config: Start configuration file with books path.

Ultimately I would like to make it possible to configure the software
entirely through this file, rather than the hodgepodge system we have
now. But that can come later.

conservancy_beancount/config.py

@@ -14,6 +14,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+import configparser
 import decimal
 import functools
 import os
@@ -74,6 +75,15 @@ class Config:
         'XDG_CONFIG_HOME': Path('.config'),
     }
 
+    def __init__(self) -> None:
+        self.file_config = configparser.ConfigParser()
+
+    def load_file(self, config_path: Optional[Path]=None) -> None:
+        if config_path is None:
+            config_path = self.config_file_path()
+        with config_path.open() as config_file:
+            self.file_config.read_file(config_file)
+
     def _dir_or_none(self, path: Path) -> Optional[Path]:
         try:
             path.mkdir(exist_ok=True)
@@ -94,6 +104,15 @@ class Config:
             retval = default or (Path.home() / self._ENVIRON_DEFAULT_PATHS[key])
         return retval
 
+    def books_path(self) -> Optional[Path]:
+        try:
+            retval = Path(self.file_config['Beancount'].get('books dir'))
+        except (KeyError, ValueError):
+            ok = False
+        else:
+            ok = retval.is_absolute()
+        return retval if ok else None
+
     def cache_dir_path(self, name: str='conservancy_beancount') -> Optional[Path]:
         cache_root = self._path_from_environ('XDG_CACHE_HOME')
         return (

tests/test_config.py

@@ -16,6 +16,7 @@
 
 import contextlib
 import decimal
+import operator
 import os
 import re
 
@@ -317,3 +318,27 @@ def test_config_file_path_with_subdir():
     expected = testutil.test_path('userconfig/conftest/config.ini')
     config = config_mod.Config()
     assert config.config_file_path('conftest') == expected
+
+@pytest.mark.parametrize('path', [
+    None,
+    testutil.test_path('userconfig/conservancy_beancount/config.ini'),
+])
+def test_load_file(path):
+    config = config_mod.Config()
+    config.load_file(path)
+    assert config.books_path() == Path('/test/conservancy_beancount')
+
+@pytest.mark.parametrize('path_func', [
+    lambda path: None,
+    operator.methodcaller('touch', 0o200),
+])
+def test_load_file_error(tmp_path, path_func):
+    config_path = tmp_path / 'nonexistent.ini'
+    path_func(config_path)
+    config = config_mod.Config()
+    with pytest.raises(OSError):
+        config.load_file(config_path)
+
+def test_no_books_path():
+    config = config_mod.Config()
+    assert config.books_path() is None