//! Subagent terminals: the subject each subagent's rows go to, and the
//! stream that keeps them.
//!
//! An agent's subagent daemon publishes each subagent's classified terminal
//! rows on `$SWARM.term.<agent>.sub.<subagent>`, under the agent's own queue
//! credential. The queue grants that credential publish on this subject
//! family and no `JetStream` subject.
//!
//! The stream exists so the swarm can list an agent's subagents: subagents
//! are spawned on demand under caller-chosen names, and the set of subjects
//! the stream holds is the list. `swarm-controller` creates one stream per
//! agent with the fixed config [`crate::subagent_term::open_or_create`]
//! spells, and takes the list from its subject counts
//! ([`crate::subagent_term::subagent_names`]).
//!
//! The name and the subject live here because three crates must agree on
//! them: the publisher in `hive-subagent-mcp`, `swarm-controller`, and the
//! queue grant in `swarm-nats.nix`, whose `{agent}` template spells the same
//! subjects.

use crate::TERM_SUBJECT_PREFIX;

/// The token between the agent and the subagent name. A subagent subject has
/// two more tokens than the agent's own `$SWARM.term.<agent>`, so neither
/// family's subscriber receives the other's rows.
const SUBAGENT_TOKEN: &str = "sub";

/// How long the stream keeps a row. The subagent list is the subjects with a
/// row inside this window, so a subagent drops off the list this long after
/// its last output.
pub const MAX_AGE: std::time::Duration = std::time::Duration::from_hours(24);

/// How large one agent's stream may grow before the discard policy reclaims
/// space. 64 MiB is enough rows from a day of ordinary subagent chatter to
/// stay well inside it while still bounding the disk one compromised or
/// runaway agent can claim for 24h.
#[cfg(feature = "subagent-term")]
const MAX_BYTES: i64 = 64 * 1024 * 1024;

/// The stream holding `agent`'s subagent rows: `term-sub-<agent>`.
#[must_use]
pub fn stream_name(agent: &str) -> String {
    format!("term-sub-{agent}")
}

/// The subject `subagent`'s rows are published on.
#[must_use]
pub fn subject(agent: &str, subagent: &str) -> String {
    format!("{TERM_SUBJECT_PREFIX}.{agent}.{SUBAGENT_TOKEN}.{subagent}")
}

/// Every [`subject`] at once: the reader's subscribe grant, which has no
/// roster to enumerate agents or subagents from.
#[must_use]
pub fn subject_wildcard() -> String {
    subject("*", "*")
}

/// Every subject [`stream_name`]'s stream captures, which is also the publish
/// grant's shape.
#[must_use]
pub fn stream_subjects(agent: &str) -> String {
    format!("{TERM_SUBJECT_PREFIX}.{agent}.{SUBAGENT_TOKEN}.>")
}

/// The subagent a stream subject names, or `None` for a subject that is not
/// exactly one subagent token under `agent`'s family.
#[must_use]
pub fn subagent_from_subject<'a>(agent: &str, subject: &'a str) -> Option<&'a str> {
    let name = subject
        .strip_prefix(TERM_SUBJECT_PREFIX)?
        .strip_prefix('.')?
        .strip_prefix(agent)?
        .strip_prefix('.')?
        .strip_prefix(SUBAGENT_TOKEN)?
        .strip_prefix('.')?;
    (!name.is_empty() && !name.contains('.')).then_some(name)
}

/// The subagents named by a stream's subjects, sorted and deduplicated.
/// Subjects outside `agent`'s family are skipped.
#[must_use]
pub fn subagent_names<'a>(agent: &str, subjects: impl IntoIterator<Item = &'a str>) -> Vec<String> {
    let mut names: Vec<String> = subjects
        .into_iter()
        .filter_map(|s| subagent_from_subject(agent, s))
        .map(str::to_owned)
        .collect();
    names.sort_unstable();
    names.dedup();
    names
}

/// The config [`open_or_create`] creates `agent`'s stream with.
///
/// `max_message_size` is taken as a parameter rather than read from a
/// constant here: it tracks the queue's live `max_payload`
/// ([`crate::max_payload`]), the same value the publisher already sizes its
/// rows against, so the stream never rejects a row the queue itself
/// accepted.
#[cfg(feature = "subagent-term")]
pub(crate) fn stream_config(
    agent: &str,
    max_message_size: i32,
) -> async_nats::jetstream::stream::Config {
    async_nats::jetstream::stream::Config {
        name: stream_name(agent),
        description: Some(format!("Terminal rows of {agent}'s subagents")),
        subjects: vec![stream_subjects(agent)],
        max_age: MAX_AGE,
        max_bytes: MAX_BYTES,
        discard: async_nats::jetstream::stream::DiscardPolicy::Old,
        max_message_size,
        ..Default::default()
    }
}

/// Open `agent`'s subagent stream, creating it if it does not exist yet. An
/// existing stream is opened as it is.
#[cfg(feature = "subagent-term")]
pub async fn open_or_create(
    client: &async_nats::Client,
    agent: &str,
) -> Result<async_nats::jetstream::stream::Stream, crate::Error> {
    let js = async_nats::jetstream::new(client.clone());
    let name = stream_name(agent);
    match js.get_stream(&name).await {
        Ok(stream) => Ok(stream),
        Err(e) => {
            tracing::info!(stream = %name, reason = %e, "subagent terminal stream not available, creating it");
            let max_message_size = i32::try_from(crate::max_payload(client)).unwrap_or(i32::MAX);
            js.create_stream(stream_config(agent, max_message_size))
                .await
                .map_err(|source| crate::Error::CreateAgentStream {
                    stream: name,
                    source,
                })
        }
    }
}

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

    /// The names the grant in `swarm-nats.nix` spells with `{agent}`.
    #[test]
    fn names_match_the_queue_grant() {
        assert_eq!(stream_name("iris"), "term-sub-iris");
        assert_eq!(subject("iris", "scout"), "$SWARM.term.iris.sub.scout");
        assert_eq!(stream_subjects("iris"), "$SWARM.term.iris.sub.>");
    }

    #[test]
    fn a_subject_reads_back_as_its_subagent() {
        assert_eq!(
            subagent_from_subject("iris", &subject("iris", "scout")),
            Some("scout")
        );
    }

    /// The agent's own terminal, another agent's subagent, and anything
    /// deeper than one token are not subagents of `iris`.
    #[test]
    fn other_subjects_name_no_subagent() {
        for s in [
            "$SWARM.term.iris",
            "$SWARM.term.h1.iris",
            "$SWARM.term.iris.sub",
            "$SWARM.term.iris.sub.",
            "$SWARM.term.iris.sub.a.b",
            "$SWARM.term.iris-2.sub.scout",
            "$SWARM.term.argus.sub.scout",
            "$SWARM.agent-state.iris.sub.scout",
        ] {
            assert_eq!(subagent_from_subject("iris", s), None, "{s}");
        }
    }

    #[test]
    fn the_list_is_sorted_unique_and_scoped_to_the_agent() {
        let subjects = [
            "$SWARM.term.iris.sub.zed",
            "$SWARM.term.iris.sub.alpha",
            "$SWARM.term.argus.sub.other",
            "$SWARM.term.iris.sub.alpha",
        ];
        assert_eq!(subagent_names("iris", subjects), ["alpha", "zed"]);
    }

    /// The config the controller creates caps disk per agent and never
    /// fails a publish because of that cap — `discard: Old` reclaims the
    /// oldest rows instead of rejecting the newest.
    #[cfg(feature = "subagent-term")]
    #[test]
    fn stream_config_caps_bytes_and_discards_the_oldest() {
        let cfg = stream_config("iris", 8_388_608);
        assert_eq!(cfg.max_bytes, MAX_BYTES);
        assert_eq!(
            cfg.discard,
            async_nats::jetstream::stream::DiscardPolicy::Old
        );
        assert_eq!(cfg.max_message_size, 8_388_608);
    }
}