STSheets/tests/align/warp.test.ts

import { test, expect, describe } from "bun:test";
import { makeWarp, stretches, addManual, moveAnchor, deleteAnchor, type Anchor } from "../../src/align/warp.ts";

const M = (midiSec: number, audioSec: number): Anchor => ({ midiSec, audioSec, kind: "manual" });
const A = (midiSec: number, audioSec: number): Anchor => ({ midiSec, audioSec, kind: "auto" });
const close = (a: number, b: number, eps = 1e-9) => expect(Math.abs(a - b)).toBeLessThan(eps);

describe("makeWarp", () => {
  test("zero anchors is the identity", () => {
    const w = makeWarp([]);
    expect(w.anchors).toEqual([]);
    for (const x of [-2, 0, 3.5, 100]) {
      expect(w.toAudio(x)).toBe(x);
      expect(w.toMidi(x)).toBe(x);
    }
  });

  test("single anchor is a pure offset", () => {
    const w = makeWarp([M(1, 1.5)]);
    expect(w.toAudio(1)).toBe(1.5);
    expect(w.toAudio(3)).toBe(3.5);
    expect(w.toAudio(-1)).toBe(-0.5);
    expect(w.toMidi(1.5)).toBe(1);
    expect(w.toMidi(0)).toBe(-0.5);
  });

  test("two anchors interpolate linearly and extrapolate with the same slope", () => {
    const w = makeWarp([M(1, 1), M(3, 5)]); // slope 2
    expect(w.toAudio(2)).toBe(3);
    expect(w.toAudio(0)).toBe(-1);
    expect(w.toAudio(5)).toBe(9);
    expect(w.toMidi(3)).toBe(2);
  });

  test("three anchors: outer segments use the nearest interior slope", () => {
    const w = makeWarp([M(1, 1), M(3, 5), M(5, 6)]); // slopes 2, then 0.5
    expect(w.toAudio(4)).toBe(5.5); // interior
    expect(w.toAudio(0)).toBe(-1); // before first: slope 2
    expect(w.toAudio(7)).toBe(7); // after last: slope 0.5 -> 6 + 2*0.5
  });

  test("toMidi(toAudio(x)) round-trips", () => {
    const w = makeWarp([M(0.5, 0.2), A(2, 2.9), M(4, 4.1), A(9, 8.0)]);
    for (let x = -3; x <= 12; x += 0.37) close(w.toMidi(w.toAudio(x)), x);
    for (let y = -3; y <= 12; y += 0.41) close(w.toAudio(w.toMidi(y)), y);
  });

  test("sorts anchors by midiSec and keeps them as copies", () => {
    const input = [M(3, 5), M(1, 1)];
    const w = makeWarp(input);
    expect(w.anchors.map((a) => a.midiSec)).toEqual([1, 3]);
    expect(w.toAudio(2)).toBe(3);
    input[0]!.audioSec = 999;
    expect(w.toAudio(3)).toBe(5);
  });

  test("throws when audioSec is not strictly increasing with midiSec", () => {
    expect(() => makeWarp([M(1, 2), M(3, 1)])).toThrow();
    expect(() => makeWarp([M(1, 2), M(3, 2)])).toThrow();
  });

  test("throws on duplicate midiSec", () => {
    expect(() => makeWarp([M(1, 1), M(1, 2)])).toThrow();
  });
});

describe("stretches", () => {
  test("no anchors: one stretch with ratio 1", () => {
    expect(stretches([], 10)).toEqual([{ fromMidi: 0, toMidi: 10, ratio: 1, warn: false }]);
  });

  test("single anchor: two ratio-1 edge stretches split at the anchor", () => {
    expect(stretches([M(4, 4.2)], 10)).toEqual([
      { fromMidi: 0, toMidi: 4, ratio: 1, warn: false },
      { fromMidi: 4, toMidi: 10, ratio: 1, warn: false },
    ]);
  });

  test("interior stretches get their ratio; edges take the nearest interior ratio", () => {
    const s = stretches([M(1, 1), M(3, 5), M(5, 6)], 7);
    expect(s.map((x) => [x.fromMidi, x.toMidi])).toEqual([
      [0, 1],
      [1, 3],
      [3, 5],
      [5, 7],
    ]);
    expect(s.map((x) => x.ratio)).toEqual([2, 2, 0.5, 0.5]);
    expect(s.map((x) => x.warn)).toEqual([true, true, true, true]);
  });

  test("warn when tempo changes by more than 5%", () => {
    const hot = stretches([M(0, 0), M(10, 10.7)], 10); // ratio 1.07 -> 1/1.07-1 = -6.5%
    expect(hot.length).toBe(1);
    close(hot[0]!.ratio, 1.07);
    expect(hot[0]!.warn).toBe(true);
    const mild = stretches([M(0, 0), M(10, 10.4)], 10); // ratio 1.04 -> -3.8%
    expect(mild[0]!.warn).toBe(false);
  });

  test("drops zero-length edge stretches when an anchor sits at 0 or at the end", () => {
    const s = stretches([M(0, 0.5), M(10, 10.5)], 10);
    expect(s).toEqual([{ fromMidi: 0, toMidi: 10, ratio: 1, warn: false }]);
  });
});

describe("addManual", () => {
  test("adds a manual anchor into an empty list", () => {
    expect(addManual([], { midiSec: 2, audioSec: 2.5 })).toEqual([M(2, 2.5)]);
  });

  test("removes only the auto immediate neighbours, keeps manual ones and farther autos", () => {
    // M0 | A2 | A4 | M8 ; insert manual at 6 -> A4 (immediate left, auto) goes; A2 stays (not adjacent); M8 stays
    const base = [M(0, 0), A(2, 2), A(4, 4.5), M(8, 8)];
    expect(addManual(base, { midiSec: 6, audioSec: 6.2 })).toEqual([
      M(0, 0),
      A(2, 2),
      M(6, 6.2),
      M(8, 8),
    ]);
  });

  test("keeps manual neighbours untouched", () => {
    const base = [M(0, 0), M(8, 8)];
    expect(addManual(base, { midiSec: 4, audioSec: 4 })).toEqual([M(0, 0), M(4, 4), M(8, 8)]);
  });

  test("removes auto neighbours on both sides", () => {
    const base = [M(0, 0), A(2, 2), A(6, 6.5), M(10, 10)];
    expect(addManual(base, { midiSec: 4, audioSec: 4.1 })).toEqual([M(0, 0), M(4, 4.1), M(10, 10)]);
  });

  test("throws if the new anchor would cross a neighbour's audio time", () => {
    const base = [M(0, 0), M(8, 8)];
    expect(() => addManual(base, { midiSec: 4, audioSec: 9 })).toThrow();
    expect(() => addManual(base, { midiSec: 4, audioSec: -1 })).toThrow();
  });

  test("throws on an existing midi position", () => {
    expect(() => addManual([M(4, 4)], { midiSec: 4, audioSec: 4.5 })).toThrow();
  });
});

describe("moveAnchor", () => {
  test("moves an anchor, makes it manual and removes adjacent autos", () => {
    const base = [M(0, 0), A(3, 3), M(6, 6), A(9, 9)];
    // move M(6) to midi 5 audio 5.5; immediate auto neighbours: A(3) left (removed), A(9) right (removed)
    expect(moveAnchor(base, 2, { midiSec: 5, audioSec: 5.5 })).toEqual([M(0, 0), M(5, 5.5)]);
  });

  test("turns an auto anchor into a manual one", () => {
    const base = [M(0, 0), A(4, 4.5), M(8, 8)];
    expect(moveAnchor(base, 1, { midiSec: 4.2, audioSec: 4.6 })).toEqual([M(0, 0), M(4.2, 4.6), M(8, 8)]);
  });

  test("throws when moved past a manual neighbour", () => {
    const base = [M(0, 0), M(4, 4), M(8, 8)];
    expect(() => moveAnchor(base, 1, { midiSec: 9, audioSec: 4 })).toThrow();
    expect(() => moveAnchor(base, 1, { midiSec: 4, audioSec: 8.5 })).toThrow();
  });

  test("throws when moved past an auto neighbour", () => {
    const base = [M(0, 0), A(4, 4), M(8, 8)];
    expect(() => moveAnchor(base, 2, { midiSec: 3, audioSec: 3 })).toThrow();
  });

  test("throws on a bad index", () => {
    expect(() => moveAnchor([M(1, 1)], 3, { midiSec: 2, audioSec: 2 })).toThrow();
  });
});

describe("deleteAnchor", () => {
  test("removes the anchor at index", () => {
    expect(deleteAnchor([M(1, 1), A(2, 2), M(3, 3)], 1)).toEqual([M(1, 1), M(3, 3)]);
  });

  test("throws on a bad index", () => {
    expect(() => deleteAnchor([M(1, 1)], 1)).toThrow();
  });
});