webdaw-modules/src/createNotes.ts

a set of modules for building a web-based DAW

import { MIDIEvent, NoteEvent, NoteOnEvent, NoteOffEvent } from "./MIDIEvent";

// MIDIEventGeneric and MIDINoteGeneric are declared to support other MIDI playback libraries such as heartbeat
export interface MIDIEventGeneric {
  id?: string;
  bar?: number;
  ticks: number;
  noteNumber: number;
  trackId?: string;
}

export interface MIDINoteGeneric {
  id: string;
  noteOn: MIDIEventGeneric;
  noteOff: MIDIEventGeneric;
}

export interface MIDINote extends MIDINoteGeneric {
  noteOn: NoteOnEvent;
  noteOff: NoteOffEvent;
  durationTicks?: number;
  durationMillis?: number;
  startTicks?: number;
  endTicks?: number;
  startMillis?: number;
  endMillis?: number;
}

let index = 0;

export const createNotes = (events: MIDIEvent[]): MIDINote[] => {
  let filtered: NoteEvent[] = events.reduce((acc, val) => {
    // console.log(val.type);
    if (val.type === 0x80 || val.type === 0x90) {
      acc.push(val as NoteEvent);
    }
    return acc;
  }, [] as NoteEvent[]);
  // filtered = sortMIDIEvents(filtered);
  const notes: MIDINote[] = [];
  const tmp: { [id: string]: NoteEvent } = {};
  filtered.forEach(e => {
    const id = `${e.trackId}-${e.noteNumber}`;
    // console.log(e.ticks, e.type, id);
    if (e.type === 0x90) {
      if (tmp[id]) {
        // console.warn(`note existed already! ${id}`);
      } else {
        tmp[id] = e;
      }
    } else if (e.type === 0x80) {
      if (!tmp[id]) {
        // console.warn(`note doesn't exist! ${id}`);
      } else {
        const noteOn = tmp[id];
        const note: MIDINote = {
          id: `note-${new Date().getTime()}-${index++}`,
          noteOn: noteOn as NoteOnEvent,
          noteOff: e,
          // durationTicks: e.ticks - noteOn.ticks,
          // durationMillis: e.millis - noteOn.millis,
          // startTicks: noteOn.ticks,
          // startMillis: noteOn.millis,
          // endTicks: e.ticks,
          // endMillis: e.millis,
        };
        notes.push(note);
        delete tmp[id];
      }
    }
  });
  // console.log(notes);
  return notes;
};