config: Add Config.fiscal_year_begin() method.

conservancy_beancount/config.py

@@ -15,9 +15,11 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 import configparser
+import datetime
 import decimal
 import functools
 import os
+import re
 import urllib.parse as urlparse
 
 import requests.auth
@@ -27,6 +29,7 @@ from pathlib import Path
 from typing import (
     NamedTuple,
     Optional,
+    Tuple,
     Type,
 )
 
@@ -84,6 +87,9 @@ class Config:
         with config_path.open() as config_file:
             self.file_config.read_file(config_file)
 
+    def load_string(self, config_str: str) -> None:
+        self.file_config.read_string(config_str)
+
     def _dir_or_none(self, path: Path) -> Optional[Path]:
         try:
             path.mkdir(exist_ok=True)
@@ -124,6 +130,24 @@ class Config:
         config_root = self._path_from_environ('XDG_CONFIG_HOME')
         return Path(config_root, name, 'config.ini')
 
+    def fiscal_year_begin(self) -> Tuple[int, int]:
+        s = self.file_config.get('Beancount', 'fiscal year begin', fallback='3 1')
+        match = re.match(r'([01]?[0-9])(?:\s*[-./ ]\s*([0-3]?[0-9]))?$', s.strip())
+        if match is None:
+            raise ValueError(f"fiscal year begin {s!r} has unknown format")
+        try:
+            month = int(match.group(1))
+            day = int(match.group(2) or 1)
+            # To check date validity we use an arbitrary year that's
+            # 1. definitely using the modern calendar
+            # 2. far enough in the past to not have books (pre-Unix epoch)
+            # 3. not a leap year
+            datetime.date(1959, month, day)
+        except ValueError as e:
+            raise ValueError(f"fiscal year begin {s!r} is invalid date: {e.args[0]}")
+        else:
+            return (month, day)
+
     def payment_threshold(self) -> decimal.Decimal:
         return decimal.Decimal(0)
 

tests/test_config.py

@@ -342,3 +342,40 @@ def test_load_file_error(tmp_path, path_func):
 def test_no_books_path():
     config = config_mod.Config()
     assert config.books_path() is None
+
+@pytest.mark.parametrize('value,month,day', [
+    ('2', 2, 1),
+    ('3 ', 3, 1),
+    ('  4', 4, 1),
+    (' 5 ', 5, 1),
+    ('6 1', 6, 1),
+    ('  06  03  ', 6, 3),
+    ('6-05', 6, 5),
+    ('06 - 10', 6, 10),
+    ('6/15', 6, 15),
+    ('06  /  20', 6, 20),
+    ('10.25', 10, 25),
+    (' 10 . 30 ', 10, 30),
+])
+def test_fiscal_year_begin(value, month, day):
+    config = config_mod.Config()
+    config.load_string(f'[Beancount]\nfiscal year begin = {value}\n')
+    assert config.fiscal_year_begin() == (month, day)
+
+@pytest.mark.parametrize('value', [
+    'text',
+    '1900',
+    '13',
+    '010',
+    '2 30',
+    '4-31',
+])
+def test_bad_fiscal_year_begin(value):
+    config = config_mod.Config()
+    config.load_string(f'[Beancount]\nfiscal year begin = {value}\n')
+    with pytest.raises(ValueError):
+        config.fiscal_year_begin()
+
+def test_default_fiscal_year_begin():
+    config = config_mod.Config()
+    assert config.fiscal_year_begin() == (3, 1)