//! The live session registry. Every session mutation -- spawn, delete,
//! token changes -- funnels through [`SessionManager`] under one lock, so
//! in-memory state and `config.ron` can't come apart (the same pattern as
//! dev-updater's `registry.rs`).
//!
//! A live session is a driver plus one event pump: the driver reports
//! [`Event`]s into an mpsc channel; the pump assigns each a sequence
//! number, appends it to the session's transcript file, and fans it out to
//! SSE subscribers. The transcript is the source of truth -- subscribers
//! that fall behind or reconnect catch up from the file by cursor.

pub mod claude;
pub mod driver;
pub mod echo;
pub mod llama;
pub mod transcript;
pub mod transport;

use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex, RwLock};
use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{Context, Result, bail};
use serde::Serialize;
use tokio::sync::{broadcast, mpsc};

use crate::config::{
    Config, DriverKind, ProviderConfig, SessionConfig, SetupConfig, SshConfig, TokenEntry,
};
use claude::ClaudeDriver;
use driver::{Driver, Event, ImageRef, SessionStatus};
use echo::EchoDriver;
use llama::LlamaDriver;
use transcript::{SeqEvent, Transcript};
use transport::Transport;

/// Fan-out buffer per session. A subscriber that falls further behind than
/// this is caught up from the transcript file instead (see `routes`), so
/// the size only bounds memory, not correctness.
const EVENT_BUFFER: usize = 256;

pub fn now() -> f64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs_f64()
}

/// What the phone needs to spawn a session -- the spawn screen's fields.
pub struct SpawnSpec {
    /// Which machine, and which of its providers.
    pub setup: String,
    pub provider: String,
    pub title: Option<String>,
    pub model: Option<String>,
    pub cwd: Option<PathBuf>,
    pub permission_mode: Option<String>,
    /// Driver-interpreted settings; see `SessionConfig::params`.
    pub params: std::collections::BTreeMap<String, String>,
}

/// One row of `GET /sessions`.
#[derive(Debug, Clone, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct SessionInfo {
    pub id: String,
    pub provider: String,
    /// Id of the machine it runs on, which is what the session stored.
    pub setup: String,
    /// That machine's current label, resolved when this row is built --
    /// so renaming a setup renames it everywhere it appears, rather than
    /// leaving old sessions showing the old name.
    pub setup_name: String,
    pub title: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub model: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub cwd: Option<PathBuf>,
    pub status: SessionStatus,
    pub last_activity: f64,
    pub created: f64,
}

/// A running session: its driver plus the shared state the event pump
/// keeps current. Cheap to clone-by-`Arc` into request handlers.
pub struct LiveSession {
    meta: SessionConfig,
    driver: Box<dyn Driver>,
    /// The same channel the driver reports into; the manager injects
    /// `UserMessage`/`Answered` here so they take a sequence number in
    /// order with everything else.
    sink: mpsc::UnboundedSender<Event>,
    events: broadcast::Sender<SeqEvent>,
    transcript_path: PathBuf,
    shared: Arc<Shared>,
}

/// The pump-maintained view of a session, read by the list endpoint.
/// `model` also lives here (not in the immutable meta) because it can
/// change mid-session via `set_model`.
struct Shared {
    status: Mutex<SessionStatus>,
    last_activity: Mutex<f64>,
    model: Mutex<Option<String>>,
}

impl LiveSession {
    /// Records the user's message in the transcript, then hands it to the
    /// driver -- which queues it for injection mid-run rather than at the
    /// end of the turn (the point of the whole app).
    pub fn send_message(&self, text: String, images: Vec<ImageRef>) {
        // Attachments render in the transcript like any produced image --
        // the files route serves uploads by the same ref.
        for image in &images {
            let _ = self.sink.send(Event::Image {
                image: image.clone(),
            });
        }
        let _ = self.sink.send(Event::UserMessage { text: text.clone() });
        self.driver.send_user_message(text, images);
    }

    pub fn answer_question(&self, question_id: &str, answer: &str) {
        let _ = self.sink.send(Event::Answered {
            id: question_id.to_string(),
            answer: answer.to_string(),
        });
        self.driver.answer_question(question_id, answer);
    }

    pub fn interrupt(&self) {
        self.driver.interrupt();
    }

    /// Stops this session's process without deleting anything.
    pub fn shutdown(&self) {
        self.driver.shutdown();
    }

    pub fn compact(&self) {
        self.driver.compact();
    }

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

    pub fn transcript_path(&self) -> &Path {
        &self.transcript_path
    }

    /// The session's directory (attachments in, produced files out live in
    /// `attachments/` and `files/` under it).
    pub fn dir(&self) -> &Path {
        self.transcript_path
            .parent()
            .expect("transcript lives in the session dir")
    }

    /// Stores one uploaded attachment, returning the id `POST /message`
    /// references it by. Removed with the session directory on delete --
    /// the same path out as everything else in it.
    pub fn save_attachment(&self, bytes: &[u8], content_type: &str) -> Result<String> {
        // An unrecognized type is almost always a phone photo whose
        // content type the picker didn't set; jpg is the useful guess.
        let extension = crate::media::extension_for(content_type).unwrap_or("jpg");
        let name = format!("{}.{extension}", random_hex());
        let dir = self.dir().join("attachments");
        crate::private::create_dir(&dir)?;
        std::fs::write(dir.join(&name), bytes)
            .with_context(|| format!("write attachment {name}"))?;
        Ok(name)
    }

    /// `setup_name` is passed in rather than stored: only the manager
    /// holds the config, and the label can change under a running session.
    fn info(&self, setup_name: &str) -> SessionInfo {
        SessionInfo {
            id: self.meta.id.clone(),
            provider: self.meta.provider.clone(),
            setup: self.meta.setup.clone(),
            setup_name: setup_name.to_string(),
            title: self.meta.title.clone(),
            model: self.shared.model.lock().unwrap().clone(),
            cwd: self.meta.cwd.clone(),
            status: *self.shared.status.lock().unwrap(),
            last_activity: *self.shared.last_activity.lock().unwrap(),
            created: self.meta.created,
        }
    }
}

struct Inner {
    config: Config,
    live: HashMap<String, Arc<LiveSession>>,
}

pub struct SessionManager {
    config_path: PathBuf,
    /// Per-session directories (transcript, attachments, produced images)
    /// live under here, each named by session id.
    data_dir: PathBuf,
    /// Downloaded GGUF models, shared by every session that names one --
    /// which is why they live beside the session directories rather than
    /// inside one.
    models_dir: PathBuf,
    inner: RwLock<Inner>,
}

impl SessionManager {
    /// Loads the config and relaunches a driver for every persisted
    /// session -- for the real drivers that is the `--resume`/session-file
    /// crash-recovery story; the echo driver just starts fresh over the
    /// same transcript. Must be called inside a tokio runtime (each
    /// session spawns its event pump).
    pub fn new(config_path: PathBuf, data_dir: PathBuf, models_dir: PathBuf) -> Result<Self> {
        let config = Config::load(&config_path)?;
        crate::private::create_dir(&data_dir)?;

        let mut live = HashMap::new();
        for meta in &config.sessions {
            // One unlaunchable session -- a corrupt transcript, an
            // unreachable ssh host, a provider that was edited away --
            // shows as exited rather than taking the whole server down
            // with it, and can still be deleted from the phone.
            match resolve(&config, meta).and_then(|(setup, provider)| {
                launch(meta.clone(), &setup, &provider, &data_dir, &models_dir)
            }) {
                Ok(session) => {
                    live.insert(meta.id.clone(), session);
                }
                Err(err) => {
                    tracing::error!("couldn't relaunch session {}: {err:#}", meta.id);
                }
            }
        }
        let manager = Self {
            config_path,
            data_dir,
            models_dir,
            inner: RwLock::new(Inner { config, live }),
        };
        manager.seed_setup()?;
        Ok(manager)
    }

    /// Writes a starting `claude-cli` provider into a config that has none,
    /// so a fresh install has something to spawn and a worked example of
    /// the schema to edit. Runs local by default -- a session is given a
    /// host when the CLI lives elsewhere, which is a per-session choice.
    /// Gives a fresh install something to spawn. Only ever fires when
    /// there are no setups at all -- deleting the last one is a choice,
    /// not a state to be repaired.
    fn seed_setup(&self) -> Result<()> {
        let mut inner = self.inner.write().unwrap();
        if !inner.config.setups.is_empty() {
            return Ok(());
        }
        let mut candidate = inner.config.clone();
        candidate.setups.push(Config::seed());
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        tracing::info!(
            "no setups configured -- added \"{}\"",
            crate::config::LOCAL_SETUP
        );
        Ok(())
    }

    /// The one path by which the config changes.
    ///
    /// Clone, apply, save, and only then commit: a failed write leaves
    /// what was already there and reports why, so what this server
    /// believes and what is on disk cannot come apart. The ordering is
    /// the whole trick -- mutating in place and then saving would leave a
    /// server that had accepted a change nothing on disk records.
    fn update<T>(&self, apply: impl FnOnce(&mut Config) -> Result<T>) -> Result<T> {
        let mut inner = self.inner.write().unwrap();
        let mut candidate = inner.config.clone();
        let outcome = apply(&mut candidate)?;
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        Ok(outcome)
    }

    /// Adds a machine with the providers it was found to have.
    ///
    /// `providers` comes from probing rather than from the caller (see
    /// `crate::setups`), which is why this takes them as an argument: the
    /// probe is async and this is not, so the route does the asking and
    /// this does the writing.
    pub fn add_setup(
        &self,
        name: &str,
        ssh: Option<SshConfig>,
        providers: Vec<ProviderConfig>,
    ) -> Result<SetupConfig> {
        let name = name.trim().to_string();
        if name.is_empty() {
            bail!("a setup needs a name");
        }
        self.update(|config| {
            if config.setup_named(&name).is_some() {
                bail!("there is already a setup called \"{name}\"");
            }
            // Ids are derived once and then fixed, so a label can be
            // edited later without orphaning the sessions that named it.
            let mut id = crate::setups::id_from(&name);
            while config.setup(&id).is_some() {
                id = format!("{id}-{}", &random_hex()[..4]);
            }
            let setup = SetupConfig {
                id,
                name: name.clone(),
                ssh,
                providers,
            };
            config.setups.push(setup.clone());
            Ok(setup)
        })
    }

    /// Renames a machine, or replaces what was discovered on it.
    pub fn update_setup(
        &self,
        id: &str,
        name: Option<&str>,
        providers: Option<Vec<ProviderConfig>>,
    ) -> Result<SetupConfig> {
        self.update(|config| {
            if let Some(name) = name {
                let name = name.trim();
                if name.is_empty() {
                    bail!("a setup needs a name");
                }
                if config.setups.iter().any(|s| s.name == name && s.id != id) {
                    bail!("there is already a setup called \"{name}\"");
                }
            }
            let setup = config
                .setups
                .iter_mut()
                .find(|setup| setup.id == id)
                .with_context(|| format!("no setup with id \"{id}\""))?;
            if let Some(name) = name {
                setup.name = name.trim().to_string();
            }
            if let Some(providers) = providers {
                setup.providers = providers;
            }
            Ok(setup.clone())
        })
    }

    /// Removes a machine, provided nothing is still running on it.
    ///
    /// Refused rather than cascaded: deleting a machine should not
    /// silently kill conversations, and the person asking is better placed
    /// to decide which of those sessions they still want.
    pub fn delete_setup(&self, id: &str) -> Result<()> {
        self.update(|config| {
            if config.setup(id).is_none() {
                bail!("no setup with id \"{id}\"");
            }
            let using: Vec<&str> = config
                .sessions
                .iter()
                .filter(|session| session.setup == id)
                .map(|session| session.title.as_str())
                .collect();
            if !using.is_empty() {
                bail!(
                    "{} session(s) still run on it: {}. Delete them first.",
                    using.len(),
                    using.join(", "),
                );
            }
            config.setups.retain(|setup| setup.id != id);
            Ok(())
        })
    }

    pub fn tokens(&self) -> Vec<TokenEntry> {
        self.inner.read().unwrap().config.tokens.clone()
    }

    /// Replaces the enrolled token list. With one device this is rotation:
    /// the old hash is invalidated the moment the new config is saved.
    pub fn set_tokens(&self, tokens: Vec<TokenEntry>) -> Result<()> {
        let mut inner = self.inner.write().unwrap();
        let mut candidate = inner.config.clone();
        candidate.tokens = tokens;
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        Ok(())
    }

    /// Every session, in config order, with live status joined in. A
    /// session that failed to relaunch reports as exited.
    /// Stops every session's process, for a server that is going away.
    ///
    /// Drivers set `kill_on_drop`, which covers a session being deleted
    /// while the server keeps running -- but not the server itself being
    /// signalled, because nothing drops on the way out of a SIGTERM. That
    /// leaves the children orphaned, which for a `llama-server` holding a
    /// model means gigabytes of memory nobody owns any more. So exiting
    /// asks them all to stop first.
    pub fn shutdown_all(&self) {
        let inner = self.inner.read().unwrap();
        for session in inner.live.values() {
            session.shutdown();
        }
        tracing::info!("stopped {} session process(es)", inner.live.len());
    }

    pub fn sessions(&self) -> Vec<SessionInfo> {
        let inner = self.inner.read().unwrap();
        inner
            .config
            .sessions
            .iter()
            .map(|meta| match inner.live.get(&meta.id) {
                Some(session) => session.info(label_of(&inner.config, &meta.setup)),
                None => SessionInfo {
                    id: meta.id.clone(),
                    setup: meta.setup.clone(),
                    setup_name: label_of(&inner.config, &meta.setup).to_string(),
                    provider: meta.provider.clone(),
                    title: meta.title.clone(),
                    model: meta.model.clone(),
                    cwd: meta.cwd.clone(),
                    status: SessionStatus::Exited,
                    last_activity: meta.created,
                    created: meta.created,
                },
            })
            .collect()
    }

    pub fn session(&self, id: &str) -> Option<Arc<LiveSession>> {
        self.inner.read().unwrap().live.get(id).cloned()
    }

    /// Every provider this server offers, built-in echo included.
    /// Every machine this server can run something on, each with what it
    /// can run. One list rather than two, because the pair is the choice.
    pub fn setups(&self) -> Vec<SetupConfig> {
        self.inner.read().unwrap().config.setups.clone()
    }

    pub fn spawn_session(&self, spec: SpawnSpec) -> Result<SessionInfo> {
        let mut inner = self.inner.write().unwrap();
        let setup = inner
            .config
            .setup(&spec.setup)
            .with_context(|| {
                format!(
                    "no setup with id \"{}\" -- configured: {}",
                    spec.setup,
                    // Ids, since that is what was looked up. Listing the
                    // labels made the failure read as a contradiction:
                    // "no setup named X -- configured: X", when X was a
                    // label and the id was something else.
                    names(inner.config.setups.iter().map(|s| s.id.as_str())),
                )
            })?
            .clone();
        let provider = setup
            .provider(&spec.provider)
            .with_context(|| {
                format!(
                    "setup \"{}\" has no provider named \"{}\" -- it offers: {}",
                    spec.setup,
                    spec.provider,
                    names(setup.providers.iter().map(|p| p.name.as_str())),
                )
            })?
            .clone();
        let id = unique_id(&inner.config);
        let title = spec
            .title
            .filter(|title| !title.trim().is_empty())
            .unwrap_or_else(|| format!("{} session", provider.name));
        let meta = SessionConfig {
            id: id.clone(),
            setup: setup.id.clone(),
            provider: provider.name.clone(),
            title,
            model: spec.model.or_else(|| provider.models.first().cloned()),
            cwd: spec.cwd,
            permission_mode: spec.permission_mode,
            params: spec.params,
            created: now(),
        };

        let session = launch(
            meta.clone(),
            &setup,
            &provider,
            &self.data_dir,
            &self.models_dir,
        )?;
        let mut candidate = inner.config.clone();
        candidate.sessions.push(meta);
        if let Err(err) = candidate.save(&self.config_path) {
            // The path out of everything the launch created, taken in the
            // same change: drop the session and its directory so a failed
            // save leaves no orphan.
            drop(session);
            let _ = std::fs::remove_dir_all(self.data_dir.join(&id));
            return Err(err);
        }
        inner.config = candidate;
        let info = session.info(&setup.name);
        inner.live.insert(id, session);
        Ok(info)
    }

    /// Changes a session's model: persisted (so a respawn keeps it and the
    /// list shows it) and handed to the driver, which switches in place
    /// where its dialect can. Through the manager, not the session, so the
    /// config and the live view can't disagree.
    pub fn set_session_model(&self, id: &str, model: &str) -> Result<()> {
        let mut inner = self.inner.write().unwrap();
        if !inner.config.sessions.iter().any(|meta| meta.id == id) {
            bail!("no session {id}");
        }
        let mut candidate = inner.config.clone();
        for meta in candidate.sessions.iter_mut().filter(|meta| meta.id == id) {
            meta.model = Some(model.to_string());
        }
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        if let Some(session) = inner.live.get(id) {
            *session.shared.model.lock().unwrap() = Some(model.to_string());
            session.driver.set_model(model);
        }
        Ok(())
    }

    /// Kills the process, releases everything the spawn created, and
    /// deletes the transcript and files -- the complete path out.
    pub fn delete_session(&self, id: &str) -> Result<()> {
        let mut inner = self.inner.write().unwrap();
        if !inner.config.sessions.iter().any(|meta| meta.id == id) {
            bail!("no session {id}");
        }
        let mut candidate = inner.config.clone();
        candidate.sessions.retain(|meta| meta.id != id);
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        if let Some(session) = inner.live.remove(id) {
            session.driver.shutdown();
        }
        let dir = self.data_dir.join(id);
        if dir.exists() {
            std::fs::remove_dir_all(&dir).with_context(|| format!("remove {}", dir.display()))?;
        }
        Ok(())
    }
}

/// The provider and host a session's config names, or a message saying
/// which one is missing. Both are looked up fresh at every launch, so
/// editing either takes effect on the next respawn.
fn resolve(config: &Config, meta: &SessionConfig) -> Result<(SetupConfig, ProviderConfig)> {
    let setup = config
        .setup(&meta.setup)
        .with_context(|| format!("no setup named \"{}\"", meta.setup))?;
    let provider = setup.provider(&meta.provider).with_context(|| {
        format!(
            "setup \"{}\" has no provider named \"{}\"",
            meta.setup, meta.provider
        )
    })?;
    Ok((setup.clone(), provider.clone()))
}

/// A setup's current label, or its id when the setup has been deleted --
/// which is what a session left behind by a removed machine shows, and is
/// better than an empty column or a guess at what it used to be called.
fn label_of<'a>(config: &'a Config, id: &'a str) -> &'a str {
    config.setup(id).map_or(id, |setup| setup.name.as_str())
}

/// Names for a failure message: what there is, so the reader can see what
/// they meant instead of only that they were wrong.
fn names<'a>(all: impl Iterator<Item = &'a str>) -> String {
    let all: Vec<_> = all.collect();
    if all.is_empty() {
        "none".to_string()
    } else {
        all.join(", ")
    }
}

/// 8 random bytes, hex -- short enough for a URL, unique enough forever at
/// this scale.
pub fn random_hex() -> String {
    use rand::Rng;
    let mut bytes = [0u8; 8];
    rand::rng().fill_bytes(&mut bytes);
    bytes.iter().map(|b| format!("{b:02x}")).collect()
}

/// A [`random_hex`] id not already taken -- checked out of caution.
fn unique_id(config: &Config) -> String {
    loop {
        let id = random_hex();
        if !config.sessions.iter().any(|meta| meta.id == id) {
            return id;
        }
    }
}

/// Creates the session directory, opens its transcript (continuing the
/// sequence numbering if one exists), starts the driver, and spawns the
/// event pump connecting them.
fn launch(
    meta: SessionConfig,
    setup: &SetupConfig,
    provider: &ProviderConfig,
    data_dir: &Path,
    models_dir: &Path,
) -> Result<Arc<LiveSession>> {
    let dir = data_dir.join(&meta.id);
    crate::private::create_dir(&dir)?;
    let transcript_path = dir.join("transcript.jsonl");
    let transcript = Transcript::open(&transcript_path)?;

    let (sink, source) = mpsc::unbounded_channel();
    let (events, _) = broadcast::channel(EVENT_BUFFER);
    let shared = Arc::new(Shared {
        status: Mutex::new(SessionStatus::Idle),
        last_activity: Mutex::new(now()),
        model: Mutex::new(meta.model.clone()),
    });

    let driver: Box<dyn Driver> = match provider.kind {
        DriverKind::Echo => Box::new(EchoDriver::new(sink.clone())),
        DriverKind::LlamaCpp => Box::new(LlamaDriver::spawn(
            &meta,
            provider,
            &Transport::for_setup(setup),
            models_dir,
            &transcript_path,
            sink.clone(),
        )?),
        DriverKind::ClaudeCli => Box::new(ClaudeDriver::spawn(
            &meta,
            provider,
            &Transport::for_setup(setup),
            &dir,
            sink.clone(),
        )?),
    };

    tokio::spawn(pump(
        transcript,
        source,
        Arc::clone(&shared),
        events.clone(),
    ));

    Ok(Arc::new(LiveSession {
        meta,
        driver,
        sink,
        events,
        transcript_path,
        shared,
    }))
}

/// The one writer of a session's transcript: assigns sequence numbers,
/// appends, updates the shared status/activity view, fans out. Ends when
/// every sender is dropped -- i.e. when the session is deleted and its
/// last in-flight task finishes.
///
/// The appends are synchronous file writes from an async task,
/// deliberately: each is one small line on a local disk, and funneling
/// them through one task is what makes the sequence numbering safe.
async fn pump(
    mut transcript: Transcript,
    mut source: mpsc::UnboundedReceiver<Event>,
    shared: Arc<Shared>,
    events: broadcast::Sender<SeqEvent>,
) {
    while let Some(event) = source.recv().await {
        let ts = now();
        match transcript.append(event, ts) {
            Ok(entry) => {
                if let Event::Status { state } = &entry.event {
                    *shared.status.lock().unwrap() = *state;
                }
                *shared.last_activity.lock().unwrap() = ts;
                // No subscribers is fine; the transcript already has it.
                let _ = events.send(entry);
            }
            Err(err) => tracing::error!("transcript append failed: {err:#}"),
        }
    }
}

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

    fn echo_spec() -> SpawnSpec {
        SpawnSpec {
            params: Default::default(),
            setup: crate::config::LOCAL_SETUP_ID.to_string(),
            provider: crate::config::ECHO_PROVIDER.to_string(),
            title: None,
            model: None,
            cwd: None,
            permission_mode: None,
        }
    }

    /// Reads events from `rx` until `stop` matches one (returning all seen
    /// so far) or five seconds pass (panicking with what was seen).
    async fn collect_until(
        rx: &mut broadcast::Receiver<SeqEvent>,
        mut stop: impl FnMut(&Event) -> bool,
    ) -> Vec<SeqEvent> {
        let mut seen = Vec::new();
        let deadline = tokio::time::Instant::now() + Duration::from_secs(5);
        loop {
            let entry = tokio::time::timeout_at(deadline, rx.recv())
                .await
                .unwrap_or_else(|_| panic!("timed out; events so far: {seen:?}"))
                .expect("event stream closed");
            let done = stop(&entry.event);
            seen.push(entry);
            if done {
                return seen;
            }
        }
    }

    fn is_idle(event: &Event) -> bool {
        matches!(
            event,
            Event::Status {
                state: SessionStatus::Idle
            }
        )
    }

    /// Collects one full echo turn: everything up to the idle that follows
    /// the turn's `UsageDelta`. Stopping at the first idle would be racy --
    /// the driver emits an idle at construction, and a subscriber attached
    /// just before the pump processes it would stop there, mid-spawn.
    async fn collect_turn(rx: &mut broadcast::Receiver<SeqEvent>) -> Vec<SeqEvent> {
        let mut saw_usage = false;
        collect_until(rx, |event| {
            saw_usage |= matches!(event, Event::UsageDelta { .. });
            saw_usage && is_idle(event)
        })
        .await
    }

    #[tokio::test]
    async fn spawn_message_and_delete_round_trip() {
        let dir = tempfile::tempdir().expect("tempdir");
        let config_path = dir.path().join("config.ron");
        let data_dir = dir.path().join("sessions");
        let manager = SessionManager::new(
            config_path.clone(),
            data_dir.clone(),
            data_dir.join("models"),
        )
        .expect("manager");

        let info = manager.spawn_session(echo_spec()).expect("spawn");
        // Untitled sessions are named after the provider that runs them.
        assert_eq!(info.title, "echo session");
        // Persisted: a fresh load of the config file knows the session.
        let persisted = Config::load(&config_path).expect("reload config");
        assert_eq!(persisted.sessions.len(), 1);
        assert_eq!(persisted.sessions[0].id, info.id);

        let session = manager.session(&info.id).expect("live session");
        let mut rx = session.subscribe();
        session.send_message("hello there".to_string(), Vec::new());
        let seen = collect_turn(&mut rx).await;

        // The user's message is in the stream, before the echoed reply.
        let user_at = seen
            .iter()
            .position(|entry| {
                matches!(&entry.event, Event::UserMessage { text } if text == "hello there")
            })
            .expect("user message in the stream");
        let echoed: String = seen[user_at..]
            .iter()
            .filter_map(|entry| match &entry.event {
                Event::AssistantText { delta } => Some(delta.as_str()),
                _ => None,
            })
            .collect();
        assert_eq!(echoed, "You said: hello there");

        // The transcript replays the same events by cursor.
        let replay = transcript::read_after(session.transcript_path(), 0).expect("replay");
        assert!(replay.len() >= seen.len());
        let cursor = seen[user_at].seq;
        let after = transcript::read_after(session.transcript_path(), cursor).expect("replay");
        assert_eq!(after.first().map(|entry| entry.seq), Some(cursor + 1));

        // Delete is the complete path out: config, registry, and files.
        manager.delete_session(&info.id).expect("delete");
        assert!(manager.sessions().is_empty());
        assert!(manager.session(&info.id).is_none());
        assert!(!data_dir.join(&info.id).exists());
        assert!(
            Config::load(&config_path)
                .expect("reload")
                .sessions
                .is_empty()
        );
        assert!(manager.delete_session(&info.id).is_err());
    }

    #[tokio::test]
    async fn questions_round_trip_through_answer() {
        let dir = tempfile::tempdir().expect("tempdir");
        let manager = SessionManager::new(
            dir.path().join("config.ron"),
            dir.path().join("sessions"),
            dir.path().join("models"),
        )
        .expect("manager");
        let info = manager.spawn_session(echo_spec()).expect("spawn");
        let session = manager.session(&info.id).expect("live session");

        let mut rx = session.subscribe();
        session.send_message("/question deploy?".to_string(), Vec::new());
        let seen = collect_until(&mut rx, |event| {
            matches!(
                event,
                Event::Status {
                    state: SessionStatus::AwaitingInput
                }
            )
        })
        .await;
        let question_id = seen
            .iter()
            .find_map(|entry| match &entry.event {
                Event::Question { id, .. } => Some(id.clone()),
                _ => None,
            })
            .expect("question event");

        session.answer_question(&question_id, "Yes");
        let seen = collect_until(&mut rx, is_idle).await;
        assert!(seen.iter().any(|entry| matches!(
            &entry.event,
            Event::Answered { id, answer } if *id == question_id && answer == "Yes"
        )));
    }

    #[tokio::test]
    async fn a_restart_relaunches_sessions_and_continues_the_numbering() {
        let dir = tempfile::tempdir().expect("tempdir");
        let config_path = dir.path().join("config.ron");
        let data_dir = dir.path().join("sessions");

        let manager = SessionManager::new(
            config_path.clone(),
            data_dir.clone(),
            data_dir.join("models"),
        )
        .expect("manager");
        let info = manager.spawn_session(echo_spec()).expect("spawn");
        let session = manager.session(&info.id).expect("live session");
        let mut rx = session.subscribe();
        session.send_message("first".to_string(), Vec::new());
        let seen = collect_turn(&mut rx).await;
        let last_seq = seen.last().expect("events").seq;
        drop(rx);
        drop(session);
        drop(manager);

        // A new manager over the same state: the session is back, and new
        // events continue the sequence rather than restarting it -- which
        // is what makes a phone's cursor survive a backend restart.
        let manager = SessionManager::new(config_path, data_dir.clone(), data_dir.join("models"))
            .expect("manager restart");
        let listed = manager.sessions();
        assert_eq!(listed.len(), 1);
        assert_eq!(listed[0].id, info.id);
        let session = manager.session(&info.id).expect("relaunched session");
        let mut rx = session.subscribe();
        session.send_message("second".to_string(), Vec::new());
        let seen = collect_turn(&mut rx).await;
        assert!(seen.first().expect("events").seq > last_seq);
    }
}