Implement in_month command check

Commands decorated with in_month can only be used in one of the allowed
months.

1 files changed, 20 insertions, 1 deletions

diff --git a/bot/decorators.py b/bot/decorators.py
index d0371df4..8a1f00ee 100644
--- a/bot/decorators.py
+++ b/bot/decorators.py
@@ -2,6 +2,7 @@ import logging
 import random
 import typing
 from asyncio import Lock
+from datetime import datetime
 from functools import wraps
 from weakref import WeakValueDictionary
 
@@ -9,7 +10,7 @@ from discord import Colour, Embed
 from discord.ext import commands
 from discord.ext.commands import CheckFailure, Context
 
-from bot.constants import ERROR_REPLIES
+from bot.constants import ERROR_REPLIES, Month
 
 log = logging.getLogger(__name__)
 
@@ -20,6 +21,24 @@ class InChannelCheckFailure(CheckFailure):
     pass
 
 
+def in_month(*allowed_months: Month) -> typing.Callable:
+    """
+    Check whether the command was invoked in one of `enabled_months`.
+
+    Uses the current UTC month at the time of running the predicate.
+    """
+    async def predicate(ctx: Context) -> bool:
+        current_month = datetime.utcnow().month
+        can_run = current_month in allowed_months
+
+        log.debug(
+            f"Command '{ctx.command}' is locked to months {allowed_months}. "
+            f"Invoking it in month {current_month} is {'allowed' if can_run else 'disallowed'}."
+        )
+        return can_run
+    return commands.check(predicate)
+
+
 def with_role(*role_ids: int) -> typing.Callable:
     """Check to see whether the invoking user has any of the roles specified in role_ids."""
     async def predicate(ctx: Context) -> bool: