import { describe, expect, it } from 'vitest';
import { applyCentDust, DUST_MAX_STEPS, DUST_STEP } from '../src/dust';

describe('applyCentDust', () => {
  it('adds a suffix between 0.0001 and 0.0999 in 0.0001 steps', () => {
    for (let i = 0; i < 50; i++) {
      const dusted = applyCentDust(100_000000n, () => false);
      const dust = dusted - 100_000000n;
      expect(dust >= DUST_STEP).toBe(true);
      expect(dust <= BigInt(DUST_MAX_STEPS) * DUST_STEP).toBe(true);
      expect(dust % DUST_STEP).toBe(0n);
    }
  });

  it('avoids amounts already taken by concurrent invoices', () => {
    const taken = new Set<bigint>([100_000100n, 100_000200n]);
    // rng that picks steps 1, then 2, then 3…
    const seq = [0, 0.0011, 0.0021];
    let call = 0;
    const rng = () => seq[Math.min(call++, seq.length - 1)]!;
    const dusted = applyCentDust(100_000000n, (c) => taken.has(c), rng);
    expect(dusted).toBe(100_000300n);
  });

  it('falls back to a deterministic sweep when random attempts collide', () => {
    const taken = (c: bigint) => c !== 100_000000n + BigInt(DUST_MAX_STEPS) * DUST_STEP;
    const dusted = applyCentDust(100_000000n, taken, () => 0); // rng always proposes step 1 (taken)
    expect(dusted).toBe(100_000000n + BigInt(DUST_MAX_STEPS) * DUST_STEP);
  });

  it('throws when every suffix is exhausted', () => {
    expect(() => applyCentDust(100_000000n, () => true)).toThrow(/no unique dust suffix/);
  });
});