personal-website/src/lib/derby/generic.ts

// Algemeen kansmodel voor de overige koersen: zelfde opzet als het Derby-model
// (z-scores × gewichten → softmax), maar zonder proef- en marktsignaal.
// Signalen: uitslagen, snelheid (beste recente km-tijd), niveau (prijzengeld
// van de laatste starts), startpositie en uitvalrisico.

import type { Result } from './data';
import type { Race, Runner } from './races';

export type GWeights = {
	form: number;
	speed: number;
	level: number;
	draw: number;
	risk: number;
	halfLife: number;
	temperature: number;
	lambda: number;
};

export const gFeatureKeys = ['form', 'speed', 'level', 'draw'] as const;
export type GFeatureKey = (typeof gFeatureKeys)[number];

export const gDefaults: GWeights = {
	form: 1,
	speed: 1,
	level: 0.6,
	draw: 0.4,
	risk: 1,
	halfLife: 2,
	temperature: 1,
	lambda: 0.8
};

/** rensport: geen tijden, startbox minder belangrijk over 1900 m */
export const defaultsFor = (race: Race): GWeights =>
	race.discipline === 'ren' ? { ...gDefaults, speed: 0, draw: 0.2, level: 0.8 } : { ...gDefaults };

export const gPresets: Record<string, Partial<GWeights>> = {
	Standaard: {},
	Vorm: { form: 1.6, speed: 0.5, level: 0.4 },
	Snelheid: { form: 0.5, speed: 1.6, level: 0.4 },
	Niveau: { form: 0.6, speed: 0.6, level: 1.5 }
};

const SCALE = 0.55;
const POSITION_POINTS: Record<number, number> = {
	1: 1,
	2: 0.75,
	3: 0.6,
	4: 0.45,
	5: 0.35,
	6: 0.25
};
const positionPoints = (r: Result) => (r === 'D' ? 0 : (POSITION_POINTS[r] ?? 0.1));
const DRAW_SCORE = [0, 0.6, 0.7, 0.6, 0.45, 0.4, 0.25, 0.1, 0, -0.2, -0.3];

export type GFeatures = {
	form: number;
	speed: number;
	level: number;
	draw: number;
	pFail: number;
	/** welke signalen ontbraken en het veldgemiddelde kregen */
	estimated: GFeatureKey[];
};

const mean = (xs: number[]) => xs.reduce((a, b) => a + b, 0) / xs.length;

function rawForm(h: Runner, w: GWeights): number | null {
	if (h.form.length === 0) return null;
	const decay = h.form.map((_, i) => Math.pow(0.5, i / w.halfLife));
	return (
		h.form.reduce((s: number, r, i) => s + decay[i] * positionPoints(r), 0) /
		decay.reduce((a, b) => a + b, 0)
	);
}

export function gFeatures(runners: Runner[], w: GWeights): GFeatures[] {
	const raw = runners.map((h) => ({
		form: rawForm(h, w),
		speed: h.times.length ? -Math.min(...h.times) : null,
		level: h.purses.length ? mean(h.purses.map((p) => Math.log(p))) : null
	}));
	const fill = (k: 'form' | 'speed' | 'level') => {
		const known = raw.map((r) => r[k]).filter((v): v is number => v !== null);
		return known.length ? mean(known) : 0;
	};
	const avg = { form: fill('form'), speed: fill('speed'), level: fill('level') };

	return runners.map((h, i) => {
		const estimated: GFeatureKey[] = [];
		const pick = (k: 'form' | 'speed' | 'level') => {
			const v = raw[i][k];
			if (v === null) estimated.push(k);
			return v ?? avg[k];
		};
		const disq = h.form.filter((r) => r === 'D').length;
		const poor = h.form.filter((r) => r !== 'D' && r >= 7).length;
		// debutanten: geen bewijs dat ze in de draf blijven
		const base = h.form.length === 0 ? 0.12 : 0.03;
		const pFail = Math.min(0.5, base + 0.1 * disq + 0.03 * poor);
		return {
			form: pick('form'),
			speed: pick('speed'),
			level: pick('level'),
			draw: DRAW_SCORE[h.n] ?? 0,
			pFail,
			estimated
		};
	});
}

/**
 * ondergrens voor de spreiding per signaal, anders wordt 0,2 s verschil in een
 * veld met drie bijna gelijke tijden een enorme z-score
 */
const SD_FLOOR: Record<GFeatureKey, number> = { form: 0.08, speed: 1, level: 0.3, draw: 0.15 };

function zscores(values: number[], floor: number): number[] {
	const m = mean(values);
	const sd = Math.max(floor, Math.sqrt(mean(values.map((v) => (v - m) ** 2))));
	return values.map((v) => (v - m) / sd);
}

export type GPrediction = {
	horse: Runner;
	features: GFeatures;
	contributions: Record<GFeatureKey, number>;
	riskPenalty: number;
	logit: number;
	p: number;
};

export function gPredict(runners: Runner[], w: GWeights): GPrediction[] {
	if (runners.length === 0) return [];
	const feats = gFeatures(runners, w);
	const z = Object.fromEntries(
		gFeatureKeys.map((k) => [
			k,
			zscores(
				feats.map((f) => f[k]),
				SD_FLOOR[k]
			)
		])
	) as Record<GFeatureKey, number[]>;
	const rows = runners.map((horse, i) => {
		const contributions = Object.fromEntries(
			gFeatureKeys.map((k) => [k, w[k] * z[k][i] * SCALE])
		) as Record<GFeatureKey, number>;
		const riskPenalty = w.risk * Math.log(1 - feats[i].pFail);
		const logit = Object.values(contributions).reduce((a, b) => a + b, 0) + riskPenalty;
		return { horse, features: feats[i], contributions, riskPenalty, logit, p: 0 };
	});
	const max = Math.max(...rows.map((r) => r.logit));
	const exp = rows.map((r) => Math.exp((r.logit - max) / w.temperature));
	const total = exp.reduce((a, b) => a + b, 0);
	rows.forEach((r, i) => (r.p = exp[i] / total));
	return rows.sort((a, b) => b.p - a.p);
}