//! The per-agent status KV bucket: one key per `(hive, agent)` pair.
//!
//! Deliberately **not** a field inside [`crate::status::BUCKET`]'s hive
//! document, even though a hive already publishes its own status there.
//! Three reasons, none of which show up until the second write:
//!
//! - **Cardinality and write rate.** Hive status is one value per hive.
//!   Agent status is N values per hive, changing independently and far
//!   more often — folded into the hive document, every agent's change
//!   rewrites the whole thing, and two agents changing at once race on
//!   the same key.
//! - **A KV key is the unit of update and of watch.** A consumer that
//!   cares about one agent wants a per-key read with its own revision,
//!   not a hive-wide document to diff.
//! - **Staleness means different things.** A hive can be healthy while
//!   one agent is wedged, and the reverse; one timestamp cannot answer
//!   both questions honestly.
//!
//! The transport *is* shared — this rides the same [`async_nats::Client`]
//! and the same auth callout as [`crate::status`] and [`crate::wanted`],
//! just a different bucket.

#[cfg(feature = "kv")]
use crate::Error;

/// The KV bucket per-agent status snapshots are published into, keyed by
/// [`key`].
///
/// A constant and not an option, for the reason [`crate::status::BUCKET`]
/// gives: writer (a hive) and reader (the controller) must name the same
/// bucket, and an option is a way for the two to disagree about which one
/// that is.
pub const BUCKET: &str = "agent-status";

/// The bucket key for one agent on one hive.
///
/// `/`-joined rather than NATS's usual `.`-joined subject style: this is a
/// KV key, not a subject, and neither `hive` nor `agent` names can contain
/// `/` (`hive_types::Ident`'s charset is `[a-z0-9-]`), so the join is
/// unambiguous to split back apart if a consumer ever needs to.
///
/// Plain code span above, deliberately not an intra-doc link — this crate
/// doesn't depend on `hive_types`, and a bracketed reference to its `Ident`
/// type fails `cargo doc` with "no item named `hive_types` in scope" under
/// this workspace's `docs-rustdoc` CI job, which treats broken doc links as
/// errors.
#[must_use]
pub fn key(hive: &str, agent: &str) -> String {
    format!("{hive}/{agent}")
}

/// The inverse of [`key`]: split a bucket key back into `(hive, agent)`.
///
/// `None` for a key with zero or more than one `/` — a hive publishing
/// under [`key`] never produces one, so a malformed key means something
/// else wrote this bucket. Splitting on the *first* `/` would be equally
/// valid today (neither name can contain one), but this rejects rather
/// than guesses, so a future name-charset change can't silently start
/// misreading old keys.
#[must_use]
pub fn split_key(key: &str) -> Option<(&str, &str)> {
    let mut parts = key.splitn(3, '/');
    let hive = parts.next()?;
    let agent = parts.next()?;
    if parts.next().is_some() {
        return None;
    }
    Some((hive, agent))
}

/// One agent's status snapshot, as published under [`key`].
///
/// Mirrors the tuple `container_view::read_agent_status_live` returns on
/// the publishing side — this is that value, not a recomputation of it.
/// Nothing here stamps a time: same rule as [`crate::status`], freshness is
/// derived by the reader from when the value landed in the bucket, so a
/// hive with a wrong clock only skews its own payload.
#[derive(Debug, Clone, Default, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
pub struct AgentStatus {
    /// The agent's free-text status (`set_status`), or `None` if it has
    /// never set one, or if the container isn't running.
    pub status_text: Option<String>,
    /// Unix timestamp the status was last set. `None` alongside
    /// `status_text: None` — the two are never independently absent.
    pub status_set_at: Option<i64>,
    /// Whether the container is currently running. `false` forces the two
    /// fields above to `None` even if an on-disk status file is stale from
    /// before the container stopped — the same "stopped containers have
    /// stale state" rule `read_agent_status_live` already enforces.
    pub running: bool,
}

/// Open the agent-status bucket, creating it if nothing has yet.
///
/// `history: 1`, same rationale as [`crate::status::open_or_create`]: a
/// consumer wants the last thing each agent said, not a log of everything
/// it has ever said.
#[cfg(feature = "kv")]
pub async fn open_or_create(
    client: &async_nats::Client,
) -> Result<async_nats::jetstream::kv::Store, Error> {
    let js = async_nats::jetstream::new(client.clone());
    match js.get_key_value(BUCKET).await {
        Ok(store) => Ok(store),
        Err(e) => {
            tracing::info!(
                bucket = BUCKET,
                reason = %e,
                "agent-status bucket not available, creating it"
            );
            js.create_key_value(async_nats::jetstream::kv::Config {
                bucket: BUCKET.to_owned(),
                description: "Last status snapshot offered by each agent".to_owned(),
                history: 1,
                ..Default::default()
            })
            .await
            .map_err(|source| Error::CreateBucket {
                bucket: BUCKET,
                source,
            })
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{AgentStatus, key, split_key};

    #[test]
    fn key_joins_hive_and_agent_with_a_slash() {
        assert_eq!(key("prod", "iris"), "prod/iris");
    }

    #[test]
    fn split_key_is_the_inverse_of_key() {
        assert_eq!(split_key(&key("prod", "iris")), Some(("prod", "iris")));
    }

    #[test]
    fn split_key_rejects_a_key_with_no_slash() {
        assert_eq!(split_key("iris"), None);
    }

    #[test]
    fn split_key_rejects_a_key_with_two_slashes() {
        assert_eq!(split_key("prod/iris/extra"), None);
    }

    #[test]
    fn agent_status_round_trips() {
        let status = AgentStatus {
            status_text: Some("reviewing a pull request".to_owned()),
            status_set_at: Some(1_725_000_000),
            running: true,
        };
        let json = serde_json::to_string(&status).expect("serialises");
        let decoded: AgentStatus = serde_json::from_str(&json).expect("decodes");
        assert_eq!(decoded, status);
    }

    #[test]
    fn a_stopped_agent_serialises_with_no_status() {
        let status = AgentStatus::default();
        assert_eq!(
            serde_json::to_string(&status).expect("serialises"),
            r#"{"status_text":null,"status_set_at":null,"running":false}"#
        );
    }
}