vyndr/tests/unit/compoundTotalBases.test.js

'use strict';

/**
 * compoundTotalBases (tb-v1) — total bases as the compound outcome it is.
 *
 * The property that matters is the one an NB on TB cannot express: two hitters
 * with the SAME mean total bases but different STRUCTURE must get different
 * curves. Everything else here guards the honest-absent paths.
 */

const c = require('../../src/services/projection/compoundTotalBases');

const R = (s, d, t, hr) => ({ singles: s, doubles: d, triples: t, home_runs: hr });
const row = (h, d, t, hr) => ({ stat: { hits: h, doubles: d, triples: t, homeRuns: hr } });

describe('the PMF is a real distribution', () => {
  it('sums to 1 and its mean matches the analytic mean', () => {
    const rates = R(0.5, 0.15, 0.01, 0.12);
    const pmf = c.tbPmf(rates);
    expect(pmf.reduce((a, b) => a + b, 0)).toBeCloseTo(1, 6);
    const pmfMean = pmf.reduce((a, p, i) => a + p * i, 0);
    expect(pmfMean).toBeCloseTo(c.tbMean(rates), 4);
  });

  it('P(TB>=0) is 1 and P(>=k) is monotonically non-increasing', () => {
    const pmf = c.tbPmf(R(0.6, 0.2, 0.02, 0.1));
    expect(c.pAtLeast(pmf, 0)).toBe(1);
    let prev = 1;
    for (let k = 1; k <= 8; k += 1) {
      const p = c.pAtLeast(pmf, k);
      expect(p).toBeLessThanOrEqual(prev + 1e-12);
      prev = p;
    }
  });
});

describe('THE POINT — structure separates hitters an NB would merge', () => {
  it('a slugger and a slap hitter with the SAME mean get different curves', () => {
    const slugger = c.tbPmf(R(0, 0, 0, 0.25));   // mean 1.0, all from home runs
    const slap    = c.tbPmf(R(1.0, 0, 0, 0));    // mean 1.0, all from singles
    expect(c.tbMean(R(0, 0, 0, 0.25))).toBeCloseTo(c.tbMean(R(1.0, 0, 0, 0)), 6);
    // The 4-base tail is where an NB on TB alone is blind.
    expect(c.pAtLeast(slugger, 4)).toBeGreaterThan(10 * c.pAtLeast(slap, 4));
  });

  it('a home run is ONE event worth four bases, not four events', () => {
    // P(TB>=4) for a pure HR hitter equals P(at least one HR) exactly.
    const lambda = 0.25;
    const pmf = c.tbPmf(R(0, 0, 0, lambda));
    expect(c.pAtLeast(pmf, 4)).toBeCloseTo(1 - Math.exp(-lambda), 4);
  });
});

describe('honest-absent — never fabricate a rate', () => {
  it('derives singles exactly, reproducing stored total bases', () => {
    const rates = c.ratesFromLog([row(2, 1, 0, 1), row(1, 0, 0, 0), row(0, 0, 0, 0)]);
    // game 1: singles = 2-1-0-1 = 0
    expect(rates.singles).toBeCloseTo((0 + 1 + 0) / 3, 6);
    expect(rates.home_runs).toBeCloseTo(1 / 3, 6);
  });

  it('SKIPS an inconsistent row rather than clamping it to zero', () => {
    // hits < extra-base hits is impossible; clamping would invent a plausible line.
    const rates = c.ratesFromLog([row(0, 2, 0, 0), row(1, 0, 0, 0), row(1, 0, 0, 0), row(1, 0, 0, 0)]);
    expect(rates.games).toBe(3);
  });

  it('returns null below the minimum games — caller falls back to the ladder', () => {
    expect(c.ratesFromLog([row(1, 0, 0, 0), row(1, 0, 0, 0)])).toBeNull();
    expect(c.projectTotalBases({ rows: [row(1, 0, 0, 0)], line: 1.5 })).toBeNull();
  });

  it('a missing component is absent (rate 0), not guessed', () => {
    const pmf = c.tbPmf({ singles: 0.8 });          // no doubles/triples/HR keys
    expect(pmf.reduce((a, b) => a + b, 0)).toBeCloseTo(1, 6);
    expect(c.pAtLeast(pmf, 2)).toBeLessThan(c.pAtLeast(pmf, 1));
  });

  it('no usable component at all returns null, never a flat distribution', () => {
    expect(c.tbPmf({})).toBeNull();
    expect(c.tbPmf({ singles: 'x', doubles: null })).toBeNull();
  });
});

describe('projectTotalBases — the full read', () => {
  const rows = [row(2, 1, 0, 1), row(1, 0, 0, 0), row(0, 0, 0, 0), row(3, 1, 0, 1), row(1, 1, 0, 0)];

  it('inherits the combined multiplier rather than ignoring adjustments', () => {
    const base = c.projectTotalBases({ rows, line: 1.5, multiplier: 1 });
    const up   = c.projectTotalBases({ rows, line: 1.5, multiplier: 1.2 });
    expect(up.mean).toBeGreaterThan(base.mean);
    expect(up.p_over_line).toBeGreaterThan(base.p_over_line);
  });

  it('labels its family and carries the independence caveat', () => {
    const out = c.projectTotalBases({ rows, line: 1.5 });
    expect(out.family).toBe('compound_weighted_poisson');
    expect(out.independence_caveat).toBe(true);
    expect(out.games_used).toBe(5);
  });
});