//! 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 import;
pub mod llama;
pub mod process;
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, EventSink, 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>,
    /// How much this session asks before acting. Reported so the phone can
    /// *show* the current mode rather than assume one -- a picker that
    /// guesses its own value is how you end up changing something you
    /// thought you were confirming.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub permission_mode: Option<String>,
    /// Whether this session continues one the machine already had.
    ///
    /// Reported because it changes what deleting *means*: an imported
    /// session's real transcript belongs to the CLI and survives, so
    /// removing it here is undoing a view. A session started here has no
    /// copy anywhere else, and removing it ends the conversation. Saying
    /// "this cannot be undone" of both makes the warning worthless on the
    /// one where it is true.
    pub imported: bool,
    #[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>>,
    /// Beside the model and for the same reason: `meta` is the shape the
    /// session was *launched* with, so reporting from it would show the
    /// mode a change had already replaced.
    permission_mode: Mutex<Option<String>>,
    /// How many events this session has ever recorded.
    ///
    /// Only the import sync reads it, and only to answer one question:
    /// "did *we* write anything since I last looked?" A session and a
    /// terminal append to the same file, so that is the whole of what
    /// separates lines worth replaying from lines already shown. Status
    /// cannot answer it -- a turn that starts and finishes between two
    /// polls is idle at both, and its output then gets replayed on top of
    /// itself.
    written: Mutex<u64>,
}

impl LiveSession {
    /// Hands the user's message to the driver, which records it in the
    /// transcript by reporting that it has taken it -- see `MessageTaken`.
    ///
    /// The message is deliberately not recorded here. Sent into a running
    /// turn it waits, and writing it down on the way past would put it
    /// above output that happened before the session ever saw it.
    pub fn send_message(&self, text: String, images: Vec<ImageRef>) {
        // Attachments are the exception, recorded on the way past: they
        // are uploaded whether or not the message waits, and the phone
        // fetches them by the same ref the files route serves. So a queued
        // message's picture appears a little before its text.
        for image in &images {
            let _ = self.sink.send(Event::Image {
                image: image.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();
    }

    /// Leaves this session's process running and stops attending to it,
    /// for a server that is going away and means to come back. See
    /// [`Driver::detach`].
    pub fn detach(&self) {
        self.driver.detach();
    }

    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");
        wg_app_link::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, imported: bool) -> 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(),
            permission_mode: self.shared.permission_mode.lock().unwrap().clone(),
            imported,
            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)?;
        wg_app_link::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,
                    None,
                )
            }) {
                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 }),
        };
        Ok(manager)
    }

    /// Writes this machine into a config that has no setups, with the
    /// providers actually found on it.
    ///
    /// Discovered rather than assumed. Until 2026-08-28 this wrote a
    /// `claude-cli` provider unconditionally, so a fresh install on a
    /// machine without `claude` -- which is every machine but the dev VM
    /// -- offered a spawn option that could not work, and said so with the
    /// same confidence as a provider that had been checked for. Providers
    /// are discovered by asking the machine, and the local machine is not
    /// an exception to that.
    ///
    /// A discovery that fails seeds only `echo`, which is true wherever
    /// this server runs, and says so in the log. Seeding the hardcoded
    /// list on failure would be the original bug with an extra step, and
    /// seeding nothing would leave a fresh install with nothing to prove
    /// the pipe with.
    pub async fn seed_setup(&self) -> Result<()> {
        if !self.inner.read().unwrap().config.setups.is_empty() {
            return Ok(());
        }
        let providers = match crate::setups::discover(&transport::Transport::Here).await {
            Ok(found) => found,
            Err(err) => {
                tracing::warn!(
                    "couldn't ask this machine what it has ({err}); seeding {} only -- \
                     re-probe the setup from the app once that is fixed",
                    crate::config::ECHO_PROVIDER
                );
                vec![Config::echo_provider()]
            }
        };
        let names: Vec<&str> = providers.iter().map(|p| p.name.as_str()).collect();

        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(providers.clone()));
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        tracing::info!(
            "no setups configured -- added \"{}\" with: {}",
            crate::config::LOCAL_SETUP,
            names.join(", ")
        );
        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(())
    }

    /// Lets go of every session's process, for a server that is going
    /// away and means to adopt them again when it comes back.
    ///
    /// Deliberately not a shutdown, and this is the load-bearing half of
    /// it: a backend restart -- a rebuild, a service restart, a crash --
    /// must not end a turn somebody is waiting on. Each process keeps its
    /// record in the session directory, and `launch` finds it there rather
    /// than starting a second one against the same conversation.
    ///
    /// What this did before was ask them all to stop and then exit
    /// immediately, which stopped nothing reliably -- the grace timer died
    /// with the runtime -- and orphaned whatever survived with nothing
    /// written down to find it by. Processes leaked either way; what is
    /// different now is that they are left on purpose and can be picked
    /// back up.
    pub fn detach_all(&self) {
        let inner = self.inner.read().unwrap();
        for session in inner.live.values() {
            session.detach();
        }
        tracing::info!(
            "left {} session process(es) running to be reattached to",
            inner.live.len()
        );
    }

    /// The session already continuing `source`, if there is one.
    ///
    /// Importing the same Claude Code session twice would leave two
    /// `--resume` processes appending to one transcript, each seeing the
    /// other's writes as work done elsewhere and replaying them. Nothing
    /// is corrupted, but both sessions show a conversation neither of them
    /// is having, which is worse than a refusal.
    pub fn session_importing(&self, source: &str) -> Option<String> {
        let inner = self.inner.read().unwrap();
        inner.config.sessions.iter().find_map(|meta| {
            let cursor = import::read_cursor(&self.data_dir.join(&meta.id))?;
            cursor
                .path
                .rsplit('/')
                .next()?
                .strip_suffix(".jsonl")
                .filter(|found| *found == source)
                .map(|_| meta.id.clone())
        })
    }

    /// Every session, in config order, with live status joined in. A
    /// session that failed to relaunch reports as exited.
    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),
                    import::read_cursor(&self.data_dir.join(&meta.id)).is_some(),
                ),
                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(),
                    permission_mode: meta.permission_mode.clone(),
                    imported: import::read_cursor(&self.data_dir.join(&meta.id)).is_some(),
                    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> {
        self.spawn_seeded(spec, None)
    }

    /// Spawns a session that continues one the machine already had.
    ///
    /// The same path as any other spawn, with a [`Seed`] written into the
    /// session directory before the driver starts -- which is all an
    /// import is, because `claude.rs` already resumes when it finds a
    /// resume token. A separate spawn path would be a second way to start
    /// a session, and the driver would have to learn which one it was.
    pub fn spawn_imported(&self, spec: SpawnSpec, seed: Seed) -> Result<SessionInfo> {
        self.spawn_seeded(spec, Some(seed))
    }

    fn spawn_seeded(&self, spec: SpawnSpec, seed: Option<Seed>) -> 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,
            // No model unless one was chosen. This used to fall back to
            // the provider's first listed model, which sounds like a
            // default and is not one: that list is a shortcut for the
            // spawn screen, written in whatever order somebody typed it,
            // and its first entry happened to be `fable`. Every session
            // spawned without a model -- every import, since importing
            // asks for none -- silently became a fable session. Absent
            // means absent, and the CLI then uses whatever the person
            // configured for themselves.
            model: spec.model,
            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,
            seed,
        )?;
        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;
        // Whether this one was seeded, which is the same question the
        // listing asks of the directory a moment later.
        let info = session.info(
            &setup.name,
            import::read_cursor(&self.data_dir.join(&id)).is_some(),
        );
        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.
    /// Changes how much a session asks before acting, live and persisted.
    ///
    /// Alongside the model rather than folded into it: they are set at the
    /// same moment and by the same screen, but they answer different
    /// questions, and a caller changing one must not have to restate the
    /// other.
    pub fn set_session_permission_mode(&self, id: &str, mode: &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.permission_mode = Some(mode.to_string());
        }
        candidate.save(&self.config_path)?;
        inner.config = candidate;
        if let Some(session) = inner.live.get(id) {
            *session.shared.permission_mode.lock().unwrap() = Some(mode.to_string());
            session.driver.set_permission_mode(mode);
        }
        Ok(())
    }

    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) {
            // Stopped, not detached: this is the one exit where the
            // process must not survive, because the conversation it
            // belongs to is being removed. See `Driver::stop`.
            session.driver.stop();
        }
        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.
/// Keeps an imported session's transcript level with the file the CLI
/// writes.
///
/// Both this app and a terminal append to one file -- `--resume` continues
/// the same transcript rather than forking, measured rather than assumed
/// -- so the only hard question is which new lines are *ours*. They are
/// already in the transcript, having arrived through the driver, and
/// replaying them shows every message twice.
///
/// Answered by counting what this session has recorded rather than by
/// looking at its status. Status is the obvious signal and it is wrong: a
/// turn that begins and ends between two polls reads as idle at both, and
/// its output is then replayed on top of itself. The count cannot miss
/// that, because the events went through the same pump either way.
///
/// Its path out: the sink belongs to the session, so once that is dropped
/// every send fails and this returns. Nothing else has to remember it.
fn spawn_import_sync(
    transport: Transport,
    dir: PathBuf,
    mut cursor: import::Cursor,
    sink: EventSink,
    shared: Arc<Shared>,
) {
    tokio::spawn(async move {
        // What the session had recorded when the cursor was last correct.
        let mut written_at_cursor = *shared.written.lock().unwrap();
        loop {
            tokio::time::sleep(import::SYNC_INTERVAL).await;
            if sink.is_closed() {
                return;
            }
            let Ok(lines) = import::line_count(&transport, &cursor.path).await else {
                // A file that cannot be counted is not worth reporting: it
                // is usually a machine briefly away, and the next poll asks
                // again.
                continue;
            };
            let written_now = *shared.written.lock().unwrap();
            if written_now != written_at_cursor {
                // This session produced something since the cursor was set,
                // so the new lines are its own. Skip them and resynchronise.
                cursor.lines = lines;
                written_at_cursor = written_now;
                import::write_cursor(&dir, &cursor);
                continue;
            }
            if lines <= cursor.lines {
                continue;
            }
            match import::replay_after(&transport, &cursor.path, cursor.lines).await {
                Ok(events) => {
                    tracing::info!(
                        "{} grew by {} lines with nothing from here; replaying {} events",
                        cursor.path,
                        lines - cursor.lines,
                        events.len(),
                    );
                    let count = events.len() as u64;
                    for event in events {
                        if sink.send(event).is_err() {
                            return;
                        }
                    }
                    cursor.lines = lines;
                    // The pump is about to record exactly these, so account
                    // for them rather than reading a count that may not have
                    // caught up yet.
                    written_at_cursor = written_now + count;
                    import::write_cursor(&dir, &cursor);
                }
                Err(err) => tracing::warn!("couldn't read new lines of {}: {err:#}", cursor.path),
            }
        }
    });
}

/// What an imported session starts life with: the token that makes the CLI
/// continue rather than begin, and the conversation so far.
pub struct Seed {
    /// The CLI's own session id, written where `claude.rs` looks for it.
    pub resume: String,
    /// Where that session's file is and how much of it has been shown, so
    /// the session can keep itself up to date afterwards.
    pub cursor: import::Cursor,
    /// Replayed into the transcript so the phone shows the conversation it
    /// is joining. The CLI reads the real file itself, so this is what the
    /// reader sees rather than what the model is given.
    pub events: Vec<Event>,
}

fn launch(
    meta: SessionConfig,
    setup: &SetupConfig,
    provider: &ProviderConfig,
    data_dir: &Path,
    models_dir: &Path,
    seed: Option<Seed>,
) -> Result<Arc<LiveSession>> {
    let dir = data_dir.join(&meta.id);
    wg_app_link::private::create_dir(&dir)?;
    let transcript_path = dir.join("transcript.jsonl");
    let mut transcript = Transcript::open(&transcript_path)?;
    // Before the driver starts, so the token is there when it looks and
    // the history is already in the transcript a phone will read.
    if let Some(seed) = seed {
        claude::write_resume_token(&dir, &seed.resume);
        import::write_cursor(&dir, &seed.cursor);
        let at = now();
        for event in seed.events {
            transcript.append(event, at)?;
        }
    }

    let (sink, source) = mpsc::unbounded_channel();
    let (events, _) = broadcast::channel(EVENT_BUFFER);
    let shared = Arc::new(Shared {
        // What it was last known to be doing, not an assumption. A driver
        // that has something to say corrects this within its first poll;
        // one adopting a process that has been quiet says nothing, and
        // this is then the only true answer available.
        status: Mutex::new(
            transcript::last_status(&transcript_path).unwrap_or(SessionStatus::Idle),
        ),
        last_activity: Mutex::new(now()),
        model: Mutex::new(meta.model.clone()),
        permission_mode: Mutex::new(meta.permission_mode.clone()),
        written: Mutex::new(0),
    });

    // An imported session shares its transcript file with the CLI --
    // `--resume` appends to the same one rather than forking, measured
    // rather than assumed -- so work done at a terminal belongs in this
    // session too, and arrives without anybody pressing anything.
    if let Some(cursor) = import::read_cursor(&dir) {
        spawn_import_sync(
            Transport::for_setup(setup),
            dir.clone(),
            cursor,
            sink.clone(),
            Arc::clone(&shared),
        );
    }

    let driver: Box<dyn Driver> = match provider.kind {
        DriverKind::Echo => Box::new(EchoDriver::new(sink.clone())),
        DriverKind::LlamaCpp => Box::new(LlamaDriver::launch(
            &meta,
            provider,
            &Transport::for_setup(setup),
            models_dir,
            &transcript_path,
            &dir,
            sink.clone(),
        )?),
        DriverKind::ClaudeCli => Box::new(ClaudeDriver::launch(
            &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();
        // Taking a message is how it enters the conversation, and the
        // conversation is what a phone renders -- so the event becomes the
        // message here rather than being carried alongside it. One rule
        // for where a user's message sits: where the session read it.
        let event = match event {
            Event::MessageTaken { text } => Event::UserMessage { text },
            other => other,
        };
        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;
                *shared.written.lock().unwrap() += 1;
                // 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
    }

    /// Writes this machine into `config_path` with echo and nothing else.
    ///
    /// Explicit rather than letting the manager seed itself: seeding now
    /// asks the machine what it has, so a test that relied on it would
    /// pass or fail depending on whether `claude` happens to be installed
    /// on whoever is running it. Echo is the only provider that is true
    /// everywhere, and the only one these tests need.
    fn seed_echo_only(config_path: &std::path::Path) {
        Config {
            setups: vec![Config::seed(vec![Config::echo_provider()])],
            ..Config::default()
        }
        .save(config_path)
        .expect("seed config");
    }

    #[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");
        seed_echo_only(&config_path);
        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");
        seed_echo_only(&dir.path().join("config.ron"));
        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");
        seed_echo_only(&config_path);

        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);
    }
}