//! The ACP agent's provider API key, read from the swarm secret store at
//! `swarm/agents/<agent>/acp-provider` (field `api_key`) under the agent's own
//! certificate, and handed to the spawned agent's environment only.
//!
//! A value the process already inherited (`backendEnvironmentFile`) wins and
//! the store is not asked. Without either, the agent is spawned without it.
//!
//! The key is read when the agent is spawned, and again after a turn fails
//! with [`AcpError::EmptyEndTurn`](super::AcpError::EmptyEndTurn) or
//! [`AcpError::IdleTimeout`](super::AcpError::IdleTimeout), which is how a
//! provider rejecting the key shows. A stored key that differs from the one
//! the agent was spawned with gets the agent respawned with it. Anything else
//! (the same key, an inherited value, no store, a failed or empty read) keeps
//! the running agent.

use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use std::time::Duration;

use swarm_secret_client::{
    SecretStore,
    acp::{ProviderKey, provider_key_path},
    client::{DEFAULT_CERT_MOUNT, ENV_ADDR, ENV_CACERT, Settings},
    policy,
};

/// Names the agent whose key is read; the cert-auth role and the store path
/// are both built from it.
const ENV_AGENT_NAME: &str = "HIVE_AGENT_NAME";

/// How long one read of the store may take before the agent is spawned
/// without the key.
const STORE_READ_TIMEOUT: Duration = Duration::from_secs(10);

/// A variable to add to the spawned agent's environment.
///
/// No `Debug`: `value` is the key.
pub(super) struct KeyVar {
    pub(super) name: String,
    pub(super) value: String,
}

/// Resolves the variable it is given the name of, as [`resolve`] does.
pub(super) type Resolve =
    Arc<dyn Fn(String) -> Pin<Box<dyn Future<Output = Option<KeyVar>> + Send>> + Send + Sync>;

/// A [`Resolve`] calling [`resolve`].
pub(super) fn resolver() -> Resolve {
    Arc::new(|name| Box::pin(async move { resolve(&name).await }))
}

/// Where [`resolve_with`] reads the key from. A trait so the precedence can
/// be exercised without a store.
trait KeySource {
    /// The store path, for log lines. Never the value.
    fn origin(&self) -> &str;

    /// The key stored now, or `None` when nothing is stored.
    fn fetch(&self) -> impl Future<Output = Result<Option<String>, swarm_secret_client::Error>>;
}

struct StoreSource {
    settings: Settings,
    role: String,
    path: String,
}

impl KeySource for StoreSource {
    fn origin(&self) -> &str {
        &self.path
    }

    async fn fetch(&self) -> Result<Option<String>, swarm_secret_client::Error> {
        let store = SecretStore::connect(&self.settings, &self.role, DEFAULT_CERT_MOUNT).await?;
        let stored: Option<ProviderKey> = store.read_optional(&self.path).await?;
        Ok(stored.map(|k| k.api_key))
    }
}

/// Where this agent's key would be read from, or `None` when this process
/// was given no store. Same variables as `hive-agent`'s `swarm_queue`.
fn store_source(
    get: impl Fn(&str) -> Option<String>,
) -> Result<Option<StoreSource>, swarm_secret_client::Error> {
    if get(ENV_ADDR).is_none_or(|v| v.is_empty()) {
        return Ok(None);
    }
    let agent = get(ENV_AGENT_NAME)
        .filter(|v| !v.is_empty())
        .ok_or(swarm_secret_client::Error::MissingEnv(ENV_AGENT_NAME))?;
    let settings =
        Settings::from_lookup(|k| get(k).filter(|v| k != ENV_CACERT || ca_is_usable(v)))?;
    Ok(Some(StoreSource {
        settings,
        role: policy::agent_object_name(&agent)?,
        path: provider_key_path(&agent)?,
    }))
}

/// Whether the CA bundle at `path` is a file with bytes in it. Absent means
/// the container's own trust store.
fn ca_is_usable(path: &str) -> bool {
    std::fs::metadata(path).is_ok_and(|m| m.len() > 0)
}

/// The variable to add for `name` to the agent's environment, if any.
pub(super) async fn resolve(name: &str) -> Option<KeyVar> {
    let inherited = std::env::var(name).ok();
    resolve_with(
        name,
        inherited,
        || {
            store_source(|k| std::env::var(k).ok()).unwrap_or_else(|e| {
                tracing::warn!(
                    error = %e,
                    "this agent's secret store coordinates are incomplete, so its ACP \
                     provider key cannot be read from the store"
                );
                None
            })
        },
        STORE_READ_TIMEOUT,
    )
    .await
}

/// [`resolve`] over an inherited value and a store, each logged once without
/// the key.
async fn resolve_with<S: KeySource>(
    name: &str,
    inherited: Option<String>,
    source: impl FnOnce() -> Option<S>,
    timeout: Duration,
) -> Option<KeyVar> {
    if inherited.is_some_and(|v| !v.trim().is_empty()) {
        tracing::info!(var = name, "ACP provider key is set in the environment");
        return None;
    }
    let Some(source) = source() else {
        tracing::info!(
            var = name,
            "ACP provider key is not set and this agent has no secret store; spawning without it"
        );
        return None;
    };
    let value = match tokio::time::timeout(timeout, source.fetch()).await {
        Ok(Ok(value)) => value.map(|v| v.trim().to_owned()).filter(|v| !v.is_empty()),
        Ok(Err(e)) => {
            // `%e`, not the source chain: a decode error's source can quote the stored value.
            tracing::warn!(
                var = name,
                path = source.origin(),
                error = %e,
                "reading the ACP provider key from the store failed; spawning without it"
            );
            return None;
        }
        Err(_) => {
            tracing::warn!(
                var = name,
                path = source.origin(),
                "the store did not answer within {timeout:?}; spawning the ACP agent without \
                 its provider key"
            );
            return None;
        }
    };
    let Some(value) = value else {
        tracing::info!(
            var = name,
            path = source.origin(),
            "no ACP provider key is stored; spawning without it"
        );
        return None;
    };
    tracing::info!(
        var = name,
        path = source.origin(),
        "ACP provider key read from the store"
    );
    Some(KeyVar {
        name: name.to_owned(),
        value,
    })
}

#[cfg(test)]
mod tests {
    use std::cell::Cell;

    use super::*;

    const VAR: &str = "ACP_PROVIDER_API_KEY";

    /// A store answering `answer`, counting how often it is asked.
    struct Fake {
        answer: fn() -> Result<Option<String>, swarm_secret_client::Error>,
        asked: Cell<u32>,
    }

    impl Fake {
        fn new(answer: fn() -> Result<Option<String>, swarm_secret_client::Error>) -> Self {
            Self {
                answer,
                asked: Cell::new(0),
            }
        }
    }

    impl KeySource for &Fake {
        fn origin(&self) -> &'static str {
            "swarm/agents/a1/acp-provider"
        }

        async fn fetch(&self) -> Result<Option<String>, swarm_secret_client::Error> {
            self.asked.set(self.asked.get() + 1);
            (self.answer)()
        }
    }

    async fn resolve(inherited: Option<&str>, store: Option<&Fake>) -> Option<(String, String)> {
        resolve_with(
            VAR,
            inherited.map(str::to_owned),
            || store,
            Duration::from_secs(1),
        )
        .await
        .map(|k| (k.name, k.value))
    }

    #[tokio::test]
    async fn an_inherited_key_wins_and_the_store_is_not_asked() {
        let store = Fake::new(|| Ok(Some("from-store".into())));
        assert!(resolve(Some("from-file"), Some(&store)).await.is_none());
        assert_eq!(store.asked.get(), 0);
    }

    #[tokio::test]
    async fn without_an_inherited_key_the_stored_one_is_added() {
        let store = Fake::new(|| Ok(Some("from-store\n".into())));
        assert_eq!(
            resolve(None, Some(&store)).await,
            Some((VAR.to_owned(), "from-store".to_owned()))
        );
        // An empty inherited value is no value.
        assert!(resolve(Some(" "), Some(&store)).await.is_some());
    }

    #[tokio::test]
    async fn neither_adds_nothing() {
        assert!(resolve(None, None).await.is_none());
        let empty = Fake::new(|| Ok(None));
        assert!(resolve(None, Some(&empty)).await.is_none());
        let blank = Fake::new(|| Ok(Some("  ".into())));
        assert!(resolve(None, Some(&blank)).await.is_none());
    }

    #[tokio::test]
    async fn an_unreachable_store_adds_nothing() {
        let failing = Fake::new(|| Err(swarm_secret_client::Error::MissingEnv("BAO_ADDR")));
        assert!(resolve(None, Some(&failing)).await.is_none());
        assert_eq!(failing.asked.get(), 1);
    }

    #[test]
    fn no_store_address_means_no_store() {
        let source = store_source(|_| None).expect("an absent store is legal");
        assert!(source.is_none());
    }

    #[test]
    fn a_store_without_the_agent_name_is_refused() {
        let Err(e) = store_source(|k| (k == ENV_ADDR).then(|| "https://bao:8200".to_owned()))
        else {
            panic!("a store address without an agent name is a half-delivered container");
        };
        assert!(e.to_string().contains(ENV_AGENT_NAME), "{e}");
    }

    #[test]
    fn the_store_source_reads_the_agents_own_path() {
        let env = [
            (ENV_ADDR, "https://bao:8200"),
            (ENV_AGENT_NAME, "a1"),
            ("BAO_CLIENT_CERT", "/run/credentials/c"),
            ("BAO_CLIENT_KEY", "/run/credentials/k"),
        ];
        let source = store_source(|k| {
            env.iter()
                .find(|(n, _)| *n == k)
                .map(|(_, v)| (*v).to_owned())
        })
        .expect("a complete environment")
        .expect("a store address was given");
        assert_eq!(source.path, "swarm/agents/a1/acp-provider");
        assert_eq!(source.role, policy::agent_object_name("a1").unwrap());
    }
}