//************************************************
// Author    - Jonathan Grant
// Copyright - Jonathan Grant, 2002
// 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 dateReset(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;
}