//! 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 (attended since the last state change):
//!
//! | raw      | seen   | display  | priority |
//! |----------|--------|----------|----------|
//! | working  | —      | working  | 2        |
//! | blocked  | —      | blocked  | 4        |
//! | idle     | false  | done     | 3        |
//! | idle     | true   | idle     | 1        |
//! | none     | —      | unknown  | 0        |
//!
//! "Seen" is maintained three ways: the pane is fully focused in an attached
//! client (the daemon watches tmux focus), the user jumped to it via
//! `dingger focus` / menu click, or its next transition.

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, in priority order (highest first).
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Status {
    Unknown,
    Idle,
    Working,
    Done,
    Blocked,
}

impl Status {
    #[allow(dead_code)] // herdr parity: the full vocabulary is part of the model
    pub fn label(&self) -> &'static str {
        match self {
            Status::Unknown => "unknown",
            Status::Idle => "idle",
            Status::Working => "working",
            Status::Done => "done",
            Status::Blocked => "blocked",
        }
    }

    #[allow(dead_code)] // herdr parity
    pub fn parse(label: &str) -> Option<Status> {
        match label {
            "working" => Some(Status::Working),
            "blocked" => Some(Status::Blocked),
            "done" => Some(Status::Done),
            "idle" => Some(Status::Idle),
            "unknown" => Some(Status::Unknown),
            _ => None,
        }
    }

    /// herdr's priority: blocked > done > working > idle > unknown.
    #[allow(dead_code)] // herdr parity; used once the menu bar consumes statuses from the daemon
    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,
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct PaneTrack {
    state: AgentState,
    seen: bool,
    /// Unix second the pane entered its current done/blocked episode; drives
    /// the FIFO ready queue.
    ready_since: Option<u64>,
}

pub struct Watcher {
    tracks: HashMap<String, PaneTrack>,
    /// Last published (queue, counts); avoids rewriting options every tick.
    last_published: Option<(String, (String, String, String, String))>,
    interval_secs: u64,
    sounds: bool,
}

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

    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 {
            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;
                }
            }
            std::thread::sleep(std::time::Duration::from_secs(self.interval_secs));
        }
    }

    fn tick(&mut self) -> Result<(), String> {
        let panes = tmux::list_panes()?;

        // 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 prev_track = self.tracks.get(&pane.pane_id).copied();
            let (prev_state, prev_seen) = prev_track
                .map(|track| (track.state, track.seen))
                .unwrap_or((AgentState::Unknown, true));

            // Raw state: hook reports are authoritative while the pane runs
            // the agent; screen detection is the fallback for panes that
            // never report. Viewer screens (transcripts, pickers) return
            // `skip_state_update: true` — they say nothing about state and
            // leave the previous one standing (herdr's publishing contract).
            let raw = if pane.dead {
                Some(AgentState::Idle)
            } else if let Some(agent) = pane.agent {
                if let Some(state) = hooks::hook_state(&pane.pane_id) {
                    Some(state)
                } else {
                    let screen = match tmux::capture_pane(&pane.pane_id) {
                        Ok(screen) => screen,
                        Err(err) => {
                            warn!(target = %pane.display_target, %err, "capture failed");
                            continue;
                        }
                    };
                    // 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_some(detection.state)
                }
            } else {
                // A pane that stops running an agent (agent quit into a
                // shell) is no longer an observation; a stale hook report
                // from the dead agent is not authoritative.
                Some(AgentState::Unknown)
            };

            let Some(new_state) = raw else {
                debug!(target = %pane.display_target, "observation skipped (viewer screen)");
                continue;
            };

            // Seen: attended since the last state change. Attended means the
            // pane is fully focused in an attached client, the user jumped to
            // it (`@dingger_ack`), or it was just first observed. A first
            // observation of idle is seen (nothing has happened yet); a
            // working/blocked → idle transition is an unseen completion.
            let transition = new_state != prev_state;
            // Attended also via `dingger focus` / menu click (@dingger_ack).
            let mut seen = if transition {
                !(new_state == AgentState::Idle && prev_state == AgentState::Unknown)
            } else {
                prev_seen || pane.written_ack == "1"
            };
            if !seen && pane.attended() {
                seen = true;
            }
            if transition || seen != prev_seen {
                let ready_since = if is_ready_to_attend(new_state, seen) {
                    Some(unix_now())
                } else {
                    None
                };
                self.tracks.insert(
                    pane.pane_id.clone(),
                    PaneTrack {
                        state: new_state,
                        seen,
                        ready_since,
                    },
                );
            }
            if transition {
                debug!(target = %pane.display_target, ?prev_state, ?new_state, seen, "state change");
                let _ = tmux::clear_ack(&pane.pane_id);
            } else if seen != prev_seen {
                let _ = tmux::ack(&pane.pane_id);
            }
            let display = display_status(
                self.tracks
                    .get(&pane.pane_id)
                    .unwrap_or(&PaneTrack { state: new_state, seen, ready_since: None }),
            );
            // @agent_state mirrors the display status on both transitions and
            // attendance changes (done → idle when the user focuses the pane).
            if pane.written_state != display.label() {
                if let Err(err) = tmux::set_agent_state(&pane.pane_id, display.label()) {
                    warn!(target = %pane.display_target, %err, "failed to write @agent_state");
                }
            }
            if new_state == AgentState::Unknown {
                // The agent is gone; its last hook report must not outlive it.
                hooks::drop_report(&pane.pane_id);
            }

            // Keep the pane's agent label current even when the state is
            // unchanged (e.g. an agent swap between two idle panes).
            let agent_label = pane
                .agent
                .map(detect_core::agent_label)
                .unwrap_or("")
                .to_string();
            if pane.written_agent != agent_label {
                if let Err(err) = tmux::set_agent(&pane.pane_id, pane.agent) {
                    warn!(target = %pane.display_target, %err, "failed to write @agent");
                }
            }

            if transition {
                if let Some(kind) = notification_kind_for_transition(prev_state, new_state) {
                    // herdr: a blocked pane plays the alert sound even when
                    // the user is watching; a finished pane stays silent when
                    // they are already looking at it.
                    let suppressed = pane.suppresses_notifications();
                    if !suppressed {
                        let context = format!("{} ({})", pane.display_target, agent_label);
                        send_notification(&agent_label, &kind, &context);
                    }
                    if self.sounds {
                        play_sound(&kind);
                    }
                }
            }
        }

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

    /// Publish the FIFO queue (done + blocked panes, oldest transition first)
    /// and counts as server-global options for the tmux status line and
    /// `dingger focus`.
    fn publish(&mut self, panes: &[tmux::Pane]) {
        let mut ready: Vec<(&str, String, u64)> = Vec::new(); // (pane_id, target, ready_since)
        let mut blocked = 0usize;
        let mut done = 0usize;
        let mut working = 0usize;
        for pane in panes {
            let Some(track) = self.tracks.get(&pane.pane_id) else {
                continue;
            };
            let status = display_status(track);
            match status {
                Status::Working => working += 1,
                Status::Done | Status::Blocked => {
                    if track.ready_since.is_some() {
                        if status == Status::Blocked {
                            blocked += 1;
                        } else {
                            done += 1;
                        }
                        if let Some(since) = track.ready_since {
                            ready.push((pane.pane_id.as_str(), pane.display_target.clone(), since));
                        }
                    }
                }
                Status::Idle | Status::Unknown => {}
            }
        }
        ready.sort_by_key(|(_, _, since)| *since);

        let queue = ready
            .iter()
            .map(|(pane_id, _, since)| format!("{pane_id}:{since}"))
            .collect::<Vec<_>>()
            .join(",");
        let counts = (
            ready.len().to_string(),
            blocked.to_string(),
            working.to_string(),
            done.to_string(),
        );
        let next = (queue.clone(), counts.clone());
        if self.last_published.as_ref() != Some(&next) {
            self.last_published = Some(next);
            for (name, value) in [
                ("@dingger_queue", queue.as_str()),
                ("@dingger_ready", counts.0.as_str()),
                ("@dingger_blocked", counts.1.as_str()),
                ("@dingger_working", counts.2.as_str()),
                ("@dingger_done", counts.3.as_str()),
            ] {
                if let Err(err) = tmux::set_global(name, value) {
                    warn!(%err, "failed to write {name}");
                }
            }
        }
    }
}

/// When a pane became ready for the user, as unix seconds. Ready means the
/// agent is waiting on the user: done (finished, unseen) or blocked.
fn is_ready_to_attend(state: AgentState, seen: bool) -> bool {
    match state {
        AgentState::Blocked => true,
        AgentState::Idle => !seen,
        _ => false,
    }
}

fn display_status(track: &PaneTrack) -> Status {
    match track.state {
        AgentState::Working => Status::Working,
        AgentState::Blocked => Status::Blocked,
        AgentState::Idle => {
            if track.seen {
                Status::Idle
            } else {
                Status::Done
            }
        }
        AgentState::Unknown => Status::Unknown,
    }
}

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

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

    #[test]
    fn policy_matches_herdr() {
        assert!(notification_kind_for_transition(AgentState::Working, AgentState::Blocked)
            .is_some_and(|kind| matches!(kind, NotificationKind::NeedsAttention)));
        assert!(notification_kind_for_transition(AgentState::Blocked, AgentState::Blocked).is_none());
        assert!(notification_kind_for_transition(AgentState::Unknown, AgentState::Blocked)
            .is_some_and(|kind| matches!(kind, NotificationKind::NeedsAttention)));
        assert!(notification_kind_for_transition(AgentState::Working, AgentState::Idle)
            .is_some_and(|kind| matches!(kind, NotificationKind::Finished)));
        assert!(notification_kind_for_transition(AgentState::Blocked, AgentState::Idle)
            .is_some_and(|kind| matches!(kind, NotificationKind::Finished)));
        // Unknown → Idle is a first observation, not a completion.
        assert!(notification_kind_for_transition(AgentState::Unknown, AgentState::Idle).is_none());
        assert!(notification_kind_for_transition(AgentState::Idle, AgentState::Working).is_none());
        assert!(notification_kind_for_transition(AgentState::Idle, AgentState::Unknown).is_none());
    }

    #[test]
    fn display_status_maps_herdr() {
        let unseen = PaneTrack { state: AgentState::Idle, seen: false, ready_since: Some(1) };
        let seen = PaneTrack { state: AgentState::Idle, seen: true, ready_since: None };
        assert_eq!(display_status(&unseen), Status::Done);
        assert_eq!(display_status(&seen), Status::Idle);
        assert_eq!(
            display_status(&PaneTrack { state: AgentState::Working, seen: false, ready_since: None }),
            Status::Working
        );
        assert_eq!(
            display_status(&PaneTrack { state: AgentState::Blocked, seen: false, ready_since: Some(1) }),
            Status::Blocked
        );
    }

    #[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());
    }
}