lean-ctx 3.7.3

//! Verified Savings Ledger (G1) — the per-event, auditable counterfactual store.
//!
//! Local-only and on by default (set `LEAN_CTX_SAVINGS_LEDGER=off` to disable). It never
//! leaves the machine; opt-in org roll-up + cryptographic signing are later phases. See
//! `docs/business/03-verified-savings-ledger.md`.

pub mod event;
pub mod signed_batch;
pub mod store;

pub use event::SavingsEvent;
pub use signed_batch::{BatchVerifyResult, SignedSavingsBatchV1};
pub use store::{LedgerSummary, VerifyResult};

use std::sync::OnceLock;

fn enabled() -> bool {
    enabled_from(std::env::var("LEAN_CTX_SAVINGS_LEDGER").ok().as_deref())
}

/// Pure opt-out logic (testable without mutating process env). Enabled unless explicitly
/// set to a falsy value.
fn enabled_from(value: Option<&str>) -> bool {
    match value {
        Some(v) => !matches!(
            v.trim().to_lowercase().as_str(),
            "off" | "0" | "false" | "no"
        ),
        None => true,
    }
}

/// Resolved (model_key, input_price_per_m) for this process. The active model is stable
/// within a process, so we resolve the pricing table once.
fn model_and_price() -> &'static (String, f64) {
    static CACHE: OnceLock<(String, f64)> = OnceLock::new();
    CACHE.get_or_init(|| {
        let env_model = std::env::var("LEAN_CTX_MODEL")
            .or_else(|_| std::env::var("LCTX_MODEL"))
            .ok();
        let quote =
            crate::core::gain::model_pricing::ModelPricing::load().quote(env_model.as_deref());
        (quote.model_key, quote.cost.input_per_m)
    })
}

/// Privacy-preserving repo attribution: truncated SHA-256 of the process working
/// directory. Never the file path or contents. Process-scoped (cached once).
fn repo_hash() -> &'static str {
    static CACHE: OnceLock<String> = OnceLock::new();
    CACHE.get_or_init(|| {
        use sha2::{Digest, Sha256};
        let cwd = std::env::current_dir()
            .map(|p| p.to_string_lossy().into_owned())
            .unwrap_or_default();
        let mut hasher = Sha256::new();
        hasher.update(cwd.as_bytes());
        let hex = format!("{:x}", hasher.finalize());
        hex.get(..16).unwrap_or(&hex).to_string()
    })
}

fn agent_id() -> &'static str {
    static CACHE: OnceLock<String> = OnceLock::new();
    CACHE.get_or_init(|| {
        std::env::var("LEAN_CTX_AGENT_ID")
            .or_else(|_| std::env::var("LCTX_AGENT_ID"))
            .unwrap_or_else(|_| "local".to_string())
    })
}

/// The tokenizer family that produced the token counts we record (G2). Resolved once.
fn tokenizer() -> &'static str {
    static CACHE: OnceLock<String> = OnceLock::new();
    CACHE.get_or_init(crate::core::tokens::counting_family_label)
}

/// Shared event skeleton with the per-process attribution + pricing context filled in.
/// Chain hashes are computed by `store::append`.
fn new_event(tool: &str) -> SavingsEvent {
    let (model_id, price_per_m) = model_and_price();
    SavingsEvent {
        ts: chrono::Utc::now().to_rfc3339(),
        tool: tool.to_string(),
        model_id: model_id.clone(),
        tokenizer: tokenizer().to_string(),
        baseline_tokens: 0,
        actual_tokens: 0,
        saved_tokens: 0,
        bounce_adjustment: 0,
        unit_price_per_m_usd: *price_per_m,
        saved_usd: 0.0,
        repo_hash: repo_hash().to_string(),
        agent_id: agent_id().to_string(),
        prev_hash: String::new(),
        entry_hash: String::new(),
    }
}

/// Best-effort append of one auditable savings event for a value-producing read.
/// Skips zero-saving events (keeps the ledger meaningful and cheap) and never panics.
pub fn record_read_event(original_tokens: usize, saved_tokens: usize) {
    if saved_tokens == 0 || !enabled() {
        return;
    }
    let Some(path) = store::default_path() else {
        return;
    };
    let baseline = original_tokens as u64;
    let saved = saved_tokens as u64;

    let mut event = new_event("ctx_read");
    event.baseline_tokens = baseline;
    event.actual_tokens = baseline.saturating_sub(saved);
    event.saved_tokens = saved;
    event.saved_usd = saved as f64 / 1_000_000.0 * event.unit_price_per_m_usd;
    let _ = store::append(&path, event);
}

/// Best-effort append of a *bounce* event (G7): a compressed read later invalidated by a
/// full re-read, so the earlier saving was (partly) illusory. Recorded as a negative
/// adjustment with `tool = "bounce"` so totals net out without editing the original entry.
pub fn record_bounce_event(wasted_tokens: usize) {
    if wasted_tokens == 0 || !enabled() {
        return;
    }
    let Some(path) = store::default_path() else {
        return;
    };
    let wasted = wasted_tokens as u64;

    let mut event = new_event("bounce");
    event.baseline_tokens = wasted;
    event.actual_tokens = wasted;
    event.bounce_adjustment = wasted;
    event.saved_usd = -(wasted as f64 / 1_000_000.0 * event.unit_price_per_m_usd);
    let _ = store::append(&path, event);
}

/// Total bounce-adjusted tokens recorded, optionally limited to the last `days` (by event
/// timestamp). `None` = all time. Used to net the Wrapped headline per period.
pub fn bounce_tokens(days: Option<u32>) -> u64 {
    let Some(path) = store::default_path() else {
        return 0;
    };
    store::bounce_tokens_since(&path, days)
}

/// Aggregated totals + model/day/tool slices over the whole ledger.
pub fn summary() -> LedgerSummary {
    store::default_path()
        .map(|p| store::summarize(&p))
        .unwrap_or_default()
}

/// Re-walks the hash chain and reports whether it is intact.
pub fn verify() -> VerifyResult {
    store::default_path().map_or_else(VerifyResult::empty, |p| store::verify(&p))
}

/// Re-hashes the ledger under the current (v2) canonical scheme, repairing a chain broken by
/// the legacy float round-trip bug. Returns the number of re-chained events (0 if no ledger).
pub fn rechain() -> std::io::Result<usize> {
    match store::default_path() {
        Some(p) if p.exists() => store::rechain(&p),
        _ => Ok(0),
    }
}

/// Every recorded event (for `ledger export`).
pub fn all_events() -> Vec<SavingsEvent> {
    store::default_path()
        .map(|p| store::load(&p))
        .unwrap_or_default()
}

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

    #[test]
    fn opt_out_logic_is_correct() {
        assert!(enabled_from(None), "enabled by default when unset");
        assert!(enabled_from(Some("on")));
        assert!(enabled_from(Some("1")));
        assert!(!enabled_from(Some("off")));
        assert!(!enabled_from(Some("0")));
        assert!(!enabled_from(Some("false")));
        assert!(!enabled_from(Some(" No ")), "trim + case-insensitive");
    }

    #[test]
    fn repo_hash_is_truncated_hex() {
        let h = repo_hash();
        assert_eq!(h.len(), 16);
        assert!(h.chars().all(|c| c.is_ascii_hexdigit()));
    }
}