heart_rate_simulator.js

var activities = {
  resting: { bpm: 70 },
  walking: { bpm: 90 },
  running: { bpm: 150 },
};

var activityStatus = {
  previousActivity: activities.resting,
  activity: activities.resting,
  inTransition: false,
  upDirectionTransition: false,
  currentTInterval: 0,
};

var interval = 500,
    secondsUntilBpmMax = 30,
    bpmOutputDelta = 2,
    tInterval = 0.15;

function getHeartRate(iteration, symetric) {
  t = tInterval * iteration;

  var b0 = 0.13,
    b1 = 0.49,
    b2 = 0.60,
    b3 = 0.90;

  var p1 = Math.pow(1 - t, 3) * b0,
    p2 = 3 * t * Math.pow(1 - t, 2) * b1,
    p3 = 3 * Math.pow(t, 2) * (1 - t) * b2,
    p4 = Math.pow(t, 3) * b3;

  var result = (p1 + p2 + p3 + p4);

  return symetric ? -result : result;
}

function setActivity(activity) {
  activityStatus.previousActivity = activityStatus.activity;
  switch(activity) {
    case 'resting':
      activityStatus.activity = activities.resting;
      break;
    case 'walking':
      activityStatus.activity = activities.walking;
      break;
    case 'running':
      activityStatus.activity = activities.running;
      break;
  }

  if(activityStatus.previousActivity.bpm > activityStatus.activity.bpm)
    startTransitionInUpDirection(false);
  else if(activityStatus.previousActivity.bpm < activityStatus.activity.bpm)
    startTransitionInUpDirection(true);
}

function startTransitionInUpDirection(upDirection) {
  activityStatus.inTransition = true;
  activityStatus.upDirectionTransition = upDirection;
  activityStatus.currentTInterval = 0;
}

function enterConstantActivity() {
  activityStatus.inTransition = false;
}
function startHeartRate() {
  setTimeout(function()
  {
    bpmDelta = 0;
    // Calculate bpm delta according to bpm in resting activity
    if(activityStatus.inTransition) {

      bpmDelta = getHeartRate(activityStatus.currentTInterval, !activityStatus.upDirectionTransition);
      activityStatus.currentTInterval++;
      if(activityStatus.upDirectionTransition && (bpmDelta + activityStatus.previousActivity.bpm) > activityStatus.activity.bpm)
      {
        console.log('bpmDelta: ' + bpmDelta);
        console.log('prev: ' + activityStatus.previousActivity.bpm);
        console.log('act: ' + activityStatus.activity.bpm);

        bpmDelta = activityStatus.activity.bpm - activityStatus.previousActivity.bpm;
        enterConstantActivity();
      }
      else if(!activityStatus.upDirectionTransition && (activityStatus.previousActivity.bpm + bpmDelta) <= activityStatus.activity.bpm)
      {
        console.log('bpmDelta: ' + bpmDelta);
        console.log('prev: ' + activityStatus.previousActivity.bpm);
        console.log('act: ' + activityStatus.activity.bpm);

        enterConstantActivity();
      }
    }
    else
      bpmDelta = activityStatus.activity.bpm - activityStatus.previousActivity.bpm;

    var range = Math.random() * 2;
    var delta = Math.random() >= 0.5 ? -range : range;
    var finalBpm = Math.floor(activityStatus.previousActivity.bpm + bpmDelta + delta);
    console.log(finalBpm);

    startHeartRate();
  }, interval);
}

startHeartRate();