python-app-rocketbot/rocketbot/cogs/crosspostcog.py

"""
Cog for detecting spam messages posted in multiple channels.
"""
import re
from datetime import datetime, timedelta, timezone
from typing import Optional

from discord import Member, Message, utils as discordutils, TextChannel
from discord.ext import commands

from config import CONFIG
from rocketbot.cogs.basecog import BaseCog, BotMessage, BotMessageReaction, CogSetting
from rocketbot.collections import AgeBoundList, AgeBoundDict
from rocketbot.storage import Storage
from rocketbot.utils import str_from_timedelta


class SpamContext:
	"""
	Data about a set of duplicate messages from a user.
	"""
	def __init__(self, member: Member) -> None:
		self.member: Member = member
		self.age: datetime = datetime.now()
		self.bot_message: Optional[BotMessage] = None
		self.is_kicked: bool = False
		self.is_banned: bool = False
		self.is_autobanned: bool = False
		self.spam_messages: set[Message] = set()
		self.deleted_messages: set[Message] = set()
		self.unique_channels: set[TextChannel] = set()
		self.duplicate_count: int = 0

class CrossPostCog(BaseCog, name='Crosspost Detection'):
	"""
	Detects a user posting in multiple channels in a short period
	of time: a common pattern for spammers.

	These used to be identical text, but more recent attacks have had small
	variations, such as different imgur URLs. It's reasonable to treat
	posting in many channels in a short period as suspicious on its own,
	regardless of whether they are identical.

	Repeated posts in the same channel aren't currently detected, as this can
	often be for a reason or due to trying a failed post when connectivity is
	poor. Minimum message length can be enforced for detection.
	"""
	SETTING_ENABLED = CogSetting('enabled', bool,
		brief='crosspost detection',
		description='Whether crosspost detection is enabled.')
	SETTING_WARN_COUNT = CogSetting('warncount', int,
		brief='number of messages to trigger a warning',
		description='The number of unique channels messages are ' + \
			'posted in by the same user to trigger a mod warning. The ' + \
			'messages need not be identical (see dupewarncount).',
		usage='<count:int>',
		min_value=2)
	SETTING_DUPE_WARN_COUNT = CogSetting('dupewarncount', int,
		brief='number of identical messages to trigger a warning',
		description='The number of unique channels identical messages are ' + \
			'posted in by the same user to trigger a mod warning.',
		usage='<count:int>',
		min_value=2)
	SETTING_BAN_COUNT = CogSetting('bancount', int,
		brief='number of messages to trigger a ban',
		description='The number of unique channels messages are ' + \
			'posted in by the same user to trigger an automatic ban. The ' + \
			'messages need not be identical (see dupebancount). Set ' + \
			'to a large value to effectively disable, e.g. 9999.',
		usage='<count:int>',
		min_value=2)
	SETTING_DUPE_BAN_COUNT = CogSetting('dupebancount', int,
		brief='number of identical messages to trigger a ban',
		description='The number of unique channels identical messages are ' + \
			'posted in by the same user to trigger an automatic ban. Set ' + \
			'to a large value to effectively disable, e.g. 9999.',
		usage='<count:int>',
		min_value=2)
	SETTING_MIN_LENGTH = CogSetting('minlength', int,
		brief='minimum message length',
		description='The minimum number of characters in a message to be ' + \
			'checked for duplicates. This can help ignore common short ' + \
			'messages like "lol" or a single emoji.',
		usage='<character_count:int>',
		min_value=1)
	SETTING_TIMESPAN = CogSetting('timespan', float,
		brief='time window to look for dupe messages',
		description='The number of seconds of message history to look at ' + \
			'when looking for duplicates. Shorter values are preferred, ' + \
			'both to detect bots and avoid excessive memory usage.',
		usage='<seconds:int>',
		min_value=1)

	STATE_KEY_RECENT_MESSAGES = "CrossPostCog.recent_messages"
	STATE_KEY_SPAM_CONTEXT = "CrossPostCog.spam_context"

	def __init__(self, bot):
		super().__init__(bot, 'crosspost')
		self.add_setting(CrossPostCog.SETTING_ENABLED)
		self.add_setting(CrossPostCog.SETTING_WARN_COUNT)
		self.add_setting(CrossPostCog.SETTING_DUPE_WARN_COUNT)
		self.add_setting(CrossPostCog.SETTING_BAN_COUNT)
		self.add_setting(CrossPostCog.SETTING_DUPE_BAN_COUNT)
		self.add_setting(CrossPostCog.SETTING_MIN_LENGTH)
		self.add_setting(CrossPostCog.SETTING_TIMESPAN)
		self.max_spam_contexts = 12

	async def __record_message(self, message: Message) -> None:
		if message.channel.permissions_for(message.author).ban_members:
			# User exempt from spam detection
			self.__trace("User exempt from crosspost checks")
			return
		def compute_message_hash(m: Message) -> int:
			to_hash = m.content
			# URLs sometimes differ per spam message, so simplify them
			url_regex = r'http[s]?://(?:[a-zA-Z]|[0-9]|[$-_@.&+]|[!*\(\),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+'
			to_hash = re.sub(url_regex, '<url>', to_hash)
			# Add attachment metadata
			for attachment in m.attachments:
				to_hash += f'\n[[ATT: ct={attachment.content_type} s={attachment.size} w={attachment.width} h={attachment.height}]]'
			h = hash(to_hash)
			self.__trace(f"Message hash for {m.id} is {h}")
			return h

		min_length = self.get_guild_setting(message.guild, self.SETTING_MIN_LENGTH)
		if len(message.attachments) == 0 and len(message.content) < min_length:
			# Message too short to count towards spam total
			self.__trace(f"Message len {len(message.content)} < {min_length}")
			return

		# Get config
		max_age = timedelta(seconds=self.get_guild_setting(message.guild, self.SETTING_TIMESPAN))
		warn_count: int = self.get_guild_setting(message.guild, self.SETTING_WARN_COUNT)
		dupe_warn_count: int = self.get_guild_setting(message.guild, self.SETTING_DUPE_WARN_COUNT)

		# Record message
		recent_messages: AgeBoundList[Message, datetime, timedelta] = Storage.get_state_value(message.guild, self.STATE_KEY_RECENT_MESSAGES)
		if recent_messages is None:
			recent_messages = AgeBoundList(max_age, lambda index, message : message.created_at)
			Storage.set_state_value(message.guild, self.STATE_KEY_RECENT_MESSAGES, recent_messages)
		recent_messages.max_age = max_age
		recent_messages.append(message)
		self.__trace(f"Recent messages now length {len(recent_messages)}")

		# Get all recent messages by user
		member_messages = [m for m in recent_messages if m.author.id == message.author.id]
		message_count = len(member_messages)
		self.__trace(f"Found {message_count} messages for {message.author.name}")
		if message_count < warn_count and message_count < dupe_warn_count:
			self.__trace(f"Bailing because message count {message_count} < warn count {warn_count} and < dupe warn count {dupe_warn_count}")
			return

		# Look for identical(ish) messages and unique channels
		hash_to_channels: dict[int, set[TextChannel]] = {}
		unique_channels: set[TextChannel] = set()
		max_duplicate_count = 0
		for m in member_messages:
			message_hash = compute_message_hash(m)
			dupe_message_channels: set[TextChannel] = hash_to_channels.get(message_hash)
			if dupe_message_channels is None:
				dupe_message_channels = set()
				hash_to_channels[message_hash] = dupe_message_channels
			dupe_message_channels.add(m.channel)
			unique_channels.add(m.channel)
			max_duplicate_count = max(max_duplicate_count, len(dupe_message_channels))
		channel_count = len(unique_channels)
		self.__trace(f"Found {len(hash_to_channels)} unique messages, {channel_count} unique channels, {max_duplicate_count} duplicated messages")
		if channel_count < warn_count and max_duplicate_count < dupe_warn_count:
			self.__trace(f"Bailing because channels {channel_count} < warn count {warn_count} and max dupes {max_duplicate_count} < dupe warn count {dupe_warn_count}")
			return

		# This person is a problem

		spam_lookup: AgeBoundDict[str, SpamContext, datetime, timedelta] = Storage.get_state_value(message.guild, self.STATE_KEY_SPAM_CONTEXT)
		if spam_lookup is None:
			spam_lookup = AgeBoundDict(
				max_age,
				lambda key, context : context.age)
			Storage.set_state_value(message.guild, self.STATE_KEY_SPAM_CONTEXT, spam_lookup)
		key = f'{message.author.id}'
		context = spam_lookup.get(key)
		if context is not None and message.created_at - context.age > max_age:
			context = None
		if context is None:
			context = SpamContext(message.author)
			spam_lookup[key] = context
			self.log(message.guild,
				f'\u0007{message.author.name} ({message.author.id}) ' + \
				f'posted messages in {channel_count} channels.')
		context.age = message.created_at
		context.duplicate_count = max_duplicate_count
		context.spam_messages.update(member_messages)
		context.unique_channels.update(unique_channels)
		await self.__update_from_context(context)

	async def __update_from_context(self, context: SpamContext):
		ban_count = self.get_guild_setting(context.member.guild, self.SETTING_BAN_COUNT)
		dupe_ban_count = self.get_guild_setting(context.member.guild, self.SETTING_DUPE_BAN_COUNT)
		channel_count = len(context.unique_channels)
		if channel_count >= ban_count or context.duplicate_count >= dupe_ban_count:
			if not context.is_banned:
				max_age = timedelta(seconds=self.get_guild_setting(context.member.guild, self.SETTING_TIMESPAN))
				max_age_str = str_from_timedelta(max_age)
				await context.member.ban(
					reason=f'Rocketbot: Posted in {channel_count} channels within {max_age_str} ' + \
					   f'({context.duplicate_count} identical). Banned by {self.bot.user.name}.',
					delete_message_days=1)
				context.is_kicked = True
				context.is_banned = True
				context.is_autobanned = True
				context.deleted_messages |= context.spam_messages
				self.__log_ban(context, self.bot.user.name)
			else:
				# Already banned. Nothing to update in the message.
				return
		await self.__update_message_from_context(context)

	async def __update_message_from_context(self, context: SpamContext) -> None:
		first_spam_message: Message = sorted(list(context.spam_messages), key=lambda m: m.created_at)[0]
		spam_count = len(context.spam_messages)
		channel_count = len(context.unique_channels)
		deleted_count = len(context.deleted_messages)
		duplicate_count = context.duplicate_count
		max_age = timedelta(seconds=self.get_guild_setting(context.member.guild, self.SETTING_TIMESPAN))
		max_age_str = str_from_timedelta(max_age)
		message = context.bot_message
		if message is None:
			message_type: int = BotMessage.TYPE_INFO if self.was_warned_recently(context.member) \
				else BotMessage.TYPE_MOD_WARNING
			message = BotMessage(context.member.guild, '', message_type, context)
			message.quote = discordutils.remove_markdown(first_spam_message.clean_content)
			self.record_warning(context.member)
		if context.is_autobanned:
			text = f'User {context.member.mention} auto banned for ' + \
				f'posting messages in {channel_count} channels within {max_age_str} ' + \
				f'({duplicate_count} identical). Messages from past 24 hours deleted.'
			await message.set_reactions([])
			await message.set_text(text)
		else:
			body: str = f'User {context.member.mention} posted '
			if duplicate_count == channel_count:
				body += f'identical messages in {channel_count} channels within {max_age_str} .'
			elif duplicate_count == 1:
				body += f'**different** messages in {channel_count} channels within ' + \
						f'{max_age_str}. (Showing first one).'
			else:
				body += f'messages in {channel_count} channels within {max_age_str} ' + \
						f'({duplicate_count} are identical, showing first one).'
			max_links = 10
			for msg in sorted(list(context.spam_messages), key=lambda m: m.created_at)[:max_links]:
				body += f'\n- {msg.jump_url}'
			if len(context.spam_messages) > max_links:
				body += f'\n- ...{len(context.spam_messages) - max_links} more...'
			await message.set_text(body)
			await message.set_reactions(BotMessageReaction.standard_set(
				did_delete = deleted_count >= spam_count,
				message_count = spam_count,
				did_kick = context.is_kicked,
				did_ban = context.is_banned))
		if context.bot_message is None:
			await self.post_message(message)
			context.bot_message = message

	async def on_mod_react(self,
			bot_message: BotMessage,
			reaction: BotMessageReaction,
			reacted_by: Member) -> None:
		context: SpamContext = bot_message.context
		if context is None:
			return

		channel_count = len(context.unique_channels)
		if reaction.emoji == CONFIG['trash_emoji']:
			for message in context.spam_messages - context.deleted_messages:
				await message.delete()
				context.deleted_messages.add(message)
			await self.__update_from_context(context)
			self.__log_deletion(context, reacted_by.name)
		elif reaction.emoji == CONFIG['kick_emoji']:
			await context.member.kick(
				reason=f'Rocketbot: Posted messages in {channel_count} ' + \
					f'channels. Kicked by {reacted_by.name}.')
			context.is_kicked = True
			await self.__update_from_context(context)
			self.__log_kick(context, reacted_by.name)
		elif reaction.emoji == CONFIG['ban_emoji']:
			await context.member.ban(
				reason=f'Rocketbot: Posted messages in {channel_count} ' + \
					f'channels. Banned by {reacted_by.name}.',
				delete_message_days=1)
			context.deleted_messages |= context.spam_messages
			context.is_kicked = True
			context.is_banned = True
			await self.__update_from_context(context)
			self.__log_ban(context, reacted_by.name)

	def __log_deletion(self, context: SpamContext, by_who: str) -> None:
		max_age = timedelta(seconds=self.get_guild_setting(context.member.guild, self.SETTING_TIMESPAN))
		max_age_str = str_from_timedelta(max_age)
		channel_count = len(context.unique_channels)
		duplicate_count = context.duplicate_count
		self.log(context.member.guild,
				 f'{context.member.name} ({context.member.id}) posted ' + \
				 f'messages in {channel_count} channels withint {max_age_str} ' + \
				 f'({duplicate_count} identical). Deleted by {by_who}.')

	def __log_kick(self, context: SpamContext, by_who: str) -> None:
		max_age = timedelta(seconds=self.get_guild_setting(context.member.guild, self.SETTING_TIMESPAN))
		max_age_str = str_from_timedelta(max_age)
		channel_count = len(context.unique_channels)
		duplicate_count = context.duplicate_count
		self.log(context.member.guild,
				 f'{context.member.name} ({context.member.id}) posted ' + \
				 f'messages in {channel_count} channels within {max_age_str} ' + \
				 f'({duplicate_count} identical). Kicked by {by_who}.')

	def __log_ban(self, context: SpamContext, by_who: str) -> None:
		max_age = timedelta(seconds=self.get_guild_setting(context.member.guild, self.SETTING_TIMESPAN))
		max_age_str = str_from_timedelta(max_age)
		channel_count = len(context.unique_channels)
		duplicate_count = context.duplicate_count
		self.log(context.member.guild,
				 f'{context.member.name} ({context.member.id}) posted ' + \
				 f'messages in {channel_count} channels within {max_age_str} ' + \
				 f'({duplicate_count} identical). Banned by {by_who}.')

	def __trace(self, message):
		# print(message)
		pass

	@commands.Cog.listener()
	async def on_message(self, message: Message):
		"""Event handler"""
		if message.author is None or \
				message.author.bot or \
				message.channel is None or \
				message.guild is None:
			return
		if not self.get_guild_setting(message.guild, self.SETTING_ENABLED):
			return
		self.__trace("--ON MESSAGE--")
		await self.__record_message(message)

	@commands.group(
		brief='Manages crosspost detection and handling',
	)
	@commands.has_permissions(ban_members=True)
	@commands.guild_only()
	async def crosspost(self, context: commands.Context):
		"""Detects members posting messages in multiple channels in a short period of time."""
		if context.invoked_subcommand is None:
			await context.send_help()