relon-eval-api 0.1.0-rc2

//! Shared evaluator context: host policy + sandbox state.
//!
//! `Context` is the carrier of all backend-agnostic configuration: the
//! root AST node, decorator and native-fn registries, module resolvers,
//! capability grants, and the per-run caches a backend uses to thread
//! state across `eval_root` / `run_main` invocations.
//!
//! Most fields are `pub` so that any backend implementing
//! [`crate::Evaluator`] in a different crate can read and update them.
//! Sandbox-relevant state (`capabilities`, `module_resolvers`,
//! `analyzed`) is private: reads go through the `&`-returning getters
//! and writes through the construction-time `with_*` / controlled
//! `*_module_resolver` entry points, so a host cannot silently widen
//! a sandbox after handing the context to an evaluator.

use crate::decorator::DecoratorPlugin;
use crate::module::ModuleResolver;
use crate::native_fn::RelonFunction;
use crate::value::Value;
use relon_parser::Node;
use std::collections::{HashMap, HashSet};
use std::sync::atomic::AtomicU64;
use std::sync::{Arc, Mutex};

// Canonical capability data types (`CapabilityBit`, `NativeFnGate`,
// `Capabilities`) now live in the zero-dependency `relon-cap` leaf crate
// so the analyzer can share the exact same definitions instead of
// mirroring them field-for-field. Re-exported here at their historical
// `relon_eval_api::context::{...}` (and, via `lib.rs`,
// `relon_eval_api::{...}`) paths so every existing reference keeps
// resolving unchanged. The enforcement machinery that references
// eval-api types — `CapabilityGate`, `GatedNativeFn`, `NativeFnCaps` —
// stays in this crate.
pub use relon_cap::{
    Capabilities, CapabilityBit, NativeFnGate, ResourceBudget, ResourceBudgetProfile,
};

/// Internal helper: a registered native function with its capability gate.
/// `pub` so backend crates can read both the underlying `func` and the
/// declared `gate` when dispatching a call.
pub struct GatedNativeFn {
    pub func: Arc<dyn RelonFunction>,
    pub gate: NativeFnGate,
}

/// Shared execution environment for one or more evaluations.
///
/// Holds the document root, registered plugins, cached modules, and
/// sandbox [`Capabilities`]. Thread-safe.
///
/// Most fields are `pub` so any backend implementing [`crate::Evaluator`]
/// from a separate crate can read and update them. The sandbox-policy
/// fields (`capabilities`, `module_resolvers`, `analyzed`) are private;
/// hosts and backends go through the constructor / `register_*` /
/// `with_*` helpers and the `&`-returning getters instead.
pub struct Context {
    pub root_node: Option<Arc<Node>>,
    pub decorators: HashMap<String, Arc<dyn DecoratorPlugin>>,
    pub functions: HashMap<String, GatedNativeFn>,
    /// Schema-rooted Phase D: native methods registered against a
    /// specific schema. Keyed by `(schema_name, method_name)` so a
    /// host can attach `register_method("Money", "cents_value", gate,
    /// func)` and the evaluator dispatches `m.cents_value()` to it
    /// when `m`'s brand is `"Money"`. Mirrors the analyzer's
    /// `tree.method_signatures` shape; the `#native` directive on a
    /// `with { ... }` method declares the slot, the host fills it at
    /// runtime through this map.
    /// P2-4: nested map keyed `schema -> method -> entry` so per-call
    /// `try_call_native_method` looks up without minting a
    /// `(String, String)` tuple on every dispatch. The outer/inner
    /// `HashMap::get(&str)` paths borrow the schema/method names
    /// directly, eliminating the prior 2 × `String::from`
    /// allocations on every comparator / index / arithmetic dispatch.
    pub native_methods: HashMap<String, HashMap<String, GatedNativeFn>>,
    pub schemas: HashMap<String, Value>,
    /// Ordered module-resolution chain consulted front-to-back by the
    /// evaluator's `#import` handling. Private: mutation goes through
    /// [`Context::prepend_module_resolver`] /
    /// [`Context::append_module_resolver`] so the sandbox's resolver
    /// order (e.g. the default-deny tail installed for
    /// [`Context::sandboxed`]) cannot be silently replaced wholesale.
    module_resolvers: Vec<Arc<dyn ModuleResolver>>,
    pub path_cache: Mutex<HashMap<String, Value>>,
    pub module_cache: Mutex<HashMap<String, Value>>,
    /// Backing cursor table for user-callable `Iter.next()`. Keyed by
    /// the `u64` iter-id minted by [`Context::next_iter_id`] at the
    /// `iter()` call site and stamped into the resulting `Iter`-branded
    /// dict as `_id`. The `Value` graph is immutable (`Arc`-shared, no
    /// interior mutability), so cursor state must live outside it; this
    /// Context field is the canonical home — entries die when the
    /// Context is dropped, and the table is cleared at the start of
    /// every top-level `eval_root` / `run_main` so long-running hosts
    /// reusing a Context never accumulate stale cursors. Cross-Context
    /// `Iter` values surface as exhausted (`next()` returns `None`):
    /// see `NativeFnCaps::iter_cursor_fetch_and_inc`.
    pub iter_cursors: Mutex<HashMap<u64, usize>>,
    /// Monotonic per-Context id generator paired with
    /// [`Context::iter_cursors`]. Wraps at `u64::MAX`, effectively
    /// never reached in practice. Deliberately not reset on
    /// `eval_root` / `run_main` cleanup — the cursor table is, but
    /// the counter must keep climbing so a still-live `Iter` dict
    /// from the prior run can't collide with a fresh one in the
    /// new run.
    pub iter_id_counter: AtomicU64,
    /// Modules currently on the load stack, with a re-entry counter so
    /// the same canonical id can appear multiple times (e.g. via `as=`
    /// vs `spread=true`) without the inner guard's `Drop` clearing the
    /// outer frame's record. Decrement on drop, remove when zero.
    pub loading_modules: Mutex<HashMap<String, usize>>,
    pub evaluating_paths: Mutex<HashSet<String>>,
    pub step_counter: AtomicU64,
    /// Monotonic counter incremented once per closure invocation. Used
    /// by `eval_closure` to derive a fresh `cache_namespace` for each
    /// call so that path-cache entries computed inside the closure body
    /// (e.g. `&sibling.x`) are not shared across distinct invocations
    /// with different bound parameters.
    pub closure_call_counter: AtomicU64,
    /// Analyzer side-table for the entry file. Private: installed at
    /// construction time via [`Context::with_analyzed`] /
    /// [`Context::with_workspace`], read through
    /// [`Context::analyzed`] — backends never swap the tree under a
    /// live evaluation.
    analyzed: Option<Arc<relon_analyzer::AnalyzedTree>>,
    /// Pre-computed workspace tree (entry + every reachable module),
    /// produced by `relon_analyzer::analyze_entry`. When present, the
    /// evaluator's `evaluate_module_source` skips the per-module
    /// parse-plus-analyze pass and looks up the cached node and
    /// analyzed tree directly. The field is independent of
    /// `analyzed`; the latter remains the side-table for the entry
    /// file specifically, so existing callers that don't drive
    /// workspace analysis keep working unchanged.
    pub workspace: Option<Arc<relon_analyzer::WorkspaceTree>>,
    /// Sandbox capability grants. Private so the only write path is
    /// construction-time [`Context::with_capabilities`]; once the
    /// context is handed to an evaluator the grants are immutable
    /// policy, read through [`Context::capabilities`]. This is the
    /// audit guarantee: an embedder cannot widen a running sandbox by
    /// poking the field.
    capabilities: Capabilities,
    /// Set by [`Context::sandboxed`] so the backend's deferred setup
    /// step can attach the default-deny filesystem resolver after the
    /// stdlib / decorators / prelude registration. Untouched by the
    /// bare [`Context::new`] constructor.
    pub sandboxed_flag: bool,
    /// Tracks whether the backend has already installed its default
    /// stdlib / decorators / prelude into this context. Flipped from
    /// `false` to `true` by `TreeWalkEvaluator::new` (and any future
    /// backend) on first wrap, so a `Context` reused across multiple
    /// evaluator instances doesn't pay the registration cost twice
    /// and a host re-registering an intrinsic isn't silently undone
    /// on a second wrap.
    pub backend_prepared: bool,
}

impl Default for Context {
    fn default() -> Self {
        Self::new()
    }
}

impl Context {
    /// Construct a [`Context`] with no plugins / resolvers / stdlib
    /// pre-registered. Backend crates (e.g. `relon-evaluator`) attach
    /// their own stdlib + decorators + module resolvers when the host
    /// constructs an evaluator on top of this context (the tree-walking
    /// backend does this lazily in `TreeWalkEvaluator::new` so users
    /// keep the historical "call `Context::new()` then go" ergonomics).
    pub fn new() -> Self {
        Self {
            root_node: None,
            decorators: HashMap::new(),
            functions: HashMap::new(),
            native_methods: HashMap::new(),
            schemas: HashMap::new(),
            module_resolvers: Vec::new(),
            path_cache: Mutex::new(HashMap::new()),
            module_cache: Mutex::new(HashMap::new()),
            iter_cursors: Mutex::new(HashMap::new()),
            iter_id_counter: AtomicU64::new(0),
            loading_modules: Mutex::new(HashMap::new()),
            evaluating_paths: Mutex::new(HashSet::new()),
            step_counter: AtomicU64::new(0),
            closure_call_counter: AtomicU64::new(0),
            analyzed: None,
            workspace: None,
            capabilities: Capabilities::default(),
            sandboxed_flag: false,
            backend_prepared: false,
        }
    }

    /// Sandboxed counterpart to [`Self::new`]. The bare construction is
    /// identical; the only difference is `sandboxed_flag = true`, which
    /// the active backend reads when it installs its defaults so a
    /// default-deny filesystem resolver is appended after the standard
    /// `std/...` resolver. The tree-walking backend implements this
    /// hook in `TreeWalkEvaluator::new`.
    pub fn sandboxed() -> Self {
        let mut this = Self::new();
        this.sandboxed_flag = true;
        this
    }

    pub fn with_root(mut self, node: Node) -> Self {
        self.root_node = Some(Arc::new(node));
        self
    }

    pub fn with_analyzed(mut self, tree: Arc<relon_analyzer::AnalyzedTree>) -> Self {
        self.analyzed = Some(tree);
        self
    }

    /// Wire a pre-computed workspace tree into the context. The
    /// workspace's entry tree (if present) is also installed as
    /// `analyzed` so callers that read either field see consistent
    /// data — gives single-file consumers the same view they had
    /// before, and gives module-loading code a fast path to skip
    /// per-module parse + analyze.
    pub fn with_workspace(mut self, workspace: Arc<relon_analyzer::WorkspaceTree>) -> Self {
        if let Some(entry) = workspace.modules.get(&workspace.entry_id) {
            self.analyzed = Some(Arc::clone(entry));
        }
        self.workspace = Some(workspace);
        self
    }

    /// Set the sandbox capability grants. Construction-time only by
    /// design: the method consumes `self`, so it composes with the
    /// other `with_*` builders but cannot retarget a context that is
    /// already shared with an evaluator (those hold `Arc<Context>`).
    /// There is deliberately no `&mut self` setter — widening a
    /// sandbox mid-run is not a supported operation.
    pub fn with_capabilities(mut self, capabilities: Capabilities) -> Self {
        self.capabilities = capabilities;
        self
    }

    /// Read-only view of the sandbox capability grants.
    pub fn capabilities(&self) -> &Capabilities {
        &self.capabilities
    }

    /// Read-only view of the analyzer side-table for the entry file,
    /// when one was installed via [`Self::with_analyzed`] /
    /// [`Self::with_workspace`].
    pub fn analyzed(&self) -> Option<&Arc<relon_analyzer::AnalyzedTree>> {
        self.analyzed.as_ref()
    }

    /// Read-only view of the module-resolution chain, in consultation
    /// order (front wins).
    pub fn module_resolvers(&self) -> &[Arc<dyn ModuleResolver>] {
        &self.module_resolvers
    }

    /// Insert a resolver at the front of the chain so it is consulted
    /// before every existing resolver (front wins).
    pub fn prepend_module_resolver(&mut self, resolver: Arc<dyn ModuleResolver>) {
        self.module_resolvers.insert(0, resolver);
    }

    /// Append a resolver at the back of the chain so it is consulted
    /// only when no earlier resolver claimed the path. This is where a
    /// backend installs catch-all / default-deny resolvers (e.g. the
    /// sandboxed filesystem resolver) during its prepare step.
    pub fn append_module_resolver(&mut self, resolver: Arc<dyn ModuleResolver>) {
        self.module_resolvers.push(resolver);
    }

    /// Register a native function with explicit capability requirements.
    /// The function declares which bits it needs via `gate`; under the
    /// sandbox the call is rejected unless every set bit is granted in
    /// the context-wide [`Capabilities`].
    ///
    /// For pure functions (no host capability, no I/O, no ambient
    /// state) prefer [`Self::register_pure_fn`] — it makes the
    /// "this fn is pure" intent explicit. Passing
    /// `NativeFnGate::default()` here is equivalent.
    pub fn register_fn<S: Into<String>>(
        &mut self,
        name: S,
        gate: NativeFnGate,
        func: Arc<dyn RelonFunction>,
    ) {
        self.functions
            .insert(name.into(), GatedNativeFn { func, gate });
    }

    /// Register a pure native function: no I/O, no ambient state, no
    /// host capability required. Equivalent to
    /// `register_fn(name, NativeFnGate::default(), func)`. The all-zero
    /// gate is trivially satisfied by every `Capabilities` value, so
    /// pure fns keep working under a fully sandboxed context.
    ///
    /// Stdlib intrinsics (`len`, `range`, `string.*`, …) and
    /// deterministic host fns whose contract is "args in, value out"
    /// register through this entry point.
    pub fn register_pure_fn<S: Into<String>>(&mut self, name: S, func: Arc<dyn RelonFunction>) {
        self.register_fn(name, NativeFnGate::default(), func);
    }

    /// Schema-rooted Phase D: attach a host-supplied implementation to
    /// a `#native` method on a specific schema. The evaluator
    /// dispatches `value.method(...)` to this fn whenever `value`'s
    /// brand matches `schema` and the source-side method body is
    /// absent (declared `#native`). Capability gating mirrors
    /// [`Self::register_fn`]: the `gate` declares which
    /// [`Capabilities`] bits the body needs at runtime, and a denied
    /// caller surfaces `RuntimeError::CapabilityDenied`.
    ///
    /// Replaces the v1 pattern of `register_fn("Schema.method", ...)`
    /// with a key shape that tracks the schema-rooted dispatch model
    /// directly — no string concatenation, no shadowing of free fn
    /// names by accident.
    pub fn register_method<S: Into<String>, M: Into<String>>(
        &mut self,
        schema: S,
        method: M,
        gate: NativeFnGate,
        func: Arc<dyn RelonFunction>,
    ) {
        self.native_methods
            .entry(schema.into())
            .or_default()
            .insert(method.into(), GatedNativeFn { func, gate });
    }

    /// Pure-method counterpart to [`Self::register_method`]. Equivalent
    /// to passing [`NativeFnGate::default`] (the all-zero gate) — the
    /// method body needs no host capability, so it dispatches under
    /// every [`Capabilities`] including the zero-trust default.
    pub fn register_pure_method<S: Into<String>, M: Into<String>>(
        &mut self,
        schema: S,
        method: M,
        func: Arc<dyn RelonFunction>,
    ) {
        self.register_method(schema, method, NativeFnGate::default(), func);
    }

    pub fn register_decorator<S: Into<String>>(
        &mut self,
        name: S,
        plugin: Arc<dyn DecoratorPlugin>,
    ) {
        self.decorators.insert(name.into(), plugin);
    }

    pub fn register_schema<S: Into<String>>(&mut self, name: S, schema: Value) {
        self.schemas.insert(name.into(), schema);
    }

    pub fn enter_loading_module(&self, id: String) -> LoadingModuleGuard<'_> {
        *self
            .loading_modules
            .lock()
            .unwrap()
            .entry(id.clone())
            .or_insert(0) += 1;
        LoadingModuleGuard {
            context: self,
            module_id: id,
        }
    }

    pub fn analyzer_target(&self, id: relon_parser::NodeId) -> Option<Node> {
        self.analyzed()
            .and_then(|tree| tree.node(id).map(|arc| (**arc).clone()))
    }

    /// Mint a fresh `Iter` cursor id under this Context **and seed a
    /// zero cursor entry** so that subsequent
    /// [`Context::iter_cursor_fetch_and_inc`] calls can distinguish a
    /// "freshly minted, cursor at 0" iter from a foreign-Context iter
    /// (no entry → treated as exhausted; see policy note on
    /// `iter_cursor_fetch_and_inc`).
    ///
    /// Each `xs.iter()` consumes one id; two Contexts mint
    /// independently because each owns its own counter. Wraps at
    /// `u64::MAX` — reachable only in pathological constructions —
    /// and the `Relaxed` ordering is sufficient because the id is
    /// opaque outside of [`Context::iter_cursors`] lookup.
    pub fn next_iter_id(&self) -> u64 {
        use std::sync::atomic::Ordering;
        let id = self.iter_id_counter.fetch_add(1, Ordering::Relaxed);
        // Pre-register the cursor so the "missing entry → exhausted"
        // signal in `iter_cursor_fetch_and_inc` cleanly distinguishes
        // a foreign-Context `_id` from a fresh local one.
        self.iter_cursors.lock().unwrap().insert(id, 0);
        id
    }

    /// Atomically read the cursor for `iter_id`, and if `cursor < len`,
    /// post-increment and return the old value; otherwise return
    /// `None`. **A missing entry** (no cursor was ever minted for
    /// `iter_id` in this Context) is also reported as `None` —
    /// idempotent end-of-iter, matching the `Option::None` return
    /// type of `Iter.next() -> Option<T>`.
    ///
    /// Cross-Context policy (deliberate): if the host hands an
    /// `Iter` value built in Context A to Context B and then calls
    /// `next()`, Context B's table has no entry for that id, so we
    /// return `None`. This is the gentlest reading of "an iter
    /// belongs to its originating Context" — no new error variant,
    /// no capability trap; the iter simply looks exhausted to the
    /// foreign Context. A future stricter mode could surface a
    /// dedicated `RuntimeError::IterNotOwnedByContext`, but today's
    /// host APIs don't yet expose a way to attach an iter to a
    /// Context other than via `iter()` itself, so the implicit-
    /// exhausted reading is sufficient and matches the
    /// "no implicit ambient state" design promise.
    pub fn iter_cursor_fetch_and_inc(&self, iter_id: u64, len: usize) -> Option<usize> {
        // Single-lock atomic read-check-increment. Spelled out so
        // the bounds check and the bump happen under the same
        // critical section — splitting them would let a concurrent
        // caller observe a stale "in bounds" reading after the
        // cursor moved.
        let mut cursors = self.iter_cursors.lock().unwrap();
        // Do *not* `entry(...).or_insert(0)`: a foreign-Context id
        // must surface as `None` rather than silently spawn a fresh
        // cursor in this Context's table (which would start it
        // walking from 0 against a `_source` the caller's Context
        // never validated).
        let cursor_slot = cursors.get_mut(&iter_id)?;
        if *cursor_slot < len {
            let idx = *cursor_slot;
            *cursor_slot += 1;
            Some(idx)
        } else {
            None
        }
    }
}

pub struct LoadingModuleGuard<'a> {
    context: &'a Context,
    module_id: String,
}

impl Drop for LoadingModuleGuard<'_> {
    fn drop(&mut self) {
        let mut loading = self.context.loading_modules.lock().unwrap();
        if let Some(count) = loading.get_mut(&self.module_id) {
            *count -= 1;
            if *count == 0 {
                loading.remove(&self.module_id);
            }
        }
    }
}

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

    #[test]
    fn cap_bit_indices_are_stable() {
        // Stability contract: discriminants don't shift around, so a
        // module emitted against an older codegen still keys the same
        // capability bit the host's gate / vtable expects.
        assert_eq!(CapabilityBit::ReadsFs.bit_index(), 0);
        assert_eq!(CapabilityBit::WritesFs.bit_index(), 1);
        assert_eq!(CapabilityBit::Network.bit_index(), 2);
        assert_eq!(CapabilityBit::ReadsClock.bit_index(), 3);
        assert_eq!(CapabilityBit::ReadsEnv.bit_index(), 4);
        assert_eq!(CapabilityBit::UsesRng.bit_index(), 5);
    }
}