//! The connection side of an agent's bash tasks: the status bucket and the
//! output stream. The names, keys, subjects and the status value are
//! `swarm_wire::bash_task`.
//!
//! `swarm-controller` creates the bucket once and one output stream per agent
//! with the fixed config `output_config` spells.

use swarm_wire::bash_task::{OUTPUT_MAX_AGE, output_stream_name, output_stream_subjects};

/// How large one agent's output stream may grow before the discard policy
/// reclaims space, as for the subagent rows.
const OUTPUT_MAX_BYTES: i64 = 64 * 1024 * 1024;

/// The config [`open_output`] creates `agent`'s output stream with.
///
/// `max_message_size` is the queue's live `max_payload` ([`crate::max_payload`]),
/// so the stream never rejects a row the queue itself accepted.
pub(crate) fn output_config(
    agent: &str,
    max_message_size: i32,
) -> async_nats::jetstream::stream::Config {
    async_nats::jetstream::stream::Config {
        name: output_stream_name(agent),
        description: Some(format!("Output of {agent}'s bash tasks")),
        subjects: vec![output_stream_subjects(agent)],
        max_age: OUTPUT_MAX_AGE,
        max_bytes: OUTPUT_MAX_BYTES,
        discard: async_nats::jetstream::stream::DiscardPolicy::Old,
        max_message_size,
        ..Default::default()
    }
}

/// Open the status bucket, creating it if nothing has yet. `history: 1`: a
/// reader wants each task's current state, not every state it has been in. A
/// key expires [`swarm_wire::bash_task::STATUS_MAX_AGE`] after its last write,
/// since nothing deletes the key of a finished task.
pub async fn open_status(
    client: &async_nats::Client,
) -> Result<async_nats::jetstream::kv::Store, crate::Error> {
    let js = async_nats::jetstream::new(client.clone());
    crate::kv::open_or_create_expiring(
        &js,
        swarm_wire::bash_task::BUCKET,
        "bash-task-status",
        "The state of each bash task, as its agent's bash MCP last published it".to_owned(),
        Some(swarm_wire::bash_task::STATUS_MAX_AGE),
    )
    .await
}

/// Open `agent`'s output stream, creating it if it does not exist yet.
pub async fn open_output(
    client: &async_nats::Client,
    agent: &str,
) -> Result<async_nats::jetstream::stream::Stream, crate::Error> {
    let js = async_nats::jetstream::new(client.clone());
    let name = output_stream_name(agent);
    match js.get_stream(&name).await {
        Ok(stream) => Ok(stream),
        Err(e) => {
            tracing::info!(stream = %name, reason = %e, "bash task output stream not available, creating it");
            let max_message_size = i32::try_from(crate::max_payload(client)).unwrap_or(i32::MAX);
            js.create_stream(output_config(agent, max_message_size))
                .await
                .map_err(|source| crate::Error::CreateAgentStream {
                    stream: name,
                    source,
                })
        }
    }
}

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

    #[test]
    fn the_output_stream_caps_bytes_and_discards_the_oldest() {
        let cfg = output_config("iris", 8_388_608);
        assert_eq!(cfg.name, "term-bash-iris");
        assert_eq!(cfg.subjects, vec!["$SWARM.term.iris.bash.>".to_owned()]);
        assert_eq!(cfg.max_bytes, OUTPUT_MAX_BYTES);
        assert_eq!(
            cfg.discard,
            async_nats::jetstream::stream::DiscardPolicy::Old
        );
        assert_eq!(cfg.max_message_size, 8_388_608);
    }
}