/** The curves of a Saturation (#323) and the gain that keeps it as loud as it came in. */
import { describe, expect, it } from 'vitest';
import {
  driveGain,
  SATURATION_RANGE,
  SATURATION_TYPES,
  saturate,
  saturationAutoGain,
  saturationCurve,
  toneCutoff,
} from '../../src/core/soundfx/saturation';

describe('the curves of a Saturation', () => {
  it('leave silence silent and never go past full scale, however hard they are driven', () => {
    for (const { value } of SATURATION_TYPES) {
      expect(saturate(value, 0)).toBeCloseTo(0, 12);
      for (const x of [-300, -5, -1, -0.3, 0.3, 1, 5, 300])
        expect(Math.abs(saturate(value, x))).toBeLessThanOrEqual(1);
    }
  });

  it('bend each in a shape of their own', () => {
    expect(saturate('hard', 0.5)).toBe(0.5);
    expect(saturate('hard', 3)).toBe(1);
    expect(saturate('cubic', 1)).toBe(1);
    expect(saturate('cubic', 0.5)).toBeCloseTo(0.6875, 9);
    // Foldback mirrors at ±1: 1.5 comes back to 0.5, 3 to -1.
    expect([saturate('foldback', 0.5), saturate('foldback', 1.5), saturate('foldback', 3)]).toEqual([
      0.5, 0.5, -1,
    ]);
    expect(saturate('sine', 1)).toBeCloseTo(1, 12);
    expect(saturate('sine', 2)).toBeCloseTo(0, 12);
    // Tube and Fuzz bend one half harder than the other; Rectify turns the lower half up.
    expect(saturate('tube', 2)).not.toBeCloseTo(-saturate('tube', -2), 2);
    expect(saturate('fuzz', -10)).toBeCloseTo(-0.5, 9);
    expect(saturate('rectify', -0.5)).toBeCloseTo(saturate('rectify', 0.5), 12);
  });

  it('are made once, spanning the range a drive of 48 dB reaches', () => {
    const curve = saturationCurve('hard');
    expect(saturationCurve('hard')).toBe(curve);
    expect(curve.length % 2).toBe(1);
    expect([curve[0], curve[(curve.length - 1) / 2], curve.at(-1)]).toEqual([-1, 0, 1]);
    expect(10 ** (48 / 20)).toBeLessThan(SATURATION_RANGE);
    expect(driveGain(0)).toBe(1 / SATURATION_RANGE);
  });
});

describe('the auto-gain of a Saturation', () => {
  it('leaves a curve that does nothing at -12 dBFS alone, and makes up for what a hard one takes', () => {
    expect(saturationAutoGain('hard', 0)).toBeCloseTo(0, 9);
    // Driven 24 dB into a hard clip, a sine is nearly a square at full scale: 3 dB above the
    // sine's 0 dBFS RMS, which is 12 dB over -12 dBFS. 15 dB come off.
    expect(saturationAutoGain('hard', 24)).toBeCloseTo(-15, 0);
    expect(saturationAutoGain('soft', 0)).toBeGreaterThan(0);
    expect(saturationAutoGain('soft', 0)).toBeLessThan(0.3);
  });

  it('opens the tone from 1 kHz to 20 kHz', () => {
    expect([toneCutoff(0), toneCutoff(1), toneCutoff(5)]).toEqual([1000, 20000, 20000]);
    expect(toneCutoff(0.5)).toBeCloseTo(1000 * Math.sqrt(20), 6);
  });
});