// these are human-readable month name labels, in order
cal_months_labels = ['January', 'February', 'March', 'April',
                     'May', 'June', 'July', 'August', 'September',
                     'October', 'November', 'December'];

// these are the days of the week for each month, in order
cal_days_in_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

// this is the current date
var cal_current_date = new Date();

function Calendar(month, year) {
  this.month = (isNaN(month) || month == null) ? cal_current_date.getMonth() : month;
  this.year  = (isNaN(year) || year == null) ? cal_current_date.getFullYear() : year;
}

Calendar.prototype.generateHTML = function(){

  // get first day of month
  var firstDay = new Date(this.year, this.month, 1);
  var startingDay = firstDay.getDay();
 
  // find number of days in month
  var monthLength = cal_days_in_month[this.month];
 
  // compensate for leap year
  if (this.month == 1) { // February only!
    if((this.year % 4 == 0 && this.year % 100 != 0) || this.year % 400 == 0){
      monthLength = 29;
    }
  }

  // get todays date
  var cal_today_date = new Date();
  checkDay = (cal_today_date.getMonth() == this.month && cal_today_date.getFullYear() == this.year) ? true : false;
 
  // do the header
  var monthName = cal_months_labels[this.month]
  var html = '<table class="calendar-table" cellpadding="4" cellspacing="0">';
  html += '<tr><th><a href="javascript:cal.prevMonth()">&#171;</a></th><th colspan="5">';
  html +=  monthName + "&nbsp;" + this.year;
  html += '</th><th><a href="javascript:cal.nextMonth()">&#187;</a></th></tr>';
  html += '<tr class="calendar-header">';
  for(var i = 0; i <= 6; i++ ){
    html += '<td class="calendar-header-day">';
    html += cal_days_labels[i];
    html += '</td>';
  }
  html += '</tr><tr>';

  // fill in the days
  var day = 1;
  // this loop is for is weeks (rows)
  for (var i = 0; i < 9; i++) {
    // this loop is for weekdays (cells)
    for (var j = 0; j <= 6; j++) {
      html += '<td class="calendar-day">';
      if (day <= monthLength && (i > 0 || j >= startingDay)) {
        ts = this.generateTimestamp(day);
        if (checkDay == true && day == cal_today_date.getDate())
          html += '<a class="today" href="javascript:void(0)">' + day + '</a>';
        else
          html += '<a href="javascript:void(0)">' + day + '</a>';
        day++;
      }
      html += '</td>';
    }
    // stop making rows if we've run out of days
    if (day > monthLength) {
      break;
    } else {
      html += '</tr><tr>';
    }
  }
  html += '</tr></table>';
  document.getElementById('calendar-holder').innerHTML = html;
}

Calendar.prototype.generateTimestamp = function(day) {
  month = this.month + 1;
  return "'" + day + "','" + month + "','" + this.year + "'";
}

Calendar.prototype.prevMonth = function() {
  if (this.month == 0) {
    this.month = 12;
    this.year = (this.year - 1);
  }
  this.month = (this.month - 1);
  this.generateHTML();
}

Calendar.prototype.nextMonth = function() {
  if (this.month == 11) {
    this.month = -1;
    this.year = (this.year + 1);
  }
  this.month = (this.month + 1);
  this.generateHTML();
}