Fix failing duration conversion

https://github.com/python-discord/bot/issues/446

The current ExpirationDate converter does not convert duration strings
to `datetime.datetime` objects correctly. To remedy the problem, I've
written a new Duration converter that uses regex matching to extract
the relevant duration units and `dateutil.relativedelta.relativedelta`
to compute a `datetime.datetime` that's the given duration in the
future.

I've left the old `ExpirationDate` converter in place for now, since
the new Duration converter may not be the most optimal method. However,
given the importance of being able to convert durations for moderation
tasks, I think it's better to implement Duration now and rethink the
approach later.

This commit closes #446

1 files changed, 78 insertions, 4 deletions

diff --git a/tests/test_converters.py b/tests/test_converters.py
index 3cf774c80..3cf00035f 100644
--- a/tests/test_converters.py
+++ b/tests/test_converters.py
@@ -1,11 +1,12 @@
 import asyncio
-from datetime import datetime
-from unittest.mock import MagicMock
+import datetime
+from unittest.mock import MagicMock, patch
 
 import pytest
 from discord.ext.commands import BadArgument
 
 from bot.converters import (
+    Duration,
     ExpirationDate,
     TagContentConverter,
     TagNameConverter,
@@ -17,10 +18,10 @@ from bot.converters import (
     ('value', 'expected'),
     (
         # sorry aliens
-        ('2199-01-01T00:00:00', datetime(2199, 1, 1)),
+        ('2199-01-01T00:00:00', datetime.datetime(2199, 1, 1)),
     )
 )
-def test_expiration_date_converter_for_valid(value: str, expected: datetime):
+def test_expiration_date_converter_for_valid(value: str, expected: datetime.datetime):
     converter = ExpirationDate()
     assert asyncio.run(converter.convert(None, value)) == expected
 
@@ -91,3 +92,76 @@ def test_valid_python_identifier_for_valid(value: str):
 def test_valid_python_identifier_for_invalid(value: str):
     with pytest.raises(BadArgument, match=f'`{value}` is not a valid Python identifier'):
         asyncio.run(ValidPythonIdentifier.convert(None, value))
+
+
+FIXED_UTC_NOW = datetime.datetime.fromisoformat('2019-01-01T00:00:00')
+
+
[email protected](
+    ('duration', 'expected'),
+    (
+        # Simple duration strings
+        ('1Y', datetime.datetime.fromisoformat('2020-01-01T00:00:00')),
+        ('1y', datetime.datetime.fromisoformat('2020-01-01T00:00:00')),
+        ('1year', datetime.datetime.fromisoformat('2020-01-01T00:00:00')),
+        ('1years', datetime.datetime.fromisoformat('2020-01-01T00:00:00')),
+        ('1m', datetime.datetime.fromisoformat('2019-02-01T00:00:00')),
+        ('1month', datetime.datetime.fromisoformat('2019-02-01T00:00:00')),
+        ('1months', datetime.datetime.fromisoformat('2019-02-01T00:00:00')),
+        ('1w', datetime.datetime.fromisoformat('2019-01-08T00:00:00')),
+        ('1W', datetime.datetime.fromisoformat('2019-01-08T00:00:00')),
+        ('1week', datetime.datetime.fromisoformat('2019-01-08T00:00:00')),
+        ('1weeks', datetime.datetime.fromisoformat('2019-01-08T00:00:00')),
+        ('1d', datetime.datetime.fromisoformat('2019-01-02T00:00:00')),
+        ('1D', datetime.datetime.fromisoformat('2019-01-02T00:00:00')),
+        ('1day', datetime.datetime.fromisoformat('2019-01-02T00:00:00')),
+        ('1days', datetime.datetime.fromisoformat('2019-01-02T00:00:00')),
+        ('1h', datetime.datetime.fromisoformat('2019-01-01T01:00:00')),
+        ('1H', datetime.datetime.fromisoformat('2019-01-01T01:00:00')),
+        ('1hour', datetime.datetime.fromisoformat('2019-01-01T01:00:00')),
+        ('1hours', datetime.datetime.fromisoformat('2019-01-01T01:00:00')),
+        ('1M', datetime.datetime.fromisoformat('2019-01-01T00:01:00')),
+        ('1minute', datetime.datetime.fromisoformat('2019-01-01T00:01:00')),
+        ('1minutes', datetime.datetime.fromisoformat('2019-01-01T00:01:00')),
+        ('1s', datetime.datetime.fromisoformat('2019-01-01T00:00:01')),
+        ('1S', datetime.datetime.fromisoformat('2019-01-01T00:00:01')),
+        ('1second', datetime.datetime.fromisoformat('2019-01-01T00:00:01')),
+        ('1seconds', datetime.datetime.fromisoformat('2019-01-01T00:00:01')),
+
+        # Complex duration strings
+        ('1y1m1w1d1H1M1S', datetime.datetime.fromisoformat('2020-02-09T01:01:01')),
+        ('5y100S', datetime.datetime.fromisoformat('2024-01-01T00:01:40')),
+        ('2w28H', datetime.datetime.fromisoformat('2019-01-16T04:00:00')),
+    )
+)
+def test_duration_converter_for_valid(duration: str, expected: datetime):
+    converter = Duration()
+
+    with patch('bot.converters.datetime') as mock_datetime:
+        mock_datetime.utcnow.return_value = FIXED_UTC_NOW
+        assert asyncio.run(converter.convert(None, duration)) == expected
+
+
[email protected](
+    ('duration'),
+    (
+        # Units in wrong order
+        ('1d1w'),
+        ('1s1y'),
+
+        # Unknown substrings
+        ('1MVes'),
+        ('1y3breads'),
+
+        # Missing amount
+        ('ym'),
+
+        # Garbage
+        ('Guido van Rossum'),
+        ('lemon lemon lemon lemon lemon lemon lemon'),
+    )
+)
+def test_duration_converter_for_invalid(duration: str):
+    converter = Duration()
+    with pytest.raises(BadArgument, match=f'`{duration}` is not a valid duration string.'):
+        asyncio.run(converter.convert(None, duration))