config: Accept a source date for displaying rates.

For output formats that can show both a cost and a price,
this will be used to distinguish them.

oxrlib/config.py

@@ -26,7 +26,7 @@ class Configuration:
     DEFAULT_CONFIG_PATH = pathlib.Path(HOME_PATH, '.config', 'oxrlib.ini')
     LOCALE = babel.core.Locale.default()
     SENTINEL = object()
-    PREPOSITIONS = frozenset(['in', 'to', 'into'])
+    CURRENCY_PREPOSITIONS = frozenset(['in', 'to', 'into'])
     TODAY = datetime.date.today()
 
     def __init__(self, arglist):
@@ -152,7 +152,13 @@ class Configuration:
             help="Convert or show rates to this currency, in three-letter code format. "
             "If not specified, defaults to the user's preferred currency.",
         )
-        hist_parser.add_argument('word4', nargs='?', help=argparse.SUPPRESS)
+        hist_parser.add_argument(
+            'word4', nargs='?', metavar='from date',
+            help="Include source rates for this date, if provided. "
+            "Raw output format does not show source rates.",
+        )
+        hist_parser.add_argument('word5', nargs='?', help=argparse.SUPPRESS)
+        hist_parser.add_argument('word6', nargs='?', help=argparse.SUPPRESS)
 
         return prog_parser
 
@@ -208,7 +214,7 @@ class Configuration:
         self._read_from_conffile('signed_currencies', 'Historical', pref_currency,
                                  currency_list, convert_fallback=True)
         self._read_from_conffile('ledger', 'Historical', False, getter='getboolean')
-        raw_words = iter(getattr(self.args, 'word' + c) for c in '1234')
+        raw_words = iter(getattr(self.args, 'word' + c) for c in '123456')
         words = iter(word for word in raw_words if word is not None)
         try:
             next_word = next(words)
@@ -221,11 +227,35 @@ class Configuration:
                 # If it wasn't, set a value that can't be parsed as a currency.
                 next_word = next(words, 'none given')
             self.args.from_currency = self._convert_or_error(currency_code, next_word)
-            next_word = next(words)
-            if next_word.lower() in self.PREPOSITIONS:
-                next_word = next(words, next_word)
-            self.args.to_currency = self._convert_or_error(currency_code, next_word)
         except StopIteration:
+            pass
+        self.args.to_currency = None
+        self.args.from_date = None
+        for next_word in words:
+            next_lower = next_word.lower()
+            if next_lower in self.CURRENCY_PREPOSITIONS:
+                attr_to_set = 'to_currency'
+                next_word = next(words, 'none given')
+            elif next_lower == 'from':
+                attr_to_set = 'from_date'
+                next_word = next(words, 'none given')
+            elif next_word.isalpha():
+                attr_to_set = 'to_currency'
+            else:
+                attr_to_set = 'from_date'
+            have_arg = getattr(self.args, attr_to_set)
+            if have_arg is not None:
+                self.error(f"tried to set {attr_to_set.replace('_', ' ')} multiple times")
+            elif attr_to_set == 'from_date':
+                convert_func = lambda s: self._date_from_s(s)[0]
+                typename = 'date'
+            else:
+                convert_func = currency_code
+                typename = None
+            setattr(self.args, attr_to_set, self._convert_or_error(
+                convert_func, next_word, attr_to_set, typename,
+            ))
+        if self.args.to_currency is None:
             self.args.to_currency = pref_currency
         if ((len(date_spec) == 1)
             and self.args.from_currency

tests/test_Configuration.py

@@ -46,26 +46,34 @@ def test_historical_default_base(ini_filename, expected_currency, use_switch, an
     config = config_from(ini_filename, arglist)
     assert config.args.base == expected_currency
 
-@pytest.mark.parametrize('amount,from_curr,preposition,to_curr', [
+@pytest.mark.parametrize('amount,from_curr,prep1,to_curr,prep2,from_date', [
-    (None, 'JPY', None, None),
+    (None, 'JPY', None, None, None, None),
-    (None, 'gbp', None, 'Aud'),
+    (None, 'gbp', None, 'Aud', None, None),
-    (None, 'CHF', 'to', 'eur'),
+    (None, 'CHF', 'to', 'eur', None, None),
-    (decimal.Decimal('1000'), 'chf', None, None),
+    (decimal.Decimal('1000'), 'chf', None, None, None, None),
-    (decimal.Decimal('999'), 'Eur', None, 'Chf'),
+    (decimal.Decimal('999'), 'Eur', None, 'Chf', None, None),
-    (decimal.Decimal('12.34'), 'gbp', 'IN', 'eur'),
+    (decimal.Decimal('12.34'), 'gbp', 'IN', 'eur', None, None),
+    (None, 'JPY', None, None, None, '12-15'),
+    (None, 'gbp', None, 'Aud', 'From', '12.15'),
+    (None, 'CHF', 'to', 'eur', 'from', '15'),
+    (decimal.Decimal('1000'), 'chf', None, None, None, '12-15'),
+    (decimal.Decimal('999'), 'Eur', None, 'Chf', None, '2016.12.15'),
+    (decimal.Decimal('12.34'), 'gbp', 'IN', 'eur', 'from', '2016-12-15'),
 ])
-def test_historical_argparsing_success(amount, from_curr, preposition, to_curr, any_date):
+def test_historical_argparsing_success(amount, from_curr, prep1, to_curr, prep2, from_date, any_date):
     oxrlib.config.Configuration.TODAY = datetime.date(2017, 1, 1)
     # This locale's currency should not be used in any test cases above.
     oxrlib.config.Configuration.LOCALE = babel.core.Locale('en', 'IN')
     arglist = ['historical', any_date.isoformat()]
-    arglist.extend(str(s) for s in [amount, from_curr, preposition, to_curr]
+    arglist.extend(str(s) for s in [amount, from_curr, prep1, to_curr, prep2, from_date]
                    if s is not None)
     config = config_from(os.devnull, arglist)
     expect_to_curr = 'INR' if to_curr is None else to_curr.upper()
     assert config.args.amount == amount
     assert config.args.from_currency == from_curr.upper()
     assert config.args.to_currency == expect_to_curr
+    expect_from_date = None if from_date is None else datetime.date(2016, 12, 15)
+    assert config.args.from_date == expect_from_date
 
 @pytest.mark.parametrize('arglist', [
     ['100'],
@@ -76,6 +84,10 @@ def test_historical_argparsing_success(amount, from_curr, preposition, to_curr,
     ['44', 'eur', 'in', 'chf', 'pronto'],
     ['eur', 'into'],
     ['50', 'jpy', 'in'],
+    ['115', 'usd', 'in', '12-15'],
+    ['125', 'jpy', 'from', 'chf'],
+    ['135', 'chf', 'eur', 'gbp'],
+    ['145', 'brl', '12-16', '2020-12-18'],
 ])
 def test_historical_argparsing_failure(arglist, any_date):
     arglist = ['historical', any_date.isoformat()] + arglist