jQuery(document).ready(function()
{
  jQuery("#btnGetMatches").click(buttonClick);
});


function buttonClick(event)
{
  var yearToMatch = jQuery("#txtYearToMatch").val();
  var startYear = jQuery("#txtStartYear").val();
  var endYear   = jQuery("#txtEndYear").val();
  
  // Make sure all three inputs are years >= 1582.
  if (!isYear(yearToMatch) || !isYear(startYear) || !isYear(endYear))
  {
    alert("Enter year and range, then click button.");
    return;
  }
  
  if ((endYear - startYear) > 400)
  {
    alert("Range must be <= 400");
    return;
  }
  
  // First day of year (month 0, day 1).
  var d = new Date(yearToMatch, 0, 1);
  
  // Day of week for first day of year (0 = Sun, 1 = Mon, ..)
  var firstDay = d.getDay();
  
  // Have leap year iff February has 29 days.
  isLeapYear = ((new Date(yearToMatch, 1, 29)).getMonth() == 1);
 
  // To hold matching years.
  var matches = new Array();
 
  // Have matching year iff first day and leap year status the same.
  for (var year = startYear; year <= endYear; year++)
  {
    var d1 = new Date(year, 0, 1);
    var firstDay1 = d1.getDay();
    isLeapYear1 = ((new Date(year, 1, 29)).getMonth() == 1);
    if ((firstDay1 == firstDay) && (isLeapYear1 == isLeapYear))
      matches.push(year);
  } // for year
 
  // html to poke into result box at bottom.
  var html = "";
  if (matches.length == 0)
  {
    html  = "No matches for <b>" + yearToMatch + "</b> between ";
    html += "<b>" + startYear + "</b> and <b>" + endYear + "</b>."
  }
  else
  {
    html  = "Matches for <b>" + yearToMatch + "</b>: ";
    html += "<p>";
    for (var k = 0; k < matches.length; k++)
      html += "" + matches[k] + ", ";
    // Remove last comma and space.
    html = html.substring(0, html.length - 2);
    html += "</p>";
  }
 
  jQuery("#matches").html(html);
 
} // function buttonClick


function isYear(year)
{
  var regExp = /^\d{4}$/;
  return (regExp.test(year) && (year >= 1582));
}