brahman/crates/shared/brahman-sidecar/src/discovery.rs

//! `brahman-sidecar::discovery` — API reusable para que un módulo
//! consumer encuentre proveedores vivos vía broker, sin hardcodear
//! sockets ni reimplementar el patrón a mano.
//!
//! Es la generalización de `discover_producer_socket` del CLI
//! `nouser attract --remote`: declarás el `TypeRef` que querés
//! consumir y el broker te empuja un `MatchEvent::Available` con el
//! `producer_service_socket` del primer proveedor matched.
//!
//! Pipeline:
//! 1. `build_consumer_card(label, flow_name, type_name)` arma una
//!    Card mínima (Ente, Oneshot, Virtual) con un input flow.
//! 2. `await_provider(card, timeout)` se conecta al brahman-init,
//!    espera hasta `timeout` por `MatchEvent::Available`, devuelve
//!    el socket del proveedor electo, y envía Farewell.
//! 3. Para mundos blocking (CLIs, tests, std-thread loops) hay
//!    `await_provider_blocking` que arma su propio runtime
//!    `current_thread`.
//!
//! Quién elige al proveedor es el broker, no este módulo. Si el
//! broker tiene `priority_contexts` activo, podés cambiar de
//! proveedor sin tocar el consumer; el matching dinámico se respeta.

use std::path::PathBuf;
use std::time::{Duration, Instant};

use brahman_card::{
    Card, CardKind, Flow, Flows, Lifecycle, Payload, Priority, Supervision, TypeRef,
};
use brahman_handshake::client::{Client, ClientError};
use brahman_handshake::messages::MatchEventKind;
use brahman_handshake::transport;

#[derive(Debug, thiserror::Error)]
pub enum ConsumerError {
    #[error("no se pudo conectar al init en {socket}: {source}")]
    Connect {
        socket: PathBuf,
        #[source]
        source: ClientError,
    },
    #[error("error en cliente brahman: {0}")]
    Client(#[from] ClientError),
    #[error("timeout {timeout:?} sin proveedor disponible para flow '{flow}' (type '{type_ref}')")]
    NoProvider {
        flow: String,
        type_ref: String,
        timeout: Duration,
    },
    #[error("no se pudo crear runtime tokio: {0}")]
    Runtime(String),
}

/// Construye una Card mínima de consumer que declara un input flow
/// con el `TypeRef::Primitive { name }` solicitado. Usá esto para
/// el caso común; si necesitás algo más rico (output flows,
/// permissions, references) construí la Card a mano y pasala a
/// [`await_provider`] directamente.
pub fn build_consumer_card(
    consumer_label: impl Into<String>,
    flow_name: impl Into<String>,
    type_name: impl Into<String>,
) -> Card {
    Card {
        payload: Payload::Virtual,
        supervision: Supervision::OneShot,
        lifecycle: Lifecycle::Oneshot,
        priority: Priority::Normal,
        kind: CardKind::Ente,
        flow: Flows {
            input: vec![Flow {
                name: flow_name.into(),
                ty: TypeRef::Primitive {
                    name: type_name.into(),
                },
                pin_to: None,
            }],
            output: vec![],
        },
        ..Card::new(consumer_label)
    }
}

/// Conecta al brahman-init, registra `consumer_card`, espera el
/// primer `MatchEvent::Available` y devuelve el `producer_service_socket`
/// que el broker emitió. Cierra la sesión con Farewell antes de
/// retornar (best-effort).
///
/// La `consumer_card` debe declarar al menos un `flow.input`; si no,
/// el broker no puede hacer matching y el await siempre dará timeout.
pub async fn await_provider(
    consumer_card: Card,
    timeout: Duration,
) -> Result<PathBuf, ConsumerError> {
    let init_path = transport::default_socket_path();

    // Capturamos descriptor para el mensaje de error antes de mover
    // la card al cliente.
    let (flow_name, type_ref_name) = describe_first_input(&consumer_card);

    let mut client = Client::connect(&init_path, consumer_card)
        .await
        .map_err(|source| ConsumerError::Connect {
            socket: init_path.clone(),
            source,
        })?;

    let deadline = Instant::now() + timeout;
    let socket = loop {
        let remaining = deadline.saturating_duration_since(Instant::now());
        if remaining.is_zero() {
            break None;
        }
        match client.await_event(remaining).await? {
            Some(ev) if ev.kind == MatchEventKind::Available => {
                break ev.producer_service_socket;
            }
            Some(_) => continue, // Lost u otros: seguir esperando hasta el deadline
            None => break None,
        }
    };

    let _ = client.farewell().await; // best-effort cleanup

    socket.ok_or(ConsumerError::NoProvider {
        flow: flow_name,
        type_ref: type_ref_name,
        timeout,
    })
}

/// Wrapper bloqueante de [`await_provider`]. Crea un runtime tokio
/// `current_thread` efímero y bloquea el thread llamador. Útil para
/// CLIs, tests y módulos std-thread (p. ej. el frontend GPUI antes
/// de tener su propio runtime async).
pub fn await_provider_blocking(
    consumer_card: Card,
    timeout: Duration,
) -> Result<PathBuf, ConsumerError> {
    let rt = tokio::runtime::Builder::new_current_thread()
        .enable_io()
        .enable_time()
        .build()
        .map_err(|e| ConsumerError::Runtime(e.to_string()))?;
    rt.block_on(await_provider(consumer_card, timeout))
}

fn describe_first_input(card: &Card) -> (String, String) {
    match card.flow.input.first() {
        Some(flow) => {
            let type_name = match &flow.ty {
                TypeRef::Primitive { name } => name.clone(),
                TypeRef::Wit { package, name, .. } => format!("{package}#{name}"),
            };
            (flow.name.clone(), type_name)
        }
        None => ("(sin input)".into(), "(sin tipo)".into()),
    }
}

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

    #[test]
    fn builder_sets_input_flow_with_primitive_type() {
        let c = build_consumer_card("nouser.cli", "embed-result", "json");
        assert_eq!(c.label, "nouser.cli");
        assert_eq!(c.kind, CardKind::Ente);
        assert!(matches!(c.lifecycle, Lifecycle::Oneshot));
        assert!(matches!(c.supervision, Supervision::OneShot));
        assert_eq!(c.flow.input.len(), 1);
        let f = &c.flow.input[0];
        assert_eq!(f.name, "embed-result");
        match &f.ty {
            TypeRef::Primitive { name } => assert_eq!(name, "json"),
            _ => panic!("expected primitive type"),
        }
        assert!(c.flow.output.is_empty());
        // El builder asigna un id real (no nil) — fundamental para que
        // el broker no colisione con otros consumers.
        assert!(c.id != Ulid::nil(), "consumer card id no debe ser nil");
    }

    #[test]
    fn builder_assigns_distinct_ids_per_call() {
        let a = build_consumer_card("a", "f", "t");
        let b = build_consumer_card("a", "f", "t");
        assert_ne!(a.id, b.id, "cada Card debería tener id propio");
    }

    #[test]
    fn describe_falls_back_when_no_input_flow() {
        let mut c = build_consumer_card("x", "f", "t");
        c.flow.input.clear();
        let (flow, ty) = describe_first_input(&c);
        assert_eq!(flow, "(sin input)");
        assert_eq!(ty, "(sin tipo)");
    }

    #[test]
    fn describe_formats_wit_type() {
        let mut c = build_consumer_card("x", "f", "t");
        c.flow.input[0].ty = TypeRef::Wit {
            package: "brahman:dht".into(),
            interface: None,
            name: "entity-result".into(),
        };
        let (_, ty) = describe_first_input(&c);
        assert_eq!(ty, "brahman:dht#entity-result");
    }
}