// marco tarini

var nHistory = 0;
var curHistory = 0;
var maxHistory = 3;

function displayHistory(){
  var i;
  
  for (i=1; i<=nHistory; i++) {
    var el = document.getElementById("history"+i);
    if (i>curHistory-maxHistory && i<=curHistory) el.style.display="inline-block";
	else el.style.display="none";
  }
  
  var up = document.getElementById("historyUp");
  var dn = document.getElementById("historyDown");
  if (curHistory<  nHistory) up.style.visibility="visible"; else up.style.visibility="hidden";
  if (curHistory>maxHistory) dn.style.visibility="visible"; else dn.style.visibility="hidden";
}

function startHistory(){
  nHistory = 0;
  while (1) {
    if (document.getElementById("history"+(nHistory+1))!=null) nHistory++; else break;
  }
  curHistory = nHistory;
  displayHistory();
}

function scrollHistoryUp(){
  curHistory++;
  displayHistory();
}

function scrollHistoryDown(){
  curHistory--;
  displayHistory();
}