//************************************************
// Author    - Jonathan Grant
// Copyright - Jonathan Grant, 2009
// E-mail    - Jonathan_Grant@jondaf.com
//************************************************

//************************************************
// This JavaScript code will enable three drop-down
// lists to be set up and displayed in a form to show
// dates and select them. It will check the selected
// year to see if it is a leap year and adjust the
// number of days in February to reflect this. It
// will also check the selected month and adjust
// the number of days available in it displayed.
//
// There are three SELECT statements required, for
// day, month and year. They can be in any order.
// The month and year SELECTs need an onChange
// event handler which calls the checkYear function
// to enable the corect number of days in the month
// to be available.
//
// The year SELECT can be one of three functions
// to display either a range of years from a given
// year to another given year, a range of years
// from a given year to a year calculated from the
// current year, or a range of years calculated
// from the current year.
//
// The reset function is necessary to reset the
// days in the month.
//************************************************


//************************************************
// Set up array of days in a month
//************************************************

monthDays = new Array(31,
                      28,
                      31,
                      30,
                      31,
                      30,
                      31,
                      31,
                      30,
                      31,
                      30,
                      31);

//************************************************
// Set up array of month names
//************************************************

monthName = new Array("January",
                      "February",
                      "March",
                      "April",
                      "May",
                      "June",
                      "July",
                      "August",
                      "September",
                      "October",
                      "November",
                      "December");

//************************************************
// Get todays date and year
//************************************************

todayDate = new Date();
todayDay = todayDate.getDate();
todayMonth = todayDate.getMonth();
todayYear = todayDate.getFullYear();

var defaultDaySelected;

//************************************************
// Function to check if a year is a leap year
//************************************************

function checkLeap(inYear) {
 isLeap = 0;

 if ((inYear % 4) == 0) {
  isLeap = 1;
 }

 if ((inYear % 100) == 0) {
  isLeap = 0;
  if ((inYear % 400) == 0) {
   isLeap = 1;
  }
 }
 return isLeap;
}

//************************************************
// Functions to display a drop-down showing a list
// of years in different ways
//************************************************

//************************************************
// This function displays variable years from
// this year - start to this year + end
//************************************************

function displayYearVariable(firstYear, lastYear, presetDate, preDate) {
 if (presetDate && (preDate != null)) {
  startDate = new Date(preDate);
  startDay = startDate.getDate();
  startMonth = startDate.getMonth();
  startYear = startDate.getFullYear();
 }
 else if (presetDate) {
  startDay = todayDay;
  startMonth = todayMonth;
  startYear = todayYear;
 }

 for (count = (todayYear - firstYear); count <= (todayYear + lastYear); count++) { 
  document.write("<OPTION VALUE='" + count + "'"); 
  if (presetDate && (count == startYear)) { 
   document.write(" SELECTED"); 
  } 
  document.write(">" + count + "</OPTION>"); 
 } 
} 

//************************************************ 
// This function displays variable years from 
// a static start year to this year + end 
//************************************************ 

function displayYearStaticStart(firstYear, lastYear, presetDate, preDate) { 
 if (presetDate && (preDate != null)) { 
  startDate = new Date(preDate); 
  startDay = startDate.getDate(); 
  startMonth = startDate.getMonth(); 
  startYear = startDate.getFullYear(); 
 } 
 else if (presetDate) { 
  startDay = todayDay; 
  startMonth = todayMonth; 
  startYear = todayYear; 
 } 

 for (count = firstYear; count <= (todayYear + lastYear); count++) { 
  document.write("<OPTION VALUE='" + count + "'"); 
  if (presetDate && (count == startYear)) { 
   document.write(" SELECTED"); 
  } 
  document.write(">" + count + "</OPTION>"); 
 } 
} 

//************************************************ 
// This function displays static years from 
// a start year to end year 
//************************************************ 

function displayYearStatic(firstYear, lastYear, presetDate, preDate) { 
 if (presetDate && (preDate != null)) { 
  startDate = new Date(preDate); 
  startDay = startDate.getDate(); 
  startMonth = startDate.getMonth(); 
  startYear = startDate.getFullYear(); 
 } 
 else if (presetDate) { 
  startDay = todayDay; 
  startMonth = todayMonth; 
  startYear = todayYear; 
 } 

 for (count = firstYear; count <= lastYear; count++) { 
  document.write("<OPTION VALUE='" + count + "'"); 
  if (presetDate && (count == startYear)) { 
   document.write(" SELECTED"); 
  } 
  document.write(">" + count + "</OPTION>"); 
 } 
} 

//************************************************ 
// Function to display a drop-down showing a list 
// of months 
//************************************************ 

function displayMonth(presetDate, preDate) { 
 if (presetDate && (preDate != null)) { 
  startDate = new Date(preDate); 
  startDay = startDate.getDate(); 
  startMonth = startDate.getMonth(); 
  startYear = startDate.getFullYear(); 
 } 
 else if (presetDate) { 
  startDay = todayDay; 
  startMonth = todayMonth; 
  startYear = todayYear; 
 } 

 for (count = 1; count <= 12; count++) { 
  document.write("<OPTION VALUE='"); 
  if (count < 10) { 
   document.write("0"); 
  } 
  document.write(count + "'"); 
  if (presetDate && ((count - 1) == startMonth)) { 
   document.write(" SELECTED"); 
  } 
  document.write(">" + monthName[count - 1] + "</OPTION>"); 
 } 
} 

//************************************************ 
// Function to display a drop-down showing a list 
// of dates, 01 to 31 
//************************************************ 

function displayDay(presetDate, preDate) { 
 if (presetDate && (preDate != null)) { 
  startDate = new Date(preDate); 
  startDay = startDate.getDate(); 
  startMonth = startDate.getMonth(); 
  startYear = startDate.getFullYear(); 
  countDays = monthDays[startMonth]; 
  leapYear = checkLeap(startYear); 

  defaultDaySelected = startDay; 
 } 
 else if (presetDate) { 
  startDay = todayDay; 
  startMonth = todayMonth; 
  startYear = todayYear; 
  countDays = monthDays[todayMonth]; 
  leapYear = checkLeap(startYear); 

  defaultDaySelected = startDay; 
 } 
 else { 
  startMonth = 0; 
  countDays = 31; 
  leapYear = 0; 
 } 

 if (startMonth == 1) { 
  countDays = countDays + leapYear; 
 } 

 for (count = 1; count <= countDays; count++) { 
  document.write("<OPTION VALUE='"); 
  if (count < 10) { 
   document.write("0"); 
  } 
  document.write(count + "'"); 
  if (presetDate && (count == startDay)) { 
   document.write(" SELECTED"); 
  } 
  document.write(">"); 
  if (count < 10) { 
   document.write("0"); 
  } 
  document.write(count + "</OPTION>"); 
 } 
} 

//************************************************ 
// Function to check the range of dates displayed 
// in the drop-down lists and to ensure that they 
// are valid, adjusting the available dates as 
// necessary 
// 
// This function requires three arguments: 
// dayObj - the drop-down day object (this.form.dayObjName) 
// monthObj - the drop-down month object (this.form.monthObjName) 
// yearObj - the drop-down year object (this.form.yearObjName) 
//************************************************ 

function checkYear(dayObj, monthObj, yearObj) { 
 yearValueInd = yearObj.selectedIndex; 
 yearValue = yearObj[yearValueInd].value; 
 monthValueInd = monthObj.selectedIndex; 
 monthValue = monthObj[monthValueInd].value; 
 dayValueInd = dayObj.selectedIndex; 
 dayValue = dayObj[dayValueInd].value; 

 dayValueSize = dayObj.length; 

 defaultDay = 0; 

 for (count = 1; count <= (dayValueSize - 1); count++) { 
  if (dayObj.options[count].defaultSelected) { 
   defaultDay = count; 
  } 
 } 

//************************************************ 
// Check whether the selected year is a leap year 
//************************************************ 

 leapYear = checkLeap(yearValue); 

//************************************************ 
// Get the number of days that the selected month 
// has in it 
//************************************************ 

 totalDays = monthDays[parseInt(monthValue, 10) - 1]; 

//************************************************ 
// Check whether the selected month is February 
// and if it is adjust the number of days in the 
// month if it is a leap year 
//************************************************ 

 if (monthValue == 2) { 
totalDays = totalDays + leapYear; 
 } 

//************************************************ 
// Adjust the day drop-down to show the correct 
// number of days available 
//************************************************ 

 dayObj.length = totalDays; 
 for (count = 1; count <= totalDays; count++) { 
  if (count < 10) { 
   countText = "0" + count; 
  } 
  else { 
   countText = count; 
  } 
  newOption = new Option(countText, count); 
  dayObj.options[count - 1] = newOption; 
 } 

//************************************************ 
// Adjust the day currently displayed in the day 
// drop down if it would now be outside of the 
// number of actual days in the displayed month 
//************************************************ 

 if (totalDays <= dayValueInd) { 
  dayValueInd = (totalDays - 1); 
 } 
 dayObj.selectedIndex = dayValueInd; 

 if (totalDays <= defaultDay) { 
  dayObj.options[totalDays - 1].defaultSelected = true; 
 } 
 else { 
  dayObj.options[defaultDay].defaultSelected = true; 
 } 
} 

/********************************************* 
 * Reset function. This is necessary in case * 
 * a default start date has been used        * 
 *********************************************/ 

function formReset(formObj, dayObj, monthObj, yearObj, presetDate, preDate) { 
 if (presetDate && (preDate != null)) { 
  startDate = new Date(preDate); 
  startDay = startDate.getDate(); 
  startMonth = startDate.getMonth(); 
  startYear = startDate.getFullYear(); 

  countDays = monthDays[startMonth]; 
  defaultDaySelected = startDay; 
 } 
 else if (presetDate) { 
  startDay = todayDay; 
  startMonth = todayMonth; 
  startYear = todayYear; 

  countDays = monthDays[startMonth]; 
  defaultDaySelected = startDay; 
 } 
 else { 
  countDays = 31; 
 } 

 leapYear = checkLeap(startYear); 
 if (startMonth == 1) { 
  countDays = countDays + leapYear; 
 } 

 dayObj.length = countDays; 
 for (count = 1; count <= countDays; count++) { 
  if (count < 10) { 
   countText = "0" + count; 
  } 
  else { 
   countText = count; 
  } 
  newOption = new Option(countText, count); 
  dayObj.options[count - 1] = newOption; 
 } 

 if (presetDate) { 
  dayObj.options[defaultDaySelected - 1].defaultSelected = true; 
 } 

 return true; 
}