//! Tune the four lifecycle constants of the `jiggly` USB-mouse-jiggler firmware
//! as a **multi-objective** optimization problem.
//!
//! The Python `tune_runtime.py` from ~/Code/jiggly grid-searches against a
//! single composite score that linearly combines several genuinely conflicting
//! goals. That's a workable workaround for grid search — you have to rank by
//! one number — but it bakes the user's weights into the search and hides the
//! tradeoffs.
//!
//! `heuropt` lets us optimize the goals as separate objectives and surface the
//! Pareto front of legitimate tradeoffs:
//!
//! 1. **minimize work-time failures** — the screen sleeping while the user is
//!    working is the worst outcome. (`mean_work_sleep`, minutes/day)
//! 2. **maximize lunch sleep** — the entire design goal. (`mean_lunch`,
//!    minutes/day, encoded as a Maximize objective)
//! 3. **minimize human interactions** — every button press is UX cost.
//!    (`mean_presses`, per day)
//! 4. **minimize after-hours waste** — keeping the screen alive past the end
//!    of the workday is screen burn for nothing. (`mean_after`, minutes/day)
//!
//! Decision: a 4-element `Vec<f64>` for `(RT, YELLOW_AT, RED_AT, FAST_RED_AT)`,
//! continuous-relaxed and rounded to integer minutes inside `evaluate`. The
//! firmware ordering constraint `YA > RA > FRA > 0` is encoded as
//! `constraint_violation` so the algorithm's feasible-beats-infeasible logic
//! handles it automatically.
//!
//! Solver: NSGA-III with 4 objectives and Das-Dennis H=6 → 84 reference
//! points, matching the population size. Each `evaluate` runs a 1,000-workday
//! Monte Carlo, so this example is also a deliberately meaty evaluator that
//! benefits from `--features parallel` (≈8× wall-clock with rayon enabled on
//! a typical laptop).
//!
//! ```bash
//! cargo run --release --example jiggly_tuning
//! cargo run --release --example jiggly_tuning --features parallel
//! ```
//!
//! Output is in jiggly's native units — `RT` as `Xh00m`, thresholds as plain
//! minutes, durations as `Xh00m` / `Mm`, probabilities as percentages.

use std::time::Instant;

use rand::Rng as _;
use rand::SeedableRng;
use rand::rngs::StdRng;

use heuropt::prelude::*;

const LUNCH_START: i32 = 12 * 60;
const LUNCH_END: i32 = 13 * 60;

const P_PRESS_YELLOW: f64 = 0.015;
const P_PRESS_RED: f64 = 0.040;
const P_PRESS_FAST_RED: f64 = 0.060;
const P_WARN10_BUMP: f64 = 0.04;
const P_WARN5_BUMP: f64 = 0.03;

// Sweet-spot lunch-sleep window (minutes spent dead during 12:00–13:00).
const SWEET_LO: u32 = 15;
const SWEET_HI: u32 = 45;

const N_DAYS: usize = 1000;

// -----------------------------------------------------------------------------
// A-posteriori decision weights (must sum to 1.0).
// -----------------------------------------------------------------------------
const W_LUNCH: f64 = 0.30; // top — design goal
const W_AFTER: f64 = 0.25; // top — minimize after-hours waste
const W_WORK: f64 = 0.20; // medium — failures bad but recoverable
const W_PRESS: f64 = 0.15; // matters with a hinge below
const W_BALANCE: f64 = 0.10; // bonus for longer yellow + red phases

// Press hinge: full reward at or below LOW, linearly drops to 0 at COMFORT_CAP,
// and any candidate with mean_presses > COMFORT_CAP is rejected outright.
//
// Counts every daily press: morning boot, 13:00 lunch retap, warning-phase
// reactions, and any death-restart presses during the workday. With ~2
// baseline presses already mandatory each day, the LOW threshold sits just
// above baseline (2 + a half warning press) and the cap allows up to
// 1.5 additional presses on top of baseline before rejecting.
const PRESS_HINGE_LOW: f64 = 2.5;
const PRESS_COMFORT_CAP: f64 = 3.5;

// Balance bonus saturates: a min(yellow_width, red_width) of >= this many
// minutes scores the full balance term.
const BALANCE_SATURATION_MIN: f64 = 10.0;

// -----------------------------------------------------------------------------
// Day model + Monte Carlo (same model as scripts/tune_runtime.py)
// -----------------------------------------------------------------------------

#[derive(Default, Clone, Copy)]
struct DayOutcome {
    presses: u32,
    slept_work: u32,
    slept_lunch: u32,
    after_hours: u32,
}

#[derive(Clone, Copy)]
struct Stats {
    /// Probability of landing in the 12:15–12:45 sweet spot.
    p_sweet: f64,
    mean_lunch: f64,
    mean_work_sleep: f64,
    mean_presses: f64,
    mean_after: f64,
}

fn sample_triangular(low: f64, mode: f64, high: f64, rng: &mut StdRng) -> f64 {
    let u: f64 = rng.random();
    let c = (mode - low) / (high - low);
    if u < c {
        low + ((high - low) * (mode - low) * u).sqrt()
    } else {
        high - ((high - low) * (high - mode) * (1.0 - u)).sqrt()
    }
}

/// Pre-sampled simulated workdays. Sampling once and reusing across all
/// `evaluate` calls is the standard SAA pattern: every parameter combination
/// is scored on the same days, so differences in objective values reflect the
/// parameters rather than Monte Carlo noise between evaluations.
struct JigglyTuning {
    days: Vec<(i32, i32, u64)>, // start_min, end_min, per-day RNG seed
}

impl JigglyTuning {
    fn new(n_days: usize, seed: u64) -> Self {
        let mut rng = StdRng::seed_from_u64(seed);
        let days = (0..n_days)
            .map(|_| {
                let s = (sample_triangular(8.0, 8.5, 9.5, &mut rng) * 60.0) as i32;
                let e = (sample_triangular(16.0, 17.5, 19.0, &mut rng) * 60.0) as i32;
                let day_seed: u64 = rng.random();
                (s, e, day_seed)
            })
            .collect();
        Self { days }
    }

    fn simulate_one(
        s: i32,
        e: i32,
        day_seed: u64,
        rt: i32,
        ya: i32,
        ra: i32,
        fra: i32,
    ) -> DayOutcome {
        let mut rng = StdRng::seed_from_u64(day_seed);
        let mut expire = s + rt;
        // Boot press at workday start: user presses to begin cycle 1.
        let mut o = DayOutcome {
            presses: 1,
            ..Default::default()
        };
        // Allow the loop to extend past the larger of (workday end, last
        // possible cycle end given any in-loop expire bumps). Cap at one
        // extra cycle's worth so a long string of presses can't blow the
        // budget.
        let t_max = e.max(expire).max(s + 2 * rt) + 1;
        let mut prev_running = true;
        for t in s..t_max {
            // 13:00 re-login press: user comes back from lunch, presses to
            // start cycle 2.
            if t == LUNCH_END && t < e {
                expire = t + rt;
                o.presses += 1;
            }
            let in_workday = t >= s && t < e;
            let at_lunch = (LUNCH_START..LUNCH_END).contains(&t);
            let device_running = t < expire;
            let device_dead = !device_running;

            // Death-restart press: when the device transitions from running
            // to dead during workday (not at lunch), user notices the screen
            // sleeping and presses to restart. Counts as a press for THIS
            // minute; subsequent at-desk minutes are now covered.
            if prev_running && device_dead && in_workday && !at_lunch {
                expire = t + rt;
                o.presses += 1;
                prev_running = true;
                continue;
            }
            prev_running = device_running;

            if device_dead && in_workday {
                if at_lunch {
                    o.slept_lunch += 1;
                } else {
                    o.slept_work += 1;
                }
            }
            if t >= e && device_running {
                o.after_hours += 1;
            }

            if !at_lunch && in_workday && device_running {
                let remaining = expire - t;
                let mut p = 0.0;
                if remaining > ra && remaining <= ya {
                    p = P_PRESS_YELLOW;
                } else if remaining > fra && remaining <= ra {
                    p = P_PRESS_RED;
                } else if remaining > 0 && remaining <= fra {
                    p = P_PRESS_FAST_RED;
                }
                if remaining == 10 {
                    p += P_WARN10_BUMP;
                }
                if remaining == 5 {
                    p += P_WARN5_BUMP;
                }
                let roll: f64 = rng.random();
                if roll < p {
                    expire = t + rt;
                    o.presses += 1;
                }
            }
        }
        o
    }

    fn aggregate(&self, rt: i32, ya: i32, ra: i32, fra: i32) -> Stats {
        let n = self.days.len() as f64;
        let mut sweet = 0u32;
        let mut sum_lunch = 0.0_f64;
        let mut sum_work = 0.0_f64;
        let mut sum_presses = 0.0_f64;
        let mut sum_after = 0.0_f64;
        for &(s, e, ds) in &self.days {
            let o = Self::simulate_one(s, e, ds, rt, ya, ra, fra);
            if (SWEET_LO..=SWEET_HI).contains(&o.slept_lunch) {
                sweet += 1;
            }
            sum_lunch += o.slept_lunch as f64;
            sum_work += o.slept_work as f64;
            sum_presses += o.presses as f64;
            sum_after += o.after_hours as f64;
        }
        Stats {
            p_sweet: sweet as f64 / n,
            mean_lunch: sum_lunch / n,
            mean_work_sleep: sum_work / n,
            mean_presses: sum_presses / n,
            mean_after: sum_after / n,
        }
    }
}

impl Problem for JigglyTuning {
    type Decision = Vec<f64>;

    fn objectives(&self) -> ObjectiveSpace {
        ObjectiveSpace::new(vec![
            Objective::minimize("work_failure_min"),
            Objective::maximize("lunch_sleep_min"),
            Objective::minimize("presses_per_day"),
            Objective::minimize("after_hours_min"),
        ])
    }

    fn evaluate(&self, x: &Vec<f64>) -> Evaluation {
        let rt = x[0].round() as i32;
        let ya = x[1].round() as i32;
        let ra = x[2].round() as i32;
        let fra = x[3].round() as i32;

        // Soft constraint: YA > RA > FRA > 0 (any violation is positive).
        let mut violation = 0.0_f64;
        if ra >= ya {
            violation += (ra - ya + 1) as f64;
        }
        if fra >= ra {
            violation += (fra - ra + 1) as f64;
        }
        if fra <= 0 {
            violation += (1 - fra) as f64;
        }

        let stats = self.aggregate(rt, ya, ra, fra);
        Evaluation::constrained(
            vec![
                stats.mean_work_sleep,
                stats.mean_lunch, // Objective is Maximize → as_minimization will negate
                stats.mean_presses,
                stats.mean_after,
            ],
            violation.max(0.0),
        )
    }
}

// -----------------------------------------------------------------------------
// Output formatting (matches the units used in tune_runtime.py)
// -----------------------------------------------------------------------------

fn fmt_minutes(m: f64) -> String {
    let total = m.round() as i32;
    let h = total / 60;
    let mm = total % 60;
    if h > 0 {
        format!("{h}h{mm:02}m")
    } else {
        format!("{mm}m")
    }
}

fn fmt_rt(m: i32) -> String {
    let h = m / 60;
    let mm = m % 60;
    format!("{h}h{mm:02}m")
}

/// One row in the Pareto-front summary table.
#[derive(Clone)]
struct Row {
    rt: i32,
    ya: i32,
    ra: i32,
    fra: i32,
    work_fail: f64,
    lunch: f64,
    presses: f64,
    after: f64,
    p_sweet: f64,
}

fn row_for(decision: &[f64], stats: &Stats) -> Row {
    Row {
        rt: decision[0].round() as i32,
        ya: decision[1].round() as i32,
        ra: decision[2].round() as i32,
        fra: decision[3].round() as i32,
        work_fail: stats.mean_work_sleep,
        lunch: stats.mean_lunch,
        presses: stats.mean_presses,
        after: stats.mean_after,
        p_sweet: stats.p_sweet,
    }
}

fn print_header() {
    println!(
        "{:<6} {:>3} {:>3} {:>3}   {:>9}   {:>9}   {:>8}   {:>8}   {:>7}",
        "RT", "YA", "RA", "FRA", "work fail↓", "lunch↑", "presses↓", "after↓", "p_sweet",
    );
    println!("{}", "-".repeat(78));
}

fn print_row(label: &str, r: &Row) {
    let prefix = if label.is_empty() {
        String::new()
    } else {
        format!("{label} ")
    };
    println!(
        "{}{:<6} {:>3} {:>3} {:>3}   {:>9}   {:>9}   {:>7.2}/d   {:>8}   {:>6.1}%",
        prefix,
        fmt_rt(r.rt),
        r.ya,
        r.ra,
        r.fra,
        fmt_minutes(r.work_fail),
        fmt_minutes(r.lunch),
        r.presses,
        fmt_minutes(r.after),
        r.p_sweet * 100.0,
    );
}

// -----------------------------------------------------------------------------
// Main
// -----------------------------------------------------------------------------

fn main() {
    let problem = JigglyTuning::new(N_DAYS, 2026);

    let bounds = vec![
        (230.0, 250.0), // RT
        (20.0, 70.0),   // YELLOW_AT
        (10.0, 40.0),   // RED_AT
        (4.0, 20.0),    // FAST_RED_AT
    ];
    let initializer = RealBounds::new(bounds.clone());
    // Canonical NSGA-II/-III operator pair (SBX + PolyMut) with bounds.
    let variation = CompositeVariation {
        crossover: SimulatedBinaryCrossover::new(bounds.clone(), 30.0, 1.0),
        mutation: PolynomialMutation::new(bounds, 20.0, 1.0 / 4.0),
    };
    // M=4, H=6 → C(9,3) = 84 reference points. Match the population size.
    let pop = 84;
    let gens = 25;
    let config = Nsga3Config {
        population_size: pop,
        generations: gens,
        reference_divisions: 6,
        seed: 42,
    };

    println!("Optimizing jiggly's 4 lifecycle constants — 4-objective Pareto search");
    println!("  algorithm: NSGA-III (84 ref points, M=4, H=6)");
    println!("  N_DAYS:    {N_DAYS} simulated workdays per evaluation");
    println!("  search:    RT∈[230,250], YA∈[20,70], RA∈[10,40], FRA∈[4,20]");
    println!(
        "  budget:    {pop} pop × {gens} gens = {} evaluations",
        pop * (gens + 1)
    );
    println!();

    let mut opt = Nsga3::new(config, initializer, variation);
    let t0 = Instant::now();
    let result = opt.run(&problem);
    let elapsed = t0.elapsed();

    println!(
        "NSGA-III finished in {:.2}s ({} evaluations, |front|={})",
        elapsed.as_secs_f64(),
        result.evaluations,
        result.pareto_front.len(),
    );
    println!();

    // Materialize each Pareto member's full Stats so we can print rich rows.
    // Multiple f64 decisions can round to the same integer combo — dedupe.
    let mut seen = std::collections::HashSet::new();
    let mut rows: Vec<Row> = result
        .pareto_front
        .iter()
        .filter_map(|c| {
            let rt = c.decision[0].round() as i32;
            let ya = c.decision[1].round() as i32;
            let ra = c.decision[2].round() as i32;
            let fra = c.decision[3].round() as i32;
            if !seen.insert((rt, ya, ra, fra)) {
                return None;
            }
            let stats = problem.aggregate(rt, ya, ra, fra);
            Some(row_for(&c.decision, &stats))
        })
        .collect();
    // Drop any infeasible front entries (shouldn't happen for a converged
    // run, but guard anyway).
    rows.retain(|r| r.ya > r.ra && r.ra > r.fra && r.fra > 0);

    println!("=== Pareto front (sorted by lunch sleep, descending) ===");
    print_header();
    rows.sort_by(|a, b| {
        b.lunch
            .partial_cmp(&a.lunch)
            .unwrap_or(std::cmp::Ordering::Equal)
    });
    for r in rows.iter().take(15) {
        print_row("", r);
    }
    if rows.len() > 15 {
        println!("  ... ({} more on the front)", rows.len() - 15);
    }
    println!();

    // Re-rank by each individual objective to surface extreme tradeoffs.
    let best_by = |key: fn(&Row) -> f64, want_high: bool| -> Option<&Row> {
        rows.iter().min_by(|a, b| {
            let ka = key(a);
            let kb = key(b);
            let cmp = ka.partial_cmp(&kb).unwrap_or(std::cmp::Ordering::Equal);
            if want_high { cmp.reverse() } else { cmp }
        })
    };
    println!("=== extreme tradeoffs ===");
    print_header();
    if let Some(r) = best_by(|r| r.work_fail, false) {
        print_row("FEWEST WORK FAILS    ", r);
    }
    if let Some(r) = best_by(|r| r.lunch, true) {
        print_row("MOST LUNCH SLEEP     ", r);
    }
    if let Some(r) = best_by(|r| r.presses, false) {
        print_row("FEWEST PRESSES       ", r);
    }
    if let Some(r) = best_by(|r| r.after, false) {
        print_row("LEAST AFTER-HOURS    ", r);
    }
    println!();

    let shipping = problem.aggregate(240, 30, 25, 20);
    let shipping_row = row_for(&[240.0, 30.0, 25.0, 20.0], &shipping);
    println!("=== firmware shipping default (RT=4h00m YEL=30 RED=25 FST=20) ===");
    print_header();
    print_row("", &shipping_row);
    println!();

    // -------------------------------------------------------------------------
    // A-posteriori pick: rank the front by weighted preferences.
    // -------------------------------------------------------------------------
    //
    // Every point on the front is incomparable in the strict Pareto sense —
    // none dominates another. To surface ONE recommendation we apply explicit
    // weights to four normalized outcome axes plus two structural terms:
    //
    //   * `lunch_sleep` (max), `after_hours` (min), `work_fail` (min) —
    //     normalized to [0, 1] across the candidate set.
    //   * `presses` — hinge: full reward when <= PRESS_HINGE_LOW, ramps to
    //     zero at PRESS_COMFORT_CAP, candidates above the cap are rejected.
    //   * `balance` — bonus for longer warning phases:
    //     `min(YA - RA, RA - FRA)` saturated at BALANCE_SATURATION_MIN.
    //
    // Anyone with different priorities can read the front above and pick a
    // different row. We add the firmware's shipping defaults to the
    // candidate set so they compete on equal footing with the front.

    let mut candidates: Vec<(String, Row)> = rows
        .iter()
        .map(|r| ("front".to_string(), r.clone()))
        .collect();
    let shipping_candidate_idx = candidates.len();
    candidates.push(("shipping default".to_string(), shipping_row.clone()));

    let scores = compute_weighted_scores(
        &candidates
            .iter()
            .map(|(_, r)| r.clone())
            .collect::<Vec<_>>(),
    );
    let mut ranked: Vec<(usize, f64)> = scores.iter().copied().enumerate().collect();
    ranked.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal));

    println!("=== ranked by weighted preferences ===");
    println!(
        "  weights: lunch_sleep {}% · after_hours {}% · work_fail {}% · presses {}% · balance {}%",
        (W_LUNCH * 100.0) as i32,
        (W_AFTER * 100.0) as i32,
        (W_WORK * 100.0) as i32,
        (W_PRESS * 100.0) as i32,
        (W_BALANCE * 100.0) as i32,
    );
    println!(
        "  press hinge: full reward ≤ {:.1}/d, ramps to 0 at {:.1}/d, REJECTED above",
        PRESS_HINGE_LOW, PRESS_COMFORT_CAP,
    );
    println!(
        "  balance bonus: min(yellow_width, red_width), saturates at {:.0} min",
        BALANCE_SATURATION_MIN,
    );
    println!(
        "  candidate set: {} Pareto-front rows + 1 shipping default",
        rows.len()
    );
    println!();
    println!("{:>4}  {:>5}  source", "rank", "score");
    print_header();
    for (rank, &(idx, score)) in ranked.iter().take(5).enumerate() {
        let (label, r) = &candidates[idx];
        println!("{:>4}  {:.3}  {label}", rank + 1, score);
        print_row("", r);
    }
    println!();

    let &(top_idx, top_score) = ranked.first().expect("at least one candidate");
    let (top_label, top) = &candidates[top_idx];
    let shipping_rank = ranked
        .iter()
        .position(|(i, _)| *i == shipping_candidate_idx)
        .map(|p| p + 1)
        .unwrap_or(0);

    let max_work = candidates
        .iter()
        .map(|(_, r)| r.work_fail)
        .fold(0.0, f64::max);

    println!("=== RECOMMENDED PICK ({top_label}) ===");
    println!(
        "  RT={}  YELLOW_AT={}  RED_AT={}  FAST_RED_AT={}",
        fmt_rt(top.rt),
        top.ya,
        top.ra,
        top.fra,
    );
    println!("  weighted score = {top_score:.3}");
    println!();
    let yellow_w = top.ya - top.ra;
    let red_w = top.ra - top.fra;
    println!("Why:");
    println!(
        "  • {} mean lunch sleep ({:.1}% land in the 12:15–12:45 sweet spot)",
        fmt_minutes(top.lunch),
        top.p_sweet * 100.0,
    );
    println!(
        "  • {} mean after-hours awake (kept tight, your second priority)",
        fmt_minutes(top.after),
    );
    println!(
        "  • {} mean work-time failure ({} better than the worst candidate)",
        fmt_minutes(top.work_fail),
        ratio_str(max_work, top.work_fail.max(1e-9)),
    );
    let press_note = if top.presses <= PRESS_HINGE_LOW {
        format!("inside your no-penalty zone ≤{:.1}/d", PRESS_HINGE_LOW)
    } else if top.presses < PRESS_COMFORT_CAP {
        format!(
            "above the {:.1}/d hinge but below your {:.1}/d cap",
            PRESS_HINGE_LOW, PRESS_COMFORT_CAP,
        )
    } else {
        format!("AT or ABOVE your {:.1}/d comfort cap", PRESS_COMFORT_CAP)
    };
    println!(
        "  • {:.2} button presses/day total — {}",
        top.presses, press_note,
    );
    println!("    (counts: boot + 13:00 retap + warning-phase reactions + death-restarts)");
    println!(
        "  • warning phases: yellow {} min, red {} min, fast-red {} min (balance score {:.2})",
        yellow_w,
        red_w,
        top.fra,
        balance_score_for(top),
    );

    if top_label != "shipping default" {
        println!();
        println!(
            "(Shipping default ranks #{shipping_rank} of {}.)",
            candidates.len(),
        );
    } else {
        println!();
        println!(
            "Note: the optimizer found {} non-dominated alternatives, but under",
            rows.len(),
        );
        println!("these weights the firmware's shipping defaults score highest.");
    }
}

/// Score every row in `rows` by a weighted sum that combines normalized
/// outcome axes with a press hinge and a phase-balance bonus.
///
/// `work_fail`, `lunch`, and `after` are normalized to `[0, 1]` across `rows`
/// (best→1, worst→0; direction-aware). `presses` uses a hinge that rewards
/// values at or below `PRESS_HINGE_LOW`, ramps linearly to zero at
/// `PRESS_COMFORT_CAP`, and rejects candidates above the cap by returning
/// `f64::NEG_INFINITY`. `balance` is a bonus for longer yellow + red
/// phases, computed as `min(YA - RA, RA - FRA)` saturated at
/// `BALANCE_SATURATION_MIN`.
fn compute_weighted_scores(rows: &[Row]) -> Vec<f64> {
    let work_min = rows
        .iter()
        .map(|r| r.work_fail)
        .fold(f64::INFINITY, f64::min);
    let work_max = rows
        .iter()
        .map(|r| r.work_fail)
        .fold(f64::NEG_INFINITY, f64::max);
    let lunch_min = rows.iter().map(|r| r.lunch).fold(f64::INFINITY, f64::min);
    let lunch_max = rows
        .iter()
        .map(|r| r.lunch)
        .fold(f64::NEG_INFINITY, f64::max);
    let after_min = rows.iter().map(|r| r.after).fold(f64::INFINITY, f64::min);
    let after_max = rows
        .iter()
        .map(|r| r.after)
        .fold(f64::NEG_INFINITY, f64::max);

    rows.iter()
        .map(|r| {
            // Hard comfort cap on presses.
            if r.presses > PRESS_COMFORT_CAP {
                return f64::NEG_INFINITY;
            }
            let work = norm_min(r.work_fail, work_min, work_max);
            let lunch = norm_max(r.lunch, lunch_min, lunch_max);
            let after = norm_min(r.after, after_min, after_max);
            // Hinge: 1.0 at or below LOW, linear ramp to 0.0 at the cap.
            let press_score = if r.presses <= PRESS_HINGE_LOW {
                1.0
            } else {
                ((PRESS_COMFORT_CAP - r.presses) / (PRESS_COMFORT_CAP - PRESS_HINGE_LOW))
                    .clamp(0.0, 1.0)
            };
            // Balance bonus: longer yellow + red is better, saturated.
            let balance_score = balance_score_for(r);

            W_LUNCH * lunch
                + W_AFTER * after
                + W_WORK * work
                + W_PRESS * press_score
                + W_BALANCE * balance_score
        })
        .collect()
}

/// Balance bonus for a row: `min(YA - RA, RA - FRA)` clamped to
/// `[0, BALANCE_SATURATION_MIN]` and divided by saturation so the result is
/// in `[0, 1]`.
fn balance_score_for(r: &Row) -> f64 {
    let yellow_w = (r.ya - r.ra) as f64;
    let red_w = (r.ra - r.fra) as f64;
    let raw = yellow_w.min(red_w).max(0.0);
    (raw / BALANCE_SATURATION_MIN).clamp(0.0, 1.0)
}

/// Normalize a minimize-direction value to `[0, 1]` (best→1, worst→0).
fn norm_min(v: f64, lo: f64, hi: f64) -> f64 {
    if (hi - lo).abs() < 1e-12 {
        1.0
    } else {
        (hi - v) / (hi - lo)
    }
}

/// Normalize a maximize-direction value to `[0, 1]` (best→1, worst→0).
fn norm_max(v: f64, lo: f64, hi: f64) -> f64 {
    if (hi - lo).abs() < 1e-12 {
        1.0
    } else {
        (v - lo) / (hi - lo)
    }
}

/// Render `worst / best` as e.g. "7.5×" for the recommendation rationale.
fn ratio_str(worst: f64, best: f64) -> String {
    if best <= 1e-9 {
        return "∞×".to_string();
    }
    format!("{:.1}×", worst / best)
}