tenuo 0.3.3

//! Authorization receipts: signer, sink, and evidence policy.

use crate::crypto::{PublicKey, Signature, SigningKey};
use crate::receipt::{Receipt, RECEIPT_VERSION};
use crate::SIGNATURE_CONTEXT;
use std::fmt;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Mutex;

const DEFAULT_RECEIPT_CAPACITY: usize = 10_000;

/// How receipt persistence interacts with the authorization outcome.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
#[non_exhaustive]
pub enum EvidencePolicy {
    #[default]
    /// Produce no receipts.
    Disabled,
    /// Produce receipts; a persistence failure is observable but does not change the outcome.
    BestEffort,
    /// Require durable evidence before the operation runs. Persistence failure denies.
    RequiredBeforeExecution,
}

/// Raw signature over a receipt's complete final signing bytes.
pub trait ReceiptSigner: Send + Sync {
    /// Public key receipts are signed under.
    fn public_key(&self) -> PublicKey;
    /// Sign a receipt over the request's exact bytes.
    fn sign_receipt(
        &self,
        request: &ReceiptSigningRequest<'_>,
    ) -> Result<Signature, ReceiptSignerError>;
}

/// Local non-blocking persistence. Remote durable sinks belong on the async surface.
pub trait ReceiptSink: Send + Sync {
    /// Store a receipt and return a reference to it.
    fn persist(&self, receipt: &Receipt) -> Result<ReceiptRef, ReceiptSinkError>;
}

/// `SIGNATURE_CONTEXT || RECEIPT_CONTEXT || version || payload`.
pub struct ReceiptSigningRequest<'a> {
    preimage: &'a [u8],
}

impl<'a> ReceiptSigningRequest<'a> {
    pub(crate) fn new(preimage: &'a [u8]) -> Self {
        Self { preimage }
    }

    /// Constant `"receipt"`. Lets one signer route by purpose.
    pub fn purpose(&self) -> &'static str {
        "receipt"
    }

    /// The exact message to sign, verbatim, with raw Ed25519.
    pub fn final_signing_bytes(&self) -> Vec<u8> {
        let mut out = Vec::with_capacity(SIGNATURE_CONTEXT.len() + self.preimage.len());
        out.extend_from_slice(SIGNATURE_CONTEXT);
        out.extend_from_slice(self.preimage);
        out
    }
}

/// In-process receipt key. `for_development` is not a production default.
pub struct LocalReceiptSigner {
    key: SigningKey,
}

impl LocalReceiptSigner {
    /// Sign receipts with an in-process key.
    pub fn new(key: SigningKey) -> Self {
        Self { key }
    }

    /// Per-process generated signer. Unattributed; not the production default.
    pub fn for_development() -> Self {
        Self {
            key: SigningKey::generate(),
        }
    }
}

impl ReceiptSigner for LocalReceiptSigner {
    fn public_key(&self) -> PublicKey {
        self.key.public_key()
    }

    fn sign_receipt(
        &self,
        request: &ReceiptSigningRequest<'_>,
    ) -> Result<Signature, ReceiptSignerError> {
        Ok(self.key.sign_raw(&request.final_signing_bytes()))
    }
}

/// In-memory sink for tests and local RequiredBeforeExecution.
pub struct MemoryReceiptSink {
    stored: Mutex<SinkBuf>,
    max: usize,
    deny_max: usize,
    overflowed: AtomicUsize,
}

struct SinkBuf {
    items: Vec<StoredReceipt>,
    allows: usize,
    denies: usize,
}

struct StoredReceipt {
    receipt: Receipt,
    deny: bool,
}

impl Default for MemoryReceiptSink {
    fn default() -> Self {
        Self::with_capacity(DEFAULT_RECEIPT_CAPACITY)
    }
}

impl MemoryReceiptSink {
    /// An empty in-memory sink. For tests.
    pub fn new() -> Self {
        Self::default()
    }

    /// Bound outbox. `max` is the cap for allow receipts and, separately,
    /// for deny receipts, so the buffer can hold up to `2 * max` items.
    /// A full side drops the new receipt, counts it, and returns
    /// [`ReceiptSinkError::Unavailable`]. Best-effort evidence swallows
    /// that error; RequiredBeforeExecution denies. A payload whose outcome
    /// cannot be read is rejected without consuming either budget.
    pub fn with_capacity(max: usize) -> Self {
        Self {
            stored: Mutex::new(SinkBuf {
                items: Vec::new(),
                allows: 0,
                denies: 0,
            }),
            max: max.max(1),
            deny_max: max.max(1),
            overflowed: AtomicUsize::new(0),
        }
    }

    /// Receipts dropped because the outbox was full.
    pub fn overflowed(&self) -> usize {
        self.overflowed.load(Ordering::Relaxed)
    }

    /// Everything stored so far.
    pub fn stored(&self) -> Vec<Receipt> {
        self.stored
            .lock()
            .map(|g| g.items.iter().map(|item| item.receipt.clone()).collect())
            .unwrap_or_default()
    }

    /// Unacknowledged receipts. Same as [`Self::stored`] after prefix drops.
    pub fn pending(&self) -> Vec<Receipt> {
        self.stored()
    }

    /// Receipts at and after `cursor` without removing them.
    pub fn peek_from(&self, cursor: usize) -> Vec<Receipt> {
        let stored = self.stored();
        if cursor >= stored.len() {
            return Vec::new();
        }
        stored[cursor..].to_vec()
    }

    /// Remove the first `count` stored receipts.
    pub fn drop_prefix(&self, count: usize) -> usize {
        let Ok(mut stored) = self.stored.lock() else {
            return 0;
        };
        let n = count.min(stored.items.len());
        let removed: Vec<bool> = stored.items.drain(..n).map(|item| item.deny).collect();
        for deny in removed {
            if deny {
                stored.denies = stored.denies.saturating_sub(1);
            } else {
                stored.allows = stored.allows.saturating_sub(1);
            }
        }
        n
    }
}

fn receipt_is_deny(receipt: &Receipt) -> Option<bool> {
    ciborium::from_reader::<crate::receipt::ReceiptPayload, _>(receipt.payload.as_slice())
        .ok()
        .map(|payload| payload.outcome == crate::receipt::Outcome::Deny)
}

impl ReceiptSink for MemoryReceiptSink {
    fn persist(&self, receipt: &Receipt) -> Result<ReceiptRef, ReceiptSinkError> {
        let deny = receipt_is_deny(receipt).ok_or(ReceiptSinkError::Unavailable)?;
        let mut stored = self
            .stored
            .lock()
            .map_err(|_| ReceiptSinkError::Unavailable)?;
        let (used, cap) = if deny {
            (stored.denies, self.deny_max)
        } else {
            (stored.allows, self.max)
        };
        if used >= cap {
            self.overflowed.fetch_add(1, Ordering::Relaxed);
            return Err(ReceiptSinkError::Unavailable);
        }
        stored.items.push(StoredReceipt {
            receipt: receipt.clone(),
            deny,
        });
        if deny {
            stored.denies += 1;
        } else {
            stored.allows += 1;
        }
        Ok(ReceiptRef {
            id: format!("mem:{}", stored.items.len()),
        })
    }
}

/// Handle returned by a sink. Not a capability.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ReceiptRef {
    /// Identifier the sink assigned to the stored receipt.
    pub id: String,
}

#[derive(Debug, Clone, PartialEq, Eq)]
/// Why a receipt could not be signed.
#[non_exhaustive]
pub enum ReceiptSignerError {
    /// The receipt signer could not be reached.
    Unavailable,
}

impl fmt::Display for ReceiptSignerError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Unavailable => write!(f, "receipt signer unavailable"),
        }
    }
}

impl std::error::Error for ReceiptSignerError {}

#[derive(Debug, Clone, PartialEq, Eq)]
/// Why a receipt could not be stored.
#[non_exhaustive]
pub enum ReceiptSinkError {
    /// The sink could not be reached.
    Unavailable,
}

impl fmt::Display for ReceiptSinkError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Unavailable => write!(f, "receipt sink unavailable"),
        }
    }
}

impl std::error::Error for ReceiptSinkError {}

pub(crate) fn sign_payload(
    payload_bytes: &[u8],
    signer: &dyn ReceiptSigner,
) -> Result<Receipt, ReceiptSignerError> {
    let preimage = Receipt::signing_preimage(RECEIPT_VERSION, payload_bytes);
    let request = ReceiptSigningRequest::new(&preimage);
    let signature = signer.sign_receipt(&request)?;
    Ok(Receipt {
        receipt_version: RECEIPT_VERSION,
        payload: payload_bytes.to_vec(),
        signer_key: signer.public_key(),
        signature,
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::crypto::SigningKey;
    use crate::receipt::{Receipt, ReceiptPayload};

    #[test]
    fn local_signer_verifies_against_core() {
        let signer = LocalReceiptSigner::for_development();
        let payload = ReceiptPayload::allow(
            vec![0xA1, 0x01, 0x02],
            "tool:read",
            1_700_000_000,
            "inv-1",
            [3u8; 64],
        );
        let bytes = payload.to_cbor().unwrap();
        let receipt = sign_payload(&bytes, &signer).unwrap();
        let verified = receipt.verify_signature().unwrap();
        assert_eq!(verified.action, "tool:read");
        assert_eq!(verified.request_id, "inv-1");
    }

    #[test]
    fn memory_sink_round_trips() {
        let sink = MemoryReceiptSink::new();
        let signer = LocalReceiptSigner::for_development();
        let payload = ReceiptPayload::allow(vec![0xA0], "tool:read", 1, "inv-2", [1u8; 64]);
        let receipt = sign_payload(&payload.to_cbor().unwrap(), &signer).unwrap();
        let reference = sink.persist(&receipt).unwrap();
        assert!(reference.id.starts_with("mem:"));
        assert_eq!(sink.stored().len(), 1);
        assert_eq!(sink.peek_from(0).len(), 1);
        assert_eq!(sink.peek_from(0).len(), 1);
        assert_eq!(sink.drop_prefix(1), 1);
        assert!(sink.pending().is_empty());
    }

    #[test]
    fn memory_sink_overflow_is_counted_and_unavailable() {
        let sink = MemoryReceiptSink::with_capacity(1);
        let signer = LocalReceiptSigner::for_development();
        let payload = ReceiptPayload::allow(vec![0xA0], "tool:read", 1, "inv-2", [1u8; 64]);
        let receipt = sign_payload(&payload.to_cbor().unwrap(), &signer).unwrap();
        assert!(sink.persist(&receipt).is_ok());
        assert_eq!(sink.persist(&receipt), Err(ReceiptSinkError::Unavailable));
        assert_eq!(sink.stored().len(), 1);
        assert_eq!(sink.overflowed(), 1);
    }

    #[test]
    fn deny_receipts_do_not_consume_allow_budget() {
        let sink = MemoryReceiptSink::with_capacity(1);
        let signer = LocalReceiptSigner::for_development();
        let deny = sign_payload(
            &ReceiptPayload::deny_before_pop(vec![0xA0], "tool:read", 1, "deny-1", "denied")
                .to_cbor()
                .unwrap(),
            &signer,
        )
        .unwrap();
        let allow = sign_payload(
            &ReceiptPayload::allow(vec![0xA0], "tool:read", 1, "inv-2", [1u8; 64])
                .to_cbor()
                .unwrap(),
            &signer,
        )
        .unwrap();
        assert!(sink.persist(&deny).is_ok());
        assert_eq!(sink.persist(&deny), Err(ReceiptSinkError::Unavailable));
        assert!(sink.persist(&allow).is_ok());
        assert_eq!(sink.stored().len(), 2);
        assert_eq!(sink.overflowed(), 1);
    }

    #[test]
    fn undecodable_payload_does_not_consume_allow_budget() {
        let sink = MemoryReceiptSink::with_capacity(1);
        let signer = LocalReceiptSigner::for_development();
        let mut garbage = sign_payload(
            &ReceiptPayload::allow(vec![0xA0], "tool:read", 1, "inv-2", [1u8; 64])
                .to_cbor()
                .unwrap(),
            &signer,
        )
        .unwrap();
        garbage.payload = vec![0xff, 0x00];
        assert_eq!(sink.persist(&garbage), Err(ReceiptSinkError::Unavailable));
        let allow = sign_payload(
            &ReceiptPayload::allow(vec![0xA0], "tool:read", 1, "inv-2", [1u8; 64])
                .to_cbor()
                .unwrap(),
            &signer,
        )
        .unwrap();
        assert!(sink.persist(&allow).is_ok());
        assert_eq!(sink.stored().len(), 1);
    }

    #[test]
    fn required_persist_failure_denies_without_running() {
        use crate::constraints::ConstraintSet;
        use crate::planes::Authorizer;
        use crate::sdk::signer::LocalSigner;
        use crate::sdk::{Call, Guard, PresentedAuthority, RevocationMode};
        use crate::warrant::Warrant;
        use std::collections::HashMap;
        use std::sync::atomic::{AtomicUsize, Ordering};
        use std::sync::Arc;
        use std::time::Duration;

        struct FailSink;
        impl ReceiptSink for FailSink {
            fn persist(&self, _: &Receipt) -> Result<ReceiptRef, ReceiptSinkError> {
                Err(ReceiptSinkError::Unavailable)
            }
        }

        let issuer = SigningKey::generate();
        let holder = SigningKey::generate();
        let warrant = Warrant::builder()
            .capability("read", ConstraintSet::new())
            .holder(holder.public_key())
            .ttl(Duration::from_secs(300))
            .build(&issuer)
            .unwrap();
        let mut authorizer = Authorizer::new();
        authorizer.add_trusted_root(issuer.public_key());
        let guard = Guard::builder()
            .authorizer(authorizer)
            .revocation(RevocationMode::TtlOnly {
                max_lifetime: Duration::from_secs(3600),
            })
            .evidence_policy(EvidencePolicy::RequiredBeforeExecution)
            .receipt_signer(Arc::new(LocalReceiptSigner::for_development()))
            .receipt_sink(Arc::new(FailSink))
            .build()
            .unwrap();
        let authority =
            PresentedAuthority::new(vec![warrant], Arc::new(LocalSigner::new(holder))).unwrap();
        let args = HashMap::new();
        let call = Call::borrowed("read", &args);
        let runs = AtomicUsize::new(0);
        let err = guard
            .guard(&authority, &call, |_| {
                runs.fetch_add(1, Ordering::SeqCst);
                Ok::<_, &str>(())
            })
            .err()
            .unwrap();
        assert_eq!(runs.load(Ordering::SeqCst), 0);
        match err {
            crate::sdk::GuardError::Denied(denial) => {
                assert_eq!(
                    denial.sdk_kind(),
                    Some(crate::sdk::SdkDenialKind::EvidenceUnavailable)
                );
            }
            crate::sdk::GuardError::Operation(_) => panic!("operation must not run"),
        }
    }

    #[test]
    fn best_effort_persist_failure_still_allows() {
        use crate::constraints::ConstraintSet;
        use crate::planes::Authorizer;
        use crate::sdk::signer::LocalSigner;
        use crate::sdk::{Call, Guard, PresentedAuthority, RevocationMode};
        use crate::warrant::Warrant;
        use std::collections::HashMap;
        use std::sync::Arc;
        use std::time::Duration;

        struct FailSink;
        impl ReceiptSink for FailSink {
            fn persist(&self, _: &Receipt) -> Result<ReceiptRef, ReceiptSinkError> {
                Err(ReceiptSinkError::Unavailable)
            }
        }

        let issuer = SigningKey::generate();
        let holder = SigningKey::generate();
        let warrant = Warrant::builder()
            .capability("read", ConstraintSet::new())
            .holder(holder.public_key())
            .ttl(Duration::from_secs(300))
            .build(&issuer)
            .unwrap();
        let mut authorizer = Authorizer::new();
        authorizer.add_trusted_root(issuer.public_key());
        let guard = Guard::builder()
            .authorizer(authorizer)
            .revocation(RevocationMode::TtlOnly {
                max_lifetime: Duration::from_secs(3600),
            })
            .evidence_policy(EvidencePolicy::BestEffort)
            .receipt_signer(Arc::new(LocalReceiptSigner::for_development()))
            .receipt_sink(Arc::new(FailSink))
            .build()
            .unwrap();
        let authority =
            PresentedAuthority::new(vec![warrant], Arc::new(LocalSigner::new(holder))).unwrap();
        let args = HashMap::new();
        let call = Call::borrowed("read", &args);
        let decision = guard.check(&authority, &call).expect("allow");
        assert!(decision.receipt.is_some());
        decision.receipt.unwrap().verify_signature().unwrap();
    }

    #[test]
    fn observer_does_not_emit_receipts() {
        use crate::constraints::ConstraintSet;
        use crate::planes::Authorizer;
        use crate::sdk::signer::LocalSigner;
        use crate::sdk::{Call, Guard, PresentedAuthority, PresentedRequest, RevocationMode};
        use crate::warrant::Warrant;
        use chrono::Utc;
        use std::collections::HashMap;
        use std::sync::Arc;
        use std::time::Duration;

        let issuer = SigningKey::generate();
        let holder = SigningKey::generate();
        let warrant = Warrant::builder()
            .capability("read", ConstraintSet::new())
            .holder(holder.public_key())
            .ttl(Duration::from_secs(300))
            .build(&issuer)
            .unwrap();
        let mut authorizer = Authorizer::new();
        authorizer.add_trusted_root(issuer.public_key());
        let sink = Arc::new(MemoryReceiptSink::new());
        let guard = Guard::builder()
            .authorizer(authorizer)
            .revocation(RevocationMode::TtlOnly {
                max_lifetime: Duration::from_secs(3600),
            })
            .evidence_policy(EvidencePolicy::BestEffort)
            .receipt_signer(Arc::new(LocalReceiptSigner::for_development()))
            .receipt_sink(sink.clone())
            .build()
            .unwrap();
        let authority =
            PresentedAuthority::new(vec![warrant], Arc::new(LocalSigner::new(holder))).unwrap();
        let args = HashMap::new();
        let call = Call::borrowed("read", &args);
        assert!(guard.check(&authority, &call).unwrap().receipt.is_some());
        assert_eq!(sink.stored().len(), 1);
        guard
            .observe_until(Utc::now() + chrono::Duration::hours(1))
            .observe(PresentedRequest::Holder(&authority), &call, || {
                Ok::<_, &str>(())
            })
            .unwrap();
        assert_eq!(sink.stored().len(), 1);
    }
}