var NumberOfLayers = 7;
var min_num = 1;
var max_num = NumberOfLayers;
var diff = max_num - min_num + 1 ;
var randnum = Math.floor(Math.random() * diff + min_num);
var currentLayer = randnum;
var aBPaused = 0;
var timerInt1;
var b = 'b';
var n = 'n';
var abPause = '<a href="javascript:;" onclick="clrDelay()">Pause</a>';
var abPlay = '<a href="javascript:;" onclick="setDelay()">Play</a>';
var abNav = '<<a href="javascript:;" onclick="switchLayer(' + b + ')">Back</a>&nbsp;&nbsp;<a href="javascript:;" onclick="switchLayer(' + n + ')">Next</a>>';

function switchLayer(navType) {
  document.getElementById("ab"+currentLayer).style.visibility = "hidden";
  switch (navType) {
    case "n":
    case "s":
      if (currentLayer>=NumberOfLayers) {
        currentLayer=1;
      } else {
        currentLayer++;
      }
      break;
    case "b":
      currentLayer--;
      if (currentLayer<1) {
        currentLayer=NumberOfLayers;
      }
      break;
  }
  document.getElementById("ab"+currentLayer).style.visibility = "visible";
}

function displayNav() {
  for (var i = 1; i<=NumberOfLayers; i++) {
    document.getElementById("an"+i).innerHTML = abNav;
  }
  document.getElementById("ab"+currentLayer).style.visibility = "visible";
}

function clrDelay() {
  clearInterval(timerInt1);
  aBPaused = 1;
  document.getElementById("pp1").innerHTML = abPlay;
  document.getElementById("pp2").innerHTML = abPlay;
  document.getElementById("pp3").innerHTML = abPlay;
  document.getElementById("pp4").innerHTML = abPlay;
  document.getElementById("pp5").innerHTML = abPlay;
  document.getElementById("pp6").innerHTML = abPlay;
  document.getElementById("pp7").innerHTML = abPlay;
}

function setDelay() {
  timerInt1 = setInterval("switchLayer('s')",10100);
  aBPaused = 0;
  document.getElementById("pp1").innerHTML = abPause;
  document.getElementById("pp2").innerHTML = abPause;
  document.getElementById("pp3").innerHTML = abPause;
  document.getElementById("pp4").innerHTML = abPause;
  document.getElementById("pp5").innerHTML = abPause;
  document.getElementById("pp6").innerHTML = abPause;
  document.getElementById("pp7").innerHTML = abPause;
}