//! htop command: live-updating system and agent process dashboard.
//!
//! Sends an initial message to a Matrix room showing load average and
//! per-agent process info, then edits it in-place every 5 seconds using
//! Matrix replacement events.  A single htop session per room is enforced;
//! a new `htop` invocation stops any existing session and starts a fresh one.
//! Sessions auto-stop after the configured duration (default 5 minutes).

use std::collections::HashMap;
use std::sync::Arc;
use std::time::Duration;

use tokio::sync::{Mutex as TokioMutex, watch};

use crate::agents::{AgentPool, AgentStatus};
use crate::slog;
use crate::transport::ChatTransport;

use super::bot::markdown_to_html;

/// A parsed htop command from a Matrix message body.
#[derive(Debug, PartialEq)]
pub enum HtopCommand {
    /// Start (or restart) monitoring.  `duration_secs` is the auto-stop
    /// timeout; defaults to 300 (5 minutes).
    Start { duration_secs: u64 },
    /// Stop any active monitoring session for the room.
    Stop,
}

/// Per-room htop session: holds the stop-signal sender so callers can cancel.
pub struct HtopSession {
    /// Send `true` to request a graceful stop of the background loop.
    pub stop_tx: watch::Sender<bool>,
}

/// Per-room htop session map type alias.
///
/// Keys are platform-agnostic room ID strings (e.g. `"!abc:example.com"` on
/// Matrix) so this type works with any [`ChatTransport`] implementation.
pub type HtopSessions = Arc<TokioMutex<HashMap<String, HtopSession>>>;

/// Parse an htop command from a raw Matrix message body.
///
/// Strips the bot mention prefix and checks whether the first word is `htop`.
/// Returns `None` when the message is not an htop command.
///
/// Recognised forms (after stripping the bot mention):
/// - `htop`          → `Start { duration_secs: 300 }`
/// - `htop stop`     → `Stop`
/// - `htop 10m`      → `Start { duration_secs: 600 }`
/// - `htop 120`      → `Start { duration_secs: 120 }` (bare seconds)
pub fn extract_htop_command(message: &str, bot_name: &str, bot_user_id: &str) -> Option<HtopCommand> {
    let stripped = strip_mention(message, bot_name, bot_user_id);
    let trimmed = stripped.trim();

    // Strip leading punctuation (e.g. the comma in "@timmy, htop")
    let trimmed = trimmed.trim_start_matches(|c: char| !c.is_alphanumeric());

    let (cmd, args) = match trimmed.split_once(char::is_whitespace) {
        Some((c, a)) => (c, a.trim()),
        None => (trimmed, ""),
    };

    if !cmd.eq_ignore_ascii_case("htop") {
        return None;
    }

    if args.eq_ignore_ascii_case("stop") {
        return Some(HtopCommand::Stop);
    }

    let duration_secs = parse_duration(args).unwrap_or(300);
    Some(HtopCommand::Start { duration_secs })
}

/// Parse an optional duration argument.
///
/// Accepts `""` (empty → `None`), `"5m"` / `"10M"` (minutes), or a bare
/// integer interpreted as seconds.
fn parse_duration(s: &str) -> Option<u64> {
    if s.is_empty() {
        return None;
    }
    if let Some(mins_str) = s.strip_suffix('m').or_else(|| s.strip_suffix('M')) {
        return mins_str.parse::<u64>().ok().map(|m| m * 60);
    }
    s.parse::<u64>().ok()
}

/// Strip the bot mention prefix from a raw Matrix message body.
///
/// Mirrors the logic in `commands::strip_bot_mention` so htop detection works
/// without depending on private symbols in that module.
fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a str {
    let trimmed = message.trim();

    if let Some(rest) = strip_prefix_ci(trimmed, bot_user_id) {
        return rest;
    }
    if let Some(localpart) = bot_user_id.split(':').next()
        && let Some(rest) = strip_prefix_ci(trimmed, localpart)
    {
        return rest;
    }
    if let Some(rest) = strip_prefix_ci(trimmed, bot_name) {
        return rest;
    }
    trimmed
}

fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
    if text.len() < prefix.len() {
        return None;
    }
    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
        return None;
    }
    let rest = &text[prefix.len()..];
    match rest.chars().next() {
        None => Some(rest),
        Some(c) if c.is_alphanumeric() || c == '-' || c == '_' => None,
        _ => Some(rest),
    }
}

// ---------------------------------------------------------------------------
// System stats
// ---------------------------------------------------------------------------

/// Read the system load average using the `uptime` command.
///
/// Returns a short string like `"load average: 1.23, 0.98, 0.75"` on success,
/// or `"load: unknown"` on failure.
fn get_load_average() -> String {
    let output = std::process::Command::new("uptime")
        .output()
        .ok()
        .and_then(|o| String::from_utf8(o.stdout).ok())
        .unwrap_or_default();

    // uptime output typically contains "load average: X, Y, Z" (Linux/macOS)
    // or "load averages: X Y Z" (some BSD variants).
    if let Some(idx) = output.find("load average") {
        output[idx..].trim().trim_end_matches('\n').to_string()
    } else {
        "load: unknown".to_string()
    }
}

/// Process stats for a single agent, gathered from `ps`.
#[derive(Debug, Default)]
struct AgentProcessStats {
    cpu_pct: f64,
    mem_pct: f64,
    num_procs: usize,
}

/// Gather CPU% and MEM% for processes whose command line contains `worktree_path`.
///
/// Runs `ps aux` and sums all matching lines.  Returns `None` when no
/// matching process is found.
fn gather_process_stats(worktree_path: &str) -> Option<AgentProcessStats> {
    let output = std::process::Command::new("ps")
        .args(["aux"])
        .output()
        .ok()
        .and_then(|o| String::from_utf8(o.stdout).ok())?;

    let mut stats = AgentProcessStats::default();

    for line in output.lines().skip(1) {
        // Avoid matching against our own status display (the ps command itself)
        if !line.contains(worktree_path) {
            continue;
        }
        let parts: Vec<&str> = line.split_whitespace().collect();
        // ps aux columns: USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND...
        if parts.len() >= 4
            && let (Ok(cpu), Ok(mem)) = (parts[2].parse::<f64>(), parts[3].parse::<f64>())
        {
            stats.cpu_pct += cpu;
            stats.mem_pct += mem;
            stats.num_procs += 1;
        }
    }

    if stats.num_procs > 0 {
        Some(stats)
    } else {
        None
    }
}

// ---------------------------------------------------------------------------
// Message formatting
// ---------------------------------------------------------------------------

/// Build the Markdown text for the htop dashboard.
///
/// `tick` is the number of updates sent so far (0 = initial).
/// `total_duration_secs` is the configured auto-stop timeout.
///
/// Output uses a compact single-line format per agent so it renders
/// without wrapping on narrow screens (~40 chars), such as mobile
/// Matrix clients.
pub fn build_htop_message(agents: &AgentPool, tick: u32, total_duration_secs: u64) -> String {
    let elapsed_secs = (tick as u64) * 5;
    let remaining_secs = total_duration_secs.saturating_sub(elapsed_secs);
    let remaining_mins = remaining_secs / 60;
    let remaining_secs_rem = remaining_secs % 60;

    let load = get_load_average();

    let mut lines = vec![
        format!(
            "**htop** · auto-stops in {}m{}s",
            remaining_mins, remaining_secs_rem
        ),
        load,
        String::new(),
    ];

    let all_agents = agents.list_agents().unwrap_or_default();
    let active: Vec<_> = all_agents
        .iter()
        .filter(|a| matches!(a.status, AgentStatus::Running | AgentStatus::Pending))
        .collect();

    if active.is_empty() {
        lines.push("*No agents currently running.*".to_string());
    } else {
        for agent in &active {
            let story_label = agent
                .story_id
                .split('_')
                .next()
                .unwrap_or(&agent.story_id)
                .to_string();
            let stats = agent
                .worktree_path
                .as_deref()
                .and_then(gather_process_stats)
                .unwrap_or_default();
            lines.push(format!(
                "**{}** #{} cpu:{:.1}% mem:{:.1}%",
                agent.agent_name, story_label, stats.cpu_pct, stats.mem_pct,
            ));
        }
    }

    lines.join("\n")
}

// ---------------------------------------------------------------------------
// Background monitoring loop
// ---------------------------------------------------------------------------

/// Run the htop background loop: update the message every 5 seconds until
/// the stop signal is received or the timeout expires.
///
/// Uses the [`ChatTransport`] abstraction so the loop works with any chat
/// platform, not just Matrix.
pub async fn run_htop_loop(
    transport: Arc<dyn ChatTransport>,
    room_id: String,
    initial_message_id: String,
    agents: Arc<AgentPool>,
    mut stop_rx: watch::Receiver<bool>,
    duration_secs: u64,
) {
    let interval_secs: u64 = 5;
    let max_ticks = (duration_secs / interval_secs).max(1);

    for tick in 1..=max_ticks {
        // Wait for the interval or a stop signal.
        let sleep = tokio::time::sleep(Duration::from_secs(interval_secs));
        tokio::pin!(sleep);

        tokio::select! {
            _ = &mut sleep => {}
            Ok(()) = stop_rx.changed() => {
                if *stop_rx.borrow() {
                    send_stopped_message(&*transport, &room_id, &initial_message_id).await;
                    return;
                }
            }
        }

        // Re-check after waking — the sender might have signalled while we slept.
        if *stop_rx.borrow() {
            send_stopped_message(&*transport, &room_id, &initial_message_id).await;
            return;
        }

        let text = build_htop_message(&agents, tick as u32, duration_secs);
        let html = markdown_to_html(&text);

        if let Err(e) = transport.edit_message(&room_id, &initial_message_id, &text, &html).await {
            slog!("[htop] Failed to update message: {e}");
            return;
        }
    }

    // Auto-stop: timeout reached.
    send_stopped_message(&*transport, &room_id, &initial_message_id).await;
}

async fn send_stopped_message(transport: &dyn ChatTransport, room_id: &str, message_id: &str) {
    let text = "**htop** — monitoring stopped.";
    let html = markdown_to_html(text);
    if let Err(e) = transport.edit_message(room_id, message_id, text, &html).await {
        slog!("[htop] Failed to send stop message: {e}");
    }
}

// ---------------------------------------------------------------------------
// Public command handlers (called from on_room_message in bot.rs)
// ---------------------------------------------------------------------------

/// Start a new htop monitoring session for `room_id`.
///
/// Stops any existing session for the room, sends the initial dashboard
/// message, and spawns a background task that edits it every 5 seconds.
///
/// Uses the [`ChatTransport`] abstraction so htop works with any platform.
pub async fn handle_htop_start(
    transport: &Arc<dyn ChatTransport>,
    room_id: &str,
    htop_sessions: &HtopSessions,
    agents: Arc<AgentPool>,
    duration_secs: u64,
) {
    // Stop any existing session (best-effort; ignore errors if already done).
    stop_existing_session(htop_sessions, room_id).await;

    // Send the initial message.
    let initial_text = build_htop_message(&agents, 0, duration_secs);
    let initial_html = markdown_to_html(&initial_text);
    let message_id = match transport.send_message(room_id, &initial_text, &initial_html).await {
        Ok(id) => id,
        Err(e) => {
            slog!("[htop] Failed to send initial message: {e}");
            return;
        }
    };

    // Create the stop channel and register the session.
    let (stop_tx, stop_rx) = watch::channel(false);
    {
        let mut sessions = htop_sessions.lock().await;
        sessions.insert(room_id.to_string(), HtopSession { stop_tx });
    }

    // Spawn the background update loop.
    let transport_clone = Arc::clone(transport);
    let sessions_clone = Arc::clone(htop_sessions);
    let room_id_owned = room_id.to_string();
    tokio::spawn(async move {
        run_htop_loop(
            transport_clone,
            room_id_owned.clone(),
            message_id,
            agents,
            stop_rx,
            duration_secs,
        )
        .await;
        // Clean up the session entry when the loop exits naturally.
        let mut sessions = sessions_clone.lock().await;
        sessions.remove(&room_id_owned);
    });
}

/// Stop the active htop session for `room_id`, if any.
///
/// When there is no active session, sends a "no active session" reply
/// to the room so the user knows the command was received.
pub async fn handle_htop_stop(
    transport: &dyn ChatTransport,
    room_id: &str,
    htop_sessions: &HtopSessions,
) {
    let had_session = stop_existing_session(htop_sessions, room_id).await;
    if !had_session {
        let msg = "No active htop session in this room.";
        let html = markdown_to_html(msg);
        if let Err(e) = transport.send_message(room_id, msg, &html).await {
            slog!("[htop] Failed to send no-session reply: {e}");
        }
    }
    // When a session was active, the background task handles the final edit.
}

/// Signal and remove the existing session for `room_id`.
///
/// Returns `true` if a session was found and stopped.
async fn stop_existing_session(htop_sessions: &HtopSessions, room_id: &str) -> bool {
    let mut sessions = htop_sessions.lock().await;
    if let Some(session) = sessions.remove(room_id) {
        // Signal the background task to stop (ignore error — task may be done).
        let _ = session.stop_tx.send(true);
        true
    } else {
        false
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    // -- extract_htop_command -----------------------------------------------

    #[test]
    fn htop_bare_command() {
        let cmd = extract_htop_command("@timmy htop", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 300 }));
    }

    #[test]
    fn htop_with_display_name() {
        let cmd = extract_htop_command("Timmy htop", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 300 }));
    }

    #[test]
    fn htop_stop() {
        let cmd = extract_htop_command("@timmy htop stop", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Stop));
    }

    #[test]
    fn htop_duration_minutes() {
        let cmd = extract_htop_command("@timmy htop 10m", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 600 }));
    }

    #[test]
    fn htop_duration_uppercase_m() {
        let cmd = extract_htop_command("@timmy htop 2M", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 120 }));
    }

    #[test]
    fn htop_duration_seconds() {
        let cmd = extract_htop_command("@timmy htop 90", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 90 }));
    }

    #[test]
    fn non_htop_command_returns_none() {
        let cmd = extract_htop_command("@timmy status", "Timmy", "@timmy:homeserver.local");
        assert!(cmd.is_none());
    }

    #[test]
    fn unrelated_message_returns_none() {
        let cmd = extract_htop_command("hello world", "Timmy", "@timmy:homeserver.local");
        assert!(cmd.is_none());
    }

    #[test]
    fn htop_case_insensitive() {
        let cmd = extract_htop_command("@timmy HTOP", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 300 }));
    }

    #[test]
    fn htop_full_user_id() {
        let cmd = extract_htop_command(
            "@timmy:homeserver.local htop",
            "Timmy",
            "@timmy:homeserver.local",
        );
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 300 }));
    }

    #[test]
    fn htop_with_comma_after_mention() {
        // Some Matrix clients format mentions as "@timmy, htop"
        let cmd = extract_htop_command("@timmy, htop", "Timmy", "@timmy:homeserver.local");
        assert_eq!(cmd, Some(HtopCommand::Start { duration_secs: 300 }));
    }

    // -- parse_duration -----------------------------------------------------

    #[test]
    fn parse_duration_empty_returns_none() {
        assert_eq!(parse_duration(""), None);
    }

    #[test]
    fn parse_duration_minutes() {
        assert_eq!(parse_duration("5m"), Some(300));
    }

    #[test]
    fn parse_duration_seconds() {
        assert_eq!(parse_duration("120"), Some(120));
    }

    #[test]
    fn parse_duration_invalid_returns_none() {
        assert_eq!(parse_duration("abc"), None);
    }

    // -- build_htop_message -------------------------------------------------

    #[test]
    fn build_htop_message_no_agents() {
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        assert!(text.contains("htop"), "should mention htop: {text}");
        assert!(
            text.contains("No agents currently running"),
            "should note no agents: {text}"
        );
    }

    #[test]
    fn build_htop_message_contains_load() {
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        // Load average is gathered via `uptime`; it should appear in some form.
        assert!(
            text.contains("load"),
            "message should contain load info: {text}"
        );
    }

    #[test]
    fn build_htop_message_shows_remaining_time() {
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        assert!(
            text.contains("auto-stops in"),
            "should show remaining time: {text}"
        );
    }

    #[test]
    fn build_htop_message_load_on_own_line() {
        // Load average must be on its own line, not combined with the htop header.
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        let lines: Vec<&str> = text.lines().collect();
        let header_line = lines.first().expect("should have a header line");
        // Header line must NOT contain "load" — load is on the second line.
        assert!(
            !header_line.contains("load"),
            "load should be on its own line, not the header: {header_line}"
        );
        // Second line must contain "load".
        let load_line = lines.get(1).expect("should have a load line");
        assert!(
            load_line.contains("load"),
            "second line should contain load info: {load_line}"
        );
    }

    #[test]
    fn build_htop_message_no_table_syntax() {
        // Must not use Markdown table format (pipes/separators) — those are too
        // wide for narrow mobile screens.
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        assert!(
            !text.contains("|----"),
            "output must not contain table separator rows: {text}"
        );
        assert!(
            !text.contains("| Agent"),
            "output must not contain table header row: {text}"
        );
    }

    #[test]
    fn build_htop_message_header_fits_40_chars() {
        // The header line (htop + remaining time) must fit in ~40 rendered chars.
        let pool = Arc::new(crate::agents::AgentPool::new_test(3000));
        let text = build_htop_message(&pool, 0, 300);
        let header = text.lines().next().expect("should have a header line");
        // Strip markdown bold markers (**) for length calculation.
        let rendered = header.replace("**", "");
        assert!(
            rendered.len() <= 40,
            "header line too wide for mobile ({} chars): {rendered}",
            rendered.len()
        );
    }
}