Add the mandatory_close_duration plugin

Author: Qwerty-133

mandatory_close_duration/mandatory_close_duration.py

@@ -0,0 +1,67 @@
+from discord.ext import commands
+
+from bot import ModmailBot
+from core import time
+
+
+class StrictUserFriendlyDuration(time.UserFriendlyTime):
+    """
+    A converter which parses user-friendly time durations.
+
+    Since this converter is meant for parsing close messages while
+    closing threads, both custom close messages and time durations are
+    parsed.
+
+    Unlike the parent class, a time duration must be provided when
+    a custom close message is provided.
+    """
+
+    MODIFIERS = {'silently', 'silent', 'cancel'}
+
+    async def convert(self, ctx: commands.Context, argument: str) -> "StrictUserFriendlyDuration":
+        """
+        Parse the provided time duration along with any close message.
+
+        Fail if a custom close message is provided without a time
+        duration.
+        """
+        await super().convert(ctx, argument)
+
+        argument_passed = bool(argument)
+        not_a_modifier = argument not in self.MODIFIERS
+        if argument_passed and not_a_modifier and self.arg == argument:
+            # Fail since only a close message was provided.
+            raise commands.BadArgument("A time duration must be provided when closing with a custom message.")
+
+        return self
+
+
+ADDED_HELP_TEXT = '\n\n*Note: Providing a time duration is necessary when closing with a custom message.*'
+
+
+def setup(bot: ModmailBot) -> None:
+    """
+    Monkey patch the close command's callback.
+
+    This makes it use the StrictUserFriendlyTime converter and updates
+    the help text to reflect the new behaviour..
+    """
+    global previous_converter
+
+    command = bot.get_command('close')
+
+    previous_converter = command.callback.__annotations__['after']
+    command.callback.__annotations__['after'] = StrictUserFriendlyDuration
+    command.callback = command.callback
+
+    command.help += ADDED_HELP_TEXT
+
+
+def teardown(bot: ModmailBot) -> None:
+    """Undo changes to the close command."""
+    command = bot.get_command('close')
+
+    command.callback.__annotations__['after'] = previous_converter
+    command.callback = command.callback
+
+    command.help = command.help.remove_suffix(ADDED_HELP_TEXT)