midi-tools/tests/core/midi.test.ts

import { describe, expect, it } from "vitest";
import {
  constantTempoMidi,
  cropMidi,
  dropChannel,
  encodeMidi,
  exportMidiCsv,
  exportMidiJson,
  noteSpans,
  parseMidi,
  quantizeMidi,
  remapChannel,
  summarizeMidi,
  transposeMidi,
  type MidiDocument,
} from "../../src/core/midi";

function documentFixture(): MidiDocument {
  return {
    name: "fixture.mid",
    format: 1,
    division: 480,
    warnings: [],
    tracks: [
      {
        name: "Conductor",
        events: [
          {
            kind: "meta",
            tick: 0,
            order: 0,
            metaType: 0x51,
            data: Uint8Array.of(0x07, 0xa1, 0x20),
          },
          {
            kind: "meta",
            tick: 0,
            order: 1,
            metaType: 0x58,
            data: Uint8Array.of(4, 2, 24, 8),
          },
          {
            kind: "meta",
            tick: 0,
            order: 2,
            metaType: 0x59,
            data: Uint8Array.of(0, 0),
          },
          {
            kind: "meta",
            tick: 120,
            order: 3,
            metaType: 0x01,
            data: new TextEncoder().encode("=formula"),
          },
        ],
      },
      {
        name: "Notes",
        events: [
          {
            kind: "channel",
            tick: 35,
            order: 4,
            status: 0x9,
            channel: 0,
            data: Uint8Array.of(60, 100),
          },
          {
            kind: "channel",
            tick: 455,
            order: 5,
            status: 0x8,
            channel: 0,
            data: Uint8Array.of(60, 0),
          },
          {
            kind: "channel",
            tick: 500,
            order: 6,
            status: 0x9,
            channel: 1,
            data: Uint8Array.of(64, 90),
          },
          {
            kind: "channel",
            tick: 970,
            order: 7,
            status: 0x8,
            channel: 1,
            data: Uint8Array.of(64, 0),
          },
        ],
      },
    ],
  };
}

describe("Standard MIDI parsing and encoding", () => {
  it("parses type 0 running status and round-trips notes", () => {
    const bytes = Uint8Array.of(
      0x4d,
      0x54,
      0x68,
      0x64,
      0,
      0,
      0,
      6,
      0,
      0,
      0,
      1,
      1,
      0xe0,
      0x4d,
      0x54,
      0x72,
      0x6b,
      0,
      0,
      0,
      12,
      0,
      0x90,
      60,
      100,
      0x83,
      0x60,
      60,
      0,
      0,
      0xff,
      0x2f,
      0,
    );
    const parsed = parseMidi("running.mid", bytes);
    expect(parsed.format).toBe(0);
    expect(noteSpans(parsed)[0]).toMatchObject({
      note: 60,
      startTick: 0,
      endTick: 480,
    });
    expect(noteSpans(parseMidi("again.mid", encodeMidi(parsed)))).toHaveLength(
      1,
    );
  });

  it("summarizes tempo, meter and key and emits safe reports", () => {
    const parsed = parseMidi("fixture.mid", encodeMidi(documentFixture()));
    const summary = summarizeMidi(parsed);
    expect(summary).toMatchObject({ tracks: 2, notes: 2, durationTicks: 970 });
    expect(summary.tempos[0]?.bpm).toBe(120);
    expect(summary.timeSignatures[0]?.value).toBe("4/4");
    expect(summary.keySignatures[0]?.value).toBe("C");
    expect(exportMidiCsv(parsed)).toContain("'=formula");
    expect(JSON.parse(exportMidiJson(parsed)).tracks).toHaveLength(2);
  });

  it("uses inert filler metadata for representable long silent gaps", () => {
    const source: MidiDocument = {
      name: "gap.mid",
      format: 0,
      division: 480,
      warnings: [],
      tracks: [
        {
          name: "Gap",
          events: [
            {
              kind: "channel",
              tick: 0x10000000,
              order: 0,
              status: 0xc,
              channel: 0,
              data: Uint8Array.of(1),
            },
          ],
        },
      ],
    };
    const parsed = parseMidi("gap.mid", encodeMidi(source));
    expect(
      parsed.tracks[0]?.events.find((event) => event.kind === "channel")?.tick,
    ).toBe(0x10000000);
  });

  it("rejects unsupported formats, malformed VLQs and trailing bytes", () => {
    const typeTwo = encodeMidi(documentFixture());
    typeTwo[9] = 2;
    expect(() => parseMidi("type2.mid", typeTwo)).toThrow(/types 0 and 1/u);
    const malformed = Uint8Array.of(
      0x4d,
      0x54,
      0x68,
      0x64,
      0,
      0,
      0,
      6,
      0,
      0,
      0,
      1,
      1,
      0xe0,
      0x4d,
      0x54,
      0x72,
      0x6b,
      0,
      0,
      0,
      5,
      0x81,
      0x80,
      0x80,
      0x80,
      0,
    );
    expect(() => parseMidi("vlq.mid", malformed)).toThrow(/VLQ exceeds/u);
    const valid = encodeMidi(documentFixture());
    const trailing = new Uint8Array(valid.length + 1);
    trailing.set(valid);
    expect(() => parseMidi("trailing.mid", trailing)).toThrow(/follow/u);
  });
});

describe("MIDI editing operations", () => {
  it("transposes, quantizes and replaces tempo without mutating source", () => {
    const source = documentFixture();
    const transposed = transposeMidi(source, 12);
    expect(noteSpans(transposed).map((note) => note.note)).toEqual([72, 76]);
    expect(noteSpans(source).map((note) => note.note)).toEqual([60, 64]);
    const quantized = quantizeMidi(source, 120);
    expect(
      noteSpans(quantized).map((note) => [note.startTick, note.endTick]),
    ).toEqual([
      [0, 480],
      [480, 960],
    ]);
    expect(
      summarizeMidi(constantTempoMidi(source, 90)).tempos[0]?.bpm,
    ).toBeCloseTo(90, 3);
  });

  it("crops overlapping notes and remaps or drops a channel", () => {
    const cropped = cropMidi(documentFixture(), 240, 720);
    expect(
      noteSpans(cropped).map((note) => [note.startTick, note.endTick]),
    ).toEqual([
      [0, 215],
      [260, 480],
    ]);
    expect(
      summarizeMidi(remapChannel(documentFixture(), 2, 1)).channels,
    ).toEqual([1]);
    expect(summarizeMidi(dropChannel(documentFixture(), 1)).channels).toEqual([
      2,
    ]);
    expect(() => transposeMidi(documentFixture(), 100)).toThrow(
      /outside MIDI/u,
    );
  });
});