// distribution-stats.test.mjs — Tests for scanners/lib/distribution-stats.mjs
// Zero external dependencies: node:test + node:assert only.

import { describe, it } from 'node:test';
import assert from 'node:assert/strict';
import { jensenShannonDivergence, buildDistribution } from '../../scanners/lib/distribution-stats.mjs';

// ---------------------------------------------------------------------------
// buildDistribution
// ---------------------------------------------------------------------------

describe('distribution-stats — buildDistribution', () => {
  it('empty array → empty map', () => {
    const d = buildDistribution([]);
    assert.equal(d.size, 0);
  });

  it('single category normalizes to 1.0', () => {
    const d = buildDistribution(['Read', 'Read', 'Read']);
    assert.equal(d.size, 1);
    assert.equal(d.get('Read'), 1.0);
  });

  it('two equal categories normalize to 0.5 each', () => {
    const d = buildDistribution(['Read', 'Bash', 'Read', 'Bash']);
    assert.equal(d.size, 2);
    assert.equal(d.get('Read'), 0.5);
    assert.equal(d.get('Bash'), 0.5);
  });

  it('unequal distribution normalizes correctly', () => {
    const d = buildDistribution(['Read', 'Read', 'Read', 'Bash']);
    assert.equal(d.get('Read'), 0.75);
    assert.equal(d.get('Bash'), 0.25);
  });

  it('sum of probabilities equals 1.0', () => {
    const d = buildDistribution(['Read', 'Bash', 'Write', 'Grep', 'Bash']);
    let sum = 0;
    for (const v of d.values()) sum += v;
    assert.ok(Math.abs(sum - 1.0) < 1e-10, `Sum ${sum} should be ~1.0`);
  });
});

// ---------------------------------------------------------------------------
// jensenShannonDivergence
// ---------------------------------------------------------------------------

describe('distribution-stats — jensenShannonDivergence', () => {
  it('identical distributions → JSD = 0', () => {
    const P = buildDistribution(['Read', 'Bash', 'Read', 'Bash']);
    const Q = buildDistribution(['Read', 'Bash', 'Read', 'Bash']);
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(Math.abs(jsd) < 1e-10, `JSD ${jsd} should be ~0`);
  });

  it('fully disjoint distributions → JSD = 1', () => {
    const P = buildDistribution(['Read', 'Read', 'Read']);
    const Q = buildDistribution(['Bash', 'Bash', 'Bash']);
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(Math.abs(jsd - 1.0) < 1e-10, `JSD ${jsd} should be ~1.0`);
  });

  it('partially overlapping distributions → 0 < JSD < 1', () => {
    const P = buildDistribution(['Read', 'Read', 'Bash']);
    const Q = buildDistribution(['Read', 'Bash', 'Bash']);
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(jsd > 0, `JSD ${jsd} should be > 0`);
    assert.ok(jsd < 1, `JSD ${jsd} should be < 1`);
  });

  it('JSD is symmetric: JSD(P,Q) = JSD(Q,P)', () => {
    const P = buildDistribution(['Read', 'Read', 'Read', 'Bash']);
    const Q = buildDistribution(['Read', 'Bash', 'Bash', 'Bash']);
    const jsd1 = jensenShannonDivergence(P, Q);
    const jsd2 = jensenShannonDivergence(Q, P);
    assert.ok(Math.abs(jsd1 - jsd2) < 1e-10, `JSD(P,Q)=${jsd1} should equal JSD(Q,P)=${jsd2}`);
  });

  it('two empty distributions → JSD = 0', () => {
    const P = new Map();
    const Q = new Map();
    const jsd = jensenShannonDivergence(P, Q);
    assert.equal(jsd, 0);
  });

  it('one empty + one non-empty → JSD = 0.5', () => {
    const P = buildDistribution(['Read']);
    const Q = new Map();
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(Math.abs(jsd - 0.5) < 1e-10, `JSD ${jsd} should be 0.5`);
  });

  it('three categories with different distributions', () => {
    const P = buildDistribution(['Read', 'Read', 'Read', 'Write', 'Write', 'Bash']);
    const Q = buildDistribution(['Read', 'Write', 'Write', 'Write', 'Bash', 'Bash']);
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(jsd > 0, `JSD ${jsd} should be > 0`);
    assert.ok(jsd < 1, `JSD ${jsd} should be < 1`);
  });

  it('diverse vs concentrated → high JSD', () => {
    const P = buildDistribution(['Read', 'Write', 'Bash', 'Grep', 'Glob']);
    const Q = buildDistribution(['Read', 'Read', 'Read', 'Read', 'Read']);
    const jsd = jensenShannonDivergence(P, Q);
    assert.ok(jsd > 0.3, `JSD ${jsd} should be > 0.3 for diverse vs concentrated`);
  });
});
