fsci-conformance 0.3.0

#![forbid(unsafe_code)]
//! Live SciPy differential coverage for Spence's dilogarithm
//! `scipy.special.spence` — defined as Li₂(1 − z) for z ≥ 0.
//!
//! Resolves [frankenscipy-s2qtg]. fsci-special's spence had no
//! dedicated diff harness.
//!
//! 13 z-values via subprocess. Tolerances: 1e-12 abs.
//! Boundary identities: spence(0) = π²/6 ≈ 1.6449, spence(1) = 0,
//! spence(2) = -π²/12 ≈ -0.8225 (Euler reflection).

use std::collections::{BTreeMap, HashMap};
use std::fs;
use std::io::Write;
use std::path::PathBuf;
use std::process::Stdio;
use std::time::{Instant, SystemTime, UNIX_EPOCH};

use fsci_conformance::{ArmCounts, CompareLedger};
use fsci_runtime::RuntimeMode;
use fsci_special::spence;
use fsci_special::types::SpecialTensor;
use serde::{Deserialize, Serialize};

const PACKET_ID: &str = "FSCI-P2C-007";
// spence is Cephes' with Cephes' own coefficient doubles, bit-identical to SciPy. This is a TRUE
// relative tolerance, a few ulp. It used to be an absolute 5e-8, which could not see SPENCE_B
// transcribed 1 ulp off (frankenscipy-qbwth).
const REL_TOL: f64 = 1.0e-15;
const REQUIRE_SCIPY_ENV: &str = "FSCI_REQUIRE_SCIPY_ORACLE";

#[derive(Debug, Clone, Serialize)]
struct PointCase {
    case_id: String,
    z: f64,
}

#[derive(Debug, Clone, Serialize)]
struct OracleQuery {
    points: Vec<PointCase>,
}

#[derive(Debug, Clone, Deserialize)]
struct PointArm {
    case_id: String,
    value: Option<f64>,
}

#[derive(Debug, Clone, Deserialize)]
struct OracleResult {
    points: Vec<PointArm>,
}

#[derive(Debug, Clone, Serialize)]
struct CaseDiff {
    case_id: String,
    abs_diff: f64,
    pass: bool,
}

#[derive(Debug, Clone, Serialize)]
struct DiffLog {
    test_id: String,
    category: String,
    case_count: usize,
    compared: BTreeMap<String, ArmCounts>,
    max_abs_diff: f64,
    pass: bool,
    timestamp_ms: u128,
    duration_ns: u128,
    cases: Vec<CaseDiff>,
}

fn output_dir() -> PathBuf {
    PathBuf::from(env!("CARGO_MANIFEST_DIR")).join(format!("fixtures/artifacts/{PACKET_ID}/diff"))
}

fn ensure_output_dir() {
    fs::create_dir_all(output_dir()).expect("create spence diff output dir");
}

fn timestamp_ms() -> u128 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map_or(0, |d| d.as_millis())
}

fn emit_log(log: &DiffLog) {
    ensure_output_dir();
    let path = output_dir().join(format!("{}.json", log.test_id));
    let json = serde_json::to_string_pretty(log).expect("serialize spence diff log");
    fs::write(path, json).expect("write spence diff log");
}

fn fsci_eval(z: f64) -> Option<f64> {
    let arg = SpecialTensor::RealScalar(z);
    match spence(&arg, RuntimeMode::Strict) {
        Ok(SpecialTensor::RealScalar(v)) => Some(v),
        _ => None,
    }
}

fn generate_query() -> OracleQuery {
    // Cover the well-conditioned regime z ∈ [0.01, 50]. fsci's
    // spence has precision gaps at z→0+ (~1.5e-3 abs at z=1e-6)
    // and z→∞ (~5.8e-6 abs at z=1000) — tracked alongside the
    // broader special-function precision sweep in
    // frankenscipy-0om9c.
    let zs = [
        0.01_f64,
        0.05,
        0.1,
        0.5,
        1.0,
        1.5,
        2.0,
        3.0,
        5.0,
        10.0,
        25.0,
        50.0,
        // One point in each of Cephes' four argument ranges where the 16-digit SPENCE_B
        // missed SciPy by 1-6 ulp.
        0.651_541_973_701_075_2,
        0.265_877_344_675_972_1,
        1.950_863_934_790_465_5,
        2.868_172_090_875_553_7,
    ];
    let mut points = Vec::new();
    for &z in &zs {
        points.push(PointCase {
            case_id: format!("z{z}"),
            z,
        });
    }
    OracleQuery { points }
}

fn scipy_oracle_or_skip(query: &OracleQuery) -> Option<OracleResult> {
    let script = r#"
import json
import math
import sys
from scipy import special

def finite_or_none(v):
    try:
        v = float(v)
    except Exception:
        return None
    return v if math.isfinite(v) else None

q = json.load(sys.stdin)
points = []
for case in q["points"]:
    cid = case["case_id"]
    z = float(case["z"])
    try:
        value = special.spence(z)
        points.append({"case_id": cid, "value": finite_or_none(value)})
    except Exception:
        points.append({"case_id": cid, "value": None})
print(json.dumps({"points": points}))
"#;

    let query_json = serde_json::to_string(query).expect("serialize spence query");
    let mut child = match fsci_conformance::scipy_oracle_command()
        .arg("-c")
        .arg(script)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped())
        .spawn()
    {
        Ok(c) => c,
        Err(e) => {
            assert!(
                std::env::var(REQUIRE_SCIPY_ENV).is_err(),
                "failed to spawn python3 for spence oracle: {e}"
            );
            eprintln!("skipping spence oracle: python3 not available ({e})");
            return None;
        }
    };
    {
        let stdin = child.stdin.as_mut().expect("open spence oracle stdin");
        if let Err(err) = stdin.write_all(query_json.as_bytes()) {
            let output = child.wait_with_output().expect("wait for failed oracle");
            let stderr = String::from_utf8_lossy(&output.stderr);
            assert!(
                std::env::var(REQUIRE_SCIPY_ENV).is_err(),
                "spence oracle stdin write failed: {err}; stderr: {stderr}"
            );
            eprintln!("skipping spence oracle: stdin write failed ({err})\n{stderr}");
            return None;
        }
    }
    let output = child.wait_with_output().expect("wait for spence oracle");
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        assert!(
            std::env::var(REQUIRE_SCIPY_ENV).is_err(),
            "spence oracle failed: {stderr}"
        );
        eprintln!("skipping spence oracle: scipy not available\n{stderr}");
        return None;
    }
    let stdout = String::from_utf8_lossy(&output.stdout);
    Some(serde_json::from_str(&stdout).expect("parse spence oracle JSON"))
}

#[test]
fn diff_special_spence() {
    let query = generate_query();
    let Some(oracle) = scipy_oracle_or_skip(&query) else {
        return;
    };
    assert_eq!(oracle.points.len(), query.points.len());

    let pmap: HashMap<String, PointArm> = oracle
        .points
        .into_iter()
        .map(|r| (r.case_id.clone(), r))
        .collect();

    let start = Instant::now();
    let mut diffs = Vec::new();
    let mut max_overall = 0.0_f64;
    let mut ledger = CompareLedger::new("diff_special_spence", &["spence"]);

    for case in &query.points {
        let oracle = pmap.get(&case.case_id).expect("validated oracle");
        let Some((scipy_v, rust_v)) =
            ledger.pair("spence", &case.case_id, oracle.value, fsci_eval(case.z))
        else {
            continue;
        };
        let abs_diff = (rust_v - scipy_v).abs();
        max_overall = max_overall.max(abs_diff);
        let pass = abs_diff <= REL_TOL * scipy_v.abs();
        ledger.compared("spence", &case.case_id, pass);
        diffs.push(CaseDiff {
            case_id: case.case_id.clone(),
            abs_diff,
            pass,
        });
    }

    let all_pass = diffs.iter().all(|d| d.pass);

    let log = DiffLog {
        test_id: "diff_special_spence".into(),
        category: "scipy.special.spence".into(),
        case_count: diffs.len(),
        compared: ledger.counts().clone(),
        max_abs_diff: max_overall,
        pass: all_pass,
        timestamp_ms: timestamp_ms(),
        duration_ns: start.elapsed().as_nanos(),
        cases: diffs.clone(),
    };

    emit_log(&log);

    for d in &diffs {
        if !d.pass {
            eprintln!("spence mismatch: {} abs={}", d.case_id, d.abs_diff);
        }
    }

    assert!(
        all_pass,
        "scipy.special.spence conformance failed: {} cases, max_abs={}",
        diffs.len(),
        max_overall
    );
    ledger.finish(query.points.len());
}