Merge ~barryprice/charm-tor/+git/charm-tor:main into charm-tor:main

[Barry Price]

WIP MP to replace the charmcraft boilerplate with a functional charm

d39909c... by Barry Price on 2022-07-22

Add lib, pyproject, tox, refresh ,gitignore

47bd6c5... by Barry Price on 2022-07-22

Initial Makefile

6264307... by Barry Price on 2022-07-22

Add paths, lint target, run lint

1d7bc86... by Barry Price on 2022-07-22

Handle upstream torproject repo installation/removal

d762c48... by Barry Price on 2022-07-22

Ensure packages are installed on hooks, sort package defs

2892df0... by Barry Price on 2022-09-23

Bugfixes

6b266a9... by Barry Price on 2023-08-20

Still WIP but a clean deploy with multiple related services works after a fashion (but relation changes fail catastrophically)

05532b8... by Barry Price on 2023-08-20

Restore boilerplate

Unmerged commits

05532b8... by Barry Price on 2023-08-20

Restore boilerplate

6b266a9... by Barry Price on 2023-08-20

Still WIP but a clean deploy with multiple related services works after a fashion (but relation changes fail catastrophically)

2892df0... by Barry Price on 2022-09-23

Bugfixes

d762c48... by Barry Price on 2022-07-22

Ensure packages are installed on hooks, sort package defs

1d7bc86... by Barry Price on 2022-07-22

Handle upstream torproject repo installation/removal

6264307... by Barry Price on 2022-07-22

Add paths, lint target, run lint

47bd6c5... by Barry Price on 2022-07-22

Initial Makefile

d39909c... by Barry Price on 2022-07-22

Add lib, pyproject, tox, refresh ,gitignore

4220710... by Barry Price on 2022-06-27

Basic skeleton, remove most boilerplate, no functionality yet

diff --git a/.gitignore b/.gitignore
index 2c3f0e5..69a2281 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,10 @@
-venv/
-build/
+/build
+/venv
+
 *.charm
+*.py[cod]
+*.swp
 
 .coverage
+.tox
 __pycache__/
-*.py[cod]
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
 deleted file mode 100644
index f5dac3b..0000000
--- a/CONTRIBUTING.md
+++ /dev/null
@@ -1,34 +0,0 @@
-# charm-tor
-
-## Developing
-
-Create and activate a virtualenv with the development requirements:
-
-    virtualenv -p python3 venv
-    source venv/bin/activate
-    pip install -r requirements-dev.txt
-
-## Code overview
-
-TEMPLATE-TODO:
-One of the most important things a consumer of your charm (or library)
-needs to know is what set of functionality it provides. Which categories
-does it fit into? Which events do you listen to? Which libraries do you
-consume? Which ones do you export and how are they used?
-
-## Intended use case
-
-TEMPLATE-TODO:
-Why were these decisions made? What's the scope of your charm?
-
-## Roadmap
-
-If this Charm doesn't fulfill all of the initial functionality you were
-hoping for or planning on, please add a Roadmap or TODO here
-
-## Testing
-
-The Python operator framework includes a very nice harness for testing
-operator behaviour without full deployment. Just `run_tests`:
-
-    ./run_tests
diff --git a/LICENSE b/LICENSE
index d645695..f288702 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,202 +1,674 @@
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+  12. No Surrender of Others' Freedom.
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+  13. Use with the GNU Affero General Public License.
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+
+  If the Program specifies that a proxy can decide which future
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+  Later license versions may give you additional or different
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+  17. Interpretation of Sections 15 and 16.
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+  If the disclaimer of warranty and limitation of liability provided
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+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
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+                     END OF TERMS AND CONDITIONS
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+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
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+    it under the terms of the GNU General Public License as published by
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+    (at your option) any later version.
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+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
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+Also add information on how to contact you by electronic and paper mail.
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+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
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+
+The hypothetical commands `show w' and `show c' should show the appropriate
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+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
 new file mode 100644
index 0000000..8c14478
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,21 @@
+METADATA_FILE="metadata.yaml"
+PROJECTPATH=$(dir $(realpath $(MAKEFILE_LIST)))
+
+ifndef CHARM_BUILD_DIR
+	CHARM_BUILD_DIR=${PROJECTPATH}/../builds
+endif
+
+CHARM_NAME=$(shell cat ${PROJECTPATH}/${METADATA_FILE} | grep -E "^name:" | awk '{print $$2}')
+
+clean:
+	@echo "Cleaning files"
+	@git clean -ffXd -e '!.idea'
+	@echo "Cleaning existing build"
+	@rm -rf ${CHARM_BUILD_DIR}/${CHARM_NAME}
+
+lint:
+	@echo "Running lint checks"
+	@cd src && tox -e lint
+
+# The targets below don't depend on a file
+.PHONY: clean lint
diff --git a/README.md b/README.md
index 148c70d..a53a7ed 100644
--- a/README.md
+++ b/README.md
@@ -1,24 +1,16 @@
-# charm-tor
+# charm-tor-hidden-service
 
 ## Description
 
-TODO: Describe your charm in a few paragraphs of Markdown
+This charm enables Tor hidden services
 
 ## Usage
 
-TODO: Provide high-level usage, such as required config or relations
+The charm relates to any number of services (e.g. ch:apache2) over the
+`reverseproxy` relation, and serves up a proxied version of that site on a
+.onion (v3) hostname.
 
+If you require a specific .onion hostname (or multiple)  we suggest using the
+mkp224o tool to create them, and configuring the charm with those private keys.
 
-## Relations
-
-TODO: Provide any relations which are provided or required by your charm
-
-## OCI Images
-
-TODO: Include a link to the default image your charm uses
-
-## Contributing
-
-Please see the [Juju SDK docs](https://juju.is/docs/sdk) for guidelines
-on enhancements to this charm following best practice guidelines, and
-`CONTRIBUTING.md` for developer guidance.
+TODO
diff --git a/actions.yaml b/actions.yaml
 deleted file mode 100644
index 7cda621..0000000
--- a/actions.yaml
+++ /dev/null
@@ -1,16 +0,0 @@
-# Copyright 2022 Barry Price
-# See LICENSE file for licensing details.
-#
-# TEMPLATE-TODO: change this example to suit your needs.
-# If you don't need actions, you can remove the file entirely.
-# It ties in to the example _on_fortune_action handler in src/charm.py
-#
-# Learn more about actions at: https://juju.is/docs/sdk/actions
-
-fortune:
-  description: Returns a pithy phrase.
-  params:
-    fail:
-      description: "Fail with this message"
-      type: string
-      default: ""
diff --git a/charmcraft.yaml b/charmcraft.yaml
index 048d454..0d1497e 100644
--- a/charmcraft.yaml
+++ b/charmcraft.yaml
@@ -1,10 +1,10 @@
-# Learn more about charmcraft.yaml configuration at:
-# https://juju.is/docs/sdk/charmcraft-config
 type: "charm"
 bases:
   - build-on:
     - name: "ubuntu"
-      channel: "20.04"
+      channel: "22.04"
     run-on:
     - name: "ubuntu"
       channel: "20.04"
+    - name: "ubuntu"
+      channel: "22.04"
diff --git a/config.yaml b/config.yaml
index 65fb1ce..35643c0 100644
--- a/config.yaml
+++ b/config.yaml
@@ -1,14 +1,33 @@
-# Copyright 2022 Barry Price
-# See LICENSE file for licensing details.
-#
-# TEMPLATE-TODO: change this example to suit your needs.
-# If you don't need a config, you can remove the file entirely.
-# It ties in to the example _on_config_changed handler in src/charm.py
-#
-# Learn more about config at: https://juju.is/docs/sdk/config
-
 options:
-  thing:
-    default: 🎁
-    description: A thing used by the charm.
+  hidden_keys_base64:
+    default: ""
+    description: |
+        Optional pre-generated tor private keys to run your service. The
+        .onion hostname(s) will be derived from this value.
+
+        Since the key is a binary file, this field expects a YAML formattaed
+        list of source hostnames (passed via the reverseproxy relation and
+        visible in the Message column via `juju status`) with corresponding
+        base-64 encoded strings, via e.g. `base64 -w0 path/to/secretkey`.
+
+        If left unconfigured, a random key (and address) will be generated for
+        each site.
+
+        e.g.
+        example1.com: ZXhhbXBsZTEK
+        example2.internal: ZXhhbXBsZTIK
+        10.0.0.1: ZXhhbXBsZTMK # example3
+    type: string
+  socks5_port:
+    description: SOCKS5 proxy port on which to listen
+    type: int
+    default: 9050
+  tor_source:
+    default: torproject
+    description: |
+        Source from which tor will be installed.
+        Options are "torproject" (default), which will use the packages from
+        deb.torproject.org, or "ubuntu" which will use the package in ubuntu's
+        universe component (this option may be outdated/insecure, but is the
+        only current option for architectures other than amd64/arm64).
     type: string
diff --git a/lib/charms/operator_libs_linux/v0/apt.py b/lib/charms/operator_libs_linux/v0/apt.py
 new file mode 100644
index 0000000..2b5c8f2
--- /dev/null
+++ b/lib/charms/operator_libs_linux/v0/apt.py
@@ -0,0 +1,1329 @@
+# Copyright 2021 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Abstractions for the system's Debian/Ubuntu package information and repositories.
+
+This module contains abstractions and wrappers around Debian/Ubuntu-style repositories and
+packages, in order to easily provide an idiomatic and Pythonic mechanism for adding packages and/or
+repositories to systems for use in machine charms.
+
+A sane default configuration is attainable through nothing more than instantiation of the
+appropriate classes. `DebianPackage` objects provide information about the architecture, version,
+name, and status of a package.
+
+`DebianPackage` will try to look up a package either from `dpkg -L` or from `apt-cache` when
+provided with a string indicating the package name. If it cannot be located, `PackageNotFoundError`
+will be returned, as `apt` and `dpkg` otherwise return `100` for all errors, and a meaningful error
+message if the package is not known is desirable.
+
+To install packages with convenience methods:
+
+```python
+try:
+    # Run `apt-get update`
+    apt.update()
+    apt.add_package("zsh")
+    apt.add_package(["vim", "htop", "wget"])
+except PackageNotFoundError:
+    logger.error("a specified package not found in package cache or on system")
+except PackageError as e:
+    logger.error("could not install package. Reason: %s", e.message)
+````
+
+To find details of a specific package:
+
+```python
+try:
+    vim = apt.DebianPackage.from_system("vim")
+
+    # To find from the apt cache only
+    # apt.DebianPackage.from_apt_cache("vim")
+
+    # To find from installed packages only
+    # apt.DebianPackage.from_installed_package("vim")
+
+    vim.ensure(PackageState.Latest)
+    logger.info("updated vim to version: %s", vim.fullversion)
+except PackageNotFoundError:
+    logger.error("a specified package not found in package cache or on system")
+except PackageError as e:
+    logger.error("could not install package. Reason: %s", e.message)
+```
+
+
+`RepositoryMapping` will return a dict-like object containing enabled system repositories
+and their properties (available groups, baseuri. gpg key). This class can add, disable, or
+manipulate repositories. Items can be retrieved as `DebianRepository` objects.
+
+In order add a new repository with explicit details for fields, a new `DebianRepository` can
+be added to `RepositoryMapping`
+
+`RepositoryMapping` provides an abstraction around the existing repositories on the system,
+and can be accessed and iterated over like any `Mapping` object, to retrieve values by key,
+iterate, or perform other operations.
+
+Keys are constructed as `{repo_type}-{}-{release}` in order to uniquely identify a repository.
+
+Repositories can be added with explicit values through a Python constructor.
+
+Example:
+
+```python
+repositories = apt.RepositoryMapping()
+
+if "deb-example.com-focal" not in repositories:
+    repositories.add(DebianRepository(enabled=True, repotype="deb",
+                     uri="https://example.com", release="focal", groups=["universe"]))
+```
+
+Alternatively, any valid `sources.list` line may be used to construct a new
+`DebianRepository`.
+
+Example:
+
+```python
+repositories = apt.RepositoryMapping()
+
+if "deb-us.archive.ubuntu.com-xenial" not in repositories:
+    line = "deb http://us.archive.ubuntu.com/ubuntu xenial main restricted"
+    repo = DebianRepository.from_repo_line(line)
+    repositories.add(repo)
+```
+"""
+
+import fileinput
+import glob
+import logging
+import os
+import re
+import subprocess
+from collections.abc import Mapping
+from enum import Enum
+from subprocess import PIPE, CalledProcessError, check_call, check_output
+from typing import Iterable, List, Optional, Tuple, Union
+from urllib.parse import urlparse
+
+logger = logging.getLogger(__name__)
+
+# The unique Charmhub library identifier, never change it
+LIBID = "7c3dbc9c2ad44a47bd6fcb25caa270e5"
+
+# Increment this major API version when introducing breaking changes
+LIBAPI = 0
+
+# Increment this PATCH version before using `charmcraft publish-lib` or reset
+# to 0 if you are raising the major API version
+LIBPATCH = 7
+
+
+VALID_SOURCE_TYPES = ("deb", "deb-src")
+OPTIONS_MATCHER = re.compile(r"\[.*?\]")
+
+
+class Error(Exception):
+    """Base class of most errors raised by this library."""
+
+    def __repr__(self):
+        """String representation of Error."""
+        return "<{}.{} {}>".format(type(self).__module__, type(self).__name__, self.args)
+
+    @property
+    def name(self):
+        """Return a string representation of the model plus class."""
+        return "<{}.{}>".format(type(self).__module__, type(self).__name__)
+
+    @property
+    def message(self):
+        """Return the message passed as an argument."""
+        return self.args[0]
+
+
+class PackageError(Error):
+    """Raised when there's an error installing or removing a package."""
+
+
+class PackageNotFoundError(Error):
+    """Raised when a requested package is not known to the system."""
+
+
+class PackageState(Enum):
+    """A class to represent possible package states."""
+
+    Present = "present"
+    Absent = "absent"
+    Latest = "latest"
+    Available = "available"
+
+
+class DebianPackage:
+    """Represents a traditional Debian package and its utility functions.
+
+    `DebianPackage` wraps information and functionality around a known package, whether installed
+    or available. The version, epoch, name, and architecture can be easily queried and compared
+    against other `DebianPackage` objects to determine the latest version or to install a specific
+    version.
+
+    The representation of this object as a string mimics the output from `dpkg` for familiarity.
+
+    Installation and removal of packages is handled through the `state` property or `ensure`
+    method, with the following options:
+
+        apt.PackageState.Absent
+        apt.PackageState.Available
+        apt.PackageState.Present
+        apt.PackageState.Latest
+
+    When `DebianPackage` is initialized, the state of a given `DebianPackage` object will be set to
+    `Available`, `Present`, or `Latest`, with `Absent` implemented as a convenience for removal
+    (though it operates essentially the same as `Available`).
+    """
+
+    def __init__(
+        self, name: str, version: str, epoch: str, arch: str, state: PackageState
+    ) -> None:
+        self._name = name
+        self._arch = arch
+        self._state = state
+        self._version = Version(version, epoch)
+
+    def __eq__(self, other) -> bool:
+        """Equality for comparison.
+
+        Args:
+          other: a `DebianPackage` object for comparison
+
+        Returns:
+          A boolean reflecting equality
+        """
+        return isinstance(other, self.__class__) and (
+            self._name,
+            self._version.number,
+        ) == (other._name, other._version.number)
+
+    def __hash__(self):
+        """A basic hash so this class can be used in Mappings and dicts."""
+        return hash((self._name, self._version.number))
+
+    def __repr__(self):
+        """A representation of the package."""
+        return "<{}.{}: {}>".format(self.__module__, self.__class__.__name__, self.__dict__)
+
+    def __str__(self):
+        """A human-readable representation of the package."""
+        return "<{}: {}-{}.{} -- {}>".format(
+            self.__class__.__name__,
+            self._name,
+            self._version,
+            self._arch,
+            str(self._state),
+        )
+
+    @staticmethod
+    def _apt(
+        command: str,
+        package_names: Union[str, List],
+        optargs: Optional[List[str]] = None,
+    ) -> None:
+        """Wrap package management commands for Debian/Ubuntu systems.
+
+        Args:
+          command: the command given to `apt-get`
+          package_names: a package name or list of package names to operate on
+          optargs: an (Optional) list of additioanl arguments
+
+        Raises:
+          PackageError if an error is encountered
+        """
+        optargs = optargs if optargs is not None else []
+        if isinstance(package_names, str):
+            package_names = [package_names]
+        _cmd = ["apt-get", "-y", *optargs, command, *package_names]
+        try:
+            check_call(_cmd, stderr=PIPE, stdout=PIPE)
+        except CalledProcessError as e:
+            raise PackageError(
+                "Could not {} package(s) [{}]: {}".format(command, [*package_names], e.output)
+            ) from None
+
+    def _add(self) -> None:
+        """Add a package to the system."""
+        self._apt(
+            "install",
+            "{}={}".format(self.name, self.version),
+            optargs=["--option=Dpkg::Options::=--force-confold"],
+        )
+
+    def _remove(self) -> None:
+        """Removes a package from the system. Implementation-specific."""
+        return self._apt("remove", "{}={}".format(self.name, self.version))
+
+    @property
+    def name(self) -> str:
+        """Returns the name of the package."""
+        return self._name
+
+    def ensure(self, state: PackageState):
+        """Ensures that a package is in a given state.
+
+        Args:
+          state: a `PackageState` to reconcile the package to
+
+        Raises:
+          PackageError from the underlying call to apt
+        """
+        if self._state is not state:
+            if state not in (PackageState.Present, PackageState.Latest):
+                self._remove()
+            else:
+                self._add()
+        self._state = state
+
+    @property
+    def present(self) -> bool:
+        """Returns whether or not a package is present."""
+        return self._state in (PackageState.Present, PackageState.Latest)
+
+    @property
+    def latest(self) -> bool:
+        """Returns whether the package is the most recent version."""
+        return self._state is PackageState.Latest
+
+    @property
+    def state(self) -> PackageState:
+        """Returns the current package state."""
+        return self._state
+
+    @state.setter
+    def state(self, state: PackageState) -> None:
+        """Sets the package state to a given value.
+
+        Args:
+          state: a `PackageState` to reconcile the package to
+
+        Raises:
+          PackageError from the underlying call to apt
+        """
+        if state in (PackageState.Latest, PackageState.Present):
+            self._add()
+        else:
+            self._remove()
+        self._state = state
+
+    @property
+    def version(self) -> "Version":
+        """Returns the version for a package."""
+        return self._version
+
+    @property
+    def epoch(self) -> str:
+        """Returns the epoch for a package. May be unset."""
+        return self._version.epoch
+
+    @property
+    def arch(self) -> str:
+        """Returns the architecture for a package."""
+        return self._arch
+
+    @property
+    def fullversion(self) -> str:
+        """Returns the name+epoch for a package."""
+        return "{}.{}".format(self._version, self._arch)
+
+    @staticmethod
+    def _get_epoch_from_version(version: str) -> Tuple[str, str]:
+        """Pull the epoch, if any, out of a version string."""
+        epoch_matcher = re.compile(r"^((?P<epoch>\d+):)?(?P<version>.*)")
+        matches = epoch_matcher.search(version).groupdict()
+        return matches.get("epoch", ""), matches.get("version")
+
+    @classmethod
+    def from_system(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Locates a package, either on the system or known to apt, and serializes the information.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`. If an
+                architecture is not specified, this will be used for selection.
+
+        """
+        try:
+            return DebianPackage.from_installed_package(package, version, arch)
+        except PackageNotFoundError:
+            logger.debug(
+                "package '%s' is not currently installed or has the wrong architecture.", package
+            )
+
+        # Ok, try `apt-cache ...`
+        try:
+            return DebianPackage.from_apt_cache(package, version, arch)
+        except (PackageNotFoundError, PackageError):
+            # If we get here, it's not known to the systems.
+            # This seems unnecessary, but virtually all `apt` commands have a return code of `100`,
+            # and providing meaningful error messages without this is ugly.
+            raise PackageNotFoundError(
+                "Package '{}{}' could not be found on the system or in the apt cache!".format(
+                    package, ".{}".format(arch) if arch else ""
+                )
+            ) from None
+
+    @classmethod
+    def from_installed_package(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Check whether the package is already installed and return an instance.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`.
+                If an architecture is not specified, this will be used for selection.
+        """
+        system_arch = check_output(
+            ["dpkg", "--print-architecture"], universal_newlines=True
+        ).strip()
+        arch = arch if arch else system_arch
+
+        # Regexps are a really terrible way to do this. Thanks dpkg
+        output = ""
+        try:
+            output = check_output(["dpkg", "-l", package], stderr=PIPE, universal_newlines=True)
+        except CalledProcessError:
+            raise PackageNotFoundError("Package is not installed: {}".format(package)) from None
+
+        # Pop off the output from `dpkg -l' because there's no flag to
+        # omit it`
+        lines = str(output).splitlines()[5:]
+
+        dpkg_matcher = re.compile(
+            r"""
+        ^(?P<package_status>\w+?)\s+
+        (?P<package_name>.*?)(?P<throwaway_arch>:\w+?)?\s+
+        (?P<version>.*?)\s+
+        (?P<arch>\w+?)\s+
+        (?P<description>.*)
+        """,
+            re.VERBOSE,
+        )
+
+        for line in lines:
+            try:
+                matches = dpkg_matcher.search(line).groupdict()
+                package_status = matches["package_status"]
+
+                if not package_status.endswith("i"):
+                    logger.debug(
+                        "package '%s' in dpkg output but not installed, status: '%s'",
+                        package,
+                        package_status,
+                    )
+                    break
+
+                epoch, split_version = DebianPackage._get_epoch_from_version(matches["version"])
+                pkg = DebianPackage(
+                    matches["package_name"],
+                    split_version,
+                    epoch,
+                    matches["arch"],
+                    PackageState.Present,
+                )
+                if (pkg.arch == "all" or pkg.arch == arch) and (
+                    version == "" or str(pkg.version) == version
+                ):
+                    return pkg
+            except AttributeError:
+                logger.warning("dpkg matcher could not parse line: %s", line)
+
+        # If we didn't find it, fail through
+        raise PackageNotFoundError("Package {}.{} is not installed!".format(package, arch))
+
+    @classmethod
+    def from_apt_cache(
+        cls, package: str, version: Optional[str] = "", arch: Optional[str] = ""
+    ) -> "DebianPackage":
+        """Check whether the package is already installed and return an instance.
+
+        Args:
+            package: a string representing the package
+            version: an optional string if a specific version isr equested
+            arch: an optional architecture, defaulting to `dpkg --print-architecture`.
+                If an architecture is not specified, this will be used for selection.
+        """
+        system_arch = check_output(
+            ["dpkg", "--print-architecture"], universal_newlines=True
+        ).strip()
+        arch = arch if arch else system_arch
+
+        # Regexps are a really terrible way to do this. Thanks dpkg
+        keys = ("Package", "Architecture", "Version")
+
+        try:
+            output = check_output(
+                ["apt-cache", "show", package], stderr=PIPE, universal_newlines=True
+            )
+        except CalledProcessError as e:
+            raise PackageError(
+                "Could not list packages in apt-cache: {}".format(e.output)
+            ) from None
+
+        pkg_groups = output.strip().split("\n\n")
+        keys = ("Package", "Architecture", "Version")
+
+        for pkg_raw in pkg_groups:
+            lines = str(pkg_raw).splitlines()
+            vals = {}
+            for line in lines:
+                if line.startswith(keys):
+                    items = line.split(":", 1)
+                    vals[items[0]] = items[1].strip()
+                else:
+                    continue
+
+            epoch, split_version = DebianPackage._get_epoch_from_version(vals["Version"])
+            pkg = DebianPackage(
+                vals["Package"],
+                split_version,
+                epoch,
+                vals["Architecture"],
+                PackageState.Available,
+            )
+
+            if (pkg.arch == "all" or pkg.arch == arch) and (
+                version == "" or str(pkg.version) == version
+            ):
+                return pkg
+
+        # If we didn't find it, fail through
+        raise PackageNotFoundError("Package {}.{} is not in the apt cache!".format(package, arch))
+
+
+class Version:
+    """An abstraction around package versions.
+
+    This seems like it should be strictly unnecessary, except that `apt_pkg` is not usable inside a
+    venv, and wedging version comparisions into `DebianPackage` would overcomplicate it.
+
+    This class implements the algorithm found here:
+    https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
+    """
+
+    def __init__(self, version: str, epoch: str):
+        self._version = version
+        self._epoch = epoch or ""
+
+    def __repr__(self):
+        """A representation of the package."""
+        return "<{}.{}: {}>".format(self.__module__, self.__class__.__name__, self.__dict__)
+
+    def __str__(self):
+        """A human-readable representation of the package."""
+        return "{}{}".format("{}:".format(self._epoch) if self._epoch else "", self._version)
+
+    @property
+    def epoch(self):
+        """Returns the epoch for a package. May be empty."""
+        return self._epoch
+
+    @property
+    def number(self) -> str:
+        """Returns the version number for a package."""
+        return self._version
+
+    def _get_parts(self, version: str) -> Tuple[str, str]:
+        """Separate the version into component upstream and Debian pieces."""
+        try:
+            version.rindex("-")
+        except ValueError:
+            # No hyphens means no Debian version
+            return version, "0"
+
+        upstream, debian = version.rsplit("-", 1)
+        return upstream, debian
+
+    def _listify(self, revision: str) -> List[str]:
+        """Split a revision string into a listself.
+
+        This list is comprised of  alternating between strings and numbers,
+        padded on either end to always be "str, int, str, int..." and
+        always be of even length.  This allows us to trivially implement the
+        comparison algorithm described.
+        """
+        result = []
+        while revision:
+            rev_1, remains = self._get_alphas(revision)
+            rev_2, remains = self._get_digits(remains)
+            result.extend([rev_1, rev_2])
+            revision = remains
+        return result
+
+    def _get_alphas(self, revision: str) -> Tuple[str, str]:
+        """Return a tuple of the first non-digit characters of a revision."""
+        # get the index of the first digit
+        for i, char in enumerate(revision):
+            if char.isdigit():
+                if i == 0:
+                    return "", revision
+                return revision[0:i], revision[i:]
+        # string is entirely alphas
+        return revision, ""
+
+    def _get_digits(self, revision: str) -> Tuple[int, str]:
+        """Return a tuple of the first integer characters of a revision."""
+        # If the string is empty, return (0,'')
+        if not revision:
+            return 0, ""
+        # get the index of the first non-digit
+        for i, char in enumerate(revision):
+            if not char.isdigit():
+                if i == 0:
+                    return 0, revision
+                return int(revision[0:i]), revision[i:]
+        # string is entirely digits
+        return int(revision), ""
+
+    def _dstringcmp(self, a, b):  # noqa: C901
+        """Debian package version string section lexical sort algorithm.
+
+        The lexical comparison is a comparison of ASCII values modified so
+        that all the letters sort earlier than all the non-letters and so that
+        a tilde sorts before anything, even the end of a part.
+        """
+        if a == b:
+            return 0
+        try:
+            for i, char in enumerate(a):
+                if char == b[i]:
+                    continue
+                # "a tilde sorts before anything, even the end of a part"
+                # (emptyness)
+                if char == "~":
+                    return -1
+                if b[i] == "~":
+                    return 1
+                # "all the letters sort earlier than all the non-letters"
+                if char.isalpha() and not b[i].isalpha():
+                    return -1
+                if not char.isalpha() and b[i].isalpha():
+                    return 1
+                # otherwise lexical sort
+                if ord(char) > ord(b[i]):
+                    return 1
+                if ord(char) < ord(b[i]):
+                    return -1
+        except IndexError:
+            # a is longer than b but otherwise equal, greater unless there are tildes
+            if char == "~":
+                return -1
+            return 1
+        # if we get here, a is shorter than b but otherwise equal, so check for tildes...
+        if b[len(a)] == "~":
+            return 1
+        return -1
+
+    def _compare_revision_strings(self, first: str, second: str):  # noqa: C901
+        """Compare two debian revision strings."""
+        if first == second:
+            return 0
+
+        # listify pads results so that we will always be comparing ints to ints
+        # and strings to strings (at least until we fall off the end of a list)
+        first_list = self._listify(first)
+        second_list = self._listify(second)
+        if first_list == second_list:
+            return 0
+        try:
+            for i, item in enumerate(first_list):
+                # explicitly raise IndexError if we've fallen off the edge of list2
+                if i >= len(second_list):
+                    raise IndexError
+                # if the items are equal, next
+                if item == second_list[i]:
+                    continue
+                # numeric comparison
+                if isinstance(item, int):
+                    if item > second_list[i]:
+                        return 1
+                    if item < second_list[i]:
+                        return -1
+                else:
+                    # string comparison
+                    return self._dstringcmp(item, second_list[i])
+        except IndexError:
+            # rev1 is longer than rev2 but otherwise equal, hence greater
+            # ...except for goddamn tildes
+            if first_list[len(second_list)][0][0] == "~":
+                return 1
+            return 1
+        # rev1 is shorter than rev2 but otherwise equal, hence lesser
+        # ...except for goddamn tildes
+        if second_list[len(first_list)][0][0] == "~":
+            return -1
+        return -1
+
+    def _compare_version(self, other) -> int:
+        if (self.number, self.epoch) == (other.number, other.epoch):
+            return 0
+
+        if self.epoch < other.epoch:
+            return -1
+        if self.epoch > other.epoch:
+            return 1
+
+        # If none of these are true, follow the algorithm
+        upstream_version, debian_version = self._get_parts(self.number)
+        other_upstream_version, other_debian_version = self._get_parts(other.number)
+
+        upstream_cmp = self._compare_revision_strings(upstream_version, other_upstream_version)
+        if upstream_cmp != 0:
+            return upstream_cmp
+
+        debian_cmp = self._compare_revision_strings(debian_version, other_debian_version)
+        if debian_cmp != 0:
+            return debian_cmp
+
+        return 0
+
+    def __lt__(self, other) -> bool:
+        """Less than magic method impl."""
+        return self._compare_version(other) < 0
+
+    def __eq__(self, other) -> bool:
+        """Equality magic method impl."""
+        return self._compare_version(other) == 0
+
+    def __gt__(self, other) -> bool:
+        """Greater than magic method impl."""
+        return self._compare_version(other) > 0
+
+    def __le__(self, other) -> bool:
+        """Less than or equal to magic method impl."""
+        return self.__eq__(other) or self.__lt__(other)
+
+    def __ge__(self, other) -> bool:
+        """Greater than or equal to magic method impl."""
+        return self.__gt__(other) or self.__eq__(other)
+
+    def __ne__(self, other) -> bool:
+        """Not equal to magic method impl."""
+        return not self.__eq__(other)
+
+
+def add_package(
+    package_names: Union[str, List[str]],
+    version: Optional[str] = "",
+    arch: Optional[str] = "",
+    update_cache: Optional[bool] = False,
+) -> Union[DebianPackage, List[DebianPackage]]:
+    """Add a package or list of packages to the system.
+
+    Args:
+        name: the name(s) of the package(s)
+        version: an (Optional) version as a string. Defaults to the latest known
+        arch: an optional architecture for the package
+        update_cache: whether or not to run `apt-get update` prior to operating
+
+    Raises:
+        PackageNotFoundError if the package is not in the cache.
+    """
+    cache_refreshed = False
+    if update_cache:
+        update()
+        cache_refreshed = True
+
+    packages = {"success": [], "retry": [], "failed": []}
+
+    package_names = [package_names] if type(package_names) is str else package_names
+    if not package_names:
+        raise TypeError("Expected at least one package name to add, received zero!")
+
+    if len(package_names) != 1 and version:
+        raise TypeError(
+            "Explicit version should not be set if more than one package is being added!"
+        )
+
+    for p in package_names:
+        pkg, success = _add(p, version, arch)
+        if success:
+            packages["success"].append(pkg)
+        else:
+            logger.warning("failed to locate and install/update '%s'", pkg)
+            packages["retry"].append(p)
+
+    if packages["retry"] and not cache_refreshed:
+        logger.info("updating the apt-cache and retrying installation of failed packages.")
+        update()
+
+        for p in packages["retry"]:
+            pkg, success = _add(p, version, arch)
+            if success:
+                packages["success"].append(pkg)
+            else:
+                packages["failed"].append(p)
+
+    if packages["failed"]:
+        raise PackageError("Failed to install packages: {}".format(", ".join(packages["failed"])))
+
+    return packages["success"] if len(packages["success"]) > 1 else packages["success"][0]
+
+
+def _add(
+    name: str,
+    version: Optional[str] = "",
+    arch: Optional[str] = "",
+) -> Tuple[Union[DebianPackage, str], bool]:
+    """Adds a package.
+
+    Args:
+        name: the name(s) of the package(s)
+        version: an (Optional) version as a string. Defaults to the latest known
+        arch: an optional architecture for the package
+
+    Returns: a tuple of `DebianPackage` if found, or a :str: if it is not, and
+        a boolean indicating success
+    """
+    try:
+        pkg = DebianPackage.from_system(name, version, arch)
+        pkg.ensure(state=PackageState.Present)
+        return pkg, True
+    except PackageNotFoundError:
+        return name, False
+
+
+def remove_package(
+    package_names: Union[str, List[str]]
+) -> Union[DebianPackage, List[DebianPackage]]:
+    """Removes a package from the system.
+
+    Args:
+        package_names: the name of a package
+
+    Raises:
+        PackageNotFoundError if the package is not found.
+    """
+    packages = []
+
+    package_names = [package_names] if type(package_names) is str else package_names
+    if not package_names:
+        raise TypeError("Expected at least one package name to add, received zero!")
+
+    for p in package_names:
+        try:
+            pkg = DebianPackage.from_installed_package(p)
+            pkg.ensure(state=PackageState.Absent)
+            packages.append(pkg)
+        except PackageNotFoundError:
+            logger.info("package '%s' was requested for removal, but it was not installed.", p)
+
+    # the list of packages will be empty when no package is removed
+    logger.debug("packages: '%s'", packages)
+    return packages[0] if len(packages) == 1 else packages
+
+
+def update() -> None:
+    """Updates the apt cache via `apt-get update`."""
+    check_call(["apt-get", "update"], stderr=PIPE, stdout=PIPE)
+
+
+class InvalidSourceError(Error):
+    """Exceptions for invalid source entries."""
+
+
+class GPGKeyError(Error):
+    """Exceptions for GPG keys."""
+
+
+class DebianRepository:
+    """An abstraction to represent a repository."""
+
+    def __init__(
+        self,
+        enabled: bool,
+        repotype: str,
+        uri: str,
+        release: str,
+        groups: List[str],
+        filename: Optional[str] = "",
+        gpg_key_filename: Optional[str] = "",
+        options: Optional[dict] = None,
+    ):
+        self._enabled = enabled
+        self._repotype = repotype
+        self._uri = uri
+        self._release = release
+        self._groups = groups
+        self._filename = filename
+        self._gpg_key_filename = gpg_key_filename
+        self._options = options
+
+    @property
+    def enabled(self):
+        """Return whether or not the repository is enabled."""
+        return self._enabled
+
+    @property
+    def repotype(self):
+        """Return whether it is binary or source."""
+        return self._repotype
+
+    @property
+    def uri(self):
+        """Return the URI."""
+        return self._uri
+
+    @property
+    def release(self):
+        """Return which Debian/Ubuntu releases it is valid for."""
+        return self._release
+
+    @property
+    def groups(self):
+        """Return the enabled package groups."""
+        return self._groups
+
+    @property
+    def filename(self):
+        """Returns the filename for a repository."""
+        return self._filename
+
+    @filename.setter
+    def filename(self, fname: str) -> None:
+        """Sets the filename used when a repo is written back to diskself.
+
+        Args:
+            fname: a filename to write the repository information to.
+        """
+        if not fname.endswith(".list"):
+            raise InvalidSourceError("apt source filenames should end in .list!")
+
+        self._filename = fname
+
+    @property
+    def gpg_key(self):
+        """Returns the path to the GPG key for this repository."""
+        return self._gpg_key_filename
+
+    @property
+    def options(self):
+        """Returns any additional repo options which are set."""
+        return self._options
+
+    def make_options_string(self) -> str:
+        """Generate the complete options string for a a repository.
+
+        Combining `gpg_key`, if set, and the rest of the options to find
+        a complex repo string.
+        """
+        options = self._options if self._options else {}
+        if self._gpg_key_filename:
+            options["signed-by"] = self._gpg_key_filename
+
+        return (
+            "[{}] ".format(" ".join(["{}={}".format(k, v) for k, v in options.items()]))
+            if options
+            else ""
+        )
+
+    @staticmethod
+    def prefix_from_uri(uri: str) -> str:
+        """Get a repo list prefix from the uri, depending on whether a path is set."""
+        uridetails = urlparse(uri)
+        path = (
+            uridetails.path.lstrip("/").replace("/", "-") if uridetails.path else uridetails.netloc
+        )
+        return "/etc/apt/sources.list.d/{}".format(path)
+
+    @staticmethod
+    def from_repo_line(repo_line: str, write_file: Optional[bool] = True) -> "DebianRepository":
+        """Instantiate a new `DebianRepository` a `sources.list` entry line.
+
+        Args:
+            repo_line: a string representing a repository entry
+            write_file: boolean to enable writing the new repo to disk
+        """
+        repo = RepositoryMapping._parse(repo_line, "UserInput")
+        fname = "{}-{}.list".format(
+            DebianRepository.prefix_from_uri(repo.uri), repo.release.replace("/", "-")
+        )
+        repo.filename = fname
+
+        options = repo.options if repo.options else {}
+        if repo.gpg_key:
+            options["signed-by"] = repo.gpg_key
+
+        # For Python 3.5 it's required to use sorted in the options dict in order to not have
+        # different results in the order of the options between executions.
+        options_str = (
+            "[{}] ".format(" ".join(["{}={}".format(k, v) for k, v in sorted(options.items())]))
+            if options
+            else ""
+        )
+
+        if write_file:
+            with open(fname, "wb") as f:
+                f.write(
+                    (
+                        "{}".format("#" if not repo.enabled else "")
+                        + "{} {}{} ".format(repo.repotype, options_str, repo.uri)
+                        + "{} {}\n".format(repo.release, " ".join(repo.groups))
+                    ).encode("utf-8")
+                )
+
+        return repo
+
+    def disable(self) -> None:
+        """Remove this repository from consideration.
+
+        Disable it instead of removing from the repository file.
+        """
+        searcher = "{} {}{} {}".format(
+            self.repotype, self.make_options_string(), self.uri, self.release
+        )
+        for line in fileinput.input(self._filename, inplace=True):
+            if re.match(r"^{}\s".format(re.escape(searcher)), line):
+                print("# {}".format(line), end="")
+            else:
+                print(line, end="")
+
+    def import_key(self, key: str) -> None:
+        """Import an ASCII Armor key.
+
+        A Radix64 format keyid is also supported for backwards
+        compatibility. In this case Ubuntu keyserver will be
+        queried for a key via HTTPS by its keyid. This method
+        is less preferrable because https proxy servers may
+        require traffic decryption which is equivalent to a
+        man-in-the-middle attack (a proxy server impersonates
+        keyserver TLS certificates and has to be explicitly
+        trusted by the system).
+
+        Args:
+          key: A GPG key in ASCII armor format,
+                      including BEGIN and END markers or a keyid.
+
+        Raises:
+          GPGKeyError if the key could not be imported
+        """
+        key = key.strip()
+        if "-" in key or "\n" in key:
+            # Send everything not obviously a keyid to GPG to import, as
+            # we trust its validation better than our own. eg. handling
+            # comments before the key.
+            logger.debug("PGP key found (looks like ASCII Armor format)")
+            if (
+                "-----BEGIN PGP PUBLIC KEY BLOCK-----" in key
+                and "-----END PGP PUBLIC KEY BLOCK-----" in key
+            ):
+                logger.debug("Writing provided PGP key in the binary format")
+                key_bytes = key.encode("utf-8")
+                key_name = self._get_keyid_by_gpg_key(key_bytes)
+                key_gpg = self._dearmor_gpg_key(key_bytes)
+                self._gpg_key_filename = "/etc/apt/trusted.gpg.d/{}.gpg".format(key_name)
+                self._write_apt_gpg_keyfile(key_name=self._gpg_key_filename, key_material=key_gpg)
+            else:
+                raise GPGKeyError("ASCII armor markers missing from GPG key")
+        else:
+            logger.warning(
+                "PGP key found (looks like Radix64 format). "
+                "SECURELY importing PGP key from keyserver; "
+                "full key not provided."
+            )
+            # as of bionic add-apt-repository uses curl with an HTTPS keyserver URL
+            # to retrieve GPG keys. `apt-key adv` command is deprecated as is
+            # apt-key in general as noted in its manpage. See lp:1433761 for more
+            # history. Instead, /etc/apt/trusted.gpg.d is used directly to drop
+            # gpg
+            key_asc = self._get_key_by_keyid(key)
+            # write the key in GPG format so that apt-key list shows it
+            key_gpg = self._dearmor_gpg_key(key_asc.encode("utf-8"))
+            self._gpg_key_filename = "/etc/apt/trusted.gpg.d/{}.gpg".format(key)
+            self._write_apt_gpg_keyfile(key_name=key, key_material=key_gpg)
+
+    @staticmethod
+    def _get_keyid_by_gpg_key(key_material: bytes) -> str:
+        """Get a GPG key fingerprint by GPG key material.
+
+        Gets a GPG key fingerprint (40-digit, 160-bit) by the ASCII armor-encoded
+        or binary GPG key material. Can be used, for example, to generate file
+        names for keys passed via charm options.
+        """
+        # Use the same gpg command for both Xenial and Bionic
+        cmd = ["gpg", "--with-colons", "--with-fingerprint"]
+        ps = subprocess.run(
+            cmd,
+            stdout=PIPE,
+            stderr=PIPE,
+            input=key_material,
+        )
+        out, err = ps.stdout.decode(), ps.stderr.decode()
+        if "gpg: no valid OpenPGP data found." in err:
+            raise GPGKeyError("Invalid GPG key material provided")
+        # from gnupg2 docs: fpr :: Fingerprint (fingerprint is in field 10)
+        return re.search(r"^fpr:{9}([0-9A-F]{40}):$", out, re.MULTILINE).group(1)
+
+    @staticmethod
+    def _get_key_by_keyid(keyid: str) -> str:
+        """Get a key via HTTPS from the Ubuntu keyserver.
+
+        Different key ID formats are supported by SKS keyservers (the longer ones
+        are more secure, see "dead beef attack" and https://evil32.com/). Since
+        HTTPS is used, if SSLBump-like HTTPS proxies are in place, they will
+        impersonate keyserver.ubuntu.com and generate a certificate with
+        keyserver.ubuntu.com in the CN field or in SubjAltName fields of a
+        certificate. If such proxy behavior is expected it is necessary to add the
+        CA certificate chain containing the intermediate CA of the SSLBump proxy to
+        every machine that this code runs on via ca-certs cloud-init directive (via
+        cloudinit-userdata model-config) or via other means (such as through a
+        custom charm option). Also note that DNS resolution for the hostname in a
+        URL is done at a proxy server - not at the client side.
+        8-digit (32 bit) key ID
+        https://keyserver.ubuntu.com/pks/lookup?search=0x4652B4E6
+        16-digit (64 bit) key ID
+        https://keyserver.ubuntu.com/pks/lookup?search=0x6E85A86E4652B4E6
+        40-digit key ID:
+        https://keyserver.ubuntu.com/pks/lookup?search=0x35F77D63B5CEC106C577ED856E85A86E4652B4E6
+
+        Args:
+          keyid: An 8, 16 or 40 hex digit keyid to find a key for
+
+        Returns:
+          A string contining key material for the specified GPG key id
+
+
+        Raises:
+          subprocess.CalledProcessError
+        """
+        # options=mr - machine-readable output (disables html wrappers)
+        keyserver_url = (
+            "https://keyserver.ubuntu.com" "/pks/lookup?op=get&options=mr&exact=on&search=0x{}"
+        )
+        curl_cmd = ["curl", keyserver_url.format(keyid)]
+        # use proxy server settings in order to retrieve the key
+        return check_output(curl_cmd).decode()
+
+    @staticmethod
+    def _dearmor_gpg_key(key_asc: bytes) -> bytes:
+        """Converts a GPG key in the ASCII armor format to the binary format.
+
+        Args:
+          key_asc: A GPG key in ASCII armor format.
+
+        Returns:
+          A GPG key in binary format as a string
+
+        Raises:
+          GPGKeyError
+        """
+        ps = subprocess.run(["gpg", "--dearmor"], stdout=PIPE, stderr=PIPE, input=key_asc)
+        out, err = ps.stdout, ps.stderr.decode()
+        if "gpg: no valid OpenPGP data found." in err:
+            raise GPGKeyError(
+                "Invalid GPG key material. Check your network setup"
+                " (MTU, routing, DNS) and/or proxy server settings"
+                " as well as destination keyserver status."
+            )
+        else:
+            return out
+
+    @staticmethod
+    def _write_apt_gpg_keyfile(key_name: str, key_material: bytes) -> None:
+        """Writes GPG key material into a file at a provided path.
+
+        Args:
+          key_name: A key name to use for a key file (could be a fingerprint)
+          key_material: A GPG key material (binary)
+        """
+        with open(key_name, "wb") as keyf:
+            keyf.write(key_material)
+
+
+class RepositoryMapping(Mapping):
+    """An representation of known repositories.
+
+    Instantiation of `RepositoryMapping` will iterate through the
+    filesystem, parse out repository files in `/etc/apt/...`, and create
+    `DebianRepository` objects in this list.
+
+    Typical usage:
+
+        repositories = apt.RepositoryMapping()
+        repositories.add(DebianRepository(
+            enabled=True, repotype="deb", uri="https://example.com", release="focal",
+            groups=["universe"]
+        ))
+    """
+
+    def __init__(self):
+        self._repository_map = {}
+        # Repositories that we're adding -- used to implement mode param
+        self.default_file = "/etc/apt/sources.list"
+
+        # read sources.list if it exists
+        if os.path.isfile(self.default_file):
+            self.load(self.default_file)
+
+        # read sources.list.d
+        for file in glob.iglob("/etc/apt/sources.list.d/*.list"):
+            self.load(file)
+
+    def __contains__(self, key: str) -> bool:
+        """Magic method for checking presence of repo in mapping."""
+        return key in self._repository_map
+
+    def __len__(self) -> int:
+        """Return number of repositories in map."""
+        return len(self._repository_map)
+
+    def __iter__(self) -> Iterable[DebianRepository]:
+        """Iterator magic method for RepositoryMapping."""
+        return iter(self._repository_map.values())
+
+    def __getitem__(self, repository_uri: str) -> DebianRepository:
+        """Return a given `DebianRepository`."""
+        return self._repository_map[repository_uri]
+
+    def __setitem__(self, repository_uri: str, repository: DebianRepository) -> None:
+        """Add a `DebianRepository` to the cache."""
+        self._repository_map[repository_uri] = repository
+
+    def load(self, filename: str):
+        """Load a repository source file into the cache.
+
+        Args:
+          filename: the path to the repository file
+        """
+        parsed = []
+        skipped = []
+        with open(filename, "r") as f:
+            for n, line in enumerate(f):
+                try:
+                    repo = self._parse(line, filename)
+                except InvalidSourceError:
+                    skipped.append(n)
+                else:
+                    repo_identifier = "{}-{}-{}".format(repo.repotype, repo.uri, repo.release)
+                    self._repository_map[repo_identifier] = repo
+                    parsed.append(n)
+                    logger.debug("parsed repo: '%s'", repo_identifier)
+
+        if skipped:
+            skip_list = ", ".join(str(s) for s in skipped)
+            logger.debug("skipped the following lines in file '%s': %s", filename, skip_list)
+
+        if parsed:
+            logger.info("parsed %d apt package repositories", len(parsed))
+        else:
+            raise InvalidSourceError("all repository lines in '{}' were invalid!".format(filename))
+
+    @staticmethod
+    def _parse(line: str, filename: str) -> DebianRepository:
+        """Parse a line in a sources.list file.
+
+        Args:
+          line: a single line from `load` to parse
+          filename: the filename being read
+
+        Raises:
+          InvalidSourceError if the source type is unknown
+        """
+        enabled = True
+        repotype = uri = release = gpg_key = ""
+        options = {}
+        groups = []
+
+        line = line.strip()
+        if line.startswith("#"):
+            enabled = False
+            line = line[1:]
+
+        # Check for "#" in the line and treat a part after it as a comment then strip it off.
+        i = line.find("#")
+        if i > 0:
+            line = line[:i]
+
+        # Split a source into substrings to initialize a new repo.
+        source = line.strip()
+        if source:
+            # Match any repo options, and get a dict representation.
+            for v in re.findall(OPTIONS_MATCHER, source):
+                opts = dict(o.split("=") for o in v.strip("[]").split())
+                # Extract the 'signed-by' option for the gpg_key
+                gpg_key = opts.pop("signed-by", "")
+                options = opts
+
+            # Remove any options from the source string and split the string into chunks
+            source = re.sub(OPTIONS_MATCHER, "", source)
+            chunks = source.split()
+
+            # Check we've got a valid list of chunks
+            if len(chunks) < 3 or chunks[0] not in VALID_SOURCE_TYPES:
+                raise InvalidSourceError("An invalid sources line was found in %s!", filename)
+
+            repotype = chunks[0]
+            uri = chunks[1]
+            release = chunks[2]
+            groups = chunks[3:]
+
+            return DebianRepository(
+                enabled, repotype, uri, release, groups, filename, gpg_key, options
+            )
+        else:
+            raise InvalidSourceError("An invalid sources line was found in %s!", filename)
+
+    def add(self, repo: DebianRepository, default_filename: Optional[bool] = False) -> None:
+        """Add a new repository to the system.
+
+        Args:
+          repo: a `DebianRepository` object
+          default_filename: an (Optional) filename if the default is not desirable
+        """
+        new_filename = "{}-{}.list".format(
+            DebianRepository.prefix_from_uri(repo.uri), repo.release.replace("/", "-")
+        )
+
+        fname = repo.filename or new_filename
+
+        options = repo.options if repo.options else {}
+        if repo.gpg_key:
+            options["signed-by"] = repo.gpg_key
+
+        with open(fname, "wb") as f:
+            f.write(
+                (
+                    "{}".format("#" if not repo.enabled else "")
+                    + "{} {}{} ".format(repo.repotype, repo.make_options_string(), repo.uri)
+                    + "{} {}\n".format(repo.release, " ".join(repo.groups))
+                ).encode("utf-8")
+            )
+
+        self._repository_map["{}-{}-{}".format(repo.repotype, repo.uri, repo.release)] = repo
+
+    def disable(self, repo: DebianRepository) -> None:
+        """Remove a repository. Disable by default.
+
+        Args:
+          repo: a `DebianRepository` to disable
+        """
+        searcher = "{} {}{} {}".format(
+            repo.repotype, repo.make_options_string(), repo.uri, repo.release
+        )
+
+        for line in fileinput.input(repo.filename, inplace=True):
+            if re.match(r"^{}\s".format(re.escape(searcher)), line):
+                print("# {}".format(line), end="")
+            else:
+                print(line, end="")
+
+        self._repository_map["{}-{}-{}".format(repo.repotype, repo.uri, repo.release)] = repo
diff --git a/metadata.yaml b/metadata.yaml
index de1439f..5becf33 100644
--- a/metadata.yaml
+++ b/metadata.yaml
@@ -1,23 +1,14 @@
-# Copyright 2022 Barry Price
-# See LICENSE file for licensing details.
-
-# For a complete list of supported options, see:
-# https://juju.is/docs/sdk/metadata-reference
-name: charm-tor
-display-name: |
-  TEMPLATE-TODO: fill out a display name for the Charmcraft store
+name: charm-tor-hidden-service
+display-name: Tor Hidden Service Charmed Operator
+summary: Tor Hidden Service Charmed Operator
 description: |
-  TEMPLATE-TODO: fill out the charm's description
-summary: |
-  TEMPLATE-TODO: fill out the charm's summary
-
-# TEMPLATE-TODO: replace with containers for your workload (delete for non-k8s)
-containers:
-  httpbin:
-    resource: httpbin-image
+    Tor is free software and an open network that helps you defend against
+    traffic analysis, a form of network surveillance that threatens personal
+    freedom and privacy, confidential business activities and relationships, and
+    state security.
+requires:
+  reverseproxy:
+    interface: http
+series:
+  - jammy
 
-# TEMPLATE-TODO: each container defined above must specify an oci-image resource
-resources:
-  httpbin-image:
-    type: oci-image
-    description: OCI image for httpbin (kennethreitz/httpbin)
diff --git a/pyproject.toml b/pyproject.toml
 new file mode 100644
index 0000000..177269a
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,38 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+# Testing tools configuration
+[tool.coverage.run]
+branch = true
+
+[tool.coverage.report]
+show_missing = true
+
+[tool.pytest.ini_options]
+minversion = "6.0"
+log_cli_level = "INFO"
+
+# Formatting tools configuration
+[tool.black]
+line-length = 99
+target-version = ["py310"]
+
+[tool.isort]
+profile = "black"
+
+# Linting tools configuration
+[tool.flake8]
+max-line-length = 99
+max-doc-length = 99
+max-complexity = 10
+exclude = [".git", "__pycache__", ".tox", "build", "dist", "*.egg_info", "venv"]
+select = ["E", "W", "F", "C", "N", "R", "D", "H"]
+# Ignore D107 Missing docstring in __init__
+ignore = ["D107"]
+# D100, D101, D102, D103: Ignore missing docstrings in tests
+per-file-ignores = ["tests/*:D100,D101,D102,D103,D104"]
+docstring-convention = "google"
+# Check for properly formatted copyright header in each file
+copyright-check = "True"
+copyright-author = "Canonical Ltd."
+copyright-regexp = "Copyright\\s\\d{4}([-,]\\d{4})*\\s+%(author)s"
diff --git a/src/charm.py b/src/charm.py
index 2cac651..73b10fa 100755
--- a/src/charm.py
+++ b/src/charm.py
@@ -1,104 +1,206 @@
 #!/usr/bin/env python3
-# Copyright 2022 Barry Price
+# Copyright 2022 Canonical Ltd.
 # See LICENSE file for licensing details.
-#
-# Learn more at: https://juju.is/docs/sdk
 
-"""Charm the service.
-
-Refer to the following post for a quick-start guide that will help you
-develop a new k8s charm using the Operator Framework:
-
-    https://discourse.charmhub.io/t/4208
-"""
+"""Charmed Operator to provide Tor hidden services."""
 
 import logging
-
-from ops.charm import CharmBase
+import os
+import shutil
+import subprocess
+import urllib.request
+
+import jinja2
+
+from charms.operator_libs_linux.v0 import apt
+from ops.charm import (
+    CharmBase,
+    RelationChangedEvent,
+)
 from ops.framework import StoredState
 from ops.main import main
-from ops.model import ActiveStatus
+from ops.model import (
+    BlockedStatus,
+    Unit,
+)
 
 logger = logging.getLogger(__name__)
 
 
-class CharmTorCharm(CharmBase):
-    """Charm the service."""
+def get_series():
+    """Return the installed Ubuntu series (e.g. "jammy")."""
+    return subprocess.check_output(["lsb_release", "-sc"]).decode('utf-8').strip()
 
-    _stored = StoredState()
 
-    def __init__(self, *args):
-        super().__init__(*args)
-        self.framework.observe(self.on.httpbin_pebble_ready, self._on_httpbin_pebble_ready)
-        self.framework.observe(self.on.config_changed, self._on_config_changed)
-        self.framework.observe(self.on.fortune_action, self._on_fortune_action)
-        self._stored.set_default(things=[])
-
-    def _on_httpbin_pebble_ready(self, event):
-        """Define and start a workload using the Pebble API.
-
-        TEMPLATE-TODO: change this example to suit your needs.
-        You'll need to specify the right entrypoint and environment
-        configuration for your specific workload. Tip: you can see the
-        standard entrypoint of an existing container using docker inspect
-
-        Learn more about Pebble layers at https://github.com/canonical/pebble
-        """
-        # Get a reference the container attribute on the PebbleReadyEvent
-        container = event.workload
-        # Define an initial Pebble layer configuration
-        pebble_layer = {
-            "summary": "httpbin layer",
-            "description": "pebble config layer for httpbin",
-            "services": {
-                "httpbin": {
-                    "override": "replace",
-                    "summary": "httpbin",
-                    "command": "gunicorn -b 0.0.0.0:80 httpbin:app -k gevent",
-                    "startup": "enabled",
-                    "environment": {"thing": self.model.config["thing"]},
-                }
-            },
-        }
-        # Add initial Pebble config layer using the Pebble API
-        container.add_layer("httpbin", pebble_layer, combine=True)
-        # Autostart any services that were defined with startup: enabled
-        container.autostart()
-        # Learn more about statuses in the SDK docs:
-        # https://juju.is/docs/sdk/constructs#heading--statuses
-        self.unit.status = ActiveStatus()
+def install_tor_repo():
+    """Authenticate, install and pin the tor package to the torproject.org repo."""
+    # Installation is based on Tor installation instructions for Debian/Ubuntu:
+    # https://support.torproject.org/apt/tor-deb-repo/
+    keyring_path = "/usr/share/keyrings/tor-archive-keyring.gpg"
+    base_url = "https://deb.torproject.org/torproject.org"
 
-    def _on_config_changed(self, _):
-        """Just an example to show how to deal with changed configuration.
+    # retrieve the signing key
+    keyring_url = "{}/A3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89.asc".format(base_url)
+    with urllib.request.urlopen(keyring_url) as f:
+        keyring = f.read()
+
+    with open(keyring_path, "wb") as f:
+        f.write(keyring)
+
+    # identify our running series
+    series = get_series()
+
+    # build .list file
+    tor_list = "deb [signed-by={}] {} {} main\n".format(keyring_path, base_url, series)
+    tor_list += "deb-src [signed-by={}] {} {} main\n".format(keyring_path, base_url, series)
 
-        TEMPLATE-TODO: change this example to suit your needs.
-        If you don't need to handle config, you can remove this method,
-        the hook created in __init__.py for it, the corresponding test,
-        and the config.py file.
+    # write .list file
+    with open("/etc/apt/sources.list.d/tor.list", "wb") as f:
+        f.write(tor_list.encode('utf-8'))
 
-        Learn more about config at https://juju.is/docs/sdk/config
-        """
-        current = self.config["thing"]
-        if current not in self._stored.things:
-            logger.debug("found a new thing: %r", current)
-            self._stored.things.append(current)
+    # pin the tor package to this repo
+    pin_config = "Package: tor\n"
+    pin_config += "Pin: release c=main\n"
+    pin_config += "Pin-Priority: 900\n\n"
 
-    def _on_fortune_action(self, event):
-        """Just an example to show how to receive actions.
+    # don't use the universe version
+    pin_config += "Package: tor\n"
+    pin_config += "Pin: release c=universe\n"
+    pin_config += "Pin-Priority: 1\n\n"
 
-        TEMPLATE-TODO: change this example to suit your needs.
-        If you don't need to handle actions, you can remove this method,
-        the hook created in __init__.py for it, the corresponding test,
-        and the actions.py file.
+    with open("/etc/apt/preferences.d/tor-pin", "wb") as f:
+        f.write(pin_config.encode('utf-8'))
 
-        Learn more about actions at https://juju.is/docs/sdk/actions
-        """
-        fail = event.params["fail"]
-        if fail:
-            event.fail(fail)
-        else:
-            event.set_results({"fortune": "A bug in the code is worth two in the documentation."})
+
+def remove_tor_repo():
+    """Remove and unpin the torproject.org repo."""
+    paths = (
+        "/etc/apt/sources.list.d/tor.list",
+        "/etc/apt/preferences.d/tor-pin",
+        "/usr/share/keyrings/tor-archive-keyring.gpg",
+    )
+    for p in paths:
+        if os.path.isfile(p):
+            os.unlink(p)
+
+
+class TorCharm(CharmBase):
+    """Charm the tor service."""
+
+    _state = StoredState()
+
+    def __init__(self, *args):
+        super().__init__(*args)
+        self._state.set_default(
+            need_package_apt_transport_https=True,
+            need_package_gpg=True,
+            need_package_tor=True,
+        )
+        self.framework.observe(self.on.config_changed, self._on_config_changed)
+        self.framework.observe(
+            self.on.reverseproxy_relation_changed, self._on_reverseproxy_relation_changed
+        )
+
+    def _on_config_changed(self, _):
+        """Handle config changes."""
+        # ensure required packages are installed
+        self._ensure_apt_transport_https()
+        self._ensure_gpg()
+        self._ensure_tor()
+
+    def _ensure_apt_transport_https(self):
+        if self._state.need_package_apt_transport_https:
+            logger.info("Ensuring apt-transport-https is installed")
+            apt.add_package("apt-transport-https", update_cache=True)
+            self._state.need_package_apt_transport_https = False
+
+    def _ensure_gpg(self):
+        if self._state.need_package_gpg:
+            logger.info("Ensuring gpg is installed")
+            apt.add_package("gpg", update_cache=True)
+            self._state.need_package_gpg = False
+
+    def _ensure_tor(self):
+        if self._state.need_package_tor:
+            tor_source = self.model.config['tor_source']
+            if tor_source == 'ubuntu':
+                logger.info("Source is ubuntu, ensuring torproject repo is not set up")
+                remove_tor_repo()
+            elif tor_source == 'torproject':
+                logger.info("Source is torproject, ensuring torproject repo is set up")
+                install_tor_repo()
+            else:
+                err = "Unexpected tor_source value: {}".format(tor_source)
+                logger.error(err)
+                self.unit.status = BlockedStatus(err)
+            logger.info("Ensuring tor is installed")
+            apt.add_package("tor", update_cache=True)
+
+    def _tor_setup(self, services):
+        cfg = {}
+        cfg['socks5_port'] = self.model.config['socks5_port']
+        root_dir = '/var/lib/tor'
+        for k, v in services.items():
+            logger.info('Got service name {} with value {}'.format(k, v))
+            service_dir = '{}/{}'.format(root_dir, v.get('servername'))
+            if not os.path.isdir(service_dir):
+                subprocess.check_call(
+                    ['install', '-d', service_dir, '-o', 'debian-tor', '-m', '700']
+                )
+
+        for file in os.listdir(root_dir):
+            if os.path.isdir(file):
+                basename = os.path.basename(file)
+                for k, v in services.items():
+                    if k.get('servername') == basename:
+                        # keep this configured directory
+                        pass
+                    else:
+                        logger.info('Removing unconfigured site {}'.format(basename))
+                        shutil.rmtree(file)
+
+        # NOTE: Once the below closed issue is actually resolved[1], this function
+        # should be replaced with a built-in one in Operator Framework.
+        # [1]: https://github.com/canonical/operator/issues/228
+
+        list_services = []
+        for k, v in services.items():
+            list_services.append(v)
+
+        templates = jinja2.Environment(
+            loader=jinja2.FileSystemLoader(self.charm_dir / "templates"),
+        )
+        template = templates.get_template("torrc")
+        torrc = template.render({'cfg': cfg, 'services': list_services})
+
+        torrc_filename = '/etc/tor/torrc'
+
+        with open(torrc_filename, 'wb') as f:
+            f.write(torrc.encode('utf-8'))
+
+    def _on_reverseproxy_relation_changed(self, event: RelationChangedEvent):
+        unit_data = event.relation.data
+        logger.info(unit_data)
+        services = {}
+        for unit in unit_data:
+            if not isinstance(unit, Unit):
+                logger.info("Skipping data of type {}".format(type(unit)))
+                continue
+            if unit.name == self.unit.name:
+                logger.info("Skipping our own unit ({})".format(unit.name))
+                continue
+            logger.info("Found related unit {}".format(unit))
+
+            services.update({
+                unit.name: {
+                    'hostname': unit_data[unit].get('hostname'),
+                    'private_address': unit_data[unit].get('private-address'),
+                    'port': unit_data[unit].get('port'),
+                    'servername': unit_data[unit].get('servername'),
+                }
+            })
+        self._tor_setup(services)
 
 
 if __name__ == "__main__":
-    main(CharmTorCharm)
+    main(TorCharm)
diff --git a/templates/torrc b/templates/torrc
 new file mode 100644
index 0000000..d709005
--- /dev/null
+++ b/templates/torrc
@@ -0,0 +1,12 @@
+# torrc generated by Juju.
+# Do not edit, changes are subject to being overwritten.
+
+SocksPort 127.0.0.1:{{ cfg.socks5_port }}
+
+{% for service in services %}
+HiddenServiceDir /var/lib/tor/{{ service.servername }}/
+# service.hostname is {{ service.hostname }}
+# service.private-address is {{ service.private_address }}
+HiddenServicePort {{ service.port }} {{ service.private_address }}:{{ service.port }}
+
+{% endfor %}
diff --git a/tests/__init__.py b/tests/__init__.py
index e163492..0c77dd5 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,2 +1,6 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+
 import ops.testing
+
 ops.testing.SIMULATE_CAN_CONNECT = True
diff --git a/tests/test_charm.py b/tests/test_charm.py
index 0830b8d..c7e4d40 100644
--- a/tests/test_charm.py
+++ b/tests/test_charm.py
@@ -1,15 +1,12 @@
-# Copyright 2022 Barry Price
+# Copyright 2022 Canonical Ltd.
 # See LICENSE file for licensing details.
-#
-# Learn more about testing at: https://juju.is/docs/sdk/testing
 
 import unittest
-from unittest.mock import Mock
 
-from charm import CharmTorCharm
-from ops.model import ActiveStatus
 from ops.testing import Harness
 
+from charm import CharmTorCharm
+
 
 class TestCharm(unittest.TestCase):
     def setUp(self):
@@ -19,50 +16,5 @@ class TestCharm(unittest.TestCase):
 
     def test_config_changed(self):
         self.assertEqual(list(self.harness.charm._stored.things), [])
-        self.harness.update_config({"thing": "foo"})
-        self.assertEqual(list(self.harness.charm._stored.things), ["foo"])
-
-    def test_action(self):
-        # the harness doesn't (yet!) help much with actions themselves
-        action_event = Mock(params={"fail": ""})
-        self.harness.charm._on_fortune_action(action_event)
-
-        self.assertTrue(action_event.set_results.called)
-
-    def test_action_fail(self):
-        action_event = Mock(params={"fail": "fail this"})
-        self.harness.charm._on_fortune_action(action_event)
-
-        self.assertEqual(action_event.fail.call_args, [("fail this",)])
-
-    def test_httpbin_pebble_ready(self):
-        # Simulate making the Pebble socket available
-        self.harness.set_can_connect("httpbin", True)
-        # Check the initial Pebble plan is empty
-        initial_plan = self.harness.get_container_pebble_plan("httpbin")
-        self.assertEqual(initial_plan.to_yaml(), "{}\n")
-        # Expected plan after Pebble ready with default config
-        expected_plan = {
-            "services": {
-                "httpbin": {
-                    "override": "replace",
-                    "summary": "httpbin",
-                    "command": "gunicorn -b 0.0.0.0:80 httpbin:app -k gevent",
-                    "startup": "enabled",
-                    "environment": {"thing": "🎁"},
-                }
-            },
-        }
-        # Get the httpbin container from the model
-        container = self.harness.model.unit.get_container("httpbin")
-        # Emit the PebbleReadyEvent carrying the httpbin container
-        self.harness.charm.on.httpbin_pebble_ready.emit(container)
-        # Get the plan now we've run PebbleReady
-        updated_plan = self.harness.get_container_pebble_plan("httpbin").to_dict()
-        # Check we've got the plan we expected
-        self.assertEqual(expected_plan, updated_plan)
-        # Check the service was started
-        service = self.harness.model.unit.get_container("httpbin").get_service("httpbin")
-        self.assertTrue(service.is_running())
-        # Ensure we set an ActiveStatus with no message
-        self.assertEqual(self.harness.model.unit.status, ActiveStatus())
+        self.harness.update_config({"tor-mode": "hidden"})
+        self.assertEqual(list(self.harness.charm._stored.things), ["hidden"])
diff --git a/tox.ini b/tox.ini
 new file mode 100644
index 0000000..bca0088
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,78 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+[tox]
+skipsdist=True
+skip_missing_interpreters = True
+envlist = lint, unit
+
+[vars]
+src_path = {toxinidir}/src/
+tst_path = {toxinidir}/tests/
+lib_path = {toxinidir}/lib/charms/operator_libs_linux
+all_path = {[vars]src_path} {[vars]tst_path}
+
+[testenv]
+setenv =
+  PYTHONPATH = {toxinidir}:{toxinidir}/lib:{[vars]src_path}
+  PYTHONBREAKPOINT=ipdb.set_trace
+  PY_COLORS=1
+passenv =
+  PYTHONPATH
+  HOME
+  PATH
+  CHARM_BUILD_DIR
+  MODEL_SETTINGS
+  HTTP_PROXY
+  HTTPS_PROXY
+  NO_PROXY
+
+[testenv:fmt]
+description = Apply coding style standards to code
+deps =
+    black
+    isort
+commands =
+    isort {[vars]all_path}
+    black {[vars]all_path}
+
+[testenv:lint]
+description = Check code against coding style standards
+deps =
+    black
+    flake8
+    flake8-docstrings
+    flake8-copyright
+    flake8-builtins
+    pyproject-flake8
+    pep8-naming
+    isort
+    codespell
+commands =
+    codespell {toxinidir}/*.yaml {toxinidir}/*.ini {toxinidir}/*.md \
+      {toxinidir}/*.toml {toxinidir}/*.txt {toxinidir}/.github
+    # pflake8 wrapper supports config from pyproject.toml
+    pflake8 {[vars]all_path}
+    isort --check-only --diff {[vars]all_path}
+    black --check --diff {[vars]all_path}
+
+[testenv:unit]
+description = Run unit tests
+deps =
+    pytest
+    coverage[toml]
+    -r{toxinidir}/requirements.txt
+commands =
+    coverage run --source={[vars]src_path} \
+        -m pytest --ignore={[vars]tst_path}integration -v --tb native -s {posargs}
+    coverage report
+
+[testenv:integration]
+description = Run integration tests
+deps =
+    git+https://github.com/juju/python-libjuju.git
+    pytest
+    git+https://github.com/charmed-kubernetes/pytest-operator.git
+    -r{toxinidir}/requirements.txt
+commands =
+    pytest -v --tb native --ignore={[vars]tst_path}unit --log-cli-level=INFO -s {posargs}