import { test, expect } from "bun:test";
import { mixStemsScaled } from "../../src/audio/mix.ts";
import type { Audio } from "../../src/core/types.ts";

test("mixStemsScaled: scaled stems sum to mix; scale is the normalisation factor", () => {
  const mk = (n: number, amp: number): Audio => {
    const x = Float32Array.from({ length: n }, (_, i) => amp * Math.sin(i / 7));
    return { sampleRate: 44100, channels: [x, x.slice()] };
  };
  const a = mk(1000, 0.9), b = mk(700, 0.8);
  const { mix, scaled, scale } = mixStemsScaled([{ audio: a, gainDb: 0 }, { audio: b, gainDb: -3 }]);
  // unnormalised peak
  const gb = Math.pow(10, -3 / 20);
  let peak = 0;
  for (let i = 0; i < 1000; i++) peak = Math.max(peak, Math.abs(a.channels[0]![i]! + (i < 700 ? b.channels[0]![i]! * gb : 0)));
  expect(peak).toBeGreaterThan(1);
  expect(Math.abs(scale - Math.pow(10, -1 / 20) / peak)).toBeLessThan(1e-6);
  expect(scaled.length).toBe(2);
  let maxDiff = 0;
  for (let c = 0; c < 2; c++) for (let i = 0; i < 1000; i++) {
    const s = scaled[0]!.channels[c]![i]! + scaled[1]!.channels[c]![i]!;
    maxDiff = Math.max(maxDiff, Math.abs(s - mix.channels[c]![i]!));
  }
  expect(maxDiff).toBeLessThan(1e-6);
});