condorcore-keyring/keyringctl

#!/usr/bin/env python
#
# SPDX-License-Identifier: GPL-3.0-or-later

from argparse import ArgumentParser
from collections import defaultdict
from contextlib import contextmanager
from logging import DEBUG
from logging import basicConfig
from logging import debug
from logging import error
from os import chdir
from os import getcwd
from pathlib import Path
from re import escape
from re import split
from re import sub
from shutil import copytree
from subprocess import PIPE
from subprocess import CalledProcessError
from subprocess import check_output
from sys import exit
from sys import stderr
from tempfile import TemporaryDirectory
from tempfile import mkdtemp
from typing import Dict
from typing import Iterable
from typing import Iterator
from typing import List
from typing import NewType
from typing import Optional
from typing import Set
from typing import Tuple
from typing import Union


Fingerprint = NewType('Fingerprint', str)
Uid = NewType('Uid', str)


@contextmanager
def cwd(new_dir: Path) -> Iterator[None]:
    """Change to a new current working directory in a context and go back to the previous dir after the context is done

    Parameters
    ----------
    new_dir: Path
        A path to change to
    """

    previous_dir = getcwd()
    chdir(new_dir)
    try:
        yield
    finally:
        chdir(previous_dir)


def natural_sort_path(_list: Iterable[Path]) -> Iterable[Path]:
    """Sort an Iterable of Paths naturally

    Parameters
    ----------
    _list: Iterable[Path]
        An iterable containing paths to be sorted

    Return
    ------
    Iterable[Path]
        An Iterable of paths that are naturally sorted
    """

    def convert_text_chunk(text: str) -> Union[int, str]:
        """Convert input text to int or str

        Parameters
        ----------
        text: str
            An input string

        Returns
        -------
        Union[int, str]
            Either an integer if text is a digit, else text in lower-case representation
        """

        return int(text) if text.isdigit() else text.lower()

    def alphanum_key(key: Path) -> List[Union[int, str]]:
        """Retrieve an alphanumeric key from a Path, that can be used in sorted()

        Parameters
        ----------
        key: Path
            A path for which to create a key

        Returns
        -------
        List[Union[int, str]]
            A list of either int or str objects that may serve as 'key' argument for sorted()
        """

        return [convert_text_chunk(c) for c in split("([0-9]+)", str(key.name))]

    return sorted(_list, key=alphanum_key)


def system(cmd: List[str], exit_on_error: bool = True) -> str:
    """Execute a command using check_output

    Parameters
    ----------
    cmd: List[str]
        A list of strings to be fed to check_output
    exit_on_error: bool
        Whether to exit the script when encountering an error (defaults to True)

    Raises
    ------
    CalledProcessError
        If not exit_on_error and `check_output()` encounters an error

    Returns
    -------
    str
        The output of cmd
    """

    try:
        return check_output(cmd, stderr=PIPE).decode()
    except CalledProcessError as e:
        stderr.buffer.write(e.stderr)
        if exit_on_error:
            exit(e.returncode)
        raise e


# TODO: simplify to lower complexity
def convert_certificate(  # noqa: ignore=C901
    working_dir: Path,
    certificate: Path,
    name_override: Optional[str] = None,
    fingerprint_filter: Optional[Set[Fingerprint]] = None,
) -> Path:
    """Convert a single file public key certificate into a decomposed directory structure of multiple PGP packets

    The output directory structure is created per user. The username is derived from the certificate (or overridden).
    Below the username directory a directory tree describes the public keys componentes split up into certifications
    and revocations, as well as per subkey and per uid certifications and revocations.

    Parameters
    ----------
    working_dir: Path
        The path of the working directory below which to create split certificates
    certificate: Path
        The path to a public key certificate
    name_override: Optional[str]
        An optional string to override the username in the to be created output directory structure
    fingerprint_filter: Optional[Set[Fingerprint]]
        An optional list of strings defining fingerprints of PGP public keys that all certificates will be filtered
        with

    Raises
    ------
    Exception
        If required PGP packets are not found

    Returns
    -------
    Path
        The path of the user_dir (which is located below working_dir)
    """

    # root packets
    certificate_fingerprint: Optional[Fingerprint] = None
    pubkey: Optional[Path] = None
    direct_sigs: Dict[Fingerprint, Dict[str, List[Path]]] = {}
    direct_revocations: Dict[Fingerprint, Dict[str, List[Path]]] = {}

    # subkey packets
    subkeys: Dict[Fingerprint, Dict[Fingerprint, Path]] = {}
    subkey_binding_sigs: Dict[Fingerprint, Dict[Fingerprint, Path]] = {}
    subkey_revocations: Dict[Fingerprint, Dict[Fingerprint, Path]] = {}

    # uid packets
    uids: Dict[Uid, Path] = {}
    uid_binding_sigs: Dict[Uid, Path] = {}
    certifications: Dict[Uid, List[Path]] = defaultdict(list)
    revocations: Dict[Uid, List[Path]] = defaultdict(list)

    # intermediate variables
    username: str = name_override or certificate.stem
    current_packet_mode: Optional[str] = None
    current_packet_fingerprint: Optional[Fingerprint] = None
    current_packet_uid: Optional[Uid] = None

    def add_packet_to_direct_sigs(
        direct_sigs: Dict[Fingerprint, Dict[str, List[Path]]],
        issuer: str,
        packet_key: Fingerprint,
        packet: Path,
    ) -> Dict[Fingerprint, Dict[str, List[Path]]]:
        """Add a packet to the set of DirectKeys

        If no key with the given packet_key exists yet, it is created.

        Parameters
        ----------
        direct_sigs: Dict[Fingerprint, Dict[str, List[Path]]]
            The signatures directly on a root key (such as DirectKey or *Certifications without a specific User ID)
        issuer: str
            The issuer of the signature
        packet: Path
            The path to the packet
        packet_key: Fingerprint
            The key identifying the packet (e.g. its Fingerprint)
        """

        if not direct_sigs.get(packet_key):
            direct_sigs = direct_sigs | {packet_key: defaultdict(list)}

        direct_sigs[packet_key][issuer].append(packet)
        return direct_sigs

    # XXX: PrimaryKeyBinding

    # TODO: remove 3rd party direct key signatures, seems to be leaked by export-clean

    debug(f"Processing certificate {certificate}")

    for packet in packet_split(working_dir=working_dir, certificate=certificate):
        debug(f"Processing packet {packet.name}")
        if packet.name.endswith("--PublicKey"):
            current_packet_mode = "pubkey"
            current_packet_fingerprint = Fingerprint(packet_dump_field(packet, "Fingerprint"))
            current_packet_uid = None

            certificate_fingerprint = current_packet_fingerprint
            pubkey = packet
        elif packet.name.endswith("--UserID"):
            current_packet_mode = "uid"
            current_packet_fingerprint = None
            current_packet_uid = simplify_user_id(Uid(packet_dump_field(packet, "Value")))

            uids[current_packet_uid] = packet
        elif packet.name.endswith("--PublicSubkey"):
            current_packet_mode = "subkey"
            current_packet_fingerprint = Fingerprint(packet_dump_field(packet, "Fingerprint"))
            current_packet_uid = None

            if not certificate_fingerprint:
                raise Exception('missing certificate fingerprint for "{packet.name}"')

            if not subkeys.get(certificate_fingerprint):
                subkeys |= {certificate_fingerprint: {current_packet_fingerprint: packet}}
            else:
                subkeys[certificate_fingerprint] |= {current_packet_fingerprint: packet}

        elif packet.name.endswith("--Signature"):
            if not certificate_fingerprint:
                raise Exception('missing certificate fingerprint for "{packet.name}"')

            issuer = packet_dump_field(packet, "Issuer")
            signature_type = packet_dump_field(packet, "Type")

            if current_packet_mode == "pubkey":
                if not current_packet_fingerprint:
                    raise Exception('missing current packet fingerprint for "{packet.name}"')

                if signature_type == "KeyRevocation" and certificate_fingerprint.endswith(issuer):
                    direct_revocations = add_packet_to_direct_sigs(
                        direct_sigs=direct_revocations,
                        issuer=issuer,
                        packet_key=current_packet_fingerprint,
                        packet=packet,
                    )
                elif signature_type in ["DirectKey", "GenericCertification"]:
                    direct_sigs = add_packet_to_direct_sigs(
                        direct_sigs=direct_sigs,
                        issuer=issuer,
                        packet_key=current_packet_fingerprint,
                        packet=packet,
                    )
                else:
                    raise Exception(f"unknown signature type: {signature_type}")
            elif current_packet_mode == "uid":
                if not current_packet_uid:
                    raise Exception('missing current packet uid for "{packet.name}"')

                if signature_type == "CertificationRevocation":
                    revocations[current_packet_uid].append(packet)
                elif signature_type == "PositiveCertification" and certificate_fingerprint.endswith(issuer):
                    uid_binding_sigs[current_packet_uid] = packet
                elif signature_type.endswith("Certification"):
                    if fingerprint_filter is not None and any([fp.endswith(issuer) for fp in fingerprint_filter]):
                        debug(f"The certification by issuer {issuer} is appended as it is found in the filter.")
                        certifications[current_packet_uid].append(packet)
                    else:
                        debug(f"The certification by issuer {issuer} is not appended because it is not in the filter")
                else:
                    raise Exception(f"unknown signature type: {signature_type}")
            elif current_packet_mode == "subkey":
                if not current_packet_fingerprint:
                    raise Exception('missing current packet fingerprint for "{packet.name}"')

                if signature_type == "SubkeyBinding":
                    if not subkey_binding_sigs.get(certificate_fingerprint):
                        subkey_binding_sigs |= {certificate_fingerprint: {current_packet_fingerprint: packet}}
                    else:
                        subkey_binding_sigs[certificate_fingerprint] |= {current_packet_fingerprint: packet}
                elif signature_type == "SubkeyRevocation":
                    if not subkey_revocations.get(certificate_fingerprint):
                        subkey_revocations |= {certificate_fingerprint: {current_packet_fingerprint: packet}}
                    else:
                        subkey_revocations[certificate_fingerprint] |= {current_packet_fingerprint: packet}
                else:
                    raise Exception(f"unknown signature type: {signature_type}")
            else:
                raise Exception(f'unknown signature root for "{packet.name}"')
        else:
            raise Exception(f'unknown packet type "{packet.name}"')

    if not certificate_fingerprint:
        raise Exception("missing certificate fingerprint")

    if not pubkey:
        raise Exception("missing certificate public-key")

    user_dir = working_dir / username
    key_dir = user_dir / certificate_fingerprint
    key_dir.mkdir(parents=True, exist_ok=True)

    persist_public_key(
        certificate_fingerprint=certificate_fingerprint,
        pubkey=pubkey,
        key_dir=key_dir,
    )

    persist_uids(
        key_dir=key_dir,
        uid_binding_sigs=uid_binding_sigs,
        uids=uids,
    )

    persist_subkeys(
        certificate_fingerprint=certificate_fingerprint,
        key_dir=key_dir,
        subkeys=subkeys,
        subkey_binding_sigs=subkey_binding_sigs,
    )

    persist_subkey_revocations(
        certificate_fingerprint=certificate_fingerprint,
        key_dir=key_dir,
        subkey_revocations=subkey_revocations,
    )

    persist_direct_sigs(
        direct_sigs=direct_sigs,
        pubkey=pubkey,
        key_dir=key_dir,
    )

    persist_direct_sigs(
        direct_sigs=direct_revocations,
        pubkey=pubkey,
        key_dir=key_dir,
        sig_type="revocation",
    )

    persist_certifications(
        certifications=certifications,
        pubkey=pubkey,
        key_dir=key_dir,
        uid_binding_sig=uid_binding_sigs,
        uids=uids,
    )

    persist_revocations(
        pubkey=pubkey,
        revocations=revocations,
        key_dir=key_dir,
        uid_binding_sig=uid_binding_sigs,
        uids=uids,
    )

    return user_dir


def persist_public_key(
    certificate_fingerprint: Fingerprint,
    pubkey: Path,
    key_dir: Path,
) -> None:
    """Persist the Public-Key packet

    Parameters
    ----------
    certificate_fingerprint: Fingerprint
        The unique fingerprint of the public key
    pubkey: Path
        The path to the public key of the root key
    key_dir: Path
        The root directory below which the basic key material is persisted
    """

    packets: List[Path] = [pubkey]
    output_file = key_dir / f"{certificate_fingerprint}.asc"
    output_file.parent.mkdir(parents=True, exist_ok=True)
    debug(f"Writing file {output_file} from {[str(packet) for packet in packets]}")
    packet_join(packets, output_file)


def persist_uids(
    key_dir: Path,
    uid_binding_sigs: Dict[Uid, Path],
    uids: Dict[Uid, Path],
) -> None:
    """Persist the User IDs that belong to a PublicKey

    The User ID material consists of PublicSubkeys and their SubkeyBindings.
    The files are written to a UID specific directory and file below key_dir/uid.

    Parameters
    ----------
    key_dir: Path
        The root directory below which the basic key material is persisted
    uid_binding_sigs: Dict[Uid, Path]
        The PositiveCertifications of a User ID and Public-Key packet
    uids: Dict[Uid, Path]
        The User IDs of a Public-Key (the root key)
    """

    for key in uid_binding_sigs.keys():
        packets = [uids[key], uid_binding_sigs[key]]
        output_file = key_dir / "uid" / key / f"{key}.asc"
        output_file.parent.mkdir(parents=True, exist_ok=True)
        debug(f"Writing file {output_file} from {[str(packet) for packet in packets]}")
        packet_join(packets, output_file)


def persist_subkeys(
    certificate_fingerprint: Fingerprint,
    key_dir: Path,
    subkeys: Dict[Fingerprint, Dict[Fingerprint, Path]],
    subkey_binding_sigs: Dict[Fingerprint, Dict[Fingerprint, Path]],
) -> None:
    """Persist all Public-Subkeys and their PublicSubkeyBinding of a root key file to file(s)

    Parameters
    ----------
    certificate_fingerprint: Fingerprint
        The unique fingerprint of the public key
    key_dir: Path
        The root directory below which the basic key material is persisted
    subkeys: Dict[Fingerprint, Dict[Fingerprint, Path]]
        The PublicSubkeys of a key
    subkey_binding_sigs: Dict[Fingerprint, Dict[Fingerprint, Path]]
        The SubkeyBinding signatures of a Public-Key (the root key)
    """

    if subkeys.get(certificate_fingerprint):
        for signature, subkey in subkeys[certificate_fingerprint].items():
            packets: List[Path] = []
            packets.extend([subkey, subkey_binding_sigs[certificate_fingerprint][signature]])
            output_file = key_dir / "subkey" / signature / f"{signature}.asc"
            output_file.parent.mkdir(parents=True, exist_ok=True)
            debug(f"Writing file {output_file} from {[str(packet) for packet in packets]}")
            packet_join(packets=packets, output=output_file)


def persist_subkey_revocations(
    certificate_fingerprint: Fingerprint,
    key_dir: Path,
    subkey_revocations: Dict[Fingerprint, Dict[Fingerprint, Path]],
) -> None:
    """Persist the SubkeyRevocations of all Public-Subkeys of a root key to file(s)

    Parameters
    ----------
    certificate_fingerprint: Fingerprint
        The unique fingerprint of the public key
    key_dir: Path
        The root directory below which the basic key material is persisted
    subkey_revocations: Dict[Fingerprint, Dict[Fingerprint, Path]]
        The SubkeyRevocations of PublicSubkeys of a key
    """

    if subkey_revocations.get(certificate_fingerprint):
        for signature, revocation in subkey_revocations[certificate_fingerprint].items():
            issuer = packet_dump_field(revocation, "Issuer")
            output_file = key_dir / "subkey" / signature / "revocation" / f"{issuer}.asc"
            output_file.parent.mkdir(parents=True, exist_ok=True)
            debug(f"Writing file {output_file} from {revocation}")
            packet_join(packets=[revocation], output=output_file)


def persist_direct_sigs(
    direct_sigs: Dict[Fingerprint, Dict[str, List[Path]]],
    pubkey: Path,
    key_dir: Path,
    sig_type: str = "certification",
) -> None:
    """Persist the signatures directly on a root key (such as DirectKeys or *Certifications without a User ID) to
    file(s)

    Parameters
    ----------
    direct_sigs: Dict[Fingerprint, Dict[str, List[Path]]]
        The certifications to write to file
    pubkey: Path
        The path to the public key of the root key
    key_dir: Path
        The root directory below which the Directkeys are persisted
    sig_type: str
        The type of direct certification to persist (defaults to 'certification'). This influences the directory name
    """

    for key, current_certifications in direct_sigs.items():
        for issuer, certifications in current_certifications.items():
            packets = [pubkey] + certifications
            output_file = key_dir / sig_type / f"{issuer}.asc"
            output_file.parent.mkdir(parents=True, exist_ok=True)
            debug(f"Writing file {output_file} from {[str(cert) for cert in certifications]}")
            packet_join(packets, output_file)


def persist_certifications(
    certifications: Dict[Uid, List[Path]],
    pubkey: Path,
    key_dir: Path,
    uid_binding_sig: Dict[Uid, Path],
    uids: Dict[Uid, Path],
) -> None:
    """Persist the certifications of a root key to file(s)

    The certifications include all CasualCertifications, GenericCertifications, PersonaCertifications and
    PositiveCertifications for all User IDs of the given root key.
    All certifications are persisted in per User ID certification directories below key_dir.

    Parameters
    ----------
    certifications: Dict[Uid, List[Path]]
        The certifications to write to file
    pubkey: Path
        The path to the public key of the root key
    key_dir: Path
        The root directory below which certifications are persisted
    uid_binding_sig: Dict[Uid, Path]
        The PositiveCertifications of a User ID and Public-Key packet
    uids: Dict[Uid, Path]
        The User IDs of a Public-Key (the root key)
    """

    for key, current_certifications in certifications.items():
        for certification in current_certifications:
            certification_dir = key_dir / "uid" / key / "certification"
            certification_dir.mkdir(parents=True, exist_ok=True)
            issuer = packet_dump_field(certification, "Issuer")

            if uids.get(key) and uid_binding_sig.get(key):
                packets = [pubkey, uids[key], uid_binding_sig[key], certification]
                output_file = certification_dir / f"{issuer}.asc"
                debug(f"Writing file {output_file} from {certification}")
                packet_join(packets, output_file)
            else:
                error(
                    f"Public key '{pubkey}' does not provide "
                    f"{'the UID binding signature' if not uid_binding_sig.get(key) else ''} for UID '{key}', "
                    "so its certifications can not be used!"
                )


def persist_revocations(
    pubkey: Path,
    revocations: Dict[Uid, List[Path]],
    key_dir: Path,
    uid_binding_sig: Dict[Uid, Path],
    uids: Dict[Uid, Path],
) -> None:
    """Persist the revocations of a root key to file(s)

    The revocations include all CertificationRevocations for all User IDs of the given root key.
    All revocations are persisted in per User ID 'revocation' directories below key_dir.

    Parameters
    ----------
    pubkey: Path
        The path to the public key of the root key
    revocations: Dict[Uid, List[Path]]
        The revocations to write to file
    key_dir: Path
        The root directory below which revocations will be persisted
    uid_binding_sig: Dict[Uid, Path]
        The PositiveCertifications of a User ID and Public-Key packet
    uids: Dict[Uid, Path]
        The User IDs of a Public-Key (the root key)
    """

    for key, current_revocations in revocations.items():
        for revocation in current_revocations:
            revocation_dir = key_dir / "uid" / key / "revocation"
            revocation_dir.mkdir(parents=True, exist_ok=True)

            issuer = packet_dump_field(revocation, "Issuer")
            packets = [pubkey, uids[key]]
            # Binding sigs only exist for 3rd-party revocations
            if key in uid_binding_sig:
                packets.append(uid_binding_sig[key])
            packets.append(revocation)
            output_file = revocation_dir / f"{issuer}.asc"
            debug(f"Writing file {output_file} from {revocation}")
            packet_join(packets, output_file)


def packet_dump(packet: Path) -> str:
    """Dump a PGP packet to string

    The `sq packet dump` command is used to retrieve a dump of information from a PGP packet

    Parameters
    ----------
    packet: Path
        The path to the PGP packet to retrieve the value from

    Returns
    -------
    str
        The contents of the packet dump
    """

    return system(["sq", "packet", "dump", str(packet)])


def packet_dump_field(packet: Path, field: str) -> str:
    """Retrieve the value of a field from a PGP packet

    Parameters
    ----------
    packet: Path
        The path to the PGP packet to retrieve the value from
    field: str
        The name of the field

    Raises
    ------
    Exception
        If the field is not found in the PGP packet

    Returns
    -------
    str
        The value of the field found in packet
    """

    dump = packet_dump(packet)
    lines = [line.strip() for line in dump.splitlines()]
    lines = list(filter(lambda line: line.startswith(f"{field}: "), lines))
    if not lines:
        raise Exception(f'Packet has no field "{field}"')
    return lines[0].split(maxsplit=1)[1]


def keyring_split(working_dir: Path, keyring: Path) -> Iterable[Path]:
    """Split a file containing a PGP keyring into separate certificate files

    The file is split using sq

    Parameters
    ----------
    working_dir: Path
        The path of the working directory below which to create the output files
    keyring: Path
        The path of a file containing a PGP keyring

    Returns
    -------
    Iterable[Path]
        An iterable over the naturally sorted list of certificate files derived from a keyring
    """

    keyring_dir = Path(mkdtemp(dir=working_dir, prefix="keyring-")).absolute()

    with cwd(keyring_dir):
        system(["sq", "keyring", "split", "--prefix", "", str(keyring)])
    return natural_sort_path(keyring_dir.iterdir())


def packet_split(working_dir: Path, certificate: Path) -> Iterable[Path]:
    """Split a file containing a PGP certificate into separate packet files

    The files are split using sq

    Parameters
    ----------
    working_dir: Path
        The path of the working directory below which to create the output files
    certificate: Path
        The absolute path of a file containing one PGP certificate

    Returns
    -------
    Iterable[Path]
        An iterable over the naturally sorted list of packet files derived from certificate
    """

    packet_dir = Path(mkdtemp(dir=working_dir, prefix="packet-")).absolute()

    with cwd(packet_dir):
        system(["sq", "packet", "split", "--prefix", "", str(certificate)])
    return natural_sort_path(packet_dir.iterdir())


def packet_join(packets: List[Path], output: Path, force: bool = False) -> None:
    """Join PGP packet data in files to a single output file

    Parameters
    ----------
    packets: List[Path]
        A list of paths to files that contain PGP packet data
    output: Path
        A file to which all PGP packet data is written
    force: bool
        Whether to force the execution of sq (defaults to False)
    """

    cmd = ["sq", "packet", "join"]
    if force:
        cmd.insert(1, "--force")
    packets_str = list(map(lambda path: str(path), packets))
    cmd.extend(packets_str)
    cmd.extend(["--output", str(output)])
    system(cmd, exit_on_error=False)


def simplify_user_id(user_id: Uid) -> Uid:
    """Simplify the User ID string to contain more filesystem friendly characters

    Parameters
    ----------
    user_id: Uid
        A User ID string (e.g. 'Foobar McFooface <foobar@foo.face>')

    Returns
    -------
    Uid
        The simplified representation of user_id
    """

    user_id_str: str = user_id.replace("@", "_at_")
    user_id_str = sub("[<>]", "", user_id_str)
    user_id_str = sub("[" + escape(r" !@#$%^&*()_-+=[]{}\|;:,.<>/?") + "]", "_", user_id_str)
    return Uid(user_id_str)


def derive_user_from_target(working_dir: Path, target_dir: Path, certificate: Path) -> Optional[str]:
    """Attempt to derive the username of a public key from a target directory

    Parameters
    ----------
    working_dir: Path
        A directory to use for temporary files
    target_dir: Path
        The directory in which to look up a username
    certificate: Path
        A public key file

    Raises
    ------
    Exception
        If more than one username is found (a public key can only belong to one individual)

    Returns
    -------
    Optional[str]
        A string representing the username a public key certificate belongs to, None otherwise
    """

    def get_certificate_fingerprint(working_dir: Path, certificate: Path) -> str:
        """Get the certificate fingerprint from a PGP public key file

        Parameters
        ----------
        working_dir: Path
            A directory to use for temporary files
        certificate: Path
            A PGP public key file

        Raises
        ------
        Exception
            If no fingerprint can be found in the provided PGP public key file

        Returns
        -------
        str
            The fingerprint of the PGP public key file
        """

        certificate_fingerprint = ""
        for packet in packet_split(working_dir=working_dir, certificate=certificate):
            if packet.name.endswith("--PublicKey"):
                certificate_fingerprint = packet_dump_field(packet, "Fingerprint")

        if not certificate_fingerprint:
            raise Exception(f"The public key file {certificate} does not provide a PublicKey fingerprint.")

        return certificate_fingerprint

    certificate_fingerprint = get_certificate_fingerprint(working_dir=working_dir, certificate=certificate)
    debug(f"Derived fingerprint '{certificate_fingerprint}' from {certificate}")

    matches = list(target_dir.glob(f"*/{certificate_fingerprint}"))

    if len(matches) > 1:
        raise Exception(
            f"More than one username found in {target_dir} when probing for fingerprint '{certificate_fingerprint}'!"
        )
    elif len(matches) == 0:
        debug(f"Can not derive username from target directory for certificate {certificate}")
        return None
    else:
        username = matches[0].parent.stem
        debug(f"Successfully derived username '{username}' from target directory for certificate {certificate}")
        return username


def convert(
    working_dir: Path,
    source: Path,
    target_dir: Path,
    name_override: Optional[str] = None,
    fingerprint_filter: Optional[Set[Fingerprint]] = None,
) -> Path:
    """Convert a path containing PGP certificate material to a decomposed directory structure

    Any input is first split by `keyring_split()` into individual certificates.

    Parameters
    ----------
    working_dir: Path
        A directory to use for temporary files
    source: Path
        A path to a file or directory to decompose
    target_dir: Path
        A directory path to write the new directory structure to
    name_override: Optional[str]
        An optional username override for the call to `convert_certificate()`
    fingerprint_filter: Optional[Set[Fingerprint]]
        An optional set of strings defining fingerprints of PGP public keys that all certificates will be filtered with

    Returns
    -------
    Path
        The directory that contains the resulting directory structure (target_dir)
    """

    directories: List[Path] = []
    keys: Iterable[Path] = source.iterdir() if source.is_dir() else [source]

    for key in keys:
        for cert in keyring_split(working_dir=working_dir, keyring=key):
            name = (
                name_override
                or derive_user_from_target(working_dir=working_dir, target_dir=target_dir, certificate=cert)
                or key.stem
            )
            directories.append(
                convert_certificate(
                    working_dir=working_dir,
                    certificate=cert,
                    name_override=name,
                    fingerprint_filter=fingerprint_filter,
                )
            )

    for path in directories:
        (target_dir / path.name).mkdir(parents=True, exist_ok=True)
        copytree(src=path, dst=(target_dir / path.name), dirs_exist_ok=True)

    return target_dir


def temp_join_keys(sources: List[Path], temp_dir: Path, force: bool) -> List[Path]:
    """Temporarily join the key material of a given set of keys in a temporary location and return their paths

    Parameters
    ----------
    sources: List[Path]
        A list of paths below which PGP packets are found
    temp_dir: Path
        The temporary directory below which to join PGP keys
    force: bool
        Whether to force the joining of files
    """

    certs: List[Path] = []

    for source_number, source in enumerate(sources):
        if source.is_dir():
            for user_number, user_dir in enumerate(sorted(source.iterdir())):
                if user_dir.is_dir():
                    for user_cert_number, user_cert_dir in enumerate(sorted(user_dir.iterdir())):
                        if user_cert_dir.is_dir():
                            cert_path = temp_dir / (
                                f"{str(source_number).zfill(4)}"
                                f"-{str(user_number).zfill(4)}"
                                f"-{str(user_cert_number).zfill(4)}.asc"
                            )
                            debug(f"Joining {user_dir.name}/{user_cert_dir.name} in {cert_path}.")
                            packet_join(
                                packets=sorted(user_cert_dir.glob("**/*.asc")),
                                output=cert_path,
                                force=force,
                            )
                            certs.append(cert_path)
        elif source.is_file() and not source.is_symlink():
            certs.append(source)

    return certs


def get_all_and_revoked_certs(certs: List[Path]) -> Tuple[List[Fingerprint], List[Fingerprint]]:
    """Get the fingerprints of all public keys and all fingerprints of all (self) revoked public keys in a directory

    Parameters
    ----------
    certs: List[Path]
        The certificates to trust

    Returns
    -------
    Tuple[List[str], List[str]]
        A tuple with the first item containing the fingerprints of all public keys and the second item containing the
        fingerprints of all self-revoked public keys
    """

    all_fingerprints: List[Fingerprint] = []
    revoked_fingerprints: List[Fingerprint] = []

    # TODO: what about direct key revocations/signatures?

    debug(f"Retrieving all and self-revoked certificates from {[str(cert_dir) for cert_dir in certs]}")
    for cert_collection in certs:
        if cert_collection.is_dir():
            for user_dir in cert_collection.iterdir():
                if user_dir.is_dir():
                    for cert_dir in user_dir.iterdir():
                        cert_fingerprint = Fingerprint(cert_dir.stem)
                        all_fingerprints.append(cert_fingerprint)
                        for revocation_cert in cert_dir.glob("revocation/*.asc"):
                            if cert_fingerprint.endswith(revocation_cert.stem):
                                debug(f"Revoking {cert_fingerprint} due to self-revocation")
                                revoked_fingerprints.append(cert_fingerprint)

    return (all_fingerprints, revoked_fingerprints)


def export_ownertrust(certs: List[Path], output: Path) -> Tuple[List[Fingerprint], List[Fingerprint]]:
    """Export ownertrust from a set of keys

    The output file format is compatible with `gpg --import-ownertrust` and lists the main fingerprint ID of all
    non-revoked keys as fully trusted.
    The exported file is used by pacman-key when importing a keyring (see
    https://man.archlinux.org/man/pacman-key.8#PROVIDING_A_KEYRING_FOR_IMPORT).

    Parameters
    ----------
    certs: List[Path]
        The certificates to trust
    output: Path
        The file path to write to
    """

    all_certs, revoked_certs = get_all_and_revoked_certs(certs=certs)
    trusted_certs = [cert for cert in all_certs if cert not in revoked_certs]

    with open(file=output, mode="w") as trusted_certs_file:
        for cert in trusted_certs:
            debug(f"Writing {cert} to {output}")
            trusted_certs_file.write(f"{cert}:4:\n")

    return (trusted_certs, all_certs)


def export_revoked(certs: List[Path], main_keys: List[Fingerprint], output: Path, min_revoker: int = 2) -> None:
    """Export the PGP revoked status from a set of keys

    The output file contains the fingerprints of all self-revoked keys and all keys for which at least two revocations
    by any main key exist.
    The exported file is used by pacman-key when importing a keyring (see
    https://man.archlinux.org/man/pacman-key.8#PROVIDING_A_KEYRING_FOR_IMPORT).

    Parameters
    ----------
    certs: List[Path]
        A list of directories with keys to check for their revocation status
    main_keys: List[Fingerprint]
        A list of strings representing the fingerprints of (current and/or revoked) main keys
    output: Path
        The file path to write to
    min_revoker: int
        The minimum amount of revocation certificates on a User ID from any main key to deem a public key as revoked
        (defaults to 2)
    """

    all_certs, revoked_certs = get_all_and_revoked_certs(certs=certs)

    debug(f"Retrieving certificates revoked by main keys from {[str(cert_dir) for cert_dir in certs]}")
    foreign_revocations: Dict[str, List[str]] = {}
    for cert_collection in certs:
        if cert_collection.is_dir():
            for user_dir in cert_collection.iterdir():
                if user_dir.is_dir():
                    for cert_dir in user_dir.iterdir():
                        debug(f"Inspecting public key {cert_dir.name}")
                        foreign_revocations[cert_dir.stem] = []
                        for revocation_cert in cert_dir.glob("uid/*/revocation/*.asc"):
                            foreign_revocations[cert_dir.stem] += [
                                revocation_cert.stem
                                for main_key in main_keys
                                if main_key.endswith(revocation_cert.stem)
                            ]

                        # TODO: find a better (less naive) approach, as this would also match on public certificates,
                        # where some UIDs are signed and others are revoked
                        if len(set(foreign_revocations[cert_dir.stem])) >= min_revoker:
                            debug(
                                f"Revoking {cert_dir.name} due to {set(foreign_revocations[cert_dir.stem])} "
                                "being main key revocations"
                            )
                            revoked_certs.append(Fingerprint(cert_dir.stem))

    with open(file=output, mode="w") as trusted_certs_file:
        for cert in set(revoked_certs):
            debug(f"Writing {cert} to {output}")
            trusted_certs_file.write(f"{cert}\n")


def get_fingerprints_from_import_source(working_dir: Path, source: Path) -> List[Fingerprint]:
    """Get all fingerprints of PGP public keys from import file(s)

    Parameters
    ----------
    working_dir: Path
        A directory to use for temporary files
    source: Path
        The path to a source file or directory

    Returns
    -------
    List[Fingerprint]
        A list of strings representing the fingerprints of PGP public keys found in source
    """

    fingerprints: List[Fingerprint] = []
    keys: List[Path] = list(source.iterdir()) if source.is_dir() else [source]

    for key in keys:
        for certificate in keyring_split(working_dir=working_dir, keyring=key):
            for packet in packet_split(working_dir=working_dir, certificate=certificate):
                if packet.name.endswith("--PublicKey"):
                    fingerprints += [Fingerprint(packet_dump_field(packet, "Fingerprint"))]

    debug(f"Fingerprints of PGP public keys in {source}: {fingerprints}")
    return fingerprints


def get_fingerprints_from_decomposed_dir(path: Path) -> List[Fingerprint]:
    """Get all fingerprints of PGP public keys from a decomposed directory structure

    Parameters
    ----------
    path: Path
        The path to a decomposed directory structure

    Returns
    -------
    List[Fingerprint]
        A list of strings representing all fingerprints of PGP public keys below path
    """

    fingerprints = [Fingerprint(path.stem) for path in list(path.absolute().glob("*/*"))]
    debug(f"Fingerprints of PGP public keys in {path}: {fingerprints}")
    return fingerprints


def get_fingerprints(working_dir: Path, input_path: Path, decomposed_paths: List[Path]) -> Set[Fingerprint]:
    """Get the fingerprints of PGP public keys from input paths and decomposed directory structures


    Parameters
    ----------
    working_dir: Path
        A directory to use for temporary files
    input_path: Path
        The path to a source file or directory
    decomposed_paths: List[Path]
        A list of paths that identify decomposed PGP data in directory structures

    Returns
    -------
    Set[Fingerprint]
        A set of strings describing fingerprints of PGP public keys
    """

    fingerprints: Set[Fingerprint] = set()

    fingerprints.update(
        get_fingerprints_from_import_source(
            working_dir=working_dir,
            source=args.source,
        )
    )

    for decomposed_path in decomposed_paths:
        fingerprints.update(get_fingerprints_from_decomposed_dir(path=decomposed_path))

    return fingerprints


def export_keyring(
    working_dir: Path,
    main: List[Path],
    sources: List[Path],
    output: Path,
    force: bool,
    pacman_integration: bool,
) -> None:
    """Export all provided PGP packet files to a single output file

    If sources contains directories, any .asc files below them are considered.

    Parameters
    ----------
    working_dir: Path
        A directory to use for temporary files
    main: List[Path]
        A list of directories or files from which to read PGP packet information, that is considered as public keys
        that are used to sign those found in sources
    sources: List[Path]
        A list of directories or files from which to read PGP packet information
    output: Path
        An output file that all PGP packet data is written to
    force: bool
        Whether to force the execution of packet_join()
    """

    main = [source.absolute() for source in main]
    sources = [source.absolute() for source in sources]
    output = output.absolute()

    main_certs = temp_join_keys(sources=main, temp_dir=Path(mkdtemp(dir=working_dir)).absolute(), force=force)
    sources_certs = temp_join_keys(sources=sources, temp_dir=Path(mkdtemp(dir=working_dir)).absolute(), force=force)
    debug(
        f"Creating keyring {output} from {[str(source_dir) for source_dir in main]} "
        f"and {[str(source_dir) for source_dir in sources]}."
    )

    output.parent.mkdir(parents=True, exist_ok=True)
    cmd = ["sq", "keyring", "merge", "-o", str(output)]
    if force:
        cmd.insert(1, "--force")
    cmd += [str(cert) for cert in sorted(main_certs)]
    cmd += [str(cert) for cert in sorted(sources_certs)]
    system(cmd, exit_on_error=False)

    if pacman_integration:
        [trusted_main_keys, all_main_keys] = export_ownertrust(
            certs=main,
            output=Path(f"{str(output).split('.gpg')[0]}-trusted"),
        )
        export_revoked(
            certs=main + sources,
            main_keys=all_main_keys,
            output=Path(f"{str(output).split('.gpg')[0]}-revoked"),
        )


def absolute_path(path: str) -> Path:
    """Return the absolute path of a given str

    Parameters
    ----------
    path: str
        A string representing a path

    Returns
    -------
    Path
        The absolute path representation of path
    """

    return Path(path).absolute()


if __name__ == "__main__":
    parser = ArgumentParser()
    parser.add_argument(
        "-v", "--verbose", action="store_true", help="Causes to print debugging messages about the progress"
    )
    parser.add_argument("--wait", action="store_true", help="Block before cleaning up the temp directory")
    parser.add_argument(
        "-f",
        "--force",
        action="store_true",
        default=False,
        help="force the execution of subcommands (e.g. overwriting of files)",
    )
    subcommands = parser.add_subparsers(dest="subcommand")

    convert_parser = subcommands.add_parser(
        "convert",
        help="import one or multiple PGP public keys and convert them to a decomposed directory structure",
    )
    convert_parser.add_argument("source", type=absolute_path, help="File or directory to convert")
    convert_parser.add_argument("--target", type=absolute_path, help="target directory")
    convert_parser.add_argument(
        "--name",
        type=str,
        default=None,
        help="override the username to use (only useful when using a single file as source)",
    )

    import_main_parser = subcommands.add_parser(
        "import-main", help="import one or several PGP keys to the main signing keys"
    )
    import_main_parser.add_argument("source", type=absolute_path, help="File or directory")
    import_main_parser.add_argument(
        "--name",
        type=str,
        default=None,
        help="override the username to use (only useful when using a single file as source)",
    )

    import_packager_parser = subcommands.add_parser(
        "import-packager", help="import one or several PGP keys to the packager keys"
    )
    import_packager_parser.add_argument("source", type=absolute_path, help="File or directory")
    import_packager_parser.add_argument(
        "--name",
        type=str,
        default=None,
        help="override the username to use (only useful when using a single file as source)",
    )

    export_keyring_parser = subcommands.add_parser(
        "export-keyring",
        help="export PGP packet data below main/ and packagers/ to output/archlinux.gpg alongside pacman integration",
    )

    export_parser = subcommands.add_parser(
        "export",
        help="export a directory structure of PGP packet data to a combined file",
    )
    export_parser.add_argument("output", type=absolute_path, help="file to write PGP packet data to")
    export_parser.add_argument(
        "-m",
        "--main",
        action="append",
        help="files or directories containing PGP packet data that is trusted (can be provided multiple times)",
        required=True,
        type=absolute_path,
    )
    export_parser.add_argument(
        "-s",
        "--source",
        action="append",
        help="files or directories containing PGP packet data (can be provided multiple times)",
        required=True,
        type=absolute_path,
    )
    export_parser.add_argument(
        "-p",
        "--pacman-integration",
        action="store_true",
        default=False,
        help="export trusted and revoked files (used by pacman) alongside the keyring",
    )

    args = parser.parse_args()

    if args.verbose:
        basicConfig(level=DEBUG)

    # temporary working directory that gets auto cleaned
    with TemporaryDirectory(prefix="arch-keyringctl-") as tempdir:
        keyring_root = Path().absolute()
        working_dir = Path(tempdir)
        debug(f"Working directory: {working_dir}")
        with cwd(working_dir):
            if "convert" == args.subcommand:
                print(convert(working_dir, args.source, target_dir=Path(mkdtemp(prefix="arch-keyringctl-")).absolute()))
            elif "import-main" == args.subcommand:
                print(
                    convert(
                        working_dir=working_dir,
                        source=args.source,
                        target_dir=keyring_root / "main",
                        name_override=args.name,
                        fingerprint_filter=get_fingerprints(
                            working_dir=working_dir,
                            input_path=args.source,
                            decomposed_paths=[keyring_root / "main", keyring_root / "packagers"],
                        ),
                    )
                )
            elif "import-packager" == args.subcommand:
                print(
                    convert(
                        working_dir=working_dir,
                        source=args.source,
                        target_dir=keyring_root / "packagers",
                        name_override=args.name,
                        fingerprint_filter=get_fingerprints(
                            working_dir=working_dir,
                            input_path=args.source,
                            decomposed_paths=[keyring_root / "main", keyring_root / "packagers"],
                        ),
                    )
                )
            elif "export-keyring" == args.subcommand:
                export_keyring(
                    working_dir=working_dir,
                    main=[keyring_root / "main"],
                    sources=[keyring_root / "packagers"],
                    output=keyring_root / "output" / "archlinux.gpg",
                    force=True,
                    pacman_integration=True,
                )
            elif "export" == args.subcommand:
                export_keyring(
                    working_dir=working_dir,
                    main=args.main,
                    sources=args.source,
                    output=args.output,
                    force=args.force,
                    pacman_integration=args.pacman_integration,
                )

            if args.wait:
                print("Press [ENTER] to continue")
                input()