function focusInput(id) {
  var element = docById(id);
  if (element == null) element = $("[name=" + name + "]")[0];
  
  if (element) {
    element.focus();
  }
}

function docById(id) {
  return document.getElementById(id);
}

function getQueryArg(arg) {
  var query = window.location.search.substring(1);
  var vars = query.split("&");
  for (var i=0;i<vars.length;i++) {
    var pair = vars[i].split("=");
    if (pair[0] == arg) {
      return pair[1];
    }
  }
}

function setFieldWatermark(field, watermark) {
  $("input[name=" + field + "]").each(function () {
    if ($(this).val().length == 0) $(this).val(watermark).addClass("watermark");
    
    $(this).focus(function () {
      if ($(this).hasClass("watermark")) $(this).val("").removeClass("watermark");
    });
    
    $(this).blur(function () {
      if ($(this).val().length == 0) $(this).val(watermark).addClass("watermark");
    });
  });
}

function startSpinner(e) {
  $("<img />", { src: "/images/ajax-loader.gif" }).addClass("spinner").appendTo(e);
}

function stopSpinner(e) {
  $(e).find("img.spinner").remove();
}

function setSessionVar(variable, value, cb) {
  $.ajax({
      type: "POST",
      url: "/includes/ajax/ajax_set_session_var.php",
      dataType: "json",
      data: { variable: variable, value: value },
      success: function(response) {
        if (typeof(cb) == "function") {
          cb(response);
        }
      }
  });
}