//! Live event stream for the per-agent web UI. The harness emits one
//! `LiveEvent` per interesting thing that happens during a turn — wake-up
//! (the popped inbox message), every line claude prints on stdout
//! (parsed from `--output-format stream-json`), and the turn-end summary.
//! The web UI subscribes via SSE and renders rows live.
//!
//! Channel type is `tokio::sync::broadcast`. New subscribers see only
//! future events; the dashboard JS deals with the cold-start case by
//! showing "connecting…" until the first event arrives.

use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};

use rusqlite::{Connection, params};
use serde::{Deserialize, Serialize};
use tokio::sync::broadcast;

const CHANNEL_CAPACITY: usize = 256;
/// Max `LiveEvent`s the `Bus` returns from `history()` and keeps in
/// sqlite. Older rows are vacuumed on a periodic sweep.
const HISTORY_CAPACITY: usize = 2000;
/// Default sqlite db path. Lives under `/state/` so it survives
/// destroy/recreate but goes away on purge. Overridable via the
/// `HYPERHIVE_EVENTS_DB` env var (used in tests and one-shot tools).
const DEFAULT_EVENTS_DB: &str = "/state/hyperhive-events.sqlite";

const SCHEMA: &str = "
CREATE TABLE IF NOT EXISTS events (
    id           INTEGER PRIMARY KEY AUTOINCREMENT,
    ts           INTEGER NOT NULL,
    kind         TEXT    NOT NULL,
    payload_json TEXT    NOT NULL
);
CREATE INDEX IF NOT EXISTS idx_events_ts ON events (ts);
";

/// One row of the agent's live stream. Serialised to JSON for SSE delivery.
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(tag = "kind", rename_all = "snake_case")]
pub enum LiveEvent {
    /// Harness popped a wake-up message and is about to invoke claude.
    /// `unread` is the count of *other* messages still in the inbox at
    /// that moment — surfaced as a badge in the live panel header.
    TurnStart {
        from: String,
        body: String,
        unread: u64,
    },
    /// One line of claude's `--output-format stream-json` stdout, parsed as
    /// a generic JSON value (so we don't have to track every claude-code
    /// event variant). The frontend pretty-prints by `type` field.
    Stream(serde_json::Value),
    /// Free-form note from the harness (e.g. "claude exited 0",
    /// "stream-json parse error: ..."). Useful when stream-json itself
    /// fails so the UI doesn't just go silent.
    Note(String),
    /// Turn finished. `ok=false` means claude exited non-zero or the
    /// harness hit a transport error.
    TurnEnd { ok: bool, note: Option<String> },
}

/// sqlite-backed event log. Wraps a `Connection` behind a `Mutex` so the
/// `Bus` (which clones cheaply) shares one writer.
struct EventStore {
    conn: Mutex<Connection>,
}

impl EventStore {
    fn open(path: &Path) -> rusqlite::Result<Self> {
        if let Some(parent) = path.parent() {
            let _ = std::fs::create_dir_all(parent);
        }
        let conn = Connection::open(path)?;
        conn.execute_batch(SCHEMA)?;
        Ok(Self {
            conn: Mutex::new(conn),
        })
    }

    fn append(&self, event: &LiveEvent) -> rusqlite::Result<()> {
        let ts = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .ok()
            .and_then(|d| i64::try_from(d.as_secs()).ok())
            .unwrap_or(0);
        let kind = match event {
            LiveEvent::TurnStart { .. } => "turn_start",
            LiveEvent::Stream(_) => "stream",
            LiveEvent::Note(_) => "note",
            LiveEvent::TurnEnd { .. } => "turn_end",
        };
        let payload = serde_json::to_string(event).unwrap_or_else(|_| "null".into());
        let conn = self.conn.lock().unwrap();
        conn.execute(
            "INSERT INTO events (ts, kind, payload_json) VALUES (?1, ?2, ?3)",
            params![ts, kind, payload],
        )?;
        Ok(())
    }

    fn recent(&self, limit: usize) -> rusqlite::Result<Vec<LiveEvent>> {
        let limit_i = i64::try_from(limit).unwrap_or(i64::MAX);
        let conn = self.conn.lock().unwrap();
        let mut stmt = conn.prepare(
            "SELECT payload_json FROM events
              ORDER BY id DESC
              LIMIT ?1",
        )?;
        let rows = stmt.query_map(params![limit_i], |row| {
            let s: String = row.get(0)?;
            Ok(serde_json::from_str::<LiveEvent>(&s).ok())
        })?;
        let mut out: Vec<LiveEvent> = rows.flatten().flatten().collect();
        out.reverse();
        Ok(out)
    }
}

#[derive(Clone)]
pub struct Bus {
    tx: Arc<broadcast::Sender<LiveEvent>>,
    /// Persistent event log. `None` only if opening the sqlite db failed
    /// at construction — we keep going so the harness doesn't die on a
    /// missing `/state/` mount in dev / test scenarios.
    store: Option<Arc<EventStore>>,
}

impl Bus {
    /// Open the default events db (`/state/hyperhive-events.sqlite`, or
    /// `HYPERHIVE_EVENTS_DB`). On failure, fall back to a no-store bus —
    /// the harness still works, just without persistent history.
    #[must_use]
    pub fn new() -> Self {
        let path = std::env::var_os("HYPERHIVE_EVENTS_DB")
            .map_or_else(|| PathBuf::from(DEFAULT_EVENTS_DB), PathBuf::from);
        let store = match EventStore::open(&path) {
            Ok(s) => Some(Arc::new(s)),
            Err(e) => {
                tracing::warn!(error = ?e, path = %path.display(), "events db open failed; running without history");
                None
            }
        };
        let (tx, _) = broadcast::channel(CHANNEL_CAPACITY);
        Self {
            tx: Arc::new(tx),
            store,
        }
    }

    pub fn emit(&self, event: LiveEvent) {
        if let Some(store) = &self.store
            && let Err(e) = store.append(&event)
        {
            tracing::warn!(error = ?e, "events: append failed");
        }
        // Lagged subscribers drop events — fine; the UI is a tail, not a log.
        let _ = self.tx.send(event);
    }

    pub fn subscribe(&self) -> broadcast::Receiver<LiveEvent> {
        self.tx.subscribe()
    }

    /// Most recent events, oldest first, capped at `HISTORY_CAPACITY`.
    /// Drives the terminal pre-fill when the operator opens the agent
    /// page; without a store (db open failed) this is empty.
    #[must_use]
    pub fn history(&self) -> Vec<LiveEvent> {
        let Some(store) = &self.store else {
            return Vec::new();
        };
        store.recent(HISTORY_CAPACITY).unwrap_or_default()
    }
}

impl Default for Bus {
    fn default() -> Self {
        Self::new()
    }
}