leviath-runtime 0.1.0

//! Lazy, hot-reloading resolution of Rhai *script providers*.
//!
//! Native providers are built eagerly at daemon startup. Script providers are
//! not: a `.rhai` file in the providers directory becomes a live provider only
//! when an agent references its name, and it is **reloaded automatically** when
//! the file changes. [`ScriptProviderLayer`] is the seam the [`ProviderRegistry`]
//! consults for any name it doesn't have natively; it caches compiled providers
//! keyed by file mtime, so:
//!
//! - first reference to `<name>` → compile + `initialize` + cache;
//! - unchanged file → cached instance (no recompile);
//! - edited file (newer mtime) → rebuild;
//! - a brand-new file that didn't exist at startup → loads on first reference;
//! - a deleted file → evicted, the provider disappears;
//! - a broken script → not resolved (logged), so selection falls through.
//!
//! [`ProviderRegistry`]: crate::ProviderRegistry

use std::collections::HashMap;
use std::path::PathBuf;
use std::sync::{Arc, Mutex, PoisonError};
use std::time::SystemTime;

use leviath_providers::{ModelCapabilities, Provider, RateLimitConfig, RhaiProvider};

/// Per-provider configuration from `[model_providers.<name>]`. All fields are
/// optional overrides - a script activates by an agent referencing its name and
/// the file existing, not by having an entry here.
#[derive(Clone, Debug, Default)]
pub struct ScriptProviderSpec {
    /// Script filename stem or path (default `<name>.rhai` in the providers dir).
    pub script: Option<String>,
    /// Rate limit applied by the Rust wrapper.
    pub rate_limit: Option<RateLimitConfig>,
    /// The `config` map passed to the script's `initialize` (base_url, api_key,
    /// and any extra keys), pre-assembled by the CLI.
    pub init_config: serde_json::Value,
}

/// A cached, compiled script provider plus the source mtime it was built from.
struct Cached {
    mtime: SystemTime,
    provider: Arc<dyn Provider>,
}

/// Lazy, hot-reloading resolver for script providers.
pub struct ScriptProviderLayer {
    dir: PathBuf,
    overrides: HashMap<String, ScriptProviderSpec>,
    default_caps: HashMap<String, ModelCapabilities>,
    request_timeout_secs: Option<u64>,
    /// `[security] allow_env_vars`: credential-shaped environment variables a
    /// provider script may read. Empty by default - a provider script runs
    /// during inference, not through a tool call, so nothing it does passes an
    /// approval prompt.
    env_allowlist: Arc<Vec<String>>,
    cache: Mutex<HashMap<String, Cached>>,
}

impl ScriptProviderLayer {
    /// Build a layer over `dir`, with per-provider `overrides`, global model
    /// capability overrides, and the global request timeout.
    pub fn new(
        dir: PathBuf,
        overrides: HashMap<String, ScriptProviderSpec>,
        default_caps: HashMap<String, ModelCapabilities>,
        request_timeout_secs: Option<u64>,
        env_allowlist: Vec<String>,
    ) -> Self {
        Self {
            dir,
            overrides,
            default_caps,
            request_timeout_secs,
            env_allowlist: Arc::new(env_allowlist),
            cache: Mutex::new(HashMap::new()),
        }
    }

    /// Resolve `<name>` to its script path: an explicit `script` override
    /// (an absolute path, or a stem/filename under the providers dir), else
    /// `<name>.rhai` in the providers dir.
    ///
    /// A *relative* override is confined to the providers directory. It used to
    /// be joined verbatim, so `script = "../../tools/evil"` reached outside it -
    /// and whatever it reached is compiled and run as a provider, which is the
    /// most privileged script surface there is. An absolute path is still
    /// honored: that is the documented way to point at a script kept elsewhere,
    /// and it can only come from the user's own config, not from a blueprint.
    ///
    /// `None` when the override escapes; the caller reports it and loads nothing.
    fn resolve_path(&self, name: &str) -> Option<PathBuf> {
        let stem = self
            .overrides
            .get(name)
            .and_then(|s| s.script.as_deref())
            .unwrap_or(name);
        let candidate = PathBuf::from(stem);
        if candidate.is_absolute() {
            return Some(candidate);
        }
        let filename = match stem.ends_with(".rhai") {
            true => stem.to_string(),
            false => format!("{stem}.rhai"),
        };
        // Reject any traversal component outright rather than normalizing it
        // away: a provider path has no legitimate reason to contain `..`, so
        // "what did the user mean by this" is the wrong question to ask.
        let joined = PathBuf::from(&filename);
        if joined
            .components()
            .any(|c| matches!(c, std::path::Component::ParentDir))
        {
            return None;
        }
        Some(self.dir.join(joined))
    }

    /// Get (or lazily load / reload) the provider named `name`, or `None` when
    /// there is no such script or it fails to load.
    ///
    /// The cache lock is taken three times - a read, then a write on whichever
    /// arm the compile lands on - and is **never held across
    /// `RhaiProvider::from_script`**, which parses and initializes an arbitrary
    /// user-authored `.rhai` file. That call is the slowest and least
    /// trustworthy thing this layer does; holding a process-wide lock across it
    /// serialized every agent's provider lookup behind one compile, and a panic
    /// inside it poisoned the cache for the whole daemon.
    ///
    /// The cost is that two callers racing on the same cold name may both
    /// compile it. Both get a working provider and the later `insert` wins -
    /// wasted work, never a wrong answer, and it self-corrects on the next
    /// lookup because entries are validated by mtime.
    pub fn get_or_load(&self, name: &str) -> Option<Arc<dyn Provider>> {
        let Some(path) = self.resolve_path(name) else {
            tracing::warn!(
                provider = %name,
                "script provider path escapes the providers directory - refusing to load"
            );
            self.evict(name);
            return None;
        };
        let Some(mtime) = std::fs::metadata(&path).and_then(|m| m.modified()).ok() else {
            // File gone (or unreadable): drop any stale entry, no provider.
            self.evict(name);
            return None;
        };
        if let Some(cached) = self.cached_fresh(name, mtime) {
            return Some(cached);
        }

        let spec = self.overrides.get(name);
        let init_config = spec
            .map(|s| s.init_config.clone())
            .unwrap_or_else(|| serde_json::json!({}));
        let rate_limit = spec.and_then(|s| s.rate_limit.clone());
        // No lock held here - see the note above.
        match RhaiProvider::from_script(
            name.to_string(),
            &path,
            init_config,
            self.default_caps.clone(),
            rate_limit,
            self.request_timeout_secs,
            self.env_allowlist.clone(),
        ) {
            Ok(p) => {
                let provider: Arc<dyn Provider> = Arc::new(p);
                self.cache
                    .lock()
                    .unwrap_or_else(PoisonError::into_inner)
                    .insert(
                        name.to_string(),
                        Cached {
                            mtime,
                            provider: provider.clone(),
                        },
                    );
                Some(provider)
            }
            Err(e) => {
                self.evict(name);
                tracing::warn!(provider = %name, error = %e, "script provider load failed");
                None
            }
        }
    }

    /// The cached provider for `name`, but only if it was built from the script
    /// as it is on disk right now. Holds the lock just long enough to clone an
    /// `Arc`.
    fn cached_fresh(&self, name: &str, mtime: SystemTime) -> Option<Arc<dyn Provider>> {
        let cache = self.cache.lock().unwrap_or_else(PoisonError::into_inner);
        let cached = cache.get(name)?;
        if cached.mtime == mtime {
            Some(cached.provider.clone())
        } else {
            None
        }
    }

    /// Drop any cached entry for `name`.
    fn evict(&self, name: &str) {
        self.cache
            .lock()
            .unwrap_or_else(PoisonError::into_inner)
            .remove(name);
    }
}

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

    const GOOD: &str = "fn initialize(config) { #{ base: config.base_url } }\n\
                        fn inference(state, request) { #{ content: \"ok\" } }";

    fn write(dir: &std::path::Path, name: &str, body: &str) -> PathBuf {
        let path = dir.join(name);
        std::fs::write(&path, body).unwrap();
        path
    }

    /// Force a file's mtime to be strictly newer, so a reload is observable even
    /// when two writes land in the same clock tick.
    fn bump_mtime(path: &std::path::Path) {
        let later = SystemTime::now() + Duration::from_secs(5);
        let f = std::fs::OpenOptions::new().write(true).open(path).unwrap();
        f.set_modified(later).unwrap();
    }

    fn layer(dir: PathBuf) -> ScriptProviderLayer {
        ScriptProviderLayer::new(dir, HashMap::new(), HashMap::new(), None, Vec::new())
    }

    #[test]
    fn loads_by_convention_and_caches() {
        let dir = tempfile::tempdir().unwrap();
        write(dir.path(), "groq.rhai", GOOD);
        let l = layer(dir.path().to_path_buf());
        let first = l.get_or_load("groq").expect("loads");
        assert_eq!(first.name(), "groq");
        // Cache hit returns the same Arc (unchanged mtime).
        let second = l.get_or_load("groq").expect("cached");
        assert!(Arc::ptr_eq(&first, &second));
    }

    #[test]
    fn missing_file_is_none() {
        let dir = tempfile::tempdir().unwrap();
        let l = layer(dir.path().to_path_buf());
        assert!(l.get_or_load("nope").is_none());
    }

    #[test]
    fn hot_reload_on_mtime_change() {
        let dir = tempfile::tempdir().unwrap();
        let path = write(dir.path(), "p.rhai", GOOD);
        let l = layer(dir.path().to_path_buf());
        let first = l.get_or_load("p").unwrap();
        // Rewrite with newer mtime → a fresh instance.
        write(dir.path(), "p.rhai", GOOD);
        bump_mtime(&path);
        let second = l.get_or_load("p").unwrap();
        assert!(!Arc::ptr_eq(&first, &second));
    }

    #[test]
    fn new_file_after_construction_loads() {
        let dir = tempfile::tempdir().unwrap();
        let l = layer(dir.path().to_path_buf());
        assert!(l.get_or_load("late").is_none());
        write(dir.path(), "late.rhai", GOOD);
        assert!(l.get_or_load("late").is_some());
    }

    #[test]
    fn deleted_file_evicts() {
        let dir = tempfile::tempdir().unwrap();
        let path = write(dir.path(), "gone.rhai", GOOD);
        let l = layer(dir.path().to_path_buf());
        assert!(l.get_or_load("gone").is_some());
        std::fs::remove_file(&path).unwrap();
        assert!(l.get_or_load("gone").is_none());
    }

    #[test]
    fn broken_script_not_resolved() {
        let dir = tempfile::tempdir().unwrap();
        write(dir.path(), "bad.rhai", "fn inference( { oops");
        let l = layer(dir.path().to_path_buf());
        assert!(l.get_or_load("bad").is_none());
        // Not cached, so a fixed file loads on the next reference.
        let path = write(dir.path(), "bad.rhai", GOOD);
        bump_mtime(&path);
        assert!(l.get_or_load("bad").is_some());
    }

    #[test]
    fn resolve_path_honors_overrides() {
        let dir = tempfile::tempdir().unwrap();
        let abs = dir.path().join("elsewhere.rhai");
        std::fs::write(&abs, GOOD).unwrap();
        let mut overrides = HashMap::new();
        // stem override
        overrides.insert(
            "a".to_string(),
            ScriptProviderSpec {
                script: Some("custom".to_string()),
                ..Default::default()
            },
        );
        // ".rhai" suffix override
        overrides.insert(
            "b".to_string(),
            ScriptProviderSpec {
                script: Some("custom.rhai".to_string()),
                ..Default::default()
            },
        );
        // absolute-path override
        overrides.insert(
            "c".to_string(),
            ScriptProviderSpec {
                script: Some(abs.to_string_lossy().into_owned()),
                ..Default::default()
            },
        );
        let l = ScriptProviderLayer::new(
            dir.path().to_path_buf(),
            overrides,
            HashMap::new(),
            None,
            Vec::new(),
        );
        assert_eq!(l.resolve_path("a"), Some(dir.path().join("custom.rhai")));
        assert_eq!(l.resolve_path("b"), Some(dir.path().join("custom.rhai")));
        assert_eq!(l.resolve_path("c"), Some(abs));
        assert_eq!(l.resolve_path("z"), Some(dir.path().join("z.rhai")));
    }

    /// A relative `script` override may not climb out of the providers
    /// directory. Whatever it reached would be compiled and run as a provider -
    /// the one script surface with no permission layer in front of it - so the
    /// traversal is refused outright rather than normalized away.
    #[test]
    fn relative_script_override_cannot_escape_the_providers_dir() {
        let dir = tempfile::tempdir().unwrap();
        let mut overrides = HashMap::new();
        for (name, script) in [
            ("a", "../../tools/evil"),
            ("b", "../evil.rhai"),
            ("c", "sub/../../evil"),
        ] {
            overrides.insert(
                name.to_string(),
                ScriptProviderSpec {
                    script: Some(script.to_string()),
                    ..Default::default()
                },
            );
        }
        let l = ScriptProviderLayer::new(
            dir.path().to_path_buf(),
            overrides,
            HashMap::new(),
            None,
            Vec::new(),
        );
        for name in ["a", "b", "c"] {
            assert_eq!(l.resolve_path(name), None, "{name} should be refused");
            assert!(l.get_or_load(name).is_none(), "{name} must not load");
        }
    }

    /// A nested path *inside* the directory is still fine - only `..` is refused.
    #[test]
    fn nested_relative_override_inside_the_dir_still_resolves() {
        let dir = tempfile::tempdir().unwrap();
        let mut overrides = HashMap::new();
        overrides.insert(
            "a".to_string(),
            ScriptProviderSpec {
                script: Some("vendor/custom".to_string()),
                ..Default::default()
            },
        );
        let l = ScriptProviderLayer::new(
            dir.path().to_path_buf(),
            overrides,
            HashMap::new(),
            None,
            Vec::new(),
        );
        assert_eq!(
            l.resolve_path("a"),
            Some(dir.path().join("vendor/custom.rhai"))
        );
    }

    #[test]
    fn init_config_reaches_the_script() {
        let dir = tempfile::tempdir().unwrap();
        // Script echoes config.base_url into state; inference returns it.
        write(
            dir.path(),
            "echo.rhai",
            "fn initialize(config) { #{ b: config.base_url } }\n\
             fn inference(state, request) { #{ content: state.b } }",
        );
        let mut overrides = HashMap::new();
        overrides.insert(
            "echo".to_string(),
            ScriptProviderSpec {
                init_config: serde_json::json!({ "base_url": "http://cfg" }),
                ..Default::default()
            },
        );
        let l = ScriptProviderLayer::new(
            dir.path().to_path_buf(),
            overrides,
            HashMap::new(),
            None,
            Vec::new(),
        );
        assert!(l.get_or_load("echo").is_some());
    }
}