Add checks.py file

- Necessary for extensions.py to work

- Copied from the 'Python' bot, with minor tweaks to make it work with SeasonalBot

1 files changed, 164 insertions, 0 deletions

diff --git a/bot/utils/checks.py b/bot/utils/checks.py
new file mode 100644
index 00000000..3031a271
--- /dev/null
+++ b/bot/utils/checks.py
@@ -0,0 +1,164 @@
+import datetime
+import logging
+from typing import Callable, Container, Iterable, Optional
+
+from discord.ext.commands import (
+    BucketType,
+    CheckFailure,
+    Cog,
+    Command,
+    CommandOnCooldown,
+    Context,
+    Cooldown,
+    CooldownMapping,
+)
+
+from bot import constants
+
+log = logging.getLogger(__name__)
+
+
+class InWhitelistCheckFailure(CheckFailure):
+    """Raised when the `in_whitelist` check fails."""
+
+    def __init__(self, redirect_channel: Optional[int]) -> None:
+        self.redirect_channel = redirect_channel
+
+        if redirect_channel:
+            redirect_message = f" here. Please use the <#{redirect_channel}> channel instead"
+        else:
+            redirect_message = ""
+
+        error_message = f"You are not allowed to use that command{redirect_message}."
+
+        super().__init__(error_message)
+
+
+def in_whitelist_check(
+    ctx: Context,
+    channels: Container[int] = (),
+    categories: Container[int] = (),
+    roles: Container[int] = (),
+    redirect: Optional[int] = constants.Channels.seasonalbot_commands,
+    fail_silently: bool = False,
+) -> bool:
+    """
+    Check if a command was issued in a whitelisted context.
+
+    The whitelists that can be provided are:
+
+    - `channels`: a container with channel ids for whitelisted channels
+    - `categories`: a container with category ids for whitelisted categories
+    - `roles`: a container with with role ids for whitelisted roles
+
+    If the command was invoked in a context that was not whitelisted, the member is either
+    redirected to the `redirect` channel that was passed (default: #bot-commands) or simply
+    told that they're not allowed to use this particular command (if `None` was passed).
+    """
+    if redirect and redirect not in channels:
+        # It does not make sense for the channel whitelist to not contain the redirection
+        # channel (if applicable). That's why we add the redirection channel to the `channels`
+        # container if it's not already in it. As we allow any container type to be passed,
+        # we first create a tuple in order to safely add the redirection channel.
+        #
+        # Note: It's possible for the redirect channel to be in a whitelisted category, but
+        # there's no easy way to check that and as a channel can easily be moved in and out of
+        # categories, it's probably not wise to rely on its category in any case.
+        channels = tuple(channels) + (redirect,)
+
+    if channels and ctx.channel.id in channels:
+        log.trace(f"{ctx.author} may use the `{ctx.command.name}` command as they are in a whitelisted channel.")
+        return True
+
+    # Only check the category id if we have a category whitelist and the channel has a `category_id`
+    if categories and hasattr(ctx.channel, "category_id") and ctx.channel.category_id in categories:
+        log.trace(f"{ctx.author} may use the `{ctx.command.name}` command as they are in a whitelisted category.")
+        return True
+
+    # Only check the roles whitelist if we have one and ensure the author's roles attribute returns
+    # an iterable to prevent breakage in DM channels (for if we ever decide to enable commands there).
+    if roles and any(r.id in roles for r in getattr(ctx.author, "roles", ())):
+        log.trace(f"{ctx.author} may use the `{ctx.command.name}` command as they have a whitelisted role.")
+        return True
+
+    log.trace(f"{ctx.author} may not use the `{ctx.command.name}` command within this context.")
+
+    # Some commands are secret, and should produce no feedback at all.
+    if not fail_silently:
+        raise InWhitelistCheckFailure(redirect)
+    return False
+
+
+def with_role_check(ctx: Context, *role_ids: int) -> bool:
+    """Returns True if the user has any one of the roles in role_ids."""
+    if not ctx.guild:  # Return False in a DM
+        log.trace(f"{ctx.author} tried to use the '{ctx.command.name}'command from a DM. "
+                  "This command is restricted by the with_role decorator. Rejecting request.")
+        return False
+
+    for role in ctx.author.roles:
+        if role.id in role_ids:
+            log.trace(f"{ctx.author} has the '{role.name}' role, and passes the check.")
+            return True
+
+    log.trace(f"{ctx.author} does not have the required role to use "
+              f"the '{ctx.command.name}' command, so the request is rejected.")
+    return False
+
+
+def without_role_check(ctx: Context, *role_ids: int) -> bool:
+    """Returns True if the user does not have any of the roles in role_ids."""
+    if not ctx.guild:  # Return False in a DM
+        log.trace(f"{ctx.author} tried to use the '{ctx.command.name}' command from a DM. "
+                  "This command is restricted by the without_role decorator. Rejecting request.")
+        return False
+
+    author_roles = [role.id for role in ctx.author.roles]
+    check = all(role not in author_roles for role in role_ids)
+    log.trace(f"{ctx.author} tried to call the '{ctx.command.name}' command. "
+              f"The result of the without_role check was {check}.")
+    return check
+
+
+def cooldown_with_role_bypass(rate: int, per: float, type: BucketType = BucketType.default, *,
+                              bypass_roles: Iterable[int]) -> Callable:
+    """
+    Applies a cooldown to a command, but allows members with certain roles to be ignored.
+
+    NOTE: this replaces the `Command.before_invoke` callback, which *might* introduce problems in the future.
+    """
+    # Make it a set so lookup is hash based.
+    bypass = set(bypass_roles)
+
+    # This handles the actual cooldown logic.
+    buckets = CooldownMapping(Cooldown(rate, per, type))
+
+    # Will be called after the command has been parse but before it has been invoked, ensures that
+    # the cooldown won't be updated if the user screws up their input to the command.
+    async def predicate(cog: Cog, ctx: Context) -> None:
+        nonlocal bypass, buckets
+
+        if any(role.id in bypass for role in ctx.author.roles):
+            return
+
+        # Cooldown logic, taken from discord.py internals.
+        current = ctx.message.created_at.replace(tzinfo=datetime.timezone.utc).timestamp()
+        bucket = buckets.get_bucket(ctx.message)
+        retry_after = bucket.update_rate_limit(current)
+        if retry_after:
+            raise CommandOnCooldown(bucket, retry_after)
+
+    def wrapper(command: Command) -> Command:
+        # NOTE: this could be changed if a subclass of Command were to be used. I didn't see the need for it
+        # so I just made it raise an error when the decorator is applied before the actual command object exists.
+        #
+        # If the `before_invoke` detail is ever a problem then I can quickly just swap over.
+        if not isinstance(command, Command):
+            raise TypeError('Decorator `cooldown_with_role_bypass` must be applied after the command decorator. '
+                            'This means it has to be above the command decorator in the code.')
+
+        command._before_invoke = predicate
+
+        return command
+
+    return wrapper