monetize_embed/

lib.rs

//! **monetize-embed — what a product compiles in.** One struct, one question:
//! *does this tenant get to do this, right now?* Answered from verified facts held in
//! memory, in nanoseconds, with monetize down or not.
//!
//! ```text
//!   monetize-server ──signed Snapshot file──▶ EntitlementCache::refresh   (start, catch-up)
//!   monetize-server ──signed EntitlementFact─▶ EntitlementCache::push      (every change)
//!   product choke point ──────────────────▶ EntitlementCache::allows     (every request)
//! ```
//!
//! # The ladder table, as the product sees it
//!
//! | state | Write (push, LFS upload) | Read (owner clone/fetch) | AnonymousRead | Admin (UI) |
//! |---|---|---|---|---|
//! | Free, Paid | allow | allow | allow (product still applies Public) | allow |
//! | Grace | allow, [`EntitlementCache::notice`] has the warning line | allow | allow | allow |
//! | Suspended | **refuse**, named reason + URL | allow | **refuse** | refuse: pay page only |
//! | Retention | refuse | allow (export) | refuse | refuse: pay page + export |
//!
//! Two rules, not negotiable: **never hold data hostage** — `Read` is allowed in every
//! state, a lapsed tenant can always clone their own repositories; and **refuse before
//! the bytes** — the product asks at `authorise_service`, before a pack is read, and
//! puts [`Verdict::Refuse::reason_line`] in report-status.
//!
//! # What is, and is not, decided here
//!
//! * The `state` in a fact is monetize's verdict at push time. The cache does **not**
//!   re-derive it as the clock moves — it does not know the policy's day counts, and the
//!   product contract says a product keeps serving on its cached entitlement when
//!   monetize is unreachable. Ladder transitions arrive as new pushes.
//! * An unknown tenant is `Free`: the product's default, never a refusal.
//! * Visibility (`Public`) and quotas (`caps`) are the product's own checks; this crate
//!   only says whether the entitlement allows the *kind* of action.
//!
//! # Cost of the read path
//!
//! [`EntitlementCache::allows`] is one `ArcSwap::load` (an atomic increment on a
//! debt-slot, ~2 ns, no lock, no allocation), one `BTreeMap` lookup on the tenant name,
//! and a match. A refusal allocates its two strings; an allow allocates nothing. Writes
//! (`push`, `refresh`) clone the map and swap the pointer — O(tenants), taken by the
//! rare path on purpose so the hot path never contends.

pub mod civil;
pub mod signing;

use std::collections::BTreeMap;
use std::sync::Arc;

use arc_swap::ArcSwap;
/// Re-exported so a caller that must CHECK a signature — a product, or the
/// operator console — links one crate and cannot end up on a different
/// ed25519-dalek than the one the canonical form was verified against.
pub use ed25519_dalek::VerifyingKey;
pub use monetize_product::{EntitlementFact, State, TenantId};
pub use signing::{Snapshot, SignatureError};

/// What the product is about to do on behalf of (or to) a tenant.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum Action {
    /// `git push`, LFS upload — anything that grows the tenant's data.
    Write,
    /// The owner's clone/fetch. Allowed in every state.
    Read,
    /// Anonymous browse/clone of a public repository.
    AnonymousRead,
    /// The tenant's own settings UI.
    Admin,
}

#[derive(Clone, PartialEq, Eq, Debug)]
pub enum Verdict {
    Allow,
    Refuse {
        state: State,
        /// Goes into report-status verbatim: `order … expired 2026-10-01; renew at …`.
        reason_line: String,
        /// The pay page for this tenant.
        url: String,
    },
}

impl Verdict {
    pub fn is_allowed(&self) -> bool {
        matches!(self, Verdict::Allow)
    }
}

#[derive(Debug, thiserror::Error)]
pub enum RefreshError {
    #[error("snapshot is not valid JSON: {0}")]
    Parse(#[from] serde_json::Error),
    #[error(transparent)]
    Signature(#[from] SignatureError),
    #[error("snapshot issued at {offered} is older than the {held} the cache holds")]
    Stale { offered: u64, held: u64 },
}

#[derive(Debug, thiserror::Error)]
#[error("public key is not a valid Ed25519 point")]
pub struct KeyError;

struct Facts {
    issued_unix_ms: u64,
    by_tenant: BTreeMap<TenantId, EntitlementFact>,
}

pub struct EntitlementCache {
    key: VerifyingKey,
    /// `{tenant}` is replaced by the tenant name.
    billing_url: String,
    facts: ArcSwap<Facts>,
}

impl EntitlementCache {
    /// `public_key` is monetize's 32-byte Ed25519 verifying key; `billing_url` is the
    /// pay page template, e.g. `https://gunnar.rs/billing/{tenant}`.
    pub fn new(public_key: &[u8; 32], billing_url: &str) -> Result<Self, KeyError> {
        let key = VerifyingKey::from_bytes(public_key).map_err(|_| KeyError)?;
        Ok(Self {
            key,
            billing_url: billing_url.to_string(),
            facts: ArcSwap::from_pointee(Facts { issued_unix_ms: 0, by_tenant: BTreeMap::new() }),
        })
    }

    pub fn public_key(&self) -> &VerifyingKey {
        &self.key
    }

    /// The hot path. See the crate doc for its cost.
    pub fn allows(&self, tenant: &TenantId, action: Action) -> Verdict {
        let facts = self.facts.load();
        let Some(fact) = facts.by_tenant.get(tenant) else {
            return Verdict::Allow; // unknown tenant = Free = the product's default
        };
        match (fact.state, action) {
            (State::Free | State::Paid | State::Grace, _) => Verdict::Allow,
            (State::Suspended | State::Retention, Action::Read) => Verdict::Allow,
            (state, action) => Verdict::Refuse {
                state,
                reason_line: self.reason_line(fact, action),
                url: self.url_for(tenant),
            },
        }
    }

    /// The Grace banner / report-status warning, if the tenant is in Grace.
    pub fn notice(&self, tenant: &TenantId) -> Option<String> {
        let facts = self.facts.load();
        let fact = facts.by_tenant.get(tenant)?;
        if fact.state != State::Grace {
            return None;
        }
        Some(format!("{}; renew at {}", self.expiry_phrase(fact), self.url_for(tenant)))
    }

    /// The state the cache holds for `tenant`; `Free` when unknown.
    pub fn state(&self, tenant: &TenantId) -> State {
        self.facts.load().by_tenant.get(tenant).map_or(State::Free, |f| f.state)
    }

    /// A copy of the whole fact (caps, paid_until, source) for the product's own checks.
    pub fn fact(&self, tenant: &TenantId) -> Option<EntitlementFact> {
        self.facts.load().by_tenant.get(tenant).cloned()
    }

    /// The issue time of the snapshot the cache holds (0 before the first refresh).
    pub fn issued_unix_ms(&self) -> u64 {
        self.facts.load().issued_unix_ms
    }

    pub fn len(&self) -> usize {
        self.facts.load().by_tenant.len()
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Replace everything with a signed [`Snapshot`] (its JSON bytes). Nothing changes
    /// unless the envelope and every fact verify and the snapshot is not older than
    /// the one held. Returns the number of tenants now known.
    pub fn refresh(&self, snapshot_bytes: &[u8]) -> Result<usize, RefreshError> {
        let snap: Snapshot = serde_json::from_slice(snapshot_bytes)?;
        signing::verify_snapshot(&snap, &self.key)?;
        let held = self.facts.load().issued_unix_ms;
        if snap.issued_unix_ms < held {
            return Err(RefreshError::Stale { offered: snap.issued_unix_ms, held });
        }
        let by_tenant: BTreeMap<TenantId, EntitlementFact> =
            snap.facts.into_iter().map(|f| (f.tenant.clone(), f)).collect();
        let n = by_tenant.len();
        self.facts.store(Arc::new(Facts { issued_unix_ms: snap.issued_unix_ms, by_tenant }));
        Ok(n)
    }

    /// One pushed fact. Verified before it replaces the tenant's current fact.
    pub fn push(&self, fact: EntitlementFact) -> Result<(), SignatureError> {
        signing::verify_fact(&fact, &self.key)?;
        let current = self.facts.load_full();
        let mut by_tenant = current.by_tenant.clone();
        by_tenant.insert(fact.tenant.clone(), fact);
        self.facts.store(Arc::new(Facts { issued_unix_ms: current.issued_unix_ms, by_tenant }));
        Ok(())
    }

    fn url_for(&self, tenant: &TenantId) -> String {
        self.billing_url.replace("{tenant}", &tenant.0)
    }

    /// `fact.plan` is the ORDER the verdict came from (a ledger reference), or
    /// an operator's label, or nothing — the field keeps its wire name because
    /// it is in the signed form; the sentence a user reads names the order.
    fn expiry_phrase(&self, fact: &EntitlementFact) -> String {
        let what = if fact.plan.is_empty() { "entitlement".to_owned() } else { format!("order {}", fact.plan) };
        match fact.paid_until_unix_ms {
            Some(until) => format!("{what} expired {}", civil::iso_date(until)),
            None => format!("{what} suspended by operator"),
        }
    }

    fn reason_line(&self, fact: &EntitlementFact, action: Action) -> String {
        let url = self.url_for(&fact.tenant);
        let expiry = self.expiry_phrase(fact);
        let what = match (fact.state, action) {
            (State::Retention, Action::Write) => "writes closed, data kept for export",
            (_, Action::Write) => "writes closed",
            (_, Action::AnonymousRead) => "anonymous access closed",
            (_, Action::Admin) => "settings closed",
            (_, Action::Read) => unreachable!("Read is allowed in every state"),
        };
        format!("{expiry}: {what}; renew at {url}")
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use ed25519_dalek::{Signer, SigningKey};

    fn key() -> SigningKey {
        SigningKey::generate(&mut rand::rngs::OsRng)
    }

    fn fact(tenant: &str, state: State, paid_until: Option<u64>) -> EntitlementFact {
        EntitlementFact {
            tenant: TenantId(tenant.into()),
            plan: "10gb".into(),
            state,
            paid_until_unix_ms: paid_until,
            caps: BTreeMap::from([("pack_bytes".to_string(), 10 << 30)]),
            source: "payment:mock:gunnar/team/sub/2026-09-03".into(),
            signature: vec![],
        }
    }

    fn signed(key: &SigningKey, mut f: EntitlementFact) -> EntitlementFact {
        f.signature = key.sign(&signing::fact_message(&f)).to_bytes().to_vec();
        f
    }

    fn snapshot(key: &SigningKey, issued: u64, facts: Vec<EntitlementFact>) -> Vec<u8> {
        let signature = key.sign(&signing::snapshot_message(issued, &facts)).to_bytes().to_vec();
        serde_json::to_vec(&Snapshot { issued_unix_ms: issued, facts, signature }).unwrap()
    }

    fn cache(key: &SigningKey) -> EntitlementCache {
        EntitlementCache::new(&key.verifying_key().to_bytes(), "https://gunnar.rs/billing/{tenant}").unwrap()
    }

    const OCT_1_2026: u64 = 1_790_812_800_000;

    #[test]
    fn genuine_snapshot_is_accepted_and_answers() {
        let k = key();
        let c = cache(&k);
        let bytes = snapshot(&k, 10, vec![signed(&k, fact("team/sub", State::Suspended, Some(OCT_1_2026)))]);
        assert_eq!(c.refresh(&bytes).unwrap(), 1);
        assert_eq!(c.state(&TenantId("team/sub".into())), State::Suspended);
        assert_eq!(c.issued_unix_ms(), 10);
    }

    #[test]
    fn forged_snapshot_is_rejected_and_changes_nothing() {
        let k = key();
        let forger = key();
        let c = cache(&k);
        let t = TenantId("team/sub".into());
        // Envelope signed by the right key, one fact forged: the whole snapshot is refused.
        let mut forged = signed(&forger, fact("team/sub", State::Paid, Some(OCT_1_2026)));
        let bytes = snapshot(&k, 10, vec![forged.clone()]);
        assert!(matches!(c.refresh(&bytes), Err(RefreshError::Signature(SignatureError::Fact(_)))));
        // Envelope signed by the wrong key.
        forged = signed(&k, forged);
        let bytes = snapshot(&forger, 10, vec![forged.clone()]);
        assert!(matches!(c.refresh(&bytes), Err(RefreshError::Signature(SignatureError::Envelope))));
        // A genuine fact whose fields were edited after signing.
        forged.state = State::Free;
        assert!(matches!(c.push(forged), Err(SignatureError::Fact(_))));
        // Garbage.
        assert!(matches!(c.refresh(b"not json"), Err(RefreshError::Parse(_))));
        assert!(c.is_empty());
        assert_eq!(c.state(&t), State::Free);
    }

    #[test]
    fn stale_snapshot_is_refused_newer_one_is_taken() {
        let k = key();
        let c = cache(&k);
        c.refresh(&snapshot(&k, 20, vec![])).unwrap();
        assert!(matches!(c.refresh(&snapshot(&k, 19, vec![])), Err(RefreshError::Stale { offered: 19, held: 20 })));
        c.refresh(&snapshot(&k, 21, vec![])).unwrap();
        assert_eq!(c.issued_unix_ms(), 21);
    }

    #[test]
    fn push_replaces_one_tenant_and_keeps_the_rest() {
        let k = key();
        let c = cache(&k);
        let a = TenantId("a".into());
        let b = TenantId("b".into());
        c.refresh(&snapshot(&k, 1, vec![signed(&k, fact("a", State::Paid, None)), signed(&k, fact("b", State::Paid, None))])).unwrap();
        c.push(signed(&k, fact("a", State::Suspended, Some(OCT_1_2026)))).unwrap();
        assert_eq!(c.state(&a), State::Suspended);
        assert_eq!(c.state(&b), State::Paid);
        assert_eq!(c.len(), 2);
    }

    /// The ladder table, row by row, column by column.
    #[test]
    fn verdict_table() {
        use Action::*;
        let k = key();
        let c = cache(&k);
        let t = TenantId("team/sub".into());
        let rows: [(State, [bool; 4]); 5] = [
            (State::Free, [true, true, true, true]),
            (State::Paid, [true, true, true, true]),
            (State::Grace, [true, true, true, true]),
            (State::Suspended, [false, true, false, false]),
            (State::Retention, [false, true, false, false]),
        ];
        for (state, expect) in rows {
            c.push(signed(&k, fact("team/sub", state, Some(OCT_1_2026)))).unwrap();
            for (action, allowed) in [Write, Read, AnonymousRead, Admin].into_iter().zip(expect) {
                let v = c.allows(&t, action);
                assert_eq!(v.is_allowed(), allowed, "{state:?} / {action:?} gave {v:?}");
                if let Verdict::Refuse { state: s, reason_line, url } = &v {
                    assert_eq!(*s, state);
                    assert_eq!(url, "https://gunnar.rs/billing/team/sub");
                    assert!(reason_line.contains("order 10gb expired 2026-10-01"), "{reason_line}");
                    assert!(reason_line.ends_with("; renew at https://gunnar.rs/billing/team/sub"), "{reason_line}");
                }
            }
            assert_eq!(c.notice(&t).is_some(), state == State::Grace, "{state:?} notice");
        }
    }

    #[test]
    fn refuse_twin_suspended_write_names_the_reason_and_unknown_tenant_is_free() {
        let k = key();
        let c = cache(&k);
        let t = TenantId("team/sub".into());
        c.push(signed(&k, fact("team/sub", State::Suspended, Some(OCT_1_2026)))).unwrap();
        assert_eq!(
            c.allows(&t, Action::Write),
            Verdict::Refuse {
                state: State::Suspended,
                reason_line: "order 10gb expired 2026-10-01: writes closed; renew at https://gunnar.rs/billing/team/sub".into(),
                url: "https://gunnar.rs/billing/team/sub".into(),
            }
        );
        let op = signed(&k, fact("ops", State::Suspended, None));
        c.push(op).unwrap();
        assert!(matches!(c.allows(&TenantId("ops".into()), Action::Write), Verdict::Refuse { reason_line, .. } if reason_line.starts_with("order 10gb suspended by operator")));
        assert_eq!(c.allows(&TenantId("nobody".into()), Action::Write), Verdict::Allow);
        assert_eq!(c.state(&TenantId("nobody".into())), State::Free);
    }
}