books: Add Loader.dispatch() classmethod.

conservancy_beancount/books.py

@@ -254,3 +254,16 @@ class Loader:
             'lineno': lineno,
         }
         return LoadResult.empty(Error(source, "no books to load in configuration", None))
+
+    @classmethod
+    def dispatch(cls,
+                loader: Optional['Loader'],
+                from_fy: Optional[Year]=None,
+                to_fy: Optional[Year]=None,
+    ) -> LoadResult:
+        if loader is None:
+            return cls.load_none()
+        elif to_fy is None:
+            return loader.load_all(from_fy)
+        else:
+            return loader.load_fy_range(from_fy or 0, to_fy)

tests/test_books_loader.py

@@ -225,3 +225,52 @@ def test_load_none_no_args():
     assert errors
     assert all(isinstance(err.source['filename'], str) for err in errors)
     assert all(isinstance(err.source['lineno'], int) for err in errors)
+
+def test_dispatch_empty():
+    result = books.Loader.dispatch(None)
+    assert not result.entries
+    assert result.errors
+
+@pytest.mark.parametrize('from_arg', [
+    None,
+    *range(2018, 2021),
+    date(2019, 2, 1),
+    date(2019, 9, 15),
+    date(2020, 1, 20),
+    date(2020, 5, 31),
+])
+def test_dispatch_load_all_from_year(conservancy_loader, from_arg):
+    try:
+        from_year = from_arg.year
+    except AttributeError:
+        from_year = from_arg or 2018
+    else:
+        if from_arg.month < FY_START_MONTH:
+            from_year -= 1
+    result = books.Loader.dispatch(conservancy_loader, from_arg)
+    check_openings(result.entries)
+    actual_years = txn_years(result.entries)
+    assert actual_years.issuperset(range(from_year, 2021))
+    assert min(actual_years) == from_year
+    assert not result.errors
+
+@pytest.mark.parametrize('from_arg,to_arg,expected', [
+    (2019, 2019, range(2019, 2020)),
+    (0, 2019, range(2019, 2020)),
+    (2018, 2019, range(2018, 2020)),
+    (1, 2018, range(2018, 2020)),
+    (-1, 2019, range(2018, 2020)),
+    (2019, 2020, range(2019, 2021)),
+    (1, 2019, range(2019, 2021)),
+    (-1, 2020, range(2019, 2021)),
+    (2010, 2030, range(2018, 2021)),
+    (20, 2010, range(2018, 2021)),
+    (-20, 2030, range(2018, 2021)),
+])
+def test_dispatch_load_all_fy_range(conservancy_loader, from_arg, to_arg, expected):
+    result = books.Loader.dispatch(conservancy_loader, from_arg, to_arg)
+    check_openings(result.entries)
+    actual_years = txn_years(result.entries)
+    assert actual_years.issuperset(iter(expected))
+    assert min(actual_years) == expected.start
+    assert not result.errors