function handleUpdate() {
  resp = httpGet("/api/v1/data");

  var data = JSON.parse(resp);
  if (data.mode == "clock") {
    document.getElementById("timer").innerHTML = getTime();
    document.getElementById("testImg").style.display = "none";

  } else if (data.mode == "timer") {
    document.getElementById("timer").innerHTML = data.timeLeft;
    document.getElementById("testImg").style.display = "none";

  } else if (data.mode == "black") {
    document.getElementById("timer").innerHTML = "";
    document.getElementById("testImg").style.display = "none";
    
  } else if (data.mode == "test") {
    document.getElementById("timer").innerHTML = "";
    document.getElementById("testImg").style.display = "block";
  }
}

function httpGet(theUrl) {
  var xmlHttp = new XMLHttpRequest();
  xmlHttp.open("GET", theUrl, false); // false for synchronous request
  xmlHttp.send(null);
  return xmlHttp.responseText;
}

function getTime() {
  var date = new Date();
  var h = date.getHours(); // 0 - 23
  var m = date.getMinutes(); // 0 - 59
  var s = date.getSeconds(); // 0 - 59

  h = h < 10 ? "0" + h : h;
  m = m < 10 ? "0" + m : m;
  s = s < 10 ? "0" + s : s;

  var time = h + ":" + m + ":" + s;
  return time;
}

setInterval(handleUpdate, 50);