vyndr/tests/unit/pitcherEngine.test.js

'use strict';

/**
 * THE PITCHER ENGINE — per-role doctrine asserted as behaviour.
 *
 * The thing these tests exist to prevent is the batter engine quietly becoming
 * the pitcher engine: same weights, same inputs, different label. A pitcher's
 * strikeouts come from stuff against a lineup, not from contact quality.
 */

const pe = require('../../src/services/model/pitcherEngine');

const FLAME = { whiff_pct: 0.34, k_pct: 0.31, chase_pct: 0.31, gb_pct: 0.38 };
const SCALPEL = { whiff_pct: 0.21, k_pct: 0.20, chase_pct: 0.36, gb_pct: 0.42 };
const SINKER = { whiff_pct: 0.20, k_pct: 0.17, chase_pct: 0.28, gb_pct: 0.55 };

describe('pitcher archetypes are classified by FUNCTION', () => {
  it('overpowering stuff is a FLAME', () => {
    expect(pe.classifyPitcher(FLAME).primary).toBe('FLAME');
  });

  it('chase without overpowering stuff is a SCALPEL', () => {
    expect(pe.classifyPitcher(SCALPEL).primary).toBe('SCALPEL');
  });

  it('heavy grounders with an ordinary strikeout rate is a SINKER', () => {
    expect(pe.classifyPitcher(SINKER).primary).toBe('SINKER');
  });

  it('nothing to classify on → null, NOT a guessed archetype', () => {
    expect(pe.classifyPitcher({})).toBeNull();
    expect(pe.classifyPitcher({ bb_pct: 0.09 })).toBeNull();
    // and an unclassified pitcher still gets a balanced map, not a lean
    expect(pe.weightsFor(null)).toEqual(pe.ARCHETYPES.DEFAULT.weights);
  });

  it('the archetypes are NOT the batter engine — they weight stuff, not contact', () => {
    const sk = require('../../src/services/model/skillProjection');
    const pitcherKeys = Object.keys(pe.weightsFor('FLAME')).sort();
    const batterKeys = Object.keys(sk.featureMapFor('BOMBER').hitWeights).sort();
    expect(pitcherKeys).not.toEqual(batterKeys);
    expect(pitcherKeys).toEqual(['chase', 'k_rate', 'whiff']);
  });

  it('a FLAME leans on whiff; a SCALPEL leans on chase', () => {
    expect(pe.weightsFor('FLAME').whiff).toBeGreaterThan(pe.weightsFor('SCALPEL').whiff);
    expect(pe.weightsFor('SCALPEL').chase).toBeGreaterThan(pe.weightsFor('FLAME').chase);
  });
});

describe('THE MATCHUP TERM — stuff against THIS lineup', () => {
  it('the same arm projects lower against a contact lineup than a whiff-prone one', () => {
    const vsContact = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.16, line: 5.5, expectedBf: 24 });
    const vsWhiffy = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.29, line: 5.5, expectedBf: 24 });
    expect(vsContact.p_over_line).toBeLessThan(vsWhiffy.p_over_line);
    expect(vsContact.projected_value).toBeLessThan(vsWhiffy.projected_value);
  });

  it('a league-average lineup leaves the pitcher near his own rate', () => {
    const own = pe.strikeoutRate({ pitcher: FLAME });
    const vsLeague = pe.strikeoutRate({ pitcher: FLAME, lineupKRate: pe.LEAGUE.k_pct });
    expect(vsLeague.k_rate).toBeCloseTo(own.k_rate, 6);
  });

  it('an ABSENT lineup leaves the rate untouched and says so — never substitutes league', () => {
    const r = pe.strikeoutRate({ pitcher: FLAME, lineupKRate: null });
    expect(r.lineup_applied).toBe(false);
    expect(r.k_rate).toBeGreaterThan(0);
  });

  it('better stuff means a higher rate, at the same lineup', () => {
    const flame = pe.strikeoutRate({ pitcher: FLAME, lineupKRate: 0.22 });
    const sink = pe.strikeoutRate({ pitcher: SINKER, lineupKRate: 0.22 });
    expect(flame.k_rate).toBeGreaterThan(sink.k_rate);
  });
});

describe('workload is opportunity, not skill', () => {
  it('a starter faces more batters than a reliever, so projects more strikeouts', () => {
    const starter = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.22, line: 4.5, role: 'starter' });
    const reliever = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.22, line: 4.5, role: 'reliever' });
    expect(starter.projected_value).toBeGreaterThan(reliever.projected_value);
    expect(starter.p_over_line).toBeGreaterThan(reliever.p_over_line);
  });

  it('more batters faced at the SAME rate means more strikeouts', () => {
    const short = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.22, line: 5.5, expectedBf: 18 });
    const long = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.22, line: 5.5, expectedBf: 28 });
    expect(long.k_rate_per_bf).toBeCloseTo(short.k_rate_per_bf, 6);  // rate unchanged
    expect(long.p_over_line).toBeGreaterThan(short.p_over_line);     // opportunity changed
  });
});

describe('honesty — abstain rather than guess', () => {
  it('no stuff profile → NO read', () => {
    expect(pe.projectStrikeouts({ pitcher: null, line: 5.5 })).toBeNull();
    expect(pe.projectStrikeouts({ pitcher: {}, line: 5.5 })).toBeNull();
  });

  it('a missing stuff input is SILENT, not a measured zero', () => {
    const full = pe.strikeoutRate({ pitcher: FLAME, lineupKRate: 0.22 });
    const noWhiff = pe.strikeoutRate({ pitcher: { ...FLAME, whiff_pct: null }, lineupKRate: 0.22 });
    const zeroWhiff = pe.strikeoutRate({ pitcher: { ...FLAME, whiff_pct: 0 }, lineupKRate: 0.22 });
    expect(noWhiff).not.toBeNull();
    expect(zeroWhiff.k_rate).toBeLessThan(noWhiff.k_rate);   // a real 0 is a fact
    expect(Math.abs(noWhiff.k_rate - full.k_rate)).toBeLessThan(Math.abs(zeroWhiff.k_rate - full.k_rate));
  });

  it('the registry gate applies — with nothing allowed, it REFUSES', () => {
    const out = pe.projectStrikeouts({
      pitcher: FLAME, lineupKRate: 0.22, line: 5.5, allowed: new Set(['something_else']),
    });
    expect(out).toBeNull();
  });

  it('the distribution is a real distribution and P(>=k) is monotone', () => {
    const out = pe.projectStrikeouts({ pitcher: FLAME, lineupKRate: 0.22, line: 5.5, expectedBf: 24 });
    expect(out.distribution.reduce((a, b) => a + b, 0)).toBeCloseTo(1, 2);
    let prev = 1;
    for (let k = 1; k <= 12; k += 1) {
      const p = pe.atLeast(out.distribution, k);
      expect(p).toBeLessThanOrEqual(prev + 1e-9);
      prev = p;
    }
  });

  it('the rate stays a probability however the ratios stack', () => {
    const wild = pe.strikeoutRate({ pitcher: { whiff_pct: 0.95, k_pct: 0.9, chase_pct: 0.9 }, lineupKRate: 0.9 });
    expect(wild.k_rate).toBeLessThanOrEqual(1);
    expect(wild.k_rate).toBeGreaterThan(0);
  });
});