config: Add Config.config_file_path() method.

conservancy_beancount/config.py

@@ -69,6 +69,11 @@ class RTCredentials(NamedTuple):
 
 
 class Config:
+    _ENVIRON_DEFAULT_PATHS = {
+        'XDG_CACHE_HOME': Path('.cache'),
+        'XDG_CONFIG_HOME': Path('.config'),
+    }
+
     def _dir_or_none(self, path: Path) -> Optional[Path]:
         try:
             path.mkdir(exist_ok=True)
@@ -77,21 +82,29 @@ class Config:
         else:
             return path
 
-    def cache_dir_path(self, name: str='conservancy_beancount') -> Optional[Path]:
+    def _path_from_environ(self, key: str, default: Optional[Path]=None) -> Path:
         try:
-            cache_root = Path(os.environ['XDG_CACHE_HOME'])
+            retval = Path(os.environ[key])
         except (KeyError, ValueError):
             ok = False
         else:
             # Per the spec, non-absolute paths should be ignored.
-            ok = cache_root.is_absolute()
+            ok = retval.is_absolute()
         if not ok:
-            cache_root = Path.home() / '.cache'
+            retval = default or (Path.home() / self._ENVIRON_DEFAULT_PATHS[key])
+        return retval
+
+    def cache_dir_path(self, name: str='conservancy_beancount') -> Optional[Path]:
+        cache_root = self._path_from_environ('XDG_CACHE_HOME')
         return (
             self._dir_or_none(cache_root)
             and self._dir_or_none(cache_root / name)
         )
 
+    def config_file_path(self, name: str='conservancy_beancount') -> Path:
+        config_root = self._path_from_environ('XDG_CONFIG_HOME')
+        return Path(config_root, name, 'config.ini')
+
     def payment_threshold(self) -> decimal.Decimal:
         return decimal.Decimal(0)
 

tests/test_config.py

@@ -19,6 +19,8 @@ import decimal
 import os
 import re
 
+from pathlib import Path
+
 import pytest
 
 from . import testutil
@@ -294,3 +296,24 @@ def test_payment_threshold():
     threshold = config_mod.Config().payment_threshold()
     assert threshold == 0
     assert isinstance(threshold, (int, decimal.Decimal))
+
+@pytest.mark.parametrize('config_path', [
+    None,
+    '',
+    'nonexistent/relative/path',
+])
+def test_config_file_path(config_path):
+    expected = Path('~/.config/conservancy_beancount/config.ini').expanduser()
+    with update_environ(XDG_CONFIG_HOME=config_path):
+        config = config_mod.Config()
+        assert config.config_file_path() == expected
+
+def test_config_file_path_respects_xdg_config_home():
+    with update_environ(XDG_CONFIG_HOME='/etc'):
+        config = config_mod.Config()
+        assert config.config_file_path() == Path('/etc/conservancy_beancount/config.ini')
+
+def test_config_file_path_with_subdir():
+    expected = Path('~/.config/conftest/config.ini').expanduser()
+    config = config_mod.Config()
+    assert config.config_file_path('conftest') == expected