fsci-conformance 0.3.0

#![forbid(unsafe_code)]
//! Live SciPy differential coverage for the generalized
//! exponential integral `scipy.special.expn` (E_n(x)).
//!
//! Resolves [frankenscipy-z5pn7]. fsci's `expn(n, x)` had no
//! dedicated diff harness.
//!
//! 5 n-values × 9 x-values = 45 cases via subprocess.
//! Tolerances: 5e-7 abs. fsci's expn lands ~7.2e-8 abs at
//! n=1, x=1 — likely a series-asymptotic seam at x≈1. Same
//! pattern as Bessel/Spence — tracked alongside frankenscipy-0om9c.

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_special::expn;
use serde::{Deserialize, Serialize};

const PACKET_ID: &str = "FSCI-P2C-007";
const ABS_TOL: f64 = 5.0e-7;
const REQUIRE_SCIPY_ENV: &str = "FSCI_REQUIRE_SCIPY_ORACLE";

#[derive(Debug, Clone, Serialize)]
struct PointCase {
    case_id: String,
    n: usize,
    x: 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,
    n: usize,
    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 expn 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 expn diff log");
    fs::write(path, json).expect("write expn diff log");
}

fn generate_query() -> OracleQuery {
    // n=1 is the "exponential integral" E_1; n=2,3,5,10 cover
    // the recurrence range.
    let ns = [1_usize, 2, 3, 5, 10];
    // x>0 (E_n diverges at 0 for n=1; E_n(0) = 1/(n-1) for n>1).
    let xs = [0.01_f64, 0.1, 0.5, 1.0, 2.0, 3.0, 5.0, 10.0, 25.0];
    let mut points = Vec::new();
    for &n in &ns {
        for &x in &xs {
            points.push(PointCase {
                case_id: format!("n{n}_x{x}"),
                n,
                x,
            });
        }
    }
    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"]
    n = int(case["n"]); x = float(case["x"])
    try:
        value = special.expn(n, x)
        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 expn 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 expn oracle: {e}"
            );
            eprintln!("skipping expn oracle: python3 not available ({e})");
            return None;
        }
    };
    {
        let stdin = child.stdin.as_mut().expect("open expn 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(),
                "expn oracle stdin write failed: {err}; stderr: {stderr}"
            );
            eprintln!("skipping expn oracle: stdin write failed ({err})\n{stderr}");
            return None;
        }
    }
    let output = child.wait_with_output().expect("wait for expn oracle");
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        assert!(
            std::env::var(REQUIRE_SCIPY_ENV).is_err(),
            "expn oracle failed: {stderr}"
        );
        eprintln!("skipping expn oracle: scipy not available\n{stderr}");
        return None;
    }
    let stdout = String::from_utf8_lossy(&output.stdout);
    Some(serde_json::from_str(&stdout).expect("parse expn oracle JSON"))
}

#[test]
fn diff_special_expn() {
    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_expn", &["expn"]);

    for case in &query.points {
        let oracle = pmap.get(&case.case_id).expect("validated oracle");
        // A non-finite fsci value is recorded by `pair` as an fsci failure, not skipped.
        let Some((scipy_v, rust_v)) = ledger.pair(
            "expn",
            &case.case_id,
            oracle.value,
            Some(expn(case.n, case.x)),
        ) else {
            continue;
        };
        let abs_diff = (rust_v - scipy_v).abs();
        max_overall = max_overall.max(abs_diff);
        ledger.compared("expn", &case.case_id, abs_diff <= ABS_TOL);
        diffs.push(CaseDiff {
            case_id: case.case_id.clone(),
            n: case.n,
            abs_diff,
            pass: abs_diff <= ABS_TOL,
        });
    }

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

    let log = DiffLog {
        test_id: "diff_special_expn".into(),
        category: "scipy.special.expn".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!("expn n={} mismatch: {} abs={}", d.n, d.case_id, d.abs_diff);
        }
    }

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