export class Metronome {
 constructor()  {
  this.context = new (window.AudioContext || window.webkitAudioContext)();
  this.loadBuffer();
 }

 loadBuffer(url="pulse.ogg") {
  var request = new XMLHttpRequest();
  request.open("GET", url, true);
  request.responseType = "arraybuffer";
  request.onload = () => this.context.decodeAudioData(request.response, (buffer) => this.buffer = buffer);
  request.send();
 }

 play(beats) {
  this.stop();
  this.src = this.context.createBufferSource();
  this.src.buffer = this.extendBuffer(beats, this.buffer);
  this.src.loop = true;
  this.src.connect(this.context.destination);
  this.src.start();
 }

 stop() {
  ("src" in this)?this.src.stop():"";
 }

 extendBuffer(beats, buffer) {
   var total = 60/beats * buffer.sampleRate;
   var ext = this.context.createBuffer(buffer.numberOfChannels, total, buffer.sampleRate);
   for(let i=0; i<buffer.numberOfChannels; i++)
     ext.getChannelData(i).set(buffer.getChannelData(i));
   return ext;
 }
}