function ajaxRequest(){
  var activexmodes=["Msxml2.XMLHTTP", "Microsoft.XMLHTTP"]; //activeX versions to check for in IE
  if (window.ActiveXObject){ //Test for support for ActiveXObject in IE first (as XMLHttpRequest in IE7 is broken)
    for (var i=0; i<activexmodes.length; i++){
      try{
        return new ActiveXObject(activexmodes[i]);
      }
      catch(e){
     //suppress error
      }
    }
  }
  else if (window.XMLHttpRequest) // if Mozilla, Safari etc
  return new XMLHttpRequest();
  else
  return false;
 }
 var mygetrequest=new ajaxRequest();
 mygetrequest.onreadystatechange=function(){
  if (mygetrequest.readyState==4){
   if (mygetrequest.status==200 || window.location.href.indexOf("http")==-1){
    var jsondata=eval("("+mygetrequest.responseText+")"); //retrieve result as an JavaScript object
    var sheetlist=jsondata.sheets;
    var output='';
      for (var i=0; i<sheetlist.length; i++){
        output+='<div class="fl"><input type="radio" class="radio" name="input_sheet" value="'+sheetlist[i].price+'">\n';
        output+='<label>'+sheetlist[i].sheet+'</label></div>';
      }
      document.getElementById("radio").innerHTML=output;
   }
   else{
    alert("An error has occured making the request");
   }
  }
};
 
mygetrequest.open("GET", "data/sheets.json", true);
mygetrequest.send(null);


function calculatePrice() {
  if (!document.getElementById) return false;
  if (!document.getElementById("calc")) return false;   
  var btn = document.getElementById("calc");
  btn.onclick = function() {
    var areaLength = parseFloat(document.formArea.input_length.value);
    var areaWidth = parseFloat(document.formArea.input_width.value);
    if ((areaLength <= 0) || (areaWidth <= 0)) {
      alert("Please enter a number greater than zero");
      return false;
    }
    if ((isNaN(areaWidth)) || (isNaN(areaLength))) {
      alert("Please enter a valid number.\nDecimals are allowed");
      return false;
    }
    var sheettype = document.formArea.input_sheet;
    for (var i=0; i<sheettype.length; i++) {
      if (sheettype[i].checked == 1) {
        var chosen = 1;
      } 
    }
    if (chosen == null) {
      alert("Please select a sheet type");
      return false;
    }
    for (var i=0; i<sheettype.length; i++) {
      if (sheettype[i].checked == 1) {
        var sheetprice = sheettype[i].value;
        cost = sheetprice * areaWidth * areaLength;
        cost = cost.toFixed(2);
      }
      document.formArea.output_cost.value = '\u00A3'+cost;
    };
  };
}

addLoadEvent(ajaxRequest);
addLoadEvent(calculatePrice);