//! Joule Code as a JCP consumer: the L0–L4 cascade gated by a metered Grant.
//!
//! The cascade's stop-at-first-close rule picks the *cheapest sufficient* tier;
//! this crate adds the missing half of the sentence — cheapest sufficient
//! **and authorized**. Every stage consultation is decided by the JCP runtime
//! against a delegation chain *before* the stage runs: the tier is the
//! `action`, the source tree is the content-addressed `resource`, and the
//! tier's energy class is debited from the grant on allow. A tier the grant
//! doesn't name (no `l4` action → no remote frontier agent, ever) or can't
//! afford is skipped, and the cascade falls through to nothing rather than
//! overspend. Every consultation — allowed and denied — seals as a JCR-1
//! receipt.
//!
//! This is the L4 story made structural: the escape hatch to a remote agent
//! exists only when a signed grant says so, with a joule ceiling the runtime
//! enforces outside any model.

use std::sync::{Arc, Mutex};

use ed25519_dalek::SigningKey;
use jcp_grant::issue;
use jcp_runtime::Runtime;
use jcp_schema::{
    Capability, ContentId, Did, Energy, Frame, FrameKind, Grant, SignedGrant, Trust,
};
use joule_code_cascade::{Request, Resolution, Stage};
use joule_code_schema::Tier;

/// The JCP action string for a tier — the verb a grant must name for the
/// cascade to consult that tier.
pub fn tier_action(tier: Tier) -> &'static str {
    match tier {
        Tier::L0 => "l0",
        Tier::L1 => "l1",
        Tier::L2 => "l2",
        Tier::L3 => "l3",
        Tier::L4 => "l4",
    }
}

/// Order-of-magnitude attempt cost per tier, in µJ, with honest `Estimator`
/// provenance — the class markers of SPEC §1.1, not measurements. A deployment
/// with a real meter substitutes measured figures via [`JcpGate::with_costs`].
pub fn tier_cost_estimate(tier: Tier) -> u64 {
    match tier {
        Tier::L0 => 1,           // picojoule class, floored at 1 µJ integer
        Tier::L1 => 10,          // nanojoule class
        Tier::L2 => 1_000,       // sub-millijoule class
        Tier::L3 => 1_000_000,   // joule class
        Tier::L4 => 10_000_000,  // tens-of-joules class — the escape hatch
    }
}

struct Inner {
    runtime: Runtime,
    chain: Vec<SignedGrant>,
    caller: Did,
    steward_sk: SigningKey,
    steward: String,
    costs: fn(Tier) -> u64,
    now: u64,
    receipts: Vec<Vec<u8>>,
}

/// A shared JCP gate for one cascade: the runtime that decides every stage
/// consultation, the delegation chain it decides against, and the receipt
/// stream it seals. Wrap each stage with [`JcpGate::wrap`].
pub struct JcpGate {
    inner: Mutex<Inner>,
}

impl JcpGate {
    /// Open a gate over a delegation chain (root first; a single grant is a
    /// one-link chain). `caller` is the acting agent — the leaf's subject.
    pub fn new(
        chain: Vec<SignedGrant>,
        caller: Did,
        steward_sk: SigningKey,
        steward: impl Into<String>,
    ) -> Arc<Self> {
        Arc::new(Self {
            inner: Mutex::new(Inner {
                runtime: Runtime::new(),
                chain,
                caller,
                steward_sk,
                steward: steward.into(),
                costs: tier_cost_estimate,
                now: 0,
                receipts: Vec::new(),
            }),
        })
    }

    /// Open a gate over a fresh, self-signed grant naming `actions` (the tier
    /// verbs `"l0"`..`"l4"`) with a `budget_uj` joule ceiling over `resource` (a
    /// repo/tree identifier). The convenience for a single-endpoint consumer
    /// that is its own issuer — the air-gapped, no-external-authority case: it
    /// grants itself exactly the tiers it is willing to use (omit `"l4"` and the
    /// remote frontier agent is unreachable, structurally) under a ceiling the
    /// runtime enforces. Deterministic local keys; the receipts still seal.
    pub fn local(resource: &str, actions: &[&str], budget_uj: u64) -> Arc<Self> {
        let issuer = SigningKey::from_bytes(&[0x6a; 32]);
        let did = Did::from_verifying_key(&issuer.verifying_key());
        let grant = Grant {
            issuer: did,
            subject: did,
            capability: Capability::new(
                ContentId::of_bytes(resource.as_bytes()),
                actions.iter().copied(),
            ),
            budget_uj,
            budget_funds: None,
            caveats: Vec::new(),
            expiry: 0,
            parent: None,
            delegate_depth: None,
            nonce: [0; 16],
        };
        let signed = issue(&issuer, grant).expect("self-issued local grant is valid");
        let steward = SigningKey::from_bytes(&[0x5e; 32]);
        Self::new(vec![signed], did, steward, "did:joule-code:local")
    }

    /// Substitute a per-tier cost table (e.g. host-calibrated figures).
    pub fn with_costs(self: &Arc<Self>, costs: fn(Tier) -> u64) -> &Arc<Self> {
        self.inner.lock().expect("gate lock").costs = costs;
        self
    }

    /// Set decision time (seconds). Time is an input, not ambient state.
    pub fn set_now(&self, now: u64) {
        self.inner.lock().expect("gate lock").now = now;
    }

    /// Wrap a stage so every consultation is decided by this gate first.
    pub fn wrap<S: Stage + 'static>(self: &Arc<Self>, stage: S) -> GatedStage<S> {
        GatedStage { stage, gate: Arc::clone(self) }
    }

    /// Joules debited so far against the leaf grant.
    pub fn spent(&self) -> u64 {
        let inner = self.inner.lock().expect("gate lock");
        let leaf = inner.chain.last().expect("non-empty chain").grant.id();
        inner.runtime.spent(&leaf)
    }

    /// The sealed JCR-1 receipts for every consultation, allowed and denied.
    pub fn receipts(&self) -> Vec<Vec<u8>> {
        self.inner.lock().expect("gate lock").receipts.clone()
    }

    /// Decide one stage consultation. On allow the tier's cost is debited from
    /// every link of the chain; either way the decision seals. Public so a
    /// consumer whose tiers are not [`Stage`]s (e.g. async tiers) can gate them
    /// directly: `if gate.authorize(tier, &req) { /* run the tier */ }`.
    pub fn authorize(&self, tier: Tier, req: &Request) -> bool {
        let mut inner = self.inner.lock().expect("gate lock");
        let leaf = inner.chain.last().expect("non-empty chain").grant.clone();
        let frame = Frame {
            kind: FrameKind::AgentTask,
            trust: Trust::Control,
            grant_id: leaf.id(),
            action: tier_action(tier).to_string(),
            resource: leaf.capability.resource,
            payload_hash: ContentId::of_bytes(format!("{}\n{}", req.prior, req.intent).as_bytes()),
        };
        let cost = Energy::estimator((inner.costs)(tier));
        let (caller, now) = (inner.caller, inner.now);
        let chain = inner.chain.clone();
        let decision = inner.runtime.decide_chained(&frame, &chain, caller, cost, now);
        let chain_ids: Vec<_> = chain.iter().map(|sg| sg.grant.id()).collect();
        if let Ok(receipt) =
            jcp_receipt::seal_chained(&frame, &chain_ids, &leaf, &decision, &inner.steward_sk, &inner.steward)
        {
            inner.receipts.push(receipt);
        }
        decision.is_allow()
    }
}

/// A cascade stage that consults the JCP gate before running. A denied tier
/// returns `None` — the cascade falls through exactly as if the tier could not
/// close the request, because for this caller it can't.
pub struct GatedStage<S: Stage> {
    stage: S,
    gate: Arc<JcpGate>,
}

impl<S: Stage> Stage for GatedStage<S> {
    fn tier(&self) -> Tier {
        self.stage.tier()
    }

    fn try_resolve(&self, req: &Request) -> Option<Resolution> {
        if !self.gate.authorize(self.stage.tier(), req) {
            return None;
        }
        self.stage.try_resolve(req)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use jcp_grant::issue;
    use jcp_schema::{Capability, Grant};
    use joule_code_cascade::Cascade;

    fn sk(s: u8) -> SigningKey {
        SigningKey::from_bytes(&[s; 32])
    }
    fn did(k: &SigningKey) -> Did {
        Did::from_verifying_key(&k.verifying_key())
    }

    /// A stage that always closes at its tier.
    struct Always(Tier);
    impl Stage for Always {
        fn tier(&self) -> Tier {
            self.0
        }
        fn try_resolve(&self, _req: &Request) -> Option<Resolution> {
            Some(Resolution {
                op: None,
                answer: Some(format!("closed at {:?}", self.0)),
                receipt: joule_code_receipt::Receipt {
                    op_id: joule_code_schema::ContentId::of_bytes(b"op"),
                    tier: self.0,
                    energy: joule_code_receipt::Energy {
                        measured_uj: None,
                        estimated_uj: tier_cost_estimate(self.0),
                        provenance: joule_code_receipt::Provenance::Estimator,
                    },
                    sequence: 0,
                    nonce: [0; 8],
                },
            })
        }
    }
    /// A stage that never closes (e.g. a cache miss).
    struct Never(Tier);
    impl Stage for Never {
        fn tier(&self) -> Tier {
            self.0
        }
        fn try_resolve(&self, _req: &Request) -> Option<Resolution> {
            None
        }
    }

    fn grant_for(actions: &[&str], budget: u64) -> (Vec<SignedGrant>, Did) {
        let issuer = sk(1);
        let agent = sk(2);
        let tree = ContentId::of_bytes(b"repo:joule-code");
        let g = Grant {
            issuer: did(&issuer),
            subject: did(&agent),
            capability: Capability::new(tree, actions.iter().copied()),
            budget_uj: budget,
            budget_funds: None,
            caveats: Vec::new(),
            expiry: 0,
            parent: None,
            delegate_depth: None,
            nonce: [0; 16],
        };
        (vec![issue(&issuer, g).unwrap()], did(&agent))
    }

    fn req() -> Request {
        Request { prior: "tree-hash".into(), intent: "rename the function".into() }
    }

    #[test]
    fn ungranted_l4_never_fires_even_when_it_would_close() {
        // The grant names l0–l3 but NOT l4: no remote frontier agent, ever.
        let (chain, caller) = grant_for(&["l0", "l1", "l2", "l3"], u64::MAX);
        let gate = JcpGate::new(chain, caller, sk(7), "did:example:joule-code");
        let cascade = Cascade::new([
            Box::new(gate.wrap(Never(Tier::L1))) as Box<dyn Stage>,
            Box::new(gate.wrap(Always(Tier::L4))),
        ]);
        assert!(cascade.resolve(&req()).is_none()); // L4 denied → nothing closes
        // both consultations sealed: one allow (L1, didn't close), one deny (L4)
        assert_eq!(gate.receipts().len(), 2);
    }

    #[test]
    fn granted_l4_closes_and_debits_its_class() {
        let (chain, caller) = grant_for(&["l1", "l4"], 20_000_000);
        let gate = JcpGate::new(chain, caller, sk(7), "did:example:joule-code");
        let cascade = Cascade::new([
            Box::new(gate.wrap(Never(Tier::L1))) as Box<dyn Stage>,
            Box::new(gate.wrap(Always(Tier::L4))),
        ]);
        let res = cascade.resolve(&req()).expect("granted L4 closes");
        assert_eq!(res.receipt.tier, Tier::L4);
        // L1 attempt (10) + L4 attempt (10_000_000) debited
        assert_eq!(gate.spent(), 10_000_010);
    }

    #[test]
    fn an_exhausted_budget_stops_the_escape_hatch() {
        // budget affords exactly one L4 consultation (plus the L1 probes)
        let (chain, caller) = grant_for(&["l1", "l4"], 10_000_020);
        let gate = JcpGate::new(chain, caller, sk(7), "did:example:joule-code");
        let cascade = Cascade::new([
            Box::new(gate.wrap(Never(Tier::L1))) as Box<dyn Stage>,
            Box::new(gate.wrap(Always(Tier::L4))),
        ]);
        assert!(cascade.resolve(&req()).is_some()); // first run closes at L4
        assert!(cascade.resolve(&req()).is_none()); // second: L4 no longer affordable
        // the deny is sealed evidence, not a silent skip
        let steward_vk = sk(7).verifying_key().to_bytes();
        let receipts = gate.receipts();
        let last = jcp_receipt::extract(receipts.last().unwrap(), "did:example:joule-code", &steward_vk).unwrap();
        assert_eq!(last.verdict, "deny");
        assert_eq!(last.deny_reason.as_deref(), Some("budget-exceeded"));
    }

    #[test]
    fn a_local_self_issued_gate_still_walls_off_l4() {
        // the air-gapped case: the runtime grants itself l0–l3 only
        let gate = JcpGate::local("repo:local", &["l0", "l1", "l2", "l3"], 1_000_000);
        let cascade = Cascade::new([
            Box::new(gate.wrap(Always(Tier::L4))) as Box<dyn Stage>,
        ]);
        assert!(cascade.resolve(&req()).is_none()); // no l4 in the self-grant
        assert_eq!(gate.spent(), 0);
        let cascade = Cascade::new([
            Box::new(gate.wrap(Always(Tier::L1))) as Box<dyn Stage>,
        ]);
        assert!(cascade.resolve(&req()).is_some()); // granted tiers still close
    }

    #[test]
    fn cheaper_tiers_stay_cheap_and_receipts_attribute_per_tier() {
        let (chain, caller) = grant_for(&["l0", "l1"], 1_000);
        let gate = JcpGate::new(chain, caller, sk(7), "did:example:joule-code");
        let cascade = Cascade::new([
            Box::new(gate.wrap(Always(Tier::L1))) as Box<dyn Stage>,
        ]);
        for _ in 0..3 {
            assert!(cascade.resolve(&req()).is_some());
        }
        assert_eq!(gate.spent(), 30);
        let steward_vk = sk(7).verifying_key().to_bytes();
        let receipts = gate.receipts();
        let (totals, bad) =
            jcp_receipt::aggregate(receipts.iter().map(|r| r.as_slice()), "did:example:joule-code", &steward_vk);
        assert_eq!(bad, 0);
        assert_eq!(totals.values().map(|t| t.spent_uj).sum::<u64>(), 30);
    }

    #[test]
    fn local_gate_authorizes_granted_tiers_and_structurally_denies_the_rest() {
        // A self-issued local grant naming l0..l3 but NOT l4.
        let gate = JcpGate::local("repo:test", &["l0", "l1", "l2", "l3"], u64::MAX);
        let request = req();
        assert!(gate.authorize(Tier::L0, &request));
        assert!(gate.authorize(Tier::L3, &request));
        // l4 is not in the grant → the remote frontier agent is unreachable.
        assert!(!gate.authorize(Tier::L4, &request));
        // Every consultation — allow and deny — sealed a receipt.
        assert_eq!(gate.receipts().len(), 3);
    }

    #[test]
    fn local_gate_budget_caps_total_spend() {
        // Budget affords two L3 consultations (1_000_000 µJ each), not a third.
        let gate = JcpGate::local("repo:test", &["l3"], 2_000_000);
        let request = req();
        assert!(gate.authorize(Tier::L3, &request));
        assert!(gate.authorize(Tier::L3, &request));
        assert!(!gate.authorize(Tier::L3, &request)); // over budget → denied
        assert_eq!(gate.spent(), 2_000_000);
    }
}