config: Add Config.cache_dir_path method.

conservancy_beancount/config.py

@@ -68,6 +68,24 @@ class RTCredentials(NamedTuple):
 
 
 class Config:
+    def _dir_or_none(self, path: Path) -> Optional[Path]:
+        try:
+            path.mkdir(exist_ok=True)
+        except OSError:
+            return None
+        else:
+            return path
+
+    def cache_dir_path(self, name: str='conservancy_beancount') -> Optional[Path]:
+        try:
+            cache_root = Path(os.environ['XDG_CACHE_DIR'])
+        except (KeyError, ValueError):
+            cache_root = Path.home() / '.cache'
+        return (
+            self._dir_or_none(cache_root)
+            and self._dir_or_none(cache_root / name)
+        )
+
     def repository_path(self) -> Optional[Path]:
         try:
             return Path(os.environ['CONSERVANCY_REPOSITORY'])

tests/conftest.py

@@ -5,10 +5,11 @@ import pytest
 from . import testutil
 
 @pytest.fixture(scope='session', autouse=True)
-def clean_environment():
+def clean_environment(tmpdir_factory):
     os.environ.pop('RTAUTH', None)
     os.environ.pop('RTPASSWD', None)
     os.environ.pop('RTSERVER', None)
     os.environ.pop('RTUSER', None)
     os.environ['CONSERVANCY_REPOSITORY'] = str(testutil.test_path('repository'))
     os.environ['HOME'] = str(testutil.test_path('userconfig'))
+    os.environ['XDG_CACHE_DIR'] = str(tmpdir_factory.mktemp('.cache'))

tests/test_config.py

@@ -206,3 +206,51 @@ def test_rt_wrapper_cache_responds_to_external_credential_changes(rt_environ):
     with update_environ(**rt_environ):
         rt2 = config.rt_wrapper(None, testutil.RTClient)
     assert rt1 is not rt2
+
+def test_cache_mkdir(tmp_path):
+    expected = tmp_path / 'TESTcache'
+    with update_environ(XDG_CACHE_DIR=tmp_path):
+        config = config_mod.Config()
+        cache_path = config.cache_dir_path(expected.name)
+    assert cache_path == tmp_path / 'TESTcache'
+    assert cache_path.is_dir()
+
+def test_cache_mkdir_parent(tmp_path):
+    xdg_cache_dir = tmp_path / 'xdgcache'
+    expected = xdg_cache_dir / 'conservancy_beancount'
+    with update_environ(XDG_CACHE_DIR=xdg_cache_dir):
+        config = config_mod.Config()
+        cache_path = config.cache_dir_path(expected.name)
+    assert cache_path == expected
+    assert cache_path.is_dir()
+
+def test_cache_mkdir_from_home(tmp_path):
+    expected = tmp_path / '.cache' / 'TESTcache'
+    with update_environ(HOME=tmp_path, XDG_CACHE_DIR=None):
+        config = config_mod.Config()
+        cache_path = config.cache_dir_path(expected.name)
+    assert cache_path == expected
+    assert cache_path.is_dir()
+
+def test_cache_mkdir_exists_ok(tmp_path):
+    expected = tmp_path / 'TESTcache'
+    expected.mkdir()
+    with update_environ(XDG_CACHE_DIR=tmp_path):
+        config = config_mod.Config()
+        cache_path = config.cache_dir_path(expected.name)
+    assert cache_path == expected
+
+def test_cache_path_conflict(tmp_path):
+    extant_path = tmp_path / 'TESTcache'
+    extant_path.touch()
+    with update_environ(XDG_CACHE_DIR=tmp_path):
+        config = config_mod.Config()
+        cache_path = config.cache_dir_path(extant_path.name)
+    assert cache_path is None
+    assert extant_path.is_file()
+
+def test_cache_path_parent_conflict(tmp_path):
+    (tmp_path / '.cache').touch()
+    with update_environ(HOME=tmp_path, XDG_CACHE_DIR=None):
+        config = config_mod.Config()
+        assert config.cache_dir_path('TESTcache') is None