = PermittedSubtrees(
                parameters.initial_permitted_subtrees
                or default_permitted_subtrees()
            )
            initial_excluded_subtrees = ExcludedSubtrees(
                parameters.initial_excluded_subtrees
                or default_excluded_subtrees()
            )

        state = _PathValidationState(
            # Step 1 a
            valid_policy_tree=PolicyTreeRoot.init_policy_tree(
                'any_policy', set(), {'any_policy'}
            ),
            # Steps 1 b-c
            permitted_subtrees=initial_permitted_subtrees,
            excluded_subtrees=initial_excluded_subtrees,
            # Steps 1 d-f
            explicit_policy=(0 if initial_explicit_policy else path_length + 1),
            inhibit_any_policy=(
                0 if initial_any_policy_inhibit else path_length + 1
            ),
            policy_mapping=(
                0 if initial_policy_mapping_inhibit else path_length + 1
            ),
            # Steps 1 g-j
            working_public_key=trust_anchor.authority.public_key,
            working_issuer_name=trust_anchor.authority.name,
            # Step 1 k
            max_path_length=max_path_length,
            # NOTE: the algorithm (for now) assumes that the AA CA of RFC 5755
            # is trusted by fiat, and does not require chaining up to a distinct
            # CA. In particular, we assume that the AA CA is the trust anchor in
            # the path. This matches the validation model used in signature
            # policies (where there are separate trust trees for attributes)
            max_aa_path_length=max_aa_path_length,
        )
        return state, acceptable_policies

    def update_policy_restrictions(self, cert: x509.Certificate):
        # Step 3 h
        if not cert.self_issued:
            # Step 3 h 1
            if self.explicit_policy != 0:
                self.explicit_policy -= 1
            # Step 3 h 2
            if self.policy_mapping != 0:
                self.policy_mapping -= 1
            # Step 3 h 3
            if self.inhibit_any_policy != 0:
                self.inhibit_any_policy -= 1

        # Step 3 i
        policy_constraints = cert.policy_constraints_value
        if policy_constraints:
            # Step 3 i 1
            require_explicit_policy = policy_constraints[
                'require_explicit_policy'
            ].native
            if require_explicit_policy is not None:
                self.explicit_policy = min(
                    self.explicit_policy, require_explicit_policy
                )
            # Step 3 i 2
            inhibit_policy_mapping = policy_constraints[
                'inhibit_policy_mapping'
            ].native
            if inhibit_policy_mapping is not None:
                self.policy_mapping = min(
                    self.policy_mapping, inhibit_policy_mapping
                )

        # Step 3 j
        if cert.inhibit_any_policy_value is not None:
            self.inhibit_any_policy = min(
                cert.inhibit_any_policy_value.native, self.inhibit_any_policy
            )

    def process_policies(
        self,
        index: int,
        certificate_policies,
        any_policy_uninhibited,
        proc_state: ValProcState,
    ):
        if certificate_policies and self.valid_policy_tree is not None:
            self.valid_policy_tree = update_policy_tree(
                certificate_policies,
                self.valid_policy_tree,
                depth=index,
                any_policy_uninhibited=any_policy_uninhibited,
            )

        # Step 2 e
        elif certificate_policies is None:
            self.valid_policy_tree = None

        # Step 2 f
        if self.valid_policy_tree is None and self.explicit_policy <= 0:
            raise PathValidationError.from_state(
                "The path could not be validated because there is no valid set "
                f"of policies for {proc_state.describe_cert()}",
                proc_state,
            )

    def check_name_constraints(self, cert, proc_state: ValProcState):
        # name constraint processing
        whitelist_result = self.permitted_subtrees.accept_cert(cert)
        if not whitelist_result:
            raise PathValidationError.from_state(
                "The path could not be validated because not all names of "
                f"{proc_state.describe_cert()} are in the permitted namespace "
                f"of the issuing authority. {whitelist_result.error_message}",
                proc_state,
            )
        blacklist_result = self.excluded_subtrees.accept_cert(cert)
        if not blacklist_result:
            raise PathValidationError.from_state(
                "The path could not be validated because some names of "
                f"{proc_state.describe_cert()} are excluded from the "
                f"namespace of the issuing authority. "
                f"{blacklist_result.error_message}",
                proc_state,
            )

    def check_certificate_signature(
        self,
        cert: x509.Certificate,
        algorithm_policy: AlgorithmUsagePolicy,
        proc_state: ValProcState,
        moment: datetime.datetime,
        sig_validator: SignatureValidator,
    ):
        sd_algo: algos.SignedDigestAlgorithm = cert['signature_algorithm']
        sd_algo_name = sd_algo['algorithm'].native
        sig_algo_allowed = algorithm_policy.signature_algorithm_allowed(
            sd_algo, moment, public_key=self.working_public_key
        )
        if not sig_algo_allowed:
            msg = (
                f"The path could not be validated because the signature "
                f"of {proc_state.describe_cert()} uses the disallowed "
                f"signature mechanism {sd_algo_name}."
            )
            if sig_algo_allowed.failure_reason is not None:
                msg += f" Reason: {sig_algo_allowed.failure_reason}."
            raise DisallowedAlgorithmError.from_state(
                msg,
                proc_state,
                banned_since=sig_algo_allowed.not_allowed_after,
            )

        try:
            sig_validator.validate_signature(
                signature=cert['signature_value'].native,
                signed_data=cert['tbs_certificate'].dump(),
                public_key_info=self.working_public_key,
                signature_algorithm=sd_algo,
            )
        except PSSParameterMismatch:
            raise PathValidationError.from_state(
                f"The signature parameters for {proc_state.describe_cert()} do "
                f"not match the constraints on the public key.",
                proc_state,
            )
        except InvalidSignature:
            raise PathValidationError.from_state(
                f"The path could not be validated because the signature of "
                f"{proc_state.describe_cert()} could not be verified",
                proc_state,
            )


# TODO allow delegation to calling library here?
SUPPORTED_EXTENSIONS = frozenset(
    [
        'authority_information_access',
        'authority_key_identifier',
        'basic_constraints',
        'crl_distribution_points',
        'extended_key_usage',
        'freshest_crl',
        'key_identifier',
        'key_usage',
        'ocsp_no_check',
        'certificate_policies',
        'policy_mappings',
        'policy_constraints',
        'inhibit_any_policy',
        'name_constraints',
        'subject_alt_name',
        'aa_controls',
        # Include the OID and human-readable name for the qcStatements
        # injection. ETSI EN 319 412-5 mandates that this extension _not_
        # be marked critical, but some CAs do it anyway.
        '1.3.6.1.5.5.7.1.3',
        'qc_statements',
    ]
)


@enum.unique
class EECertProfile(enum.Enum):
    REGULAR = 'regular'
    ATTRIBUTE_AUTHORITY = 'attribute_authority'


async def intl_validate_path(
    validation_context: ValidationContext,
    path: ValidationPath,
    proc_state: ValProcState,
    parameters: Optional[PKIXValidationParams] = None,
    cert_profile: EECertProfile = EECertProfile.REGULAR,
):
    """
    Internal copy of validate_path() that allows overriding the name of the
    end-entity certificate as used in exception messages. This functionality is
    used during chain validation when dealing with indirect CRLs issuer or
    OCSP responder certificates.

    :param validation_context:
        A pyhanko_certvalidator.context.ValidationContext object to use for
        configuring validation behavior

    :param path:
        A pyhanko_certvalidator.path.ValidationPath object of the path to validate

    :param proc_state:
        Internal state for error reporting and policy application decisions.

    :param parameters:
        Additional input parameters to the PKIX validation algorithm.
        These are not used when validating CRLs and OCSP responses.

    :param cert_profile:
        End-entity certificate profile to use.
        Currently, this is only used to decide whether to process the AAControls extension.

    :return:
        The final certificate in the path - an instance of
        asn1crypto.x509.Certificate
    """

    moment = validation_context.moment

    qualifiers = path.trust_anchor.trust_qualifiers
    if qualifiers.valid_from is not None and qualifiers.valid_from > moment:
        raise NotYetValidError.format(
            valid_from=qualifiers.valid_from, proc_state=proc_state
        )
    elif qualifiers.valid_until is not None and qualifiers.valid_until < moment:
        raise ExpiredError.format(
            expired_dt=qualifiers.valid_until, proc_state=proc_state
        )

    # Inputs

    trust_anchor = path.trust_anchor

    path_length = path.pkix_len

    # Step 1: initialization
    (
        state,
        acceptable_policies,
    ) = _PathValidationState.init_pkix_validation_state(
        path_length, trust_anchor, parameters
    )

    # Step 2: basic processing
    completed_path: ValidationPath = ValidationPath(
        trust_anchor, interm=[], leaf=None
    )

    cert: Optional[x509.Certificate]
    authority = trust_anchor.authority
    if isinstance(authority, AuthorityWithCert):
        # if the trust root has a cert, record it as validated.
        validation_context.record_validation(
            authority.certificate, completed_path
        )
        cert = authority.certificate
    else:
        cert = None

    # TODO support this for attr certs
    leaf_asserted_nonrevoked = False
    revinfo_manager = validation_context.revinfo_manager
    if isinstance(path.leaf, x509.Certificate):
        leaf_asserted_nonrevoked = revinfo_manager.check_asserted_unrevoked(
            path.leaf, moment
        )

    for index in range(1, path_length + 1):
        cert = path[index]

        proc_state.index += 1
        # Step 2 a 1
        state.check_certificate_signature(
            cert,
            validation_context.algorithm_policy,
            proc_state,
            validation_context.best_signature_time,
            validation_context.sig_validator,
        )

        # Step 2 a 2
        if not validation_context.is_whitelisted(cert):
            tolerance = validation_context.time_tolerance
            validity = cert['tbs_certificate']['validity']
            _check_validity(
                validity=validity,
                moment=moment,
                tolerance=tolerance,
                proc_state=proc_state,
            )

        # Step 2 a 3 - CRL/OCSP
        if (
            not leaf_asserted_nonrevoked
            and not revinfo_manager.check_asserted_unrevoked(cert, moment)
        ):
            await _check_revocation(
                cert=cert,
                validation_context=validation_context,
                path=path,
                proc_state=proc_state,
            )

        # Step 2 a 4
        if cert.issuer != state.working_issuer_name:
            raise PathValidationError.from_state(
                f"The path could not be validated because "
                f"{proc_state.describe_cert()} issuer name "
                f"could not be matched",
                proc_state,
            )

        # Steps 2 b-c
        if index == path_length or not cert.self_issued:
            state.check_name_constraints(cert, proc_state=proc_state)

        # Steps 2 d
        state.process_policies(
            index,
            cert.certificate_policies_value,
            #  (see step 2 d 2)
            any_policy_uninhibited=(
                state.inhibit_any_policy > 0
                or (index < path_length and cert.self_issued)
            ),
            proc_state=proc_state,
        )

        if index < path_length:
            # Step 3: prepare for certificate index+1
            _prepare_next_step(index, cert, state, proc_state=proc_state)

        if cert_profile == EECertProfile.ATTRIBUTE_AUTHORITY:
            _check_aa_controls(cert, state, index, proc_state=proc_state)

        # Step 3 o / 4 f
        # Check for critical unsupported extensions
        unsupported_critical_extensions = (
            cert.critical_extensions - SUPPORTED_EXTENSIONS
        )
        if unsupported_critical_extensions:
            raise PathValidationError.from_state(
                f"The path could not be validated because "
                f"{proc_state.describe_cert()} contains the "
                f"following unsupported critical extension"
                f"{'s' if len(unsupported_critical_extensions) != 1 else ''}"
                f": {', '.join(sorted(unsupported_critical_extensions))}",
                proc_state,
            )

        if validation_context:
            # TODO I left this in from the original code,
            #  but caching intermediate results might not be appropriate at all
            #  times. For example, handling for self-issued certs is different
            #  depending on whether they're treated as an end-entity or not.
            completed_path = completed_path.copy_and_append(cert)
            validation_context.record_validation(cert, completed_path)

    # Step 4: wrap-up procedure

    # Steps 4 c-e skipped since this method doesn't output it
    # Step 4 f skipped since this method defers that to the calling application
    # --> only policy processing remains

    if cert is not None:
        qualified_policies = _finish_policy_processing(
            state=state,
            cert=cert,
            acceptable_policies=acceptable_policies,
            path_length=path_length,
            proc_state=proc_state,
        )
        path._set_qualified_policies(qualified_policies)
        # TODO cache valid policies on intermediate certs too?
        completed_path._set_qualified_policies(qualified_policies)

    return cert


def _check_validity(
    validity: Validity, moment, tolerance, proc_state: ValProcState
):
    if moment < validity['not_before'].native - tolerance:
        raise NotYetValidError.format(
            valid_from=validity['not_before'].native, proc_state=proc_state
        )
    if moment > validity['not_after'].native + tolerance:
        raise ExpiredError.format(
            expired_dt=validity['not_after'].native, proc_state=proc_state
        )


def _finish_policy_processing(
    state, cert, acceptable_policies, path_length, proc_state: ValProcState
):
    # Step 4 a
    if state.explicit_policy != 0:
        state.explicit_policy -= 1
    # Step 4 b
    if cert.policy_constraints_value:
        if cert.policy_constraints_value['require_explicit_policy'].native == 0:
            state.explicit_policy = 0
    # Step 4 g
    # Step 4 g i
    intersection: Optional[PolicyTreeRoot]
    if state.valid_policy_tree is None:
        intersection = None

    # Step 4 g ii
    elif acceptable_policies == {'any_policy'}:
        intersection = state.valid_policy_tree

    # Step 4 g iii
    else:
        intersection = prune_unacceptable_policies(
            path_length, state.valid_policy_tree, acceptable_policies
        )
    qualified_policies: FrozenSet[QualifiedPolicy] = frozenset()
    if intersection is not None:
        # collect policies in a user-friendly format and attach them to the
        # path object
        def _enum_policies() -> Iterable[QualifiedPolicy]:
            accepted_policy: PolicyTreeNode
            assert intersection is not None
            for accepted_policy in intersection.at_depth(path_length):
                listed_pol = accepted_policy.valid_policy
                if listed_pol != 'any_policy':
                    # the first ancestor that is a child of any_policy
                    # will have an ID that makes sense in the user's policy
                    # domain (here 'ancestor' includes the node itself)
                    user_domain_policy_id = next(
                        ancestor.valid_policy
                        for ancestor in accepted_policy.path_to_root()
                        if ancestor.parent.valid_policy == 'any_policy'
                    )
                else:
                    # any_policy can't be mapped, so we don't have to do
                    # any walking up the tree. This also covers the corner case
                    # where the path length is 0 (in this case, PKIX validation
                    # is pointless, but we have to deal with it gracefully)
                    user_domain_policy_id = 'any_policy'

                yield QualifiedPolicy(
                    user_domain_policy_id=user_domain_policy_id,
                    issuer_domain_policy_id=listed_pol,
                    qualifiers=frozenset(accepted_policy.qualifier_set),
                )

        qualified_policies = frozenset(_enum_policies())
    elif state.explicit_policy == 0:
        raise PathValidationError.from_state(
            f"The path could not be validated because there is no valid set of "
            f"policies for {proc_state.describe_cert()}.",
            proc_state,
        )
    return qualified_policies


async def _check_revocation(
    cert,
    validation_context: ValidationContext,
    path: ValidationPath,
    proc_state: ValProcState,
):
    ocsp_status_good = False
    revocation_check_failed = False
    ocsp_matched = False
    crl_matched = False
    soft_fail = False
    failures = []
    cert_has_crl, cert_has_ocsp = get_declared_revinfo(cert)
    revinfo_declared = cert_has_crl or cert_has_ocsp
    rev_check_policy = (
        validation_context.revinfo_policy.revocation_checking_policy
    )
    rev_rule = (
        rev_check_policy.ee_certificate_rule
        if proc_state.is_ee_cert
        else rev_check_policy.intermediate_ca_cert_rule
    )

    ocsp_suspect_stale_since = None
    # for OCSP, we don't bother if there's nothing in the certificate's AIA
    if rev_rule.ocsp_relevant and cert_has_ocsp:
        try:
            await verify_ocsp_response(
                cert, path, validation_context, proc_state=proc_state
            )
            ocsp_status_good = True
            ocsp_matched = True
        except OCSPValidationIndeterminateError as e:
            failures.extend([failure[0] for failure in e.failures])
            revocation_check_failed = True
            ocsp_matched = True
            ocsp_suspect_stale_since = e.suspect_stale
        except OCSPNoMatchesError:
            pass
        except OCSPFetchError as e:
            if rev_rule.tolerant:
                soft_fail = True
                validation_context._report_soft_fail(e)
            else:
                failures.append(e.args[0])
                revocation_check_failed = True
        except OCSPValidationError as e:
            failures.append(e.args[0])
            revocation_check_failed = True
            ocsp_matched = True
    if not ocsp_status_good and rev_rule.ocsp_mandatory:
        if failures:
            err_str = '; '.join(str(f) for f in failures)
        else:
            err_str = 'an applicable OCSP response could not be found'
        msg = (
            f"The path could not be validated because the mandatory OCSP "
            f"check(s) for {proc_state.describe_cert()} failed: {err_str}"
        )
        if ocsp_suspect_stale_since:
            raise StaleRevinfoError.format(
                msg, ocsp_suspect_stale_since, proc_state
            )
        else:
            raise InsufficientRevinfoError.from_state(msg, proc_state)
    status_good = (
        ocsp_status_good
        and rev_rule != RevocationCheckingRule.CRL_AND_OCSP_REQUIRED
    )

    crl_status_good = False
    crl_suspect_stale_since = None
    # do not attempt to check CRLs (even cached ones) if there are no
    # distribution points, unless we have to
    crl_required_by_policy = rev_rule.crl_mandatory or (
        not status_good
        and rev_rule == RevocationCheckingRule.CRL_OR_OCSP_REQUIRED
    )
    crl_fetchable = rev_rule.crl_relevant and cert_has_crl
    if crl_required_by_policy or (crl_fetchable and not status_good):
        try:
            await verify_crl(
                cert, path, validation_context, proc_state=proc_state
            )
            revocation_check_failed = False
            crl_status_good = True
            crl_matched = True
        except CRLValidationIndeterminateError as e:
            failures.extend([failure[0] for failure in e.failures])
            revocation_check_failed = True
            crl_matched = True
            crl_suspect_stale_since = e.suspect_stale
        except CRLNoMatchesError:
            pass
        except CRLFetchError as e:
            if rev_rule.tolerant:
                soft_fail = True
                validation_context._report_soft_fail(e)
            else:
                failures.append(e.args[0])
                revocation_check_failed = True

    if not crl_status_good and rev_rule.crl_mandatory:
        if failures:
            err_str = '; '.join(str(f) for f in failures)
        else:
            err_str = 'an applicable CRL could not be found'
        msg = (
            f"The path could not be validated because the mandatory CRL "
            f"check(s) for {proc_state.describe_cert()} failed: {err_str}"
        )
        if crl_suspect_stale_since:
            raise StaleRevinfoError.format(
                msg, crl_suspect_stale_since, proc_state
            )
        else:
            raise InsufficientRevinfoError.from_state(
                msg,
                proc_state,
            )

    # If we still didn't find a match, the certificate has CRL/OCSP entries
    # but we couldn't query any of them. Let's check if this is disqualifying.
    # With 'strict' the fact that there's no match (irrespective
    # of certificate properties) is enough to cause a failure,
    # otherwise we have to check.
    expected_revinfo = rev_rule.strict or (
        revinfo_declared
        and rev_rule == RevocationCheckingRule.CHECK_IF_DECLARED
    )
    # Did we find any revinfo that "has jurisdiction"?
    matched = crl_matched or ocsp_matched
    expected_revinfo_not_found = not matched and expected_revinfo
    if not soft_fail:
        if not status_good and matched and revocation_check_failed:
            msg = (
                f"The path could not be validated because "
                f"{proc_state.describe_cert(def_interm=True)} revocation "
                f"checks failed: {'; '.join(failures)}"
            )
            maybe_stale_cutoff = (
                ocsp_suspect_stale_since or crl_suspect_stale_since
            )
            if maybe_stale_cutoff:
                stale_cutoff = (
                    max(ocsp_suspect_stale_since, crl_suspect_stale_since)
                    if ocsp_suspect_stale_since and crl_suspect_stale_since
                    else maybe_stale_cutoff
                )
                raise StaleRevinfoError.format(msg, stale_cutoff, proc_state)
            else:
                raise InsufficientRevinfoError.from_state(
                    msg,
                    proc_state,
                )
        if expected_revinfo_not_found:
            if isinstance(cert, x509.Certificate):
                subj = cert.subject.human_friendly
            else:
                subj = ""
            raise InsufficientRevinfoError.from_state(
                f"The path could not be validated because no revocation "
                f"information could be found for {proc_state.describe_cert()} "
                f"{subj}",
                proc_state,
            )


def _check_aa_controls(
    cert: x509.Certificate,
    state: _PathValidationState,
    index,
    proc_state: ValProcState,
):
    aa_controls = AAControls.read_extension_value(cert)
    if aa_controls is not None:
        if not state.aa_controls_used and index > 1:
            raise PathValidationError.from_state(
                f"AA controls extension only present on part of the "
                f"certificate chain: {proc_state.describe_cert()} has AA "
                f"controls while preceding certificates do not. ",
                proc_state,
            )
        state.aa_controls_used = True
        # deal with path length
        new_max_aa_path_length = aa_controls['path_len_constraint'].native
        if (
            new_max_aa_path_length is not None
            and new_max_aa_path_length < state.max_aa_path_length
        ):
            state.max_aa_path_length = new_max_aa_path_length
    elif state.aa_controls_used:
        raise PathValidationError.from_state(
            f"AA controls extension only present on part of the "
            f"certificate chain: {proc_state.describe_cert()} "
            f"has no AA controls ",
            proc_state,
        )


def _prepare_next_step(
    index,
    cert: x509.Certificate,
    state: _PathValidationState,
    proc_state: ValProcState,
):
    if cert.policy_mappings_value:
        policy_map = enumerate_policy_mappings(
            cert.policy_mappings_value, proc_state=proc_state
        )

        # Step 3 b
        if state.valid_policy_tree is not None:
            state.valid_policy_tree = apply_policy_mapping(
                policy_map,
                state.valid_policy_tree,
                depth=index,
                policy_mapping_uninhibited=state.policy_mapping > 0,
            )

    # Step 3 c
    state.working_issuer_name = cert.subject

    # Steps 3 d-f

    # Handle inheritance of DSA parameters from a signing CA to the
    # next in the chain
    # NOTE: we don't perform this step for RSASSA-PSS since there the
    #  parameters are drawn form the signature parameters, where they
    #  must always be present.
    copy_params = None
    if cert.public_key.algorithm == 'dsa' and cert.public_key.hash_algo is None:
        if state.working_public_key.algorithm == 'dsa':
            key_alg = state.working_public_key['algorithm']
            copy_params = key_alg['parameters'].copy()

    if copy_params:
        working_public_key = cert.public_key.copy()
        working_public_key['algorithm']['parameters'] = copy_params
        state.working_public_key = working_public_key
    else:
        state.working_public_key = cert.public_key

    # Step 3 g
    nc_value: x509.NameConstraints = cert.name_constraints_value
    if nc_value is not None:
        new_permitted_subtrees = nc_value['permitted_subtrees']
        if isinstance(new_permitted_subtrees, x509.GeneralSubtrees):
            state.permitted_subtrees.intersect_with(
                process_general_subtrees(new_permitted_subtrees)
            )
        new_excluded_subtrees = nc_value['excluded_subtrees']
        if isinstance(new_excluded_subtrees, x509.GeneralSubtrees):
            state.excluded_subtrees.union_with(
                process_general_subtrees(new_excluded_subtrees)
            )

    # Step 3 h-j
    state.update_policy_restrictions(cert)

    # Step 3 k
    if not cert.ca:
        raise PathValidationError.from_state(
            f"The path could not be validated because "
            f"{proc_state.describe_cert()} is not a CA",
            proc_state,
        )

    # Step 3 l
    if not cert.self_issued:
        if state.max_path_length == 0:
            raise PathValidationError.from_state(
                "The path could not be validated because it exceeds the "
                "maximum path length",
                proc_state,
            )
        state.max_path_length -= 1
        if state.max_aa_path_length == 0:
            raise PathValidationError.from_state(
                "The path could not be validated because it exceeds the "
                "maximum path length for an AA certificate",
                proc_state,
            )
        state.max_aa_path_length -= 1

    # Step 3 m
    if (
        cert.max_path_length is not None
        and cert.max_path_length < state.max_path_length
    ):
        state.max_path_length = cert.max_path_length

    # Step 3 n
    if (
        cert.key_usage_value
        and 'key_cert_sign' not in cert.key_usage_value.native
    ):
        raise PathValidationError.from_state(
            "The path could not be validated because "
            f"{proc_state.describe_cert()} is not allowed to sign certificates",
            proc_state,
        )
