port reaction_check in a new messages util

This is because it's a component that can be reused by all bots.

Author: shtlrs

pydis_core/utils/messages.py

@@ -0,0 +1,48 @@
+from typing import Sequence
+
+from pydis_core.utils.logging import get_logger
+from pydis_core.utils.scheduling import create_task
+
+import discord
+
+
+log = get_logger(__name__)
+
+
+def reaction_check(
+    reaction: discord.Reaction,
+    user: discord.abc.User,
+    *,
+    message_id: int,
+    allowed_emoji: Sequence[str],
+    allowed_users: Sequence[int],
+    allowed_roles: Sequence[int] | None = None,
+) -> bool:
+    """
+    Check if a reaction's emoji and author are allowed and the message is `message_id`.
+
+    If the user is not allowed, remove the reaction. Ignore reactions made by the bot.
+    If `allow_mods` is True, allow users with moderator roles even if they're not in `allowed_users`.
+    """
+    right_reaction = (
+        not user.bot
+        and reaction.message.id == message_id
+        and str(reaction.emoji) in allowed_emoji
+    )
+    if not right_reaction:
+        return False
+
+    allowed_roles = allowed_roles or []
+    has_sufficient_roles = any(role.id in allowed_roles for role in getattr(user, "roles", []))
+
+    if user.id in allowed_users or has_sufficient_roles:
+        log.trace(f"Allowed reaction {reaction} by {user} on {reaction.message.id}.")
+        return True
+
+    log.trace(f"Removing reaction {reaction} by {user} on {reaction.message.id}: disallowed user.")
+    create_task(
+        reaction.message.remove_reaction(reaction.emoji, user),
+        suppressed_exceptions=(discord.HTTPException,),
+        name=f"remove_reaction-{reaction}-{reaction.message.id}-{user}"
+    )
+    return False