// IRC module.
//
// Maintains a persistent connection to an IRC server. Parses incoming
// messages into notifications, supports sending messages and runtime
// commands (join, leave, etc.). Config changes persist to daemon.toml.
//
// Runs as a spawned local task on the daemon's LocalSet. Notifications
// flow through an mpsc channel into the main state. Reconnects
// automatically with exponential backoff.

use crate::config::{Config, IrcConfig};
use crate::notify::Notification;
use crate::{home, now};
use std::cell::RefCell;
use std::collections::VecDeque;
use std::io;
use std::rc::Rc;
use std::sync::Arc;
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::sync::mpsc;
use tracing::{error, info, warn};

const MAX_LOG_LINES: usize = 200;
const RECONNECT_BASE_SECS: u64 = 5;
const RECONNECT_MAX_SECS: u64 = 300;
const PING_INTERVAL_SECS: u64 = 120;
const PING_TIMEOUT_SECS: u64 = 30;

/// Parsed IRC message.
struct IrcMessage {
    prefix: Option<String>, // nick!user@host
    command: String,
    params: Vec<String>,
}

impl IrcMessage {
    fn parse(line: &str) -> Option<Self> {
        let line = line.trim_end_matches(|c| c == '\r' || c == '\n');
        if line.is_empty() {
            return None;
        }

        let (prefix, rest) = if line.starts_with(':') {
            let space = line.find(' ')?;
            (Some(line[1..space].to_string()), &line[space + 1..])
        } else {
            (None, line)
        };

        let (command_params, trailing) = if let Some(pos) = rest.find(" :") {
            (&rest[..pos], Some(rest[pos + 2..].to_string()))
        } else {
            (rest, None)
        };

        let mut parts: Vec<String> = command_params
            .split_whitespace()
            .map(String::from)
            .collect();

        if parts.is_empty() {
            return None;
        }

        let command = parts.remove(0).to_uppercase();
        let mut params = parts;
        if let Some(t) = trailing {
            params.push(t);
        }

        Some(IrcMessage {
            prefix,
            command,
            params,
        })
    }

    /// Extract nick from prefix (nick!user@host → nick).
    fn nick(&self) -> Option<&str> {
        self.prefix
            .as_deref()
            .and_then(|p| p.split('!').next())
    }
}

/// Shared IRC state, accessible from both the read task and RPC handlers.
pub struct IrcState {
    pub config: IrcConfig,
    pub connected: bool,
    pub channels: Vec<String>,
    pub log: VecDeque<String>,
    writer: Option<WriterHandle>,
}

/// Type-erased writer handle so we can store it without generic params.
type WriterHandle = Box<dyn AsyncWriter>;

trait AsyncWriter {
    fn write_line(&mut self, line: &str) -> std::pin::Pin<Box<dyn std::future::Future<Output = io::Result<()>> + '_>>;
}

/// Writer over a TLS stream.
struct TlsWriter {
    inner: tokio::io::WriteHalf<tokio_rustls::client::TlsStream<tokio::net::TcpStream>>,
}

impl AsyncWriter for TlsWriter {
    fn write_line(&mut self, line: &str) -> std::pin::Pin<Box<dyn std::future::Future<Output = io::Result<()>> + '_>> {
        let data = format!("{line}\r\n");
        Box::pin(async move {
            self.inner.write_all(data.as_bytes()).await
        })
    }
}

/// Writer over a plain TCP stream.
struct PlainWriter {
    inner: tokio::io::WriteHalf<tokio::net::TcpStream>,
}

impl AsyncWriter for PlainWriter {
    fn write_line(&mut self, line: &str) -> std::pin::Pin<Box<dyn std::future::Future<Output = io::Result<()>> + '_>> {
        let data = format!("{line}\r\n");
        Box::pin(async move {
            self.inner.write_all(data.as_bytes()).await
        })
    }
}

impl IrcState {
    fn new(config: IrcConfig) -> Self {
        Self {
            channels: config.channels.clone(),
            config,
            connected: false,
            log: VecDeque::with_capacity(MAX_LOG_LINES),
            writer: None,
        }
    }

    fn push_log(&mut self, line: &str) {
        if self.log.len() >= MAX_LOG_LINES {
            self.log.pop_front();
        }
        self.log.push_back(line.to_string());
    }

    async fn send_raw(&mut self, line: &str) -> io::Result<()> {
        if let Some(ref mut w) = self.writer {
            w.write_line(line).await
        } else {
            Err(io::Error::new(io::ErrorKind::NotConnected, "not connected"))
        }
    }

    async fn send_privmsg(&mut self, target: &str, msg: &str) -> io::Result<()> {
        self.send_raw(&format!("PRIVMSG {target} :{msg}")).await
    }

    async fn join(&mut self, channel: &str) -> io::Result<()> {
        self.send_raw(&format!("JOIN {channel}")).await?;
        if !self.channels.iter().any(|c| c == channel) {
            self.channels.push(channel.to_string());
        }
        Ok(())
    }

    async fn part(&mut self, channel: &str) -> io::Result<()> {
        self.send_raw(&format!("PART {channel}")).await?;
        self.channels.retain(|c| c != channel);
        Ok(())
    }
}

pub type SharedIrc = Rc<RefCell<IrcState>>;

/// Start the IRC module. Returns the shared state handle.
pub fn start(
    config: IrcConfig,
    notify_tx: mpsc::UnboundedSender<Notification>,
    daemon_config: Rc<RefCell<Config>>,
) -> SharedIrc {
    let state = Rc::new(RefCell::new(IrcState::new(config)));
    let state_clone = state.clone();

    tokio::task::spawn_local(async move {
        connection_loop(state_clone, notify_tx, daemon_config).await;
    });

    state
}

async fn connection_loop(
    state: SharedIrc,
    notify_tx: mpsc::UnboundedSender<Notification>,
    daemon_config: Rc<RefCell<Config>>,
) {
    let mut backoff = RECONNECT_BASE_SECS;

    loop {
        let config = state.borrow().config.clone();
        info!("irc: connecting to {}:{}", config.server, config.port);

        match connect_and_run(&state, &config, &notify_tx).await {
            Ok(()) => {
                info!("irc: connection closed cleanly");
            }
            Err(e) => {
                error!("irc: connection error: {e}");
            }
        }

        // Reset backoff if we had a working connection (registered
        // successfully before disconnecting)
        let was_connected = state.borrow().connected;
        state.borrow_mut().connected = false;
        state.borrow_mut().writer = None;
        if was_connected {
            backoff = RECONNECT_BASE_SECS;
        }

        // Persist current channel list to config
        {
            let channels = state.borrow().channels.clone();
            let mut dc = daemon_config.borrow_mut();
            dc.irc.channels = channels;
            dc.save();
        }

        info!("irc: reconnecting in {backoff}s");
        tokio::time::sleep(std::time::Duration::from_secs(backoff)).await;
        backoff = (backoff * 2).min(RECONNECT_MAX_SECS);
    }
}

async fn connect_and_run(
    state: &SharedIrc,
    config: &IrcConfig,
    notify_tx: &mpsc::UnboundedSender<Notification>,
) -> io::Result<()> {
    let addr = format!("{}:{}", config.server, config.port);
    let tcp = tokio::net::TcpStream::connect(&addr).await?;

    if config.tls {
        let tls_config = rustls::ClientConfig::builder_with_provider(
                rustls::crypto::ring::default_provider().into(),
            )
            .with_safe_default_protocol_versions()
            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?
            .with_root_certificates(root_certs())
            .with_no_client_auth();
        let connector = tokio_rustls::TlsConnector::from(Arc::new(tls_config));
        let server_name = rustls::pki_types::ServerName::try_from(config.server.clone())
            .map_err(|e| io::Error::new(io::ErrorKind::InvalidInput, e))?;
        let tls_stream = connector.connect(server_name, tcp).await?;

        let (reader, writer) = tokio::io::split(tls_stream);
        state.borrow_mut().writer = Some(Box::new(TlsWriter { inner: writer }));

        let buf_reader = BufReader::new(reader);
        register_and_read(state, config, buf_reader, notify_tx).await
    } else {
        let (reader, writer) = tokio::io::split(tcp);
        state.borrow_mut().writer = Some(Box::new(PlainWriter { inner: writer }));

        let buf_reader = BufReader::new(reader);
        register_and_read(state, config, buf_reader, notify_tx).await
    }
}

async fn register_and_read<R: tokio::io::AsyncRead + Unpin>(
    state: &SharedIrc,
    config: &IrcConfig,
    mut reader: BufReader<R>,
    notify_tx: &mpsc::UnboundedSender<Notification>,
) -> io::Result<()> {
    // Register
    {
        let mut s = state.borrow_mut();
        s.send_raw(&format!("NICK {}", config.nick)).await?;
        s.send_raw(&format!("USER {} 0 * :{}", config.user, config.realname)).await?;
    }

    let mut buf = Vec::new();
    let mut ping_sent = false;
    let mut deadline = tokio::time::Instant::now()
        + std::time::Duration::from_secs(PING_INTERVAL_SECS);

    loop {
        buf.clear();

        let read_result = tokio::select! {
            result = reader.read_until(b'\n', &mut buf) => result,
            _ = tokio::time::sleep_until(deadline) => {
                if ping_sent {
                    return Err(io::Error::new(
                        io::ErrorKind::TimedOut,
                        "ping timeout — no response from server",
                    ));
                }
                info!("irc: no data for {}s, sending PING", PING_INTERVAL_SECS);
                state.borrow_mut().send_raw("PING :keepalive").await?;
                ping_sent = true;
                deadline = tokio::time::Instant::now()
                    + std::time::Duration::from_secs(PING_TIMEOUT_SECS);
                continue;
            }
        };

        let n = read_result?;
        if n == 0 { break; }

        // Any data from server resets the ping timer
        ping_sent = false;
        deadline = tokio::time::Instant::now()
            + std::time::Duration::from_secs(PING_INTERVAL_SECS);

        // IRC is not guaranteed UTF-8 — lossy conversion handles Latin-1 etc.
        let line = String::from_utf8_lossy(&buf).trim_end().to_string();
        if line.is_empty() { continue; }
        let msg = match IrcMessage::parse(&line) {
            Some(m) => m,
            None => continue,
        };

        match msg.command.as_str() {
            "PING" => {
                let arg = msg.params.first().map(|s| s.as_str()).unwrap_or("");
                state.borrow_mut().send_raw(&format!("PONG :{arg}")).await?;
            }

            // RPL_WELCOME — registration complete
            "001" => {
                info!("irc: registered as {}", config.nick);
                state.borrow_mut().connected = true;

                // Join configured channels
                let channels = state.borrow().channels.clone();
                for ch in &channels {
                    if let Err(e) = state.borrow_mut().send_raw(&format!("JOIN {ch}")).await {
                        warn!("irc: failed to join {ch}: {e}");
                    }
                }
            }

            "PRIVMSG" => {
                let target = msg.params.first().map(|s| s.as_str()).unwrap_or("");
                let text = msg.params.get(1).map(|s| s.as_str()).unwrap_or("");
                let nick = msg.nick().unwrap_or("unknown");

                // Handle CTCP requests (wrapped in \x01)
                if text.starts_with('\x01') && text.ends_with('\x01') {
                    let ctcp = &text[1..text.len()-1];
                    if ctcp.starts_with("VERSION") {
                        let reply = format!(
                            "NOTICE {nick} :\x01VERSION poc-daemon 0.4.0\x01"
                        );
                        state.borrow_mut().send_raw(&reply).await.ok();
                    }
                    // Don't generate notifications for CTCP
                    continue;
                }

                // Log the message
                let log_line = if target.starts_with('#') {
                    format!("[{}] <{}> {}", target, nick, text)
                } else {
                    format!("[PM:{nick}] {text}")
                };
                state.borrow_mut().push_log(&log_line);

                // Write to per-channel/per-user log file
                if target.starts_with('#') {
                    append_log(target, nick, text);
                } else {
                    append_log(&format!("pm-{nick}"), nick, text);
                }

                // Generate notification
                let (ntype, urgency) = classify_privmsg(
                    nick,
                    target,
                    text,
                    &config.nick,
                );

                let _ = notify_tx.send(Notification {
                    ntype,
                    urgency,
                    message: log_line,
                    timestamp: now(),
                });
            }

            // Nick in use
            "433" => {
                let alt = format!("{}_", config.nick);
                warn!("irc: nick in use, trying {alt}");
                state.borrow_mut().send_raw(&format!("NICK {alt}")).await?;
            }

            "JOIN" | "PART" | "QUIT" | "KICK" | "MODE" | "TOPIC" | "NOTICE" => {
                // Could log these, but skip for now
            }

            _ => {}
        }
    }

    Ok(())
}

/// Classify a PRIVMSG into notification type and urgency.
fn classify_privmsg(nick: &str, target: &str, text: &str, my_nick: &str) -> (String, u8) {
    let my_nick_lower = my_nick.to_lowercase();
    let text_lower = text.to_lowercase();

    if !target.starts_with('#') {
        // Private message
        (format!("irc.pm.{nick}"), crate::notify::URGENT)
    } else if text_lower.contains(&my_nick_lower) {
        // Mentioned in channel
        (format!("irc.mention.{nick}"), crate::notify::NORMAL)
    } else {
        // Regular channel message
        let channel = target.trim_start_matches('#');
        (format!("irc.channel.{channel}"), crate::notify::AMBIENT)
    }
}

/// Append a message to the per-channel or per-user log file.
/// Logs go to ~/.claude/irc/logs/{target}.log (e.g. #bcachefs.log, pm-kent.log)
fn append_log(target: &str, nick: &str, text: &str) {
    use std::io::Write;
    // Sanitize target for filename (strip leading #, lowercase)
    let filename = format!("{}.log", target.trim_start_matches('#').to_lowercase());
    let dir = home().join(".claude/irc/logs");
    let _ = std::fs::create_dir_all(&dir);
    if let Ok(mut f) = std::fs::OpenOptions::new()
        .create(true)
        .append(true)
        .open(dir.join(&filename))
    {
        let secs = now() as u64;
        let _ = writeln!(f, "{secs} <{nick}> {text}");
    }
}

fn root_certs() -> rustls::RootCertStore {
    let mut roots = rustls::RootCertStore::empty();
    roots.extend(webpki_roots::TLS_SERVER_ROOTS.iter().cloned());
    roots
}

/// Handle a runtime command from RPC.
pub async fn handle_command(
    state: &SharedIrc,
    daemon_config: &Rc<RefCell<Config>>,
    cmd: &str,
    args: &[String],
) -> Result<String, String> {
    match cmd {
        "join" => {
            let channel = args.first().ok_or("usage: irc join <channel>")?;
            let channel = if channel.starts_with('#') {
                channel.clone()
            } else {
                format!("#{channel}")
            };
            state
                .borrow_mut()
                .join(&channel)
                .await
                .map_err(|e| e.to_string())?;

            // Persist
            let mut dc = daemon_config.borrow_mut();
            if !dc.irc.channels.contains(&channel) {
                dc.irc.channels.push(channel.clone());
            }
            dc.save();

            Ok(format!("joined {channel}"))
        }
        "leave" | "part" => {
            let channel = args.first().ok_or("usage: irc leave <channel>")?;
            let channel = if channel.starts_with('#') {
                channel.clone()
            } else {
                format!("#{channel}")
            };
            state
                .borrow_mut()
                .part(&channel)
                .await
                .map_err(|e| e.to_string())?;

            // Persist
            let mut dc = daemon_config.borrow_mut();
            dc.irc.channels.retain(|c| c != &channel);
            dc.save();

            Ok(format!("left {channel}"))
        }
        "send" | "msg" => {
            if args.len() < 2 {
                return Err("usage: irc send <target> <message>".into());
            }
            let target = &args[0];
            if target.starts_with('#') {
                let s = state.borrow();
                if !s.channels.iter().any(|c| c == target) {
                    return Err(format!(
                        "not in channel {target} (joined: {})",
                        s.channels.join(", ")
                    ));
                }
            }
            let msg = args[1..].join(" ");
            let nick = state.borrow().config.nick.clone();
            state
                .borrow_mut()
                .send_privmsg(target, &msg)
                .await
                .map_err(|e| e.to_string())?;
            append_log(target, &nick, &msg);
            Ok(format!("sent to {target}"))
        }
        "status" => {
            let s = state.borrow();
            Ok(format!(
                "connected={} channels={} log_lines={} nick={}",
                s.connected,
                s.channels.join(","),
                s.log.len(),
                s.config.nick,
            ))
        }
        "log" => {
            let n: usize = args
                .first()
                .and_then(|s| s.parse().ok())
                .unwrap_or(15);
            let s = state.borrow();
            let lines: Vec<&String> = s.log.iter().rev().take(n).collect();
            let mut lines: Vec<&str> = lines.iter().map(|s| s.as_str()).collect();
            lines.reverse();
            Ok(lines.join("\n"))
        }
        "nick" => {
            let new_nick = args.first().ok_or("usage: irc nick <newnick>")?;
            state
                .borrow_mut()
                .send_raw(&format!("NICK {new_nick}"))
                .await
                .map_err(|e| e.to_string())?;

            let mut dc = daemon_config.borrow_mut();
            dc.irc.nick = new_nick.clone();
            dc.save();

            Ok(format!("nick → {new_nick}"))
        }
        _ => Err(format!(
            "unknown irc command: {cmd}\n\
             commands: join, leave, send, status, log, nick"
        )),
    }
}