app/src/utils/midiToNotation.js

import { MIDI_SPLIT_POINT } from './colorScheme';

// VexFlow note names for each pitch class
const PITCH_NAMES = ['c', 'c#', 'd', 'd#', 'e', 'f', 'f#', 'g', 'g#', 'a', 'a#', 'b'];

// Duration thresholds in beats → VexFlow duration string
// Ordered from longest to shortest; we snap to nearest
const DURATION_TABLE = [
  { beats: 4,    vex: 'w',  dots: 0 },
  { beats: 3,    vex: 'h',  dots: 1 },
  { beats: 2,    vex: 'h',  dots: 0 },
  { beats: 1.5,  vex: 'q',  dots: 1 },
  { beats: 1,    vex: 'q',  dots: 0 },
  { beats: 0.75, vex: '8',  dots: 1 },
  { beats: 0.5,  vex: '8',  dots: 0 },
  { beats: 0.375,vex: '16', dots: 1 },
  { beats: 0.25, vex: '16', dots: 0 },
];

// Rest equivalents
const REST_TABLE = [
  { beats: 4,    vex: 'wr',  dots: 0 },
  { beats: 3,    vex: 'hr',  dots: 1 },
  { beats: 2,    vex: 'hr',  dots: 0 },
  { beats: 1.5,  vex: 'qr',  dots: 1 },
  { beats: 1,    vex: 'qr',  dots: 0 },
  { beats: 0.75, vex: '8r',  dots: 1 },
  { beats: 0.5,  vex: '8r',  dots: 0 },
  { beats: 0.25, vex: '16r', dots: 0 },
];

function midiToVexKey(midiNum) {
  const pitchClass = midiNum % 12;
  const octave = Math.floor(midiNum / 12) - 1;
  return `${PITCH_NAMES[pitchClass]}/${octave}`;
}

function snapDuration(beats, table) {
  let best = table[table.length - 1];
  let bestDist = Infinity;
  for (const entry of table) {
    const dist = Math.abs(beats - entry.beats);
    if (dist < bestDist) {
      bestDist = dist;
      best = entry;
    }
  }
  return best;
}

// Fill a gap with rests that sum to the given beat count
function fillWithRests(beats, clef) {
  if (beats <= 0.125) return [];
  const rests = [];
  let remaining = beats;

  while (remaining > 0.125) {
    const snap = snapDuration(remaining, REST_TABLE);
    const restKey = clef === 'treble' ? 'b/4' : 'd/3';
    rests.push({
      keys: [restKey],
      duration: snap.vex,
      dots: snap.dots,
      isRest: true,
    });
    remaining -= snap.beats;
    if (remaining < 0.125) break;
  }
  return rests;
}

// Group simultaneous notes into chords
function groupIntoChords(notes) {
  if (notes.length === 0) return [];
  const groups = [];
  let current = [notes[0]];

  for (let i = 1; i < notes.length; i++) {
    if (Math.abs(notes[i].beatPos - current[0].beatPos) < 0.05) {
      current.push(notes[i]);
    } else {
      groups.push(current);
      current = [notes[i]];
    }
  }
  groups.push(current);
  return groups;
}

export function midiToMeasures(midiObject) {
  if (!midiObject || !midiObject.tracks || midiObject.tracks.length === 0) {
    return { measures: [], timeSignature: [4, 4], bpm: 120 };
  }

  const header = midiObject.header;
  const bpm = header.tempos?.[0]?.bpm || 120;
  const timeSig = header.timeSignatures?.[0]?.timeSignature || [4, 4];
  const beatsPerMeasure = timeSig[0];
  const ppq = header.ppq || 480;

  // Collect all notes with beat positions
  const allNotes = [];
  for (const track of midiObject.tracks) {
    for (const note of track.notes) {
      const beatPos = note.ticks / ppq;
      const beatDur = note.durationTicks / ppq;
      allNotes.push({
        midi: note.midi,
        beatPos,
        beatDur,
        velocity: note.velocity,
        clef: note.midi < MIDI_SPLIT_POINT ? 'bass' : 'treble',
      });
    }
  }

  if (allNotes.length === 0) {
    return { measures: [], timeSignature: timeSig, bpm };
  }

  allNotes.sort((a, b) => a.beatPos - b.beatPos);

  // Determine total measures
  const lastBeat = Math.max(...allNotes.map(n => n.beatPos + n.beatDur));
  const totalMeasures = Math.ceil(lastBeat / beatsPerMeasure);

  const measures = [];

  for (let m = 0; m < totalMeasures; m++) {
    const measureStart = m * beatsPerMeasure;
    const measureEnd = measureStart + beatsPerMeasure;

    // Get notes that start in this measure
    const trebleNotes = allNotes
      .filter(n => n.clef === 'treble' && n.beatPos >= measureStart - 0.05 && n.beatPos < measureEnd - 0.05)
      .map(n => ({ ...n, beatPos: n.beatPos - measureStart }));
    const bassNotes = allNotes
      .filter(n => n.clef === 'bass' && n.beatPos >= measureStart - 0.05 && n.beatPos < measureEnd - 0.05)
      .map(n => ({ ...n, beatPos: n.beatPos - measureStart }));

    measures.push({
      treble: buildVoice(trebleNotes, beatsPerMeasure, 'treble'),
      bass: buildVoice(bassNotes, beatsPerMeasure, 'bass'),
      measureStart,
    });
  }

  return { measures, timeSignature: timeSig, bpm };
}

function buildVoice(notes, beatsPerMeasure, clef) {
  if (notes.length === 0) {
    // Whole rest for empty measure
    const restKey = clef === 'treble' ? 'b/4' : 'd/3';
    return [{ keys: [restKey], duration: 'wr', dots: 0, isRest: true }];
  }

  const chordGroups = groupIntoChords(notes);
  const voice = [];
  let currentBeat = 0;

  for (const group of chordGroups) {
    const chordBeat = group[0].beatPos;

    // Fill gap before this chord with rests
    if (chordBeat - currentBeat > 0.125) {
      voice.push(...fillWithRests(chordBeat - currentBeat, clef));
    }

    // Use shortest note in chord for duration (VexFlow chords share one duration)
    const minDur = Math.min(...group.map(n => n.beatDur));
    const snapped = snapDuration(minDur, DURATION_TABLE);

    // Clamp duration so it doesn't exceed measure boundary
    const remainingInMeasure = beatsPerMeasure - chordBeat;
    const finalSnap = snapped.beats > remainingInMeasure
      ? snapDuration(remainingInMeasure, DURATION_TABLE)
      : snapped;

    voice.push({
      keys: group.map(n => midiToVexKey(n.midi)).sort(),
      duration: finalSnap.vex,
      dots: finalSnap.dots,
      isRest: false,
      beatOffset: chordBeat,
    });

    currentBeat = chordBeat + finalSnap.beats;
  }

  // Fill trailing gap with rests
  if (beatsPerMeasure - currentBeat > 0.125) {
    voice.push(...fillWithRests(beatsPerMeasure - currentBeat, clef));
  }

  return voice;
}