//! Poll-and-detect loop: tmux pane capture → detection engine → herdr's
//! status model → notifications and pane-option write-back.
//!
//! Status model (herdr's, verbatim): five display statuses over two inputs,
//! the raw agent state (working/blocked/idle, from hooks or scraping) and a
//! `seen` flag:
//!
//! | raw      | seen   | display  | priority |
//! |----------|--------|----------|----------|
//! | working  | any    | working  | 2        |
//! | blocked  | any    | blocked  | 4        |
//! | idle     | false  | done     | 3        |
//! | idle     | true   | idle     | 1        |
//! | none     | any    | unknown  | 0        |
//!
//! `seen` follows herdr's `apply_pane_state_change` and
//! `mark_active_tab_seen` (src/app/actions.rs); see [`advance`].
//!
//! All per-pane state lives in tmux pane options, so a daemon restart picks
//! up exactly where it left off:
//!
//! - `@agent_state`   display status (what every surface renders)
//! - `@dingger_since` unix ms the pane entered its current status
//! - `@dingger_hook`  last state an agent extension reported
//! - `@dingger_ack`   one-shot "the user jumped here" event from `dingger focus`
//! - `@agent_session` the agent's session reference, for restore

use std::collections::HashMap;

use detect_core::{detect_agent_with_osc, AgentState};
use tracing::{debug, info, warn};

use crate::hooks;
use crate::notify::{play_sound, send_notification, NotificationKind};
use crate::tmux;

/// herdr's display statuses.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Status {
    Unknown,
    Idle,
    Working,
    Done,
    Blocked,
}

impl Status {
    pub fn label(self) -> &'static str {
        match self {
            Status::Unknown => "unknown",
            Status::Idle => "idle",
            Status::Working => "working",
            Status::Done => "done",
            Status::Blocked => "blocked",
        }
    }

    pub fn from_label(label: &str) -> Status {
        match label {
            "idle" => Status::Idle,
            "working" => Status::Working,
            "done" => Status::Done,
            "blocked" => Status::Blocked,
            _ => Status::Unknown,
        }
    }

    /// herdr's priority: blocked > done > working > idle > unknown.
    pub fn priority(self) -> u8 {
        match self {
            Status::Blocked => 4,
            Status::Done => 3,
            Status::Working => 2,
            Status::Idle => 1,
            Status::Unknown => 0,
        }
    }
}

/// herdr's notification policy (`notification_toast_for_state_change`),
/// driven by raw state transitions.
pub fn notification_kind_for_transition(
    prev_state: AgentState,
    new_state: AgentState,
) -> Option<NotificationKind> {
    if new_state == prev_state {
        return None;
    }
    match new_state {
        AgentState::Blocked => Some(NotificationKind::NeedsAttention),
        AgentState::Idle if matches!(prev_state, AgentState::Working | AgentState::Blocked) => {
            Some(NotificationKind::Finished)
        }
        _ => None,
    }
}

/// herdr's per-pane attendance record.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct PaneTrack {
    pub state: AgentState,
    pub seen: bool,
    /// Unix millisecond the pane entered its current status: the queue
    /// serves done and blocked oldest first; working and idle are listed
    /// most recent first.
    pub since: Option<u64>,
}

impl PaneTrack {
    /// A pane not observed yet. herdr: `PaneState::new` starts `seen = true`.
    pub const NEW: PaneTrack = PaneTrack {
        state: AgentState::Unknown,
        seen: true,
        since: None,
    };

    pub fn status(&self) -> Status {
        match (self.state, self.seen) {
            (AgentState::Working, _) => Status::Working,
            (AgentState::Blocked, _) => Status::Blocked,
            (AgentState::Idle, false) => Status::Done,
            (AgentState::Idle, true) => Status::Idle,
            (AgentState::Unknown, _) => Status::Unknown,
        }
    }

    /// Rebuild a track from the pane options a previous daemon wrote.
    fn restore(written_state: &str, written_since: &str) -> PaneTrack {
        let since = written_since.trim().parse::<u64>().ok();
        let (state, seen) = match written_state {
            "done" => (AgentState::Idle, false),
            "idle" => (AgentState::Idle, true),
            "working" => (AgentState::Working, true),
            "blocked" => (AgentState::Blocked, true),
            _ => return PaneTrack::NEW,
        };
        PaneTrack { state, seen, since }
    }
}

/// One observation step for a pane: herdr's `apply_pane_state_change`
/// followed by `mark_active_tab_seen`, as a pure function.
///
/// - Transition to any non-idle state: seen.
/// - Completion (working/blocked to idle): seen only if the user is looking
///   at the pane's window; otherwise the pane is done.
/// - Any other transition to idle (first observation): seen unchanged.
/// - Looking at the pane's window, or jumping to it (`acked`): seen.
pub fn advance(
    prev: PaneTrack,
    observed: AgentState,
    attended: bool,
    acked: bool,
    now: u64,
) -> PaneTrack {
    let mut next = prev;
    if observed != prev.state {
        next.state = observed;
        if observed != AgentState::Idle {
            next.seen = true;
        } else if matches!(prev.state, AgentState::Working | AgentState::Blocked) {
            next.seen = attended;
        }
    }
    if attended || acked {
        next.seen = true;
    }
    if next.status() != prev.status() || next.since.is_none() {
        next.since = Some(now);
    }
    next
}

/// The order agents are listed in: herdr's status priority; within a
/// status, done and blocked oldest first (the queue: nothing waits
/// forever), working and idle most recent first; then by place.
pub fn list_order(status: Status, since: Option<u64>) -> (std::cmp::Reverse<u8>, i128) {
    let since = since.map(i128::from);
    let key = match status {
        Status::Done | Status::Blocked => since.unwrap_or(i128::MAX),
        _ => since.map(|since| -since).unwrap_or(i128::MAX),
    };
    (std::cmp::Reverse(status.priority()), key)
}

pub struct Watcher {
    tracks: HashMap<String, PaneTrack>,
    snapshots: crate::snapshot::Recorder,
    offer: crate::restore::OfferPublisher,
    /// Last published (queue, blocked, done, working); avoids rewriting the
    /// global options every tick.
    last_published: Option<(String, usize, usize, usize)>,
    interval_secs: u64,
    sounds: bool,
    notifications: bool,
}

impl Watcher {
    pub fn new(interval_secs: u64, sounds: bool, notifications: bool) -> Self {
        Self {
            tracks: HashMap::new(),
            snapshots: Default::default(),
            offer: Default::default(),
            last_published: None,
            interval_secs: interval_secs.max(1),
            sounds,
            notifications,
        }
    }

    pub fn run(&mut self) -> Result<(), String> {
        info!(interval = self.interval_secs, "watching tmux panes");
        // dingger is a client of the tmux server, which may not exist yet:
        // it starts when the first terminal opens one. Wait for it, then
        // keep watching across server restarts.
        let mut had_server = false;
        loop {
            let started = std::time::Instant::now();
            match self.tick() {
                Ok(()) => {
                    if !had_server {
                        info!("tmux server available");
                        had_server = true;
                    }
                }
                Err(err) => {
                    if had_server {
                        warn!(%err, "tmux server unavailable; waiting for it to return");
                    }
                    had_server = false;
                }
            }
            // After the tick, so snapshots carry the states it just wrote.
            self.snapshots.tick(unix_now());
            self.offer.tick();
            debug!(ms = started.elapsed().as_millis() as u64, "tick");
            hooks::wait_for_wake(std::time::Duration::from_secs(self.interval_secs));
        }
    }

    fn tick(&mut self) -> Result<(), String> {
        let listed = std::time::Instant::now();
        let panes = tmux::list_panes()?;
        let now = unix_now();

        // Forget panes that went away.
        self.tracks
            .retain(|pane_id, _| panes.iter().any(|pane| pane.pane_id == *pane_id));
        hooks::forget(&panes.iter().map(|pane| pane.pane_id.clone()).collect::<Vec<_>>());

        for pane in &panes {
            let Some(observations) = observe(pane, listed) else {
                debug!(target = %pane.display_target, "observation skipped (viewer screen)");
                continue;
            };

            // First sight of a pane in this process: resume from its options.
            let restored = !self.tracks.contains_key(&pane.pane_id);
            let mut track = self
                .tracks
                .get(&pane.pane_id)
                .copied()
                .unwrap_or_else(|| PaneTrack::restore(&pane.written_state, &pane.written_since));
            let acked = pane.written_ack == "1";

            // Apply every observation in order: a turn that started and
            // finished between two ticks is still a completion.
            let mut alerts = Vec::new();
            for observed in observations {
                let next = advance(track, observed, pane.attended, acked, now);
                if next.state != track.state {
                    info!(
                        target = %pane.display_target,
                        prev = track.status().label(),
                        next = next.status().label(),
                        "state change"
                    );
                    // Notify on transitions observed by this process, not
                    // when resuming from options written before a restart.
                    if !restored {
                        alerts.extend(notification_kind_for_transition(track.state, next.state));
                    }
                }
                track = next;
            }
            self.tracks.insert(pane.pane_id.clone(), track);

            // Update what the user sees first, then alert.
            if acked {
                let _ = tmux::unset_pane_option(&pane.pane_id, "@dingger_ack");
            }
            self.write_pane_options(pane, track);
            for kind in alerts {
                self.notify(pane, kind);
            }
        }

        self.publish(&panes);
        Ok(())
    }

    /// Write the pane's options that changed, in one tmux command list:
    /// tmux applies it as a unit, so a daemon killed mid-write never leaves
    /// a display state that disagrees with the hook state it came from.
    fn write_pane_options(&self, pane: &tmux::Pane, track: PaneTrack) {
        let mut changes: Vec<(&str, Option<String>)> = Vec::new();
        let mut change = |name: &'static str, written: &str, value: String| {
            if written != value {
                changes.push((name, (!value.is_empty()).then_some(value)));
            }
        };
        // The authoritative hook state, so a restart keeps it; it goes with
        // the agent.
        let hook = match pane.agent {
            Some(_) => hooks::last_state(&pane.pane_id).map(state_label).unwrap_or_default(),
            None => "",
        };
        if pane.agent.is_none() || !hook.is_empty() {
            change("@dingger_hook", &pane.written_hook, hook.to_string());
        }
        change("@agent_state", &pane.written_state, track.status().label().to_string());
        change("@dingger_since", &pane.written_since, track.since.map(|s| s.to_string()).unwrap_or_default());
        change("@agent", &pane.written_agent, pane.agent.map(detect_core::agent_label).unwrap_or("").to_string());
        let name = crate::names::display_name(pane.agent, &pane.pane_title, &pane.cwd, host_name())
            .unwrap_or_default();
        change("@agent_name", &pane.written_name, name);
        // The session reference, for restore; it goes with the agent.
        match (pane.agent, hooks::session(&pane.pane_id)) {
            (Some(_), Some(session)) => change("@agent_session", &pane.written_session, session),
            (None, _) => change("@agent_session", &pane.written_session, String::new()),
            _ => {}
        }
        if let Err(err) = tmux::set_pane_options(&pane.pane_id, &changes) {
            warn!(target = %pane.display_target, %err, "failed to write pane options");
        }
    }

    fn notify(&self, pane: &tmux::Pane, kind: NotificationKind) {
        // herdr: a blocked pane plays the alert even when the user is looking
        // at it; a finished pane stays silent when they already are.
        let watching = pane.attended;
        if matches!(kind, NotificationKind::Finished) && watching {
            return;
        }
        let agent = pane.agent.map(detect_core::agent_label).unwrap_or("agent");
        if self.notifications && !watching {
            send_notification(agent, &kind, &format!("{} ({agent})", pane.display_target));
        }
        if self.sounds {
            play_sound(&kind);
        }
    }

    /// Publish the ready queue and counts as server-global options for the
    /// status line, menu bar, and focus. The queue is ordered like the menu:
    /// herdr's priority (blocked before done), oldest first within it.
    fn publish(&mut self, panes: &[tmux::Pane]) {
        let mut queue: Vec<(std::cmp::Reverse<u8>, u64, &str)> = Vec::new();
        let (mut blocked, mut done, mut working) = (0, 0, 0);
        for pane in panes {
            let Some(track) = self.tracks.get(&pane.pane_id) else {
                continue;
            };
            match track.status() {
                Status::Blocked => blocked += 1,
                Status::Done => done += 1,
                Status::Working => working += 1,
                Status::Idle | Status::Unknown => {}
            }
            // The queue: what needs the user, oldest first.
            if matches!(track.status(), Status::Blocked | Status::Done) {
                let since = track.since.unwrap_or(u64::MAX);
                queue.push((std::cmp::Reverse(track.status().priority()), since, pane.pane_id.as_str()));
            }
        }
        queue.sort();
        let queue = queue
            .iter()
            .map(|(_, _, pane_id)| *pane_id)
            .collect::<Vec<_>>()
            .join(",");

        let next = (queue, blocked, done, working);
        if self.last_published.as_ref() == Some(&next) {
            return;
        }
        for (name, value) in [
            ("@dingger_queue", next.0.clone()),
            ("@dingger_blocked", next.1.to_string()),
            ("@dingger_done", next.2.to_string()),
            ("@dingger_working", next.3.to_string()),
        ] {
            if let Err(err) = tmux::set_global(name, &value) {
                warn!(%err, "failed to write {name}");
            }
        }
        self.last_published = Some(next);
    }
}

/// The pane's raw agent states this tick, in order, or `None` when the
/// screen is a viewer (transcript, picker) that says nothing about state.
fn observe(pane: &tmux::Pane, listed: std::time::Instant) -> Option<Vec<AgentState>> {
    if pane.dead {
        return Some(vec![AgentState::Idle]);
    }
    let Some(agent) = pane.agent else {
        // The agent is gone; its last hook report must not outlive it.
        hooks::drop_reports(&pane.pane_id, listed);
        return Some(vec![AgentState::Unknown]);
    };
    // Agent-reported state is authoritative; it survives restarts through
    // the `@dingger_hook` option until the extension reports again.
    if let Some(states) = hooks::take_observations(&pane.pane_id) {
        return Some(states);
    }
    if let Some(state) = parse_state(&pane.written_hook) {
        return Some(vec![state]);
    }
    let screen = match tmux::capture_pane(&pane.pane_id) {
        Ok(screen) => screen,
        Err(err) => {
            warn!(target = %pane.display_target, %err, "capture failed");
            return None;
        }
    };
    // tmux pane_title carries the last OSC title the application set; tmux
    // does not re-expose OSC progress sequences.
    let detection = detect_agent_with_osc(Some(agent), &screen, &pane.pane_title, "");
    (!detection.skip_state_update).then(|| vec![detection.state])
}

/// The host name tmux uses as a pane's default title.
fn host_name() -> &'static str {
    static HOST: std::sync::OnceLock<String> = std::sync::OnceLock::new();
    HOST.get_or_init(|| {
        std::process::Command::new("hostname")
            .output()
            .map(|out| String::from_utf8_lossy(&out.stdout).trim().to_string())
            .unwrap_or_default()
    })
}

fn state_label(state: AgentState) -> &'static str {
    match state {
        AgentState::Idle => "idle",
        AgentState::Working => "working",
        AgentState::Blocked => "blocked",
        AgentState::Unknown => "unknown",
    }
}

fn parse_state(label: &str) -> Option<AgentState> {
    match label {
        "idle" => Some(AgentState::Idle),
        "working" => Some(AgentState::Working),
        "blocked" => Some(AgentState::Blocked),
        _ => None,
    }
}

fn unix_now() -> u64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_millis() as u64)
        .unwrap_or(0)
}

#[cfg(test)]
mod tests {
    use super::*;
    use AgentState::{Blocked, Idle, Unknown, Working};

    fn step(prev: PaneTrack, observed: AgentState, attended: bool) -> PaneTrack {
        advance(prev, observed, attended, false, 100)
    }

    #[test]
    fn notification_policy_matches_herdr() {
        assert!(matches!(
            notification_kind_for_transition(Working, Blocked),
            Some(NotificationKind::NeedsAttention)
        ));
        assert!(matches!(
            notification_kind_for_transition(Unknown, Blocked),
            Some(NotificationKind::NeedsAttention)
        ));
        assert!(matches!(
            notification_kind_for_transition(Working, Idle),
            Some(NotificationKind::Finished)
        ));
        assert!(matches!(
            notification_kind_for_transition(Blocked, Idle),
            Some(NotificationKind::Finished)
        ));
        assert!(notification_kind_for_transition(Blocked, Blocked).is_none());
        assert!(notification_kind_for_transition(Unknown, Idle).is_none());
        assert!(notification_kind_for_transition(Idle, Working).is_none());
        assert!(notification_kind_for_transition(Idle, Unknown).is_none());
    }

    // herdr: initial_idle_in_background_stays_seen
    #[test]
    fn first_observation_of_idle_is_idle() {
        let track = step(PaneTrack::NEW, Idle, false);
        assert_eq!(track.status(), Status::Idle);
        assert_eq!(track.since, Some(100));
    }

    // herdr: state_changed_idle_in_background_marks_unseen
    #[test]
    fn completion_away_from_the_window_is_done() {
        let working = step(step(PaneTrack::NEW, Idle, false), Working, false);
        assert_eq!(working.status(), Status::Working);
        let done = step(working, Idle, false);
        assert_eq!(done.status(), Status::Done);
        assert_eq!(done.since, Some(100));
    }

    // herdr: active_tab_completion_marks_pane_seen
    #[test]
    fn completion_while_looking_is_idle() {
        let working = step(PaneTrack::NEW, Working, true);
        let idle = advance(working, Idle, true, false, 150);
        assert_eq!(idle.status(), Status::Idle);
        assert_eq!(idle.since, Some(150), "idle since the turn ended");
    }

    // herdr: switch_workspace_marks_panes_seen (mark_active_tab_seen)
    #[test]
    fn looking_at_the_window_turns_done_into_idle() {
        let done = step(step(PaneTrack::NEW, Working, false), Idle, false);
        assert_eq!(done.status(), Status::Done);
        let still_done = step(done, Idle, false);
        assert_eq!(still_done.status(), Status::Done);
        let seen = advance(still_done, Idle, true, false, 170);
        assert_eq!(seen.status(), Status::Idle);
        assert_eq!(seen.since, Some(170), "idle since the user looked");
    }

    // herdr: agent_focus_marks_already_focused_done_agent_seen
    #[test]
    fn jumping_to_a_pane_turns_done_into_idle() {
        let done = step(step(PaneTrack::NEW, Working, false), Idle, false);
        let seen = advance(done, Idle, false, true, 200);
        assert_eq!(seen.status(), Status::Idle);
    }

    #[test]
    fn working_again_clears_done_and_the_next_completion_is_done_again() {
        let done = step(step(PaneTrack::NEW, Working, false), Idle, false);
        let working = advance(done, Working, false, false, 250);
        assert_eq!(working.status(), Status::Working);
        assert_eq!(working.since, Some(250));
        let done_again = advance(working, Idle, false, false, 300);
        assert_eq!(done_again.status(), Status::Done);
        assert_eq!(done_again.since, Some(300));
    }

    #[test]
    fn blocked_needs_the_user_even_while_looking() {
        let blocked = step(step(PaneTrack::NEW, Working, false), Blocked, true);
        assert_eq!(blocked.status(), Status::Blocked);
        assert_eq!(blocked.since, Some(100));
        // answering the prompt: back to work, then a completion away → done
        let done = step(step(blocked, Working, false), Idle, false);
        assert_eq!(done.status(), Status::Done);
    }

    #[test]
    fn the_stamp_survives_unchanged_ticks() {
        let done = advance(step(PaneTrack::NEW, Working, false), Idle, false, false, 50);
        assert_eq!(advance(done, Idle, false, false, 999).since, Some(50));
        let idle = advance(done, Idle, true, false, 60);
        assert_eq!(advance(idle, Idle, true, false, 999).since, Some(60));
    }

    #[test]
    fn waiting_oldest_first_the_rest_most_recent_first() {
        let mut rows = [
            ("idle old", Status::Idle, Some(10)),
            ("done new", Status::Done, Some(90)),
            ("idle unknown", Status::Idle, None),
            ("working old", Status::Working, Some(20)),
            ("idle new", Status::Idle, Some(80)),
            ("done old", Status::Done, Some(30)),
            ("blocked", Status::Blocked, Some(99)),
            ("working new", Status::Working, Some(70)),
        ];
        rows.sort_by_key(|(_, status, since)| list_order(*status, *since));
        let names: Vec<_> = rows.iter().map(|(name, ..)| *name).collect();
        assert_eq!(
            names,
            ["blocked", "done old", "done new", "working new", "working old", "idle new", "idle old", "idle unknown"]
        );
    }

    #[test]
    fn agent_exit_is_unknown() {
        let done = step(step(PaneTrack::NEW, Working, false), Idle, false);
        assert_eq!(step(done, Unknown, false).status(), Status::Unknown);
    }

    #[test]
    fn restore_resumes_where_the_previous_daemon_left_off() {
        let done = PaneTrack::restore("done", "42");
        assert_eq!(done.status(), Status::Done);
        assert_eq!(done.since, Some(42));
        // the same observation after a restart keeps it done
        assert_eq!(step(done, Idle, false).status(), Status::Done);
        assert_eq!(PaneTrack::restore("idle", "").status(), Status::Idle);
        assert_eq!(PaneTrack::restore("", "").status(), Status::Unknown);
        assert_eq!(PaneTrack::restore("idle", "42").since, Some(42), "recency survives a restart");
    }

    #[test]
    fn priority_matches_herdr() {
        assert!(Status::Blocked.priority() > Status::Done.priority());
        assert!(Status::Done.priority() > Status::Working.priority());
        assert!(Status::Working.priority() > Status::Idle.priority());
        assert!(Status::Idle.priority() > Status::Unknown.priority());
    }
}