add configuration handling module

This module contains the logic to load default, system-wide and, if
specified, additional configuration files and merges them into two
dictionaries: `config` and `email_overrides`.

Signed-off-by: Nils Philippsen <nils@redhat.com>

distgit_bugzilla_sync/config.py

@@ -0,0 +1,151 @@
+# distgit_bugzilla_sync.config - handle configuration
+#
+# Copyright © 2018-2019  Red Hat, Inc.
+#
+# This copyrighted material is made available to anyone wishing to use, modify,
+# copy, or redistribute it subject to the terms and conditions of the GNU
+# General Public License v.2, or (at your option) any later version.  This
+# program is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY expressed or implied, including the implied warranties of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+# Public License for more details.  You should have received a copy of the GNU
+# General Public License along with this program; if not, write to the Free
+# Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA. Any Red Hat trademarks that are incorporated in the source
+# code or documentation are not subject to the GNU General Public License and
+# may only be used or replicated with the express permission of Red Hat, Inc.
+
+import os
+
+import toml
+
+
+_here = os.path.dirname(__file__)
+_default_conf_root = os.path.join(_here, 'default-config-files')
+_system_conf_root = '/etc'
+
+config_files = {
+    'default': {
+        'configuration': os.path.join(_default_conf_root, 'configuration.toml'),
+        'email_overrides': os.path.join(_default_conf_root, 'email_overrides.toml'),
+    },
+    'system': {
+        'configuration': os.path.join(_system_conf_root, 'configuration.toml'),
+        'email_overrides': os.path.join(_system_conf_root, 'email_overrides.toml'),
+    },
+}
+
+
+class ConfigDict(dict):
+    """Dictionary class for configuration data.
+
+    This contains a modified update() method which allows deep-merging other
+    dictionaries."""
+
+    def update(self, other: dict):
+        """Merge data from another dictionary into this one.
+
+        Fails if any node isn't of the same type in both, to detect
+        configuration format issues early."""
+        self_set = set(self)
+        other_set = set(other)
+
+        type_error = False
+
+        # keys that are in both self and other
+        for k in self_set & other_set:
+            self_val = self[k]
+            other_val = other[k]
+            if isinstance(other_val, dict):
+                if isinstance(self_val, ConfigDict):
+                    self_val.update(other_val)
+                elif isinstance(self_val, dict):
+                    self[k] = ConfigDict(self_val)
+                    self[k].update(other_val)
+                else:
+                    type_error = True
+            elif isinstance(other_val, type(self_val)):
+                self[k] = other_val
+            else:
+                type_error = True
+
+            if type_error:
+                raise TypeError(
+                    f"[{k!r}] values of incompatible types: {self_val!r}, {other_val!r}"
+                )
+
+        # add keys -> values which are missing
+        for k in other_set - self_set:
+            v = other[k]
+            if isinstance(v, dict):
+                self[k] = ConfigDict(v)
+            else:
+                self[k] = v
+
+
+def load_configuration(addl_config_file=None, addl_email_overrides_file=None):
+    """Load stored configuration.
+
+    This function loads default, system-wide, and if specified, additional
+    configuration files into the `config` and `email_overrides`
+    dictionaries."""
+    # Load default files.
+    try:
+        default_config = toml.load(config_files['default']['configuration'])
+    except FileNotFoundError as e:
+        raise RuntimeError(
+            f"Default configuration file {config_files['default']['configuration']} not found."
+        ) from e
+
+    try:
+        default_email_overrides = toml.load(config_files['default']['email_overrides'])
+    except FileNotFoundError as e:
+        raise RuntimeError(
+            f"Default email overrides file {config_files['default']['email_overrides']} not found."
+        ) from e
+
+    # Attempt to load system-wide files.
+    try:
+        system_config = toml.load(config_files['system']['configuration'])
+    except FileNotFoundError:
+        system_config = {}
+
+    try:
+        system_email_overrides = toml.load(config_files['system']['email_overrides'])
+    except FileNotFoundError:
+        system_email_overrides = {}
+
+    # Load additional files (say, specified on the command line), if any.
+    if addl_config_file:
+        try:
+            addl_config = toml.load(addl_config_file)
+        except FileNotFoundError as e:
+            raise RuntimeError(
+                f"Additional configuration file {addl_config_file} not found."
+            ) from e
+    else:
+        addl_config = {}
+
+    if addl_email_overrides_file:
+        try:
+            addl_email_overrides = toml.load(addl_email_overrides_file)
+        except FileNotFoundError as e:
+            raise RuntimeError(
+                f"Additional email overrides file {addl_email_overrides_file} not found."
+            ) from e
+    else:
+        addl_email_overrides = {}
+
+    config.clear()
+    config.update(default_config)
+    config.update(system_config)
+    config.update(addl_config)
+
+    email_overrides.clear()
+    email_overrides.update(default_email_overrides)
+    email_overrides.update(system_email_overrides)
+    email_overrides.update(addl_email_overrides)
+
+
+config = ConfigDict()
+email_overrides = ConfigDict()

requirements.txt

@@ -4,4 +4,5 @@ dogpile.cache
 python-fedora
 PyYAML
 requests
+toml
 urllib3