veloren/server/src/automod.rs

use crate::settings::ModerationSettings;
use authc::Uuid;
use censor::Censor;
use common::comp::{AdminRole, ChatType, Group};
use hashbrown::HashMap;
use std::{
    fmt,
    sync::Arc,
    time::{Duration, Instant},
};
use tracing::info;

pub const MAX_BYTES_CHAT_MSG: usize = 256;

pub enum ActionNote {
    SpamWarn,
}

impl fmt::Display for ActionNote {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            ActionNote::SpamWarn => write!(
                f,
                "You've sent a lot of messages recently. Make sure to reduce the rate of messages \
                 or you will be automatically muted."
            ),
        }
    }
}

pub enum ActionErr {
    BannedWord,
    TooLong,
    SpamMuted(Duration),
}

impl fmt::Display for ActionErr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            ActionErr::BannedWord => write!(
                f,
                "Your message contained a banned word. If you think this is a mistake, please let \
                 a moderator know."
            ),
            ActionErr::TooLong => write!(
                f,
                "Your message was too long, no more than {} characters are permitted.",
                MAX_BYTES_CHAT_MSG
            ),
            ActionErr::SpamMuted(dur) => write!(
                f,
                "You have sent too many messages and are muted for {} seconds.",
                dur.as_secs_f32() as u64
            ),
        }
    }
}

pub struct AutoMod {
    settings: ModerationSettings,
    censor: Arc<Censor>,
    players: HashMap<Uuid, PlayerState>,
}

impl AutoMod {
    pub fn new(settings: &ModerationSettings, censor: Arc<Censor>) -> Self {
        if settings.automod {
            info!(
                "Automod enabled, players{} will be subject to automated spam/content filters",
                if settings.admins_exempt {
                    ""
                } else {
                    " (and admins)"
                }
            );
        } else {
            info!("Automod disabled");
        }

        Self {
            settings: settings.clone(),
            censor,
            players: HashMap::default(),
        }
    }

    pub fn enabled(&self) -> bool { self.settings.automod }

    fn player_mut(&mut self, player: Uuid) -> &mut PlayerState {
        self.players.entry(player).or_default()
    }

    pub fn validate_chat_msg(
        &mut self,
        player: Uuid,
        role: Option<AdminRole>,
        now: Instant,
        chat_type: &ChatType<Group>,
        msg: &str,
    ) -> Result<Option<ActionNote>, ActionErr> {
        // TODO: Consider using grapheme cluster count instead of size in bytes
        if msg.len() > MAX_BYTES_CHAT_MSG {
            Err(ActionErr::TooLong)
        } else if !self.settings.automod
            // Is this a private chat message?
            || chat_type.is_private().unwrap_or(true)
            // Is the user exempt from automoderation?
            || (role.is_some() && self.settings.admins_exempt)
        {
            Ok(None)
        } else if self.censor.check(msg) {
            Err(ActionErr::BannedWord)
        } else {
            let volume = self.player_mut(player).enforce_message_volume(now);

            if let Some(until) = self.player_mut(player).muted_until {
                Err(ActionErr::SpamMuted(until.saturating_duration_since(now)))
            } else if volume > 0.75 {
                Ok(Some(ActionNote::SpamWarn))
            } else {
                Ok(None)
            }
        }
    }
}

/// The period, in seconds, over which chat volume should be tracked to detect
/// spam.
const CHAT_VOLUME_PERIOD: f32 = 30.0;
/// The maximum permitted average number of chat messages over the chat volume
/// period.
const MAX_AVG_MSG_PER_SECOND: f32 = 1.0 / 5.0; // No more than a message every 5 seconds on average
/// The period for which a player should be muted when they exceed the message
/// spam threshold.
const SPAM_MUTE_PERIOD: Duration = Duration::from_secs(180);

#[derive(Default)]
pub struct PlayerState {
    last_msg_time: Option<Instant>,
    /// The average number of messages per second over the last N seconds.
    chat_volume: f32,
    muted_until: Option<Instant>,
}

impl PlayerState {
    // 0.0 => message is permitted, nothing unusual
    // >=1.0 => message is not permitted, chat volume exceeded
    pub fn enforce_message_volume(&mut self, now: Instant) -> f32 {
        if self.muted_until.map_or(false, |u| u <= now) {
            self.muted_until = None;
        }

        if let Some(time_since_last) = self
            .last_msg_time
            .map(|last| now.saturating_duration_since(last).as_secs_f32())
        {
            let time_proportion = (time_since_last / CHAT_VOLUME_PERIOD).min(1.0);
            self.chat_volume = self.chat_volume * (1.0 - time_proportion)
                + (1.0 / time_since_last) * time_proportion;
        } else {
            self.chat_volume = 0.0;
        }
        self.last_msg_time = Some(now);

        let min_level = 1.0 / CHAT_VOLUME_PERIOD;
        let max_level = MAX_AVG_MSG_PER_SECOND;

        let volume = ((self.chat_volume - min_level) / (max_level - min_level)).max(0.0);

        if volume > 1.0 && self.muted_until.is_none() {
            self.muted_until = now.checked_add(SPAM_MUTE_PERIOD);
        }

        volume
    }
}