import { describe, expect, it } from 'vitest';
import { decimateResult, lowpass } from '../src/sim/antialias';
import type { SimResult } from '../src/sim/types';

const fs = 48000;

// a result holding only a pickup signal at R fs
function result(x: Float32Array, R: number): SimResult {
  return {
    audio: x,
    fs: fs * R,
    frames: new Float32Array(0),
    frameTimes: new Float64Array(0),
    energy: new Float64Array(0),
    balance: new Float64Array(0),
    dt: 1 / (fs * R),
    stepsPerSample: 1,
    omegaMax: 0,
    wallSeconds: 0,
    maxStretch: 0,
  };
}

const sine = (f: number, R: number, n: number) => Float32Array.from({ length: n * R }, (_, i) => Math.sin((2 * Math.PI * f * i) / (fs * R)));

// RMS of the middle half (away from the edges)
function rms(x: Float32Array): number {
  const a = Math.floor(x.length / 4);
  const b = Math.floor((3 * x.length) / 4);
  let s = 0;
  for (let i = a; i < b; i++) s += x[i] * x[i];
  return Math.sqrt(s / (b - a));
}

describe('anti-aliased pickup', () => {
  for (const R of [2, 5]) {
    it(`R = ${R}: passes the audible band, removes what would fold back`, () => {
      const h = lowpass(R);
      expect(h.reduce((s, v) => s + v, 0)).toBeCloseTo(1, 12);
      const n = 8000;
      // 1 kHz and 20 kHz pass (to 0.1 dB)
      for (const f of [1000, 20000]) expect(Math.abs(20 * Math.log10(rms(decimateResult(result(sine(f, R, n), R), R, true).audio) / Math.SQRT1_2))).toBeLessThan(0.1);
      // 26 and 36 kHz would fold back to 22 and 12 kHz: at least 80 dB down
      for (const f of [26000, 36000]) expect(20 * Math.log10(rms(decimateResult(result(sine(f, R, n), R), R, true).audio) / Math.SQRT1_2)).toBeLessThan(-80);
    });
  }

  it('a partial result is a prefix of the complete one', () => {
    const R = 4;
    const x = Float32Array.from({ length: 6000 * R }, (_, i) => Math.sin(i * 0.01) * Math.exp(-i / 9000) + 0.3 * Math.sin(i * 1.7));
    const full = decimateResult(result(x, R), R, true).audio;
    const part = decimateResult(result(x.slice(0, 3000 * R), R), R, false).audio;
    expect(part.length).toBeGreaterThan(2800);
    expect(Array.from(part)).toEqual(Array.from(full.subarray(0, part.length)));
  });
});