//! Classifying a presented `auth_token`, and the grant for an agent's own.
//!
//! The spelling is `swarm_queue_client::agent_token`'s, shared with the agent
//! that presents it. Whether its secret is the stored one is
//! [`swarm_agent_verify::verify`]'s answer; nothing here grants on the name
//! alone.
//!
//! A token without the prefix is not this module's: it goes to introspection
//! unchanged.

use swarm_agent_verify::CredentialSource;
use swarm_queue_client::agent_token::{AgentToken, Malformed, parse_agent_token};

use crate::policy::{Permissions, Policy};

/// What a presented `auth_token` is.
pub enum Presented<'a> {
    /// An agent's own credential, to be checked against the store.
    Agent(AgentToken<'a>),
    /// Carries the agent-token prefix but is not well-formed. Denied without a
    /// lookup, and never handed to introspection: it holds a secret meant for
    /// the store, not for the `IdP`.
    Malformed(Malformed),
    /// Anything else, which is an OIDC access token for introspection.
    Bearer(&'a str),
}

/// Sort `token` onto the agent path or the introspection path.
pub fn classify(token: &str) -> Presented<'_> {
    match parse_agent_token(token) {
        Some(Ok(agent)) => Presented::Agent(agent),
        Some(Err(e)) => Presented::Malformed(e),
        None => Presented::Bearer(token),
    }
}

/// The grant for an agent token, or `None` for a denial.
///
/// The store lookup is bounded by introspection's budget, under the server's
/// `authorization.timeout`. The callout loop answers one request at a time, so
/// a store that does not answer holds every request behind it, OIDC ones
/// included, for at most that long, and this then denies.
pub async fn authorize(
    policy: &Policy,
    source: &impl CredentialSource,
    token: &AgentToken<'_>,
) -> Option<Permissions> {
    if !swarm_agent_verify::verify(source, token, crate::introspect::INTROSPECTION_TIMEOUT).await {
        return None;
    }
    let permissions = policy.agent_token_permissions(token.agent);
    if permissions.is_none() {
        tracing::warn!(
            agent = token.agent,
            "verified agent token, but no --agent-token-publish-subject is configured; denying"
        );
    }
    permissions
}

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

    /// A store holding atlas's credential, or one that never answers.
    /// The store's own denials are `swarm_agent_verify`'s tests.
    enum Fake {
        Atlas,
        Hangs,
    }

    impl CredentialSource for Fake {
        async fn lookup(&self, agent: &str) -> anyhow::Result<Option<AgentCredential>> {
            match self {
                Self::Atlas => Ok((agent == "atlas").then(|| AgentCredential {
                    value: "Ab9_-zSECRET".to_owned(),
                    agent: "atlas".to_owned(),
                    minted_at: None,
                })),
                Self::Hangs => std::future::pending().await,
            }
        }
    }

    fn policy() -> Policy {
        Policy::new(
            "hive-".to_owned(),
            "-agent".to_owned(),
            "hive-status".to_owned(),
            vec!["swarm-controller".to_owned()],
            vec![],
        )
        .expect("valid")
        .with_agent_token_subjects(vec![
            "$SWARM.term.{agent}".to_owned(),
            "$SWARM.agent-state.{agent}".to_owned(),
            "$KV.agent-icons.{agent}".to_owned(),
        ])
        .expect("valid")
    }

    async fn grant(source: &Fake, token: &str) -> Option<Permissions> {
        let Presented::Agent(token) = classify(token) else {
            panic!("{token:?} must classify as an agent token");
        };
        authorize(&policy(), source, &token).await
    }

    #[tokio::test]
    async fn a_valid_agent_token_is_granted_exactly_its_own_subjects() {
        let g = grant(&Fake::Atlas, "swarm-agent.atlas.Ab9_-zSECRET")
            .await
            .expect("granted");
        assert_eq!(
            g.publish,
            vec![
                "$SWARM.term.atlas".to_owned(),
                "$SWARM.agent-state.atlas".to_owned(),
                "$KV.agent-icons.atlas".to_owned(),
            ]
        );
    }

    #[tokio::test]
    async fn a_wrong_secret_is_denied() {
        assert!(
            grant(&Fake::Atlas, "swarm-agent.atlas.Ab9_-zSECREX")
                .await
                .is_none()
        );
    }

    /// The callout loop answers one request at a time, so a store that never
    /// answers must cost at most the bound, and then deny.
    #[tokio::test]
    async fn a_store_that_never_answers_is_denied_within_the_bound() {
        let bound = crate::introspect::INTROSPECTION_TIMEOUT;
        let started = std::time::Instant::now();
        assert!(
            grant(&Fake::Hangs, "swarm-agent.atlas.Ab9_-zSECRET")
                .await
                .is_none()
        );
        let took = started.elapsed();
        assert!(took >= bound, "denied before the bound: {took:?}");
        assert!(
            took < bound + std::time::Duration::from_millis(250),
            "denied well after the bound: {took:?}"
        );
    }

    #[tokio::test]
    async fn a_verified_agent_with_no_subjects_configured_is_denied() {
        let bare = Policy::new(
            "hive-".to_owned(),
            "-agent".to_owned(),
            "hive-status".to_owned(),
            vec![],
            vec![],
        )
        .expect("valid");
        let Presented::Agent(token) = classify("swarm-agent.atlas.Ab9_-zSECRET") else {
            panic!("an agent token");
        };
        assert!(authorize(&bare, &Fake::Atlas, &token).await.is_none());
    }

    /// Everything without the prefix reaches introspection as it arrived.
    #[test]
    fn a_token_without_the_prefix_goes_to_introspection_unchanged() {
        for token in ["authelia_at_abc.def", "atlas.Ab9_-zSECRET"] {
            let Presented::Bearer(t) = classify(token) else {
                panic!("{token:?} is not an agent token");
            };
            assert_eq!(t, token);
        }
    }

    #[test]
    fn a_malformed_agent_token_goes_nowhere() {
        assert!(matches!(
            classify("swarm-agent.atlas"),
            Presented::Malformed(_)
        ));
    }
}