ircbot 0.2.0

use std::collections::HashMap;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, OnceLock, RwLock};
use std::time::Duration;

use leaky_bucket::RateLimiter;
use regex::Regex;
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufWriter};
use tokio::sync::mpsc;

use crate::{
    connection::State,
    context::{Context, User},
    handler::{HandlerEntry, Trigger},
    irc::{CtcpMessage, Message},
    types::{Nick, Target},
    BoxError,
};
use irc_proto::{prefix::Prefix, Command, Response};

/// Command prefix recognised by the bot (e.g. `!ping`).
const CMD_PREFIX: char = '!';

/// The token sent in our client-initiated keepalive `PING`.
const KEEPALIVE_TOKEN: &str = "ircbot-keepalive";

/// How many alternate nicks to try when the requested nick is already in use
/// before giving up on registration.  Each `ERR_NICKNAMEINUSE` (433) /
/// `ERR_UNAVAILRESOURCE` (437) reply triggers one further attempt.
const MAX_NICK_ATTEMPTS: u32 = 8;

/// Upper bound on how long the cron supervisor sleeps in one cycle.  When the
/// next scheduled fire is further away than this (or there are no cron handlers
/// at all), the supervisor still wakes to re-read the live handler set, so a
/// cron handler added by a hot-reload is picked up within this window.
const CRON_RESCAN_INTERVAL: Duration = Duration::from_secs(60);

/// A shareable, atomically-swappable set of handler entries.
///
/// The outer [`Arc`] allows the handle to be cloned cheaply.  The [`RwLock`]
/// serialises writes.  The inner [`Arc`] lets a reader snapshot the current
/// handler list with a single cheap `Arc::clone` — no lock is held across
/// `.await` points.
pub type HandlerSet<T> = Arc<RwLock<Arc<Vec<HandlerEntry<T>>>>>;

// ─── public entry-point ──────────────────────────────────────────────────────

/// Handles IRC messages, dispatching to registered handlers.
///
/// Sends a periodic `PING` to the server and breaks out of the read loop (so
/// the caller can reconnect) if the corresponding `PONG` is not received within
/// the configured timeout.
///
/// The `handlers` are read from a shared [`HandlerSet`] on every incoming
/// message, so they can be swapped atomically at any point without
/// disconnecting from IRC.
///
/// # Errors
///
/// Returns an error if reading from the connection fails.
pub async fn run_bot_internal<T: Send + Sync + 'static>(
    bot: Arc<T>,
    state: State,
    handlers: HandlerSet<T>,
) -> Result<(), BoxError> {
    let State {
        nick,
        channels,
        server: _,
        keepalive_interval,
        keepalive_timeout,
        flood_burst,
        flood_rate,
        ctcp_version,
        reader,
        write_half,
        #[cfg(unix)]
            raw_fd: _,
    } = state;

    // Create the mpsc write channel.
    let (write_tx, mut write_rx) = mpsc::unbounded_channel::<String>();

    // Spawn the write loop — drains the channel into the TCP write half,
    // enforcing a token-bucket flood-control policy so that the bot cannot
    // send messages faster than the server allows.
    let write_task = tokio::spawn(async move {
        let mut writer = BufWriter::new(write_half);

        // Token-bucket flood control: start with a full burst budget and refill
        // one token every `flood_rate`. `acquire_one` returns immediately while
        // the budget lasts, then waits for the next refill once it is exhausted,
        // so the bot never sends faster than the server allows.  `max` is
        // clamped to at least 1 (a 0 burst rate-limits from the very first
        // message, which is honoured by the empty `initial` budget below).
        let limiter = RateLimiter::builder()
            .max(flood_burst.max(1))
            .initial(flood_burst)
            .refill(1)
            .interval(flood_rate)
            .build();

        while let Some(msg) = write_rx.recv().await {
            limiter.acquire_one().await;

            if writer.write_all(msg.as_bytes()).await.is_err() {
                break;
            }
            if writer.flush().await.is_err() {
                break;
            }
        }
    });

    // Spawn a single supervisor task that fires Cron-triggered handlers on
    // schedule.  Unlike a per-handler snapshot, it re-reads the live handler set
    // on every cycle, so cron handlers added, removed, or replaced via
    // [`crate::ReloadHandle::reload`] take effect without waiting for a
    // reconnect.  The task is aborted when this connection is torn down and
    // re-spawned on reconnect.
    //
    // `nick` is the originally-requested nick and stays fixed as the base for
    // generating fallbacks; `bot_nick` tracks the nick we are actually using and
    // is updated if the server reports the requested one is taken.
    let mut bot_nick = nick.clone();
    let cron_task = tokio::spawn(run_cron_supervisor(
        Arc::clone(&bot),
        Arc::clone(&handlers),
        write_tx.clone(),
        bot_nick.clone(),
    ));

    // Keepalive: set to `true` on startup (no ping pending) and whenever we
    // receive a matching PONG.  The keepalive task resets it to `false` before
    // each PING, then checks it again after the timeout.
    let pong_received = Arc::new(AtomicBool::new(true));
    let pong_received_keepalive = Arc::clone(&pong_received);
    let keepalive_write_tx = write_tx.clone();
    let (keepalive_fail_tx, keepalive_fail_rx) = tokio::sync::oneshot::channel::<()>();

    let keepalive_task = tokio::spawn(async move {
        let mut fail_tx = Some(keepalive_fail_tx);
        loop {
            tokio::time::sleep(keepalive_interval).await;
            pong_received_keepalive.store(false, Ordering::Relaxed);
            if keepalive_write_tx
                .send(format!("PING {KEEPALIVE_TOKEN}\r\n"))
                .is_err()
            {
                break;
            }
            tokio::time::sleep(keepalive_timeout).await;
            if !pong_received_keepalive.load(Ordering::Relaxed) {
                eprintln!("[ircbot] keepalive timeout — reconnecting");
                if let Some(tx) = fail_tx.take() {
                    let _ = tx.send(());
                }
                break;
            }
        }
    });

    let mut joined = false;
    // Number of alternate-nick attempts made so far (after the initial NICK).
    let mut nick_attempt = 0u32;
    let mut lines = reader.lines();
    let mut keepalive_fail_rx = keepalive_fail_rx;

    // Run the read loop; collect any IO error so we can clean up first.
    let loop_result: Result<(), BoxError> = async {
        loop {
            tokio::select! {
                result = lines.next_line() => {
                    let Some(line) = result? else { break; };
                    let line = line.trim_end_matches('\r').to_string();
                    if line.is_empty() {
                        continue;
                    }

                    if let Ok(msg) = line.parse::<Message>() {
                        match &msg.command {
                            Command::PING(srv, _) => {
                                if let Err(e) = write_tx.send(format!("PONG :{srv}\r\n")) {
                                    eprintln!("[ircbot] failed to send PONG: {e}");
                                }
                            }
                            Command::PONG(a, b) => {
                                // The keepalive token is echoed back in the
                                // trailing position: "PONG server :token" → b,
                                // or without a server: "PONG :token" → a.
                                let token = b.as_deref().unwrap_or(a.as_str());
                                if token == KEEPALIVE_TOKEN {
                                    pong_received.store(true, Ordering::Relaxed);
                                }
                            }
                            Command::Response(Response::RPL_WELCOME, _) => {
                                if !joined {
                                    joined = true;
                                    for ch in &channels {
                                        if let Err(e) = write_tx.send(format!("JOIN {ch}\r\n")) {
                                            eprintln!("[ircbot] failed to send JOIN {ch}: {e}");
                                        }
                                    }
                                }
                                dispatch(&bot, &handlers, &msg, &bot_nick, write_tx.clone()).await;
                            }
                            Command::Response(
                                Response::ERR_NICKNAMEINUSE | Response::ERR_UNAVAILRESOURCE,
                                _,
                            ) => {
                                // Only renegotiate before registration completes.
                                // A 433/437 after we've joined refers to a later
                                // NICK-change attempt and is left for handlers.
                                if !joined {
                                    nick_attempt += 1;
                                    if nick_attempt <= MAX_NICK_ATTEMPTS {
                                        let candidate = fallback_nick(nick.as_str(), nick_attempt);
                                        eprintln!(
                                            "[ircbot] nick {bot_nick:?} unavailable — retrying as {candidate:?}"
                                        );
                                        if let Err(e) =
                                            write_tx.send(format!("NICK {candidate}\r\n"))
                                        {
                                            eprintln!(
                                                "[ircbot] failed to send NICK {candidate}: {e}"
                                            );
                                        }
                                        bot_nick = Nick::from(candidate);
                                    } else {
                                        eprintln!(
                                            "[ircbot] giving up on registration after \
                                             {MAX_NICK_ATTEMPTS} nick attempts"
                                        );
                                    }
                                }
                                dispatch(&bot, &handlers, &msg, &bot_nick, write_tx.clone()).await;
                            }
                            Command::PRIVMSG(_, _) => {
                                handle_privmsg(
                                    &bot,
                                    &handlers,
                                    &msg,
                                    &bot_nick,
                                    ctcp_version.as_deref(),
                                    write_tx.clone(),
                                )
                                .await;
                            }
                            _ => {
                                dispatch(&bot, &handlers, &msg, &bot_nick, write_tx.clone()).await;
                            }
                        }
                    }
                }
                _ = &mut keepalive_fail_rx => {
                    // Keepalive timed out — exit so the caller can reconnect.
                    break;
                }
            }
        }
        Ok(())
    }
    .await;

    // Always clean up the keepalive, cron, and write tasks before returning.
    keepalive_task.abort();
    cron_task.abort();
    drop(write_tx);
    let _ = write_task.await;

    loop_result
}

// ─── cron supervisor ─────────────────────────────────────────────────────────

/// Drive every [`Trigger::Cron`] handler in `handlers`.
///
/// Each cycle re-reads the live handler set, so cron handlers added, removed,
/// or replaced via [`crate::ReloadHandle::reload`] take effect immediately,
/// then sleeps until the earliest upcoming occurrence (capped at
/// [`CRON_RESCAN_INTERVAL`]) and fires every handler that is due.  Due handlers
/// run sequentially, mirroring the message-dispatch path.
async fn run_cron_supervisor<T: Send + Sync + 'static>(
    bot: Arc<T>,
    handlers: HandlerSet<T>,
    tx: mpsc::UnboundedSender<String>,
    bot_nick: Nick,
) {
    loop {
        // Reference instant for this cycle.  All "next occurrence" computations
        // are relative to it, so the pre-sleep and post-sleep views agree.
        let now = chrono::Utc::now();

        // Earliest upcoming fire across all cron handlers in the live set.
        let fire_at = {
            let live = snapshot(&handlers);
            live.iter()
                .filter_map(|e| next_cron_fire(&e.trigger, &now))
                .min()
        };

        // Sleep until that fire, capped so reloads are noticed within a bounded
        // window (and so we idle gracefully when there are no cron handlers).
        let wait = fire_at.map_or(CRON_RESCAN_INTERVAL, |at| {
            (at - now)
                .to_std()
                .unwrap_or(Duration::ZERO)
                .min(CRON_RESCAN_INTERVAL)
        });
        tokio::time::sleep(wait).await;

        let Some(fire_at) = fire_at else { continue };
        if chrono::Utc::now() < fire_at {
            // Woken by the rescan cap before the fire was due — re-evaluate.
            continue;
        }

        // Re-read the live set so reloaded handler bodies fire, then run every
        // cron handler whose next occurrence after `now` has now arrived.
        let live = snapshot(&handlers);
        let now2 = chrono::Utc::now();
        for entry in live.iter() {
            let Trigger::Cron { target, .. } = &entry.trigger else {
                continue;
            };
            let Some(next) = next_cron_fire(&entry.trigger, &now) else {
                continue;
            };
            if next > now2 {
                continue; // not due yet
            }
            let cron_target = target.clone().unwrap_or_default();
            let ctx = Context {
                tx: tx.clone(),
                target: Target::from_raw(&cron_target),
                sender: None,
                raw: synthesize_cron_message(bot_nick.as_str()),
                bot_nick: bot_nick.clone(),
                captures: vec![],
            };
            if let Err(e) = (entry.handler)(Arc::clone(&bot), ctx).await {
                eprintln!("[ircbot] cron handler error: {e}");
            }
        }
    }
}

/// Snapshot the live handler list with a single cheap `Arc::clone`, holding the
/// read lock only momentarily.
fn snapshot<T>(handlers: &HandlerSet<T>) -> Arc<Vec<HandlerEntry<T>>> {
    let guard = handlers.read().unwrap_or_else(|e| e.into_inner());
    Arc::clone(&*guard)
}

/// The next fire time (in UTC) strictly after `after` for a [`Trigger::Cron`],
/// or `None` for any other trigger or an unparseable schedule/timezone.
///
/// The `#[on(cron = …)]` macro validates the expression and timezone at compile
/// time; only the lower-level manual API can produce an invalid one, which
/// simply never fires.
fn next_cron_fire(
    trigger: &Trigger,
    after: &chrono::DateTime<chrono::Utc>,
) -> Option<chrono::DateTime<chrono::Utc>> {
    let Trigger::Cron { schedule, tz, .. } = trigger else {
        return None;
    };
    let schedule: cron::Schedule = schedule.parse().ok()?;
    let tz: chrono_tz::Tz = tz.parse().ok()?;
    schedule
        .after(&after.with_timezone(&tz))
        .next()
        .map(|dt| dt.with_timezone(&chrono::Utc))
}

/// Build the synthetic [`Message`] used as the `raw` field of a cron-fired
/// [`Context`].  Cron handlers have no originating IRC message, so a benign one
/// tagged with a `cron` pseudo-source is fabricated.
fn synthesize_cron_message(bot_nick: &str) -> Message {
    format!(":{bot_nick}!cron@cron PING :cron")
        .parse::<Message>()
        .unwrap_or_else(|_| {
            format!(":{bot_nick}!cron@cron PRIVMSG #cron :cron")
                .parse()
                .unwrap()
        })
}

// ─── trigger matching ────────────────────────────────────────────────────────

/// Returns `Some(captures)` if `msg` matches `trigger`, `None` otherwise.
#[must_use]
pub fn check_trigger(trigger: &Trigger, msg: &Message, bot_nick: &str) -> Option<Vec<String>> {
    match trigger {
        Trigger::Command { name, target } => {
            let Command::PRIVMSG(msg_target, text) = &msg.command else {
                return None;
            };
            // Optional target filter
            if let Some(t) = target {
                if msg_target.as_str() != t.as_str() {
                    return None;
                }
            }
            let text = text.strip_prefix(CMD_PREFIX)?;
            let (cmd, rest) = text
                .split_once(' ')
                .map_or((text, ""), |(c, r)| (c, r.trim()));
            if !cmd.eq_ignore_ascii_case(name) {
                return None;
            }
            Some(if rest.is_empty() {
                vec![]
            } else {
                vec![rest.to_string()]
            })
        }

        Trigger::Message { pattern, target } => {
            let Command::PRIVMSG(msg_target, text) = &msg.command else {
                return None;
            };
            if let Some(t) = target {
                if msg_target.as_str() != t.as_str() {
                    return None;
                }
            }
            glob_match(pattern, text)
        }

        Trigger::Event {
            event,
            target,
            regex,
        } => {
            if !command_name(msg).eq_ignore_ascii_case(event) {
                return None;
            }
            if let Some(t) = target {
                if target_param(msg) != Some(t.as_str()) {
                    return None;
                }
            }
            if let Some(re_str) = regex {
                let text = trailing_param(msg).unwrap_or("");
                let re = cached_regex(re_str)?;
                let caps = re.captures(text)?;
                let groups: Vec<String> = caps
                    .iter()
                    .skip(1)
                    .filter_map(|m| m.map(|m| m.as_str().to_string()))
                    .collect();
                Some(groups)
            } else {
                Some(vec![])
            }
        }

        Trigger::Cron { .. } => None,

        Trigger::Mention { target } => {
            let Command::PRIVMSG(msg_target, text) = &msg.command else {
                return None;
            };
            if let Some(t) = target {
                if msg_target.as_str() != t.as_str() {
                    return None;
                }
            }
            let lower = text.to_ascii_lowercase();
            let nick_lower = bot_nick.to_ascii_lowercase();
            // Accept "<nick>: " or "<nick>, " address prefixes.
            // IRC nicks are restricted to ASCII characters (RFC 2812), so
            // `prefix.len()` (bytes) equals its character count and slicing
            // `text` at that offset is always on a valid UTF-8 boundary.
            let rest = [": ", ", "].iter().find_map(|sep| {
                let prefix = format!("{}{}", nick_lower, sep);
                if lower.starts_with(prefix.as_str()) {
                    Some(text[prefix.len()..].trim().to_string())
                } else {
                    None
                }
            })?;
            Some(if rest.is_empty() { vec![] } else { vec![rest] })
        }
    }
}

// ─── nick fallback ───────────────────────────────────────────────────────────

/// Generate a fallback nick from `base` for the given 1-based `attempt`, used
/// to recover from `ERR_NICKNAMEINUSE` / `ERR_UNAVAILRESOURCE` during
/// registration.
///
/// The first three attempts append underscores (`base_`, `base__`, `base___`);
/// later attempts append the attempt number (`base4`, `base5`, …) so the
/// candidates stay bounded in length while remaining distinct.
#[must_use]
fn fallback_nick(base: &str, attempt: u32) -> String {
    if attempt <= 3 {
        format!("{base}{}", "_".repeat(attempt as usize))
    } else {
        format!("{base}{attempt}")
    }
}

// ─── IRC message helpers ─────────────────────────────────────────────────────

/// The IRC command name as an uppercase ASCII string (e.g. `"PRIVMSG"`, `"001"`).
///
/// Uses the command's wire representation for known variants, and the stored
/// name directly for `Raw` variants.
fn command_name(msg: &Message) -> std::borrow::Cow<'_, str> {
    use std::borrow::Cow;
    match &msg.command {
        Command::Raw(name, _) => Cow::Borrowed(name.as_str()),
        cmd => {
            let s = String::from(cmd);
            let end = s.find(' ').unwrap_or(s.len());
            Cow::Owned(s[..end].to_ascii_uppercase())
        }
    }
}

/// The trailing parameter — the main text content of the message.
fn trailing_param(msg: &Message) -> Option<&str> {
    match &msg.command {
        Command::PRIVMSG(_, text) | Command::NOTICE(_, text) => Some(text),
        Command::PING(server, _) => Some(server),
        Command::PONG(_, Some(token)) => Some(token),
        Command::PONG(server, None) => Some(server),
        Command::JOIN(channel, _, _) => Some(channel),
        Command::PART(_, Some(reason)) => Some(reason),
        Command::PART(channel, None) => Some(channel),
        Command::QUIT(Some(message)) => Some(message),
        Command::KICK(_, _, Some(reason)) => Some(reason),
        Command::TOPIC(_, Some(topic)) => Some(topic),
        Command::TOPIC(channel, None) => Some(channel),
        Command::Response(_, args) => args.last().map(String::as_str),
        Command::Raw(_, args) => args.last().map(String::as_str),
        _ => None,
    }
}

/// The first parameter — typically the target channel or nick.
fn target_param(msg: &Message) -> Option<&str> {
    match &msg.command {
        Command::PRIVMSG(target, _) | Command::NOTICE(target, _) => Some(target),
        Command::JOIN(channel, _, _) => Some(channel),
        Command::PART(channel, _) => Some(channel),
        Command::KICK(channel, _, _) => Some(channel),
        Command::TOPIC(channel, _) => Some(channel),
        Command::INVITE(_, channel) => Some(channel),
        Command::ChannelMODE(channel, _) => Some(channel),
        Command::UserMODE(nick, _) => Some(nick),
        Command::Response(_, args) => args.first().map(String::as_str),
        Command::Raw(_, args) => args.first().map(String::as_str),
        _ => None,
    }
}

// ─── regex cache ─────────────────────────────────────────────────────────────

/// Return a clone of the compiled `Regex` for `pattern`, compiling and caching
/// it on the first call with that pattern.
fn cached_regex(pattern: &str) -> Option<Arc<Regex>> {
    static CACHE: OnceLock<RwLock<HashMap<String, Arc<Regex>>>> = OnceLock::new();
    let cache = CACHE.get_or_init(|| RwLock::new(HashMap::new()));

    // Fast path: pattern already cached.
    if let Ok(guard) = cache.read() {
        if let Some(re) = guard.get(pattern) {
            return Some(Arc::clone(re));
        }
    }

    // Slow path: compile and insert.
    let re = Arc::new(Regex::new(pattern).ok()?);
    if let Ok(mut guard) = cache.write() {
        guard
            .entry(pattern.to_string())
            .or_insert_with(|| Arc::clone(&re));
    }
    Some(re)
}

// ─── glob matching ───────────────────────────────────────────────────────────

/// Match `text` against a glob `pattern` where `*` is a capturing wildcard.
/// Returns `Some(captures)` on success, `None` on mismatch.
#[must_use]
pub fn glob_match(pattern: &str, text: &str) -> Option<Vec<String>> {
    // Convert glob to a capturing regex and look it up in the cache.
    let re_str = glob_to_regex(pattern);
    let re = cached_regex(&re_str)?;
    let caps = re.captures(text)?;
    let groups: Vec<String> = caps
        .iter()
        .skip(1) // skip whole-match
        .filter_map(|m| m.map(|m| m.as_str().to_string()))
        .collect();
    Some(groups)
}

fn glob_to_regex(pattern: &str) -> String {
    let mut out = String::from("^(?i)");
    for c in pattern.chars() {
        match c {
            '*' => out.push_str("(.*)"),
            '?' => out.push('.'),
            c if ".$+^{}[]|\\()".contains(c) => {
                out.push('\\');
                out.push(c);
            }
            c => out.push(c),
        }
    }
    out.push('$');
    out
}

// ─── dispatch ────────────────────────────────────────────────────────────────

async fn handle_privmsg<T: Send + Sync + 'static>(
    bot: &Arc<T>,
    handlers: &HandlerSet<T>,
    msg: &Message,
    bot_nick: &Nick,
    ctcp_version: Option<&str>,
    tx: tokio::sync::mpsc::UnboundedSender<String>,
) {
    let Command::PRIVMSG(_, text) = &msg.command else {
        dispatch(bot, handlers, msg, bot_nick, tx).await;
        return;
    };
    if let Some(ctcp) = CtcpMessage::parse(text) {
        match ctcp.command.as_str() {
            "PING" => {
                if let Some(sender) = msg.source_nickname() {
                    let reply = format!(
                        "NOTICE {sender} :\x01PING{}{}\x01\r\n",
                        if ctcp.arg.is_empty() { "" } else { " " },
                        ctcp.arg,
                    );
                    if let Err(e) = tx.send(reply) {
                        eprintln!("[ircbot] failed to send CTCP PING reply: {e}");
                    }
                }
                return;
            }
            "VERSION" => {
                if let Some(sender) = msg.source_nickname() {
                    // Use the caller-supplied version string if set, else the
                    // framework default of `ircbot <crate-version>`.
                    let version = ctcp_version.map_or_else(
                        || format!("ircbot {}", env!("CARGO_PKG_VERSION")),
                        ToString::to_string,
                    );
                    let reply = format!("NOTICE {sender} :\x01VERSION {version}\x01\r\n");
                    if let Err(e) = tx.send(reply) {
                        eprintln!("[ircbot] failed to send CTCP VERSION reply: {e}");
                    }
                }
                return;
            }
            _ => {}
        }
    }
    dispatch(bot, handlers, msg, bot_nick, tx).await;
}

async fn dispatch<T: Send + Sync + 'static>(
    bot: &Arc<T>,
    handlers: &HandlerSet<T>,
    msg: &Message,
    bot_nick: &Nick,
    tx: tokio::sync::mpsc::UnboundedSender<String>,
) {
    // Snapshot the current handler list under a brief read-lock, then release
    // immediately — no lock is held across any `.await` point.
    let current: Arc<Vec<HandlerEntry<T>>> = {
        let guard = handlers.read().unwrap_or_else(|e| e.into_inner());
        Arc::clone(&*guard)
    };

    let sender = match msg.prefix.as_ref() {
        Some(Prefix::Nickname(nick, user, host)) if !user.is_empty() => Some(User {
            nick: Nick::from(nick.clone()),
            user: user.clone(),
            host: host.clone(),
        }),
        _ => None,
    };
    let target = Target::from_raw(target_param(msg).unwrap_or(""));

    for entry in current.iter() {
        if let Some(captures) = check_trigger(&entry.trigger, msg, bot_nick.as_str()) {
            let ctx = Context {
                tx: tx.clone(),
                target: target.clone(),
                sender: sender.clone(),
                raw: msg.clone(),
                bot_nick: bot_nick.clone(),
                captures,
            };
            let bot_clone = Arc::clone(bot);
            let fut = (entry.handler)(bot_clone, ctx);
            if let Err(e) = fut.await {
                eprintln!("[ircbot] handler error: {e}");
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // ── fallback_nick ──────────────────────────────────────────────────────────

    #[test]
    fn fallback_nick_appends_underscores_for_early_attempts() {
        assert_eq!(fallback_nick("bot", 1), "bot_");
        assert_eq!(fallback_nick("bot", 2), "bot__");
        assert_eq!(fallback_nick("bot", 3), "bot___");
    }

    #[test]
    fn fallback_nick_appends_number_for_later_attempts() {
        assert_eq!(fallback_nick("bot", 4), "bot4");
        assert_eq!(fallback_nick("bot", 8), "bot8");
    }

    #[test]
    fn fallback_nick_candidates_are_distinct_across_all_attempts() {
        let mut seen = std::collections::HashSet::new();
        for attempt in 1..=MAX_NICK_ATTEMPTS {
            assert!(
                seen.insert(fallback_nick("bot", attempt)),
                "duplicate fallback nick at attempt {attempt}"
            );
        }
    }

    // ── CTCP VERSION ───────────────────────────────────────────────────────────

    /// Drive `handle_privmsg` with a CTCP VERSION request and return the line
    /// the bot would send back.
    async fn ctcp_version_reply(custom: Option<&str>) -> String {
        let bot = std::sync::Arc::new(());
        let handlers = crate::internal::make_handler_set::<()>(vec![]);
        let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel();
        let msg = ":alice!u@h PRIVMSG mybot :\x01VERSION\x01"
            .parse::<Message>()
            .unwrap();
        handle_privmsg(&bot, &handlers, &msg, &Nick::from("mybot"), custom, tx).await;
        rx.try_recv().expect("a CTCP VERSION reply was sent")
    }

    #[tokio::test]
    async fn ctcp_version_uses_custom_string_when_set() {
        assert_eq!(
            ctcp_version_reply(Some("rustbutler 1.2.3")).await,
            "NOTICE alice :\x01VERSION rustbutler 1.2.3\x01\r\n",
        );
    }

    #[tokio::test]
    async fn ctcp_version_defaults_to_ircbot_crate_version() {
        let reply = ctcp_version_reply(None).await;
        assert_eq!(
            reply,
            format!(
                "NOTICE alice :\x01VERSION ircbot {}\x01\r\n",
                env!("CARGO_PKG_VERSION")
            ),
        );
    }
}