import { describe, it, expect } from 'vitest';
import { random, randomInt, weightedPick } from '../../src/sim/rng';

describe('rng', () => {
  it('is deterministic for a given seed', () => {
    const a = { rngState: 42 };
    const b = { rngState: 42 };
    const seqA = [random(a), random(a), random(a)];
    const seqB = [random(b), random(b), random(b)];
    expect(seqA).toEqual(seqB);
  });

  it('returns values in [0, 1)', () => {
    const h = { rngState: 7 };
    for (let i = 0; i < 1000; i++) {
      const v = random(h);
      expect(v).toBeGreaterThanOrEqual(0);
      expect(v).toBeLessThan(1);
    }
  });

  it('randomInt stays within inclusive bounds', () => {
    const h = { rngState: 1 };
    const seen = new Set<number>();
    for (let i = 0; i < 1000; i++) {
      const v = randomInt(h, 3, 5);
      expect(v).toBeGreaterThanOrEqual(3);
      expect(v).toBeLessThanOrEqual(5);
      seen.add(v);
    }
    expect(seen.size).toBe(3);
  });

  it('weightedPick never picks zero-weight items', () => {
    const h = { rngState: 3 };
    const items = ['a', 'b', 'c'];
    for (let i = 0; i < 500; i++) {
      const v = weightedPick(h, items, (x) => (x === 'b' ? 0 : 1));
      expect(v).not.toBe('b');
    }
  });

  it('weightedPick returns undefined when all weights are zero', () => {
    const h = { rngState: 3 };
    expect(weightedPick(h, ['a'], () => 0)).toBeUndefined();
    expect(weightedPick(h, [], () => 1)).toBeUndefined();
  });
});