ITOSMPiano-BachToBasics/scripts/build_practice_collection.mjs

import fs from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import midiPackage from '../frontend/node_modules/@tonejs/midi/build/Midi.js';

const { Midi } = midiPackage;
const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
const sourceRoot = path.join(root, 'backend', 'tools', 'practice_sources');
const outputRoot = path.join(root, 'backend', 'sample_midi');
const catalog = JSON.parse(fs.readFileSync(path.join(sourceRoot, 'catalog.json'), 'utf8'));
const names = {
  burgmuller: ['순진', '아라베스크', '목가', '작은 모임', '순수', '진보', '맑은 시냇물', '우아함', '사냥', '여린 꽃', '할미새', '이별', '위안', '슈타이어 춤', '발라드', '작은 탄식', '수다쟁이', '불안'],
  schumann: ['멜로디', '군대 행진곡', '흥얼거리는 노래', '코랄', '작은 소품', '가엾은 고아', '사냥꾼의 노래', '거친 기수', '민요', '즐거운 농부', '시칠리아 춤곡', '무서운 아저씨'],
};

const field = (rdf, key) => rdf.match(new RegExp(`<mp:${key}>([^<]*)</mp:${key}>`))?.[1]?.trim() ?? '';
const clamp = (value, low, high) => Math.max(low, Math.min(high, value));

function addNote(track, note, time, duration, velocity) {
  track.addNote({ midi: clamp(note, 21, 108), time, duration: Math.max(0.08, duration), velocity });
}

function onsets(notes) {
  const grouped = new Map();
  for (const note of notes) {
    const key = Math.round(note.time * 50);
    const list = grouped.get(key) ?? [];
    list.push(note);
    grouped.set(key, list);
  }
  return [...grouped.entries()].sort(([a], [b]) => a - b).map(([key, group]) => ({ time: key / 50, notes: group }));
}

const manifest = [];
for (const item of catalog) {
  const name = item.name;
  const [series, numberText] = name.split('-');
  const number = Number(numberText);
  const source = new Midi(fs.readFileSync(path.join(sourceRoot, `${name}.mid`)));
  const rdf = fs.readFileSync(path.join(sourceRoot, `${name}.rdf`), 'utf8');
  const license = field(rdf, 'licence');
  if (license !== 'Public Domain' && !/^Creative Commons Attribution-ShareAlike (2\.5|3\.0)$/.test(license)) {
    throw new Error(`${name}: 권리 표시를 확인해야 합니다: ${license}`);
  }
  const nonempty = source.tracks.filter((track) => track.notes.length);
  if (nonempty.length < 2) throw new Error(`${name}: 양손 원본이 없습니다`);
  const rightSource = onsets(nonempty[0].notes);
  const leftSource = onsets(nonempty.at(-1).notes);
  const speed = Math.max(1, 58 / source.duration);
  const introSeconds = 5.4;
  const target = new Midi();
  target.header.setTempo(120);
  target.header.timeSignatures.push({ ticks: 0, timeSignature: source.header.timeSignatures[0]?.timeSignature ?? [4, 4] });
  const right = target.addTrack();
  right.name = 'Right Hand';
  const left = target.addTrack();
  left.name = 'Left Hand';

  // 원곡의 첫 선율 네 음을 먼저 천천히 들려준다. 본곡과 자연스럽게 이어지는 도입부다.
  const introPitches = rightSource.slice(0, 4).map((group) => Math.max(...group.notes.map((note) => note.midi)));
  const firstBass = Math.min(...leftSource[0].notes.map((note) => note.midi));
  addNote(left, firstBass, 0, 4.5, 0.48);
  introPitches.forEach((pitch, index) => addNote(right, pitch, 0.55 + index * 1.05, 0.83, 0.55 + index * 0.04));

  // 오른손은 원곡의 각 시작점에서 가장 높은 성부를 택한다. 선율의 순서와 리듬을 보존한다.
  for (const group of rightSource) {
    const note = group.notes.reduce((highest, current) => current.midi > highest.midi ? current : highest);
    addNote(right, note.midi, introSeconds + group.time * speed, Math.min(2.4, note.duration * speed * 0.92), clamp(note.velocity, 0.48, 0.87));
  }
  // 왼손은 저음을 따라가되 가까운 시작점을 정리해 초보자가 양손을 맞출 여유를 둔다.
  let previousBassTime = -10;
  for (const group of leftSource) {
    const time = introSeconds + group.time * speed;
    if (time - previousBassTime < 0.48) continue;
    const note = group.notes.reduce((lowest, current) => current.midi < lowest.midi ? current : lowest);
    addNote(left, note.midi, time, clamp(note.duration * speed * 0.9, 0.38, 2.5), 0.53);
    previousBassTime = time;
  }

  // 원곡 마지막 선율을 늦추어 다시 들려준 뒤 종지음을 충분히 유지한다.
  const endingStart = introSeconds + source.duration * speed + 0.5;
  const endingPitches = rightSource.slice(-3).map((group) => Math.max(...group.notes.map((note) => note.midi)));
  const lastBass = Math.min(...leftSource.at(-1).notes.map((note) => note.midi));
  addNote(left, lastBass, endingStart, 5.1, 0.52);
  endingPitches.forEach((pitch, index) => addNote(right, pitch, endingStart + index * 1.05, index === 2 ? 3.0 : 0.85, 0.68 - index * 0.06));

  const file = `practice-${name}.mid`;
  const duration = new Midi(target.toArray()).duration;
  if (duration < 60 || right.notes.length < 12 || left.notes.length < 6) throw new Error(`${name}: 연습곡 검증 실패`);
  const notesPerSecond = right.notes.length / duration;
  const difficulty = notesPerSecond < 2.1 ? 'beginner' : notesPerSecond < 3.5 ? 'easy' : 'intermediate';
  fs.writeFileSync(path.join(outputRoot, file), Buffer.from(target.toArray()));
  const title = `${series === 'burgmuller' ? '부르크뮐러 25곡' : '슈만 어린이를 위한 앨범'} ${number}번 ${names[series][number - 1]}`;
  manifest.push({
    storage_name: file,
    title,
    artist: series === 'burgmuller' ? '요한 프리드리히 부르크뮐러' : '로베르트 슈만',
    description: `${field(rdf, 'title')} 원곡을 양손 연습용으로 단순화했습니다. 도입부와 마무리가 포함된 전체 곡입니다. 원본: Mutopia Project ${field(rdf, 'id')}. 조판: ${field(rdf, 'maintainer')}. ${license}${license === 'Public Domain' ? '' : ' 동일 조건 편곡'}.`,
    difficulty,
    genre: series === 'burgmuller' ? '낭만주의 연습곡' : '낭만주의 소품',
    arrangement: 'piano_solo',
    tags: ['양손', '도입부', '마무리', series === 'burgmuller' ? '부르크뮐러' : '슈만', difficulty === 'beginner' ? '입문' : difficulty === 'easy' ? '쉬움' : '중급', license === 'Public Domain' ? '공개 도메인' : 'CC BY-SA'],
    source_url: item.midi_url,
    rdf_url: item.rdf_url,
    source_title: field(rdf, 'title'),
    source_id: field(rdf, 'id'),
    maintainer: field(rdf, 'maintainer'),
    license,
    duration_seconds: Math.round(duration * 10) / 10,
  });
}
fs.writeFileSync(path.join(outputRoot, 'practice_collection.json'), `${JSON.stringify(manifest, null, 2)}\n`);
console.log(`연습곡 ${manifest.length}개 생성. 재생 길이 ${Math.min(...manifest.map((item) => item.duration_seconds))}~${Math.max(...manifest.map((item) => item.duration_seconds))}초`);