app/src/utils/midiHelpers.js

import { MIDI_SPLIT_POINT } from './colorScheme';

// Piano range: C2 (36) to C7 (96)
export const LOWEST_NOTE = 36;
export const HIGHEST_NOTE = 96;

const BLACK_KEY_OFFSETS = new Set([1, 3, 6, 8, 10]);

export function isBlackKey(midiNumber) {
  return BLACK_KEY_OFFSETS.has(midiNumber % 12);
}

/**
 * Build an array of key objects with pixel positions for a given canvas width.
 * Returns [{ midiNumber, x, width, isBlack }]
 */
export function buildKeyboardLayout(canvasWidth) {
  // Count white keys in range
  const keys = [];
  const whiteKeys = [];
  for (let midi = LOWEST_NOTE; midi <= HIGHEST_NOTE; midi++) {
    if (!isBlackKey(midi)) {
      whiteKeys.push(midi);
    }
  }

  const whiteKeyWidth = canvasWidth / whiteKeys.length;
  const blackKeyWidth = whiteKeyWidth * 0.6;

  // Position white keys
  const keyMap = new Map();
  whiteKeys.forEach((midi, i) => {
    keyMap.set(midi, {
      midiNumber: midi,
      x: i * whiteKeyWidth,
      width: whiteKeyWidth,
      isBlack: false,
    });
  });

  // Position black keys between their adjacent white keys
  for (let midi = LOWEST_NOTE; midi <= HIGHEST_NOTE; midi++) {
    if (isBlackKey(midi)) {
      // Find the white key just below this black key
      const prevWhite = keyMap.get(midi - 1);
      if (prevWhite) {
        keyMap.set(midi, {
          midiNumber: midi,
          x: prevWhite.x + prevWhite.width - blackKeyWidth / 2,
          width: blackKeyWidth,
          isBlack: true,
        });
      }
    }
  }

  // Return sorted by MIDI number
  for (let midi = LOWEST_NOTE; midi <= HIGHEST_NOTE; midi++) {
    if (keyMap.has(midi)) {
      keys.push(keyMap.get(midi));
    }
  }

  return keys;
}

/**
 * Get the x position and width for a falling note block.
 */
export function noteXPosition(midiNumber, keyboardLayout) {
  const key = keyboardLayout.find((k) => k.midiNumber === midiNumber);
  if (key) return { x: key.x, width: key.width };

  // Clamp to range
  if (midiNumber < LOWEST_NOTE) {
    const first = keyboardLayout[0];
    return { x: first.x, width: first.width };
  }
  const last = keyboardLayout[keyboardLayout.length - 1];
  return { x: last.x, width: last.width };
}

// Build a fast lookup map for noteXPosition (avoids .find() per note per frame)
export function buildNotePositionMap(keyboardLayout) {
  const map = new Map();
  for (const key of keyboardLayout) {
    map.set(key.midiNumber, { x: key.x, width: key.width });
  }
  return map;
}

export function noteXPositionFast(midiNumber, positionMap) {
  const pos = positionMap.get(midiNumber);
  if (pos) return pos;

  // Clamp
  if (midiNumber < LOWEST_NOTE) return positionMap.get(LOWEST_NOTE);
  return positionMap.get(HIGHEST_NOTE);
}

/**
 * Parse a Midi object (from @tonejs/midi) into our note format.
 */
export function parseMidiFile(midiObject) {
  const notes = [];

  midiObject.tracks.forEach((track) => {
    const program = track.instrument?.number ?? 0;
    const instrument = (program >= 32 && program <= 39) ? 'bass' : 'piano';

    track.notes.forEach((note) => {
      notes.push({
        midi: note.midi,
        name: note.name,
        time: note.time,
        duration: note.duration,
        velocity: note.velocity,
        hand: note.midi < MIDI_SPLIT_POINT ? 'left' : 'right',
        instrument,
      });
    });
  });

  // Sort by start time
  notes.sort((a, b) => a.time - b.time);

  const totalDuration =
    notes.length > 0
      ? Math.max(...notes.map((n) => n.time + n.duration))
      : 0;

  return { notes, totalDuration };
}

/**
 * Get notes visible in the current time window using binary search.
 * Notes array must be sorted by `time` (start time).
 */
export function getVisibleNotes(
  notes,
  currentTime,
  lookAheadSeconds,
  maxPastSeconds = 1
) {
  const endTime = currentTime + lookAheadSeconds;

  // Find the longest note duration so we can search far enough back
  // to catch long-held notes that started early but are still visible.
  // Precompute once on first call via a cached property.
  if (notes._maxDur == null) {
    let mx = 0;
    for (let i = 0; i < notes.length; i++) {
      if (notes[i].duration > mx) mx = notes[i].duration;
    }
    notes._maxDur = mx;
  }
  const searchBack = maxPastSeconds + notes._maxDur;

  // Binary search on `time` (which IS sorted) to find the earliest
  // note that could possibly still be visible.
  const earliest = currentTime - searchBack;
  let lo = 0;
  let hi = notes.length;
  while (lo < hi) {
    const mid = (lo + hi) >> 1;
    if (notes[mid].time < earliest) {
      lo = mid + 1;
    } else {
      hi = mid;
    }
  }

  const cutoff = currentTime - maxPastSeconds;
  const result = [];
  for (let i = lo; i < notes.length && notes[i].time < endTime; i++) {
    // Only include if the note hasn't fully ended before the visible window
    if (notes[i].time + notes[i].duration >= cutoff) {
      result.push(notes[i]);
    }
  }
  return result;
}