/**
This is a JavaScript library that will allow you to easily add some basic DHTML
drop-down datepicker functionality to your forms and pages. This script is not as
full-featured as others you may find on the Internet, but it's free, it's easy to
understand, and it's easy to change.

You'll also want to include a stylesheet that makes the datepicker elements
look nice. Example styles have been included directly in this HTML page for ease
of reference.

I've tested this lightly with Internet Explorer 6 and Mozilla Firefox. I have no idea
how compatible it is with other browsers. You are free to use this in any way you'd
like, with no charge or obligation.

version 1.4
December 20, 2004
Julian Robichaux -- http://www.nsftools.com

HISTORY
--  version 1.0 (Sept. 4, 2004):
Initial release.

--  version 1.1 (Sept. 5, 2004):
Added capability to define the date format to be used, either globally (using the
defaultDateSeparator and defaultDateFormat variables) or when the displayDatePicker
function is called.

--  version 1.2 (Sept. 7, 2004):
Fixed problem where datepicker x-y coordinates weren't right inside of a table.
Fixed problem where datepicker wouldn't display over selection lists on a page.
Added a call to the datePickerClosed function (if one exists) after the datepicker 
is closed, to allow the developer to add their own custom validation after a date
has been chosen. For this to work, you must have a function called datePickerClosed
somewhere on the page, that accepts a field object as a parameter. See the
example in the comments of the updateDateField function for more details.

--  version 1.3 (Sept. 9, 2004)
Fixed problem where adding the <div> and <iFrame> used for displaying the datepicker
was causing problems on IE 6 with global variables that had handles to objects on
the page (I fixed the problem by adding the elements using document.createElement()
and document.body.appendChild() instead of document.body.innerHTML += ...).

--  version 1.4 (Dec. 20, 2004)
Added "targetDateField.focus();" to the updateDateField function (as suggested 
by Alan Lepofsky) to avoid a situation where the cursor focus is at the top of the 
form after a date has been picked. Added "padding: 0px;" to the dpButton CSS 
style, to keep the table from being so wide when displayed in Firefox.
*/

var datePickerDivID = "datepicker";
var iFrameDivID = "datepickeriframe";

var dayArrayShort = new Array('Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa');
var dayArrayMed = new Array('Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat');
var dayArrayLong = new Array('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday');
var monthArrayShort = new Array('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
var monthArrayMed = new Array('Jan', 'Feb', 'Mar', 'Apr', 'May', 'June', 'July', 'Aug', 'Sept', 'Oct', 'Nov', 'Dec');
var monthArrayLong = new Array('January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December');
  
  // these variables define the date formatting we're expecting and outputting.
  // If you want to use a different format by default, change the defaultDateSeparator
  // and defaultDateFormat variables either here or on your HTML page.
  var defaultDateSeparator = "/";		// common values would be "/" or "."
  var defaultDateFormat = "mdy"	// valid values are "mdy", "dmy", and "ymd"
  var dateSeparator = defaultDateSeparator;
  var dateFormat = defaultDateFormat;

  /**
  This is the main function you'll call from the onClick event of a button.
  Normally, you'll have something like this on your HTML page:

  Start Date: <input name="StartDate"> 
  <input type=button value="select" onclick="displayDatePicker('StartDate');">

  That will cause the datepicker to be displayed beneath the StartDate field and
  any date that is chosen will update the value of that field. If you'd rather have the
  datepicker display beneath the button that was clicked, you can code the button
  like this:

  <input type=button value="select" onclick="displayDatePicker('StartDate', this);">

  So, pretty much, the first argument (dateFieldName) is a string representing the
  name of the field that will be modified if the user picks a date, and the second
  argument (displayBelowThisObject) is optional and represents an actual node
  on the HTML document that the datepicker should be displayed below.

  In version 1.1 of this code, the dtFormat and dtSep variables were added, allowing
  you to use a specific date format or date separator for a given call to this function.
  Normally, you'll just want to set these defaults globally with the defaultDateSeparator
  and defaultDateFormat variables, but it doesn't hurt anything to add them as optional
  parameters here. An example of use is:

  <input type=button value="select" onclick="displayDatePicker('StartDate', false, 'dmy', '.');">

  This would display the datepicker beneath the StartDate field (because the 
  displayBelowThisObject parameter was false), and update the StartDate field with
  the chosen value of the datepicker using a date format of dd.mm.yyyy
  */
  function displayDatePicker(dateFieldName, displayBelowThisObject, dtFormat, dtSep)
  {
    var targetDateField = document.getElementsByName(dateFieldName).item(0);
	  
	    // if we weren't told what node to display the datepicker beneath, just display it
		  // beneath the date field we're updating
		    if (!displayBelowThisObject)
			    displayBelowThisObject = targetDateField;
				  
				    // if a date separator character was given, update the dateSeparator variable
					  if (dtSep)
					      dateSeparator = dtSep;
						    else
							    dateSeparator = defaultDateSeparator;
								  
								    // if a date format was given, update the dateFormat variable
									  if (dtFormat)
									      dateFormat = dtFormat;
										    else
											    dateFormat = defaultDateFormat;
												  
												    var x = displayBelowThisObject.offsetLeft;
													  var y = displayBelowThisObject.offsetTop + displayBelowThisObject.offsetHeight;
													    
														  // deal with elements inside tables and such
														    var parent = displayBelowThisObject;
															  while (parent.offsetParent) {
															      parent = parent.offsetParent;
																      x += parent.offsetLeft;
																	      y += parent.offsetTop;
																		    }
																			  
																			    drawDatePicker(targetDateField, x, y);
																				}


																				/**
																				Draw the datepicker object (which is just a table with calendar elements) at the
																				specified x and y coordinates, using the targetDateField object as the input tag
																				that will ultimately be populated with a date.

																				This function will normally be called by the displayDatePicker function.
																				*/
																				function drawDatePicker(targetDateField, x, y)
																				{
																				  var dt = getFieldDate(targetDateField.value);
																				    
																					  // the datepicker table will be drawn inside of a <div> with an ID defined by the
																					    // global datePickerDivID variable. If such a div doesn't yet exist on the HTML
																						  // document we're working with, add one.
																						    if (!document.getElementById(datePickerDivID)) {
																							    // don't use innerHTML to update the body, because it can cause global variables
																								    // that are currently pointing to objects on the page to have bad references
																									    //document.body.innerHTML += "<div id='" + datePickerDivID + "' class='dpDiv'></div>";
																										    var newNode = document.createElement("div");
																											    newNode.setAttribute("id", datePickerDivID);
																												    newNode.setAttribute("class", "dpDiv");
																													    newNode.setAttribute("style", "visibility: hidden;");
																														    document.body.appendChild(newNode);
																															  }
																															    
																																  // move the datepicker div to the proper x,y coordinate and toggle the visiblity
																																    var pickerDiv = document.getElementById(datePickerDivID);
																																	  pickerDiv.style.position = "absolute";
																																	    pickerDiv.style.left = x + "px";
																																		  pickerDiv.style.top = y + "px";
																																		    pickerDiv.style.visibility = (pickerDiv.style.visibility == "visible" ? "hidden" : "visible");
																																			  pickerDiv.style.zIndex = 10000;
																																			    
																																				  // draw the datepicker table
																																				    refreshDatePicker(targetDateField.name, dt.getFullYear(), dt.getMonth(), dt.getDate());
																																					}


																																					/**
																																					This is the function that actually draws the datepicker calendar.
																																					*/
																																					function refreshDatePicker(dateFieldName, year, month, day)
																																					{
																																					  // if no arguments are passed, use today's date; otherwise, month and year
																																					    // are required (if a day is passed, it will be highlighted later)
																																						  var thisDay = new Date();
																																						    
																																							  if ((month >= 0) && (year > 0)) {
																																							      thisDay = new Date(year, month, 1);
																																								    } else {
																																									    day = thisDay.getDate();
																																										    thisDay.setDate(1);
																																											  }
																																											    
																																												  // the calendar will be drawn as a table
																																												    // you can customize the table elements with a global CSS style sheet,
																																													  // or by hardcoding style and formatting elements below
																																													    var crlf = "\r\n";
																																														  var TABLE = "<table cols=7 class='dpTable'>" + crlf;
																																														    var xTABLE = "</table>" + crlf;
																																															  var TR = "<tr class='dpTR'>";
																																															    var TR_title = "<tr class='dpTitleTR'>";
																																																  var TR_days = "<tr class='dpDayTR'>";
																																																    var TR_todaybutton = "<tr class='dpTodayButtonTR'>";
																																																	  var xTR = "</tr>" + crlf;
																																																	    var TD = "<td class='dpTD'";	// leave this tag open, because we'll be adding an onClick event
																																																		  var TD_title = "<td colspan=5 class='dpTitleTD'>";
																																																		    var TD_buttons = "<td class='dpButtonTD'>";
																																																			  var TD_todaybutton = "<td colspan=7 class='dpTodayButtonTD'>";
																																																			    var TD_days = "<td class='dpDayTD'>";
																																																				  var TD_selected = "<td class='dpDayHighlightTD'";	// leave this tag open, because we'll be adding an onClick event
																																																				    var xTD = "</td>" + crlf;
																																																					  var DIV_title = "<div class='dpTitleText'>";
																																																					    var DIV_selected = "<div class='dpDayHighlight'>";
																																																						  var xDIV = "</div>";
																																																						    
																																																							  // start generating the code for the calendar table
																																																							    var html = TABLE;
																																																								  
																																																								    // this is the title bar, which displays the month and the buttons to
																																																									  // go back to a previous month or forward to the next month
																																																									    html += TR_title;
																																																										  html += TD_buttons + getButtonCode(dateFieldName, thisDay, -1, "&lt;") + xTD;
																																																										    html += TD_title + DIV_title + monthArrayLong[thisDay.getMonth()] + " " + thisDay.getFullYear() + xDIV + xTD;
																																																											  html += TD_buttons + getButtonCode(dateFieldName, thisDay, 1, "&gt;") + xTD;
																																																											    html += xTR;
																																																												  
																																																												    // this is the row that indicates which day of the week we're on
																																																													  html += TR_days;
																																																													    for(i = 0; i < dayArrayShort.length; i++)
																																																														    html += TD_days + dayArrayShort[i] + xTD;
																																																															  html += xTR;
																																																															    
																																																																  // now we'll start populating the table with days of the month
																																																																    html += TR;
																																																																	  
																																																																	    // first, the leading blanks
																																																																		  for (i = 0; i < thisDay.getDay(); i++)
																																																																		      html += TD + "&nbsp;" + xTD;
																																																																			    
																																																																				  // now, the days of the month
																																																																				    do {
																																																																					    dayNum = thisDay.getDate();
																																																																						    TD_onclick = " onclick=\"updateDateField('" + dateFieldName + "', '" + getDateString(thisDay) + "');\">";
																																																																							    
																																																																								    if (dayNum == day)
																																																																									      html += TD_selected + TD_onclick + DIV_selected + dayNum + xDIV + xTD;
																																																																										      else
																																																																											        html += TD + TD_onclick + dayNum + xTD;
																																																																													    
																																																																														    // if this is a Saturday, start a new row
																																																																															    if (thisDay.getDay() == 6)
																																																																																      html += xTR + TR;
																																																																																	      
																																																																																		      // increment the day
																																																																																			      thisDay.setDate(thisDay.getDate() + 1);
																																																																																				    } while (thisDay.getDate() > 1)
																																																																																					  
																																																																																					    // fill in any trailing blanks
																																																																																						  if (thisDay.getDay() > 0) {
																																																																																						      for (i = 6; i > thisDay.getDay(); i--)
																																																																																							        html += TD + "&nbsp;" + xTD;
																																																																																									  }
																																																																																									    html += xTR;
																																																																																										  
																																																																																										    // add a button to allow the user to easily return to today, or close the calendar
																																																																																											  var today = new Date();
																																																																																											    var todayString = "Today is " + dayArrayMed[today.getDay()] + ", " + monthArrayMed[today.getMonth()] + " " + today.getDate();
																																																																																												  html += TR_todaybutton + TD_todaybutton;
																																																																																												    html += "<button class='dpTodayButton' onClick='refreshDatePicker(\"" + dateFieldName + "\");'>this month</button> ";
																																																																																													  html += "<button class='dpTodayButton' onClick='updateDateField(\"" + dateFieldName + "\");'>close</button>";
																																																																																													    html += xTD + xTR;
																																																																																														  
																																																																																														    // and finally, close the table
																																																																																															  html += xTABLE;
																																																																																															    
																																																																																																  document.getElementById(datePickerDivID).innerHTML = html;
																																																																																																    // add an "iFrame shim" to allow the datepicker to display above selection lists
																																																																																																	  adjustiFrame();
																																																																																																	  }


																																																																																																	  /**
																																																																																																	  Convenience function for writing the code for the buttons that bring us back or forward
																																																																																																	  a month.
																																																																																																	  */
																																																																																																	  function getButtonCode(dateFieldName, dateVal, adjust, label)
																																																																																																	  {
																																																																																																	    var newMonth = (dateVal.getMonth() + adjust) % 12;
																																																																																																		  var newYear = dateVal.getFullYear() + parseInt((dateVal.getMonth() + adjust) / 12);
																																																																																																		    if (newMonth < 0) {
																																																																																																			    newMonth += 12;
																																																																																																				    newYear += -1;
																																																																																																					  }
																																																																																																					    
																																																																																																						  return "<button class='dpButton' onClick='refreshDatePicker(\"" + dateFieldName + "\", " + newYear + ", " + newMonth + ");'>" + label + "</button>";
																																																																																																						  }


																																																																																																						  /**
																																																																																																						  Convert a JavaScript Date object to a string, based on the dateFormat and dateSeparator
																																																																																																						  variables at the beginning of this script library.
																																																																																																						  */
																																																																																																						  function getDateString(dateVal)
																																																																																																						  {
																																																																																																						    var dayString = "00" + dateVal.getDate();
																																																																																																							  var monthString = "00" + (dateVal.getMonth()+1);
																																																																																																							    dayString = dayString.substring(dayString.length - 2);
																																																																																																								  monthString = monthString.substring(monthString.length - 2);
																																																																																																								    
																																																																																																									  switch (dateFormat) {
																																																																																																									      case "dmy" :
																																																																																																										        return dayString + dateSeparator + monthString + dateSeparator + dateVal.getFullYear();
																																																																																																												    case "ymd" :
																																																																																																													      return dateVal.getFullYear() + dateSeparator + monthString + dateSeparator + dayString;
																																																																																																														      case "mdy" :
																																																																																																															      default :
																																																																																																																        return monthString + dateSeparator + dayString + dateSeparator + dateVal.getFullYear();
																																																																																																																		  }
																																																																																																																		  }


																																																																																																																		  /**
																																																																																																																		  Convert a string to a JavaScript Date object.
																																																																																																																		  */
																																																																																																																		  function getFieldDate(dateString)
																																																																																																																		  {
																																																																																																																		    var dateVal;
																																																																																																																			  var dArray;
																																																																																																																			    var d, m, y;
																																																																																																																				  
																																																																																																																				    try {
																																																																																																																					    dArray = splitDateString(dateString);
																																																																																																																						    if (dArray) {
																																																																																																																							      switch (dateFormat) {
																																																																																																																								          case "dmy" :
																																																																																																																										            d = parseInt(dArray[0], 10);
																																																																																																																													          m = parseInt(dArray[1], 10) - 1;
																																																																																																																															            y = parseInt(dArray[2], 10);
																																																																																																																																		          break;
																																																																																																																																				          case "ymd" :
																																																																																																																																						            d = parseInt(dArray[2], 10);
																																																																																																																																									          m = parseInt(dArray[1], 10) - 1;
																																																																																																																																											            y = parseInt(dArray[0], 10);
																																																																																																																																														          break;
																																																																																																																																																          case "mdy" :
																																																																																																																																																		          default :
																																																																																																																																																				            d = parseInt(dArray[1], 10);
																																																																																																																																																							          m = parseInt(dArray[0], 10) - 1;
																																																																																																																																																									            y = parseInt(dArray[2], 10);
																																																																																																																																																												          break;
																																																																																																																																																														        }
																																																																																																																																																																      dateVal = new Date(y, m, d);
																																																																																																																																																																	      } else {
																																																																																																																																																																		        dateVal = new Date(dateString);
																																																																																																																																																																				    }
																																																																																																																																																																					  } catch(e) {
																																																																																																																																																																					      dateVal = new Date();
																																																																																																																																																																						    }
																																																																																																																																																																							  
																																																																																																																																																																							    return dateVal;
																																																																																																																																																																								}


																																																																																																																																																																								/**
																																																																																																																																																																								Try to split a date string into an array of elements, using common date separators.
																																																																																																																																																																								If the date is split, an array is returned; otherwise, we just return false.
																																																																																																																																																																								*/
																																																																																																																																																																								function splitDateString(dateString)
																																																																																																																																																																								{
																																																																																																																																																																								  var dArray;
																																																																																																																																																																								    if (dateString.indexOf("/") >= 0)
																																																																																																																																																																									    dArray = dateString.split("/");
																																																																																																																																																																										  else if (dateString.indexOf(".") >= 0)
																																																																																																																																																																										      dArray = dateString.split(".");
																																																																																																																																																																											    else if (dateString.indexOf("-") >= 0)
																																																																																																																																																																												    dArray = dateString.split("-");
																																																																																																																																																																													  else if (dateString.indexOf("\\") >= 0)
																																																																																																																																																																													      dArray = dateString.split("\\");
																																																																																																																																																																														    else
																																																																																																																																																																															    dArray = false;
																																																																																																																																																																																  
																																																																																																																																																																																    return dArray;
																																																																																																																																																																																	}

																																																																																																																																																																																	/**
																																																																																																																																																																																	Update the field with the given dateFieldName with the dateString that has been passed,
																																																																																																																																																																																	and hide the datepicker. If no dateString is passed, just close the datepicker without
																																																																																																																																																																																	changing the field value.

																																																																																																																																																																																	Also, if the page developer has defined a function called datePickerClosed anywhere on
																																																																																																																																																																																	the page or in an imported library, we will attempt to run that function with the updated
																																																																																																																																																																																	field as a parameter. This can be used for such things as date validation, setting default
																																																																																																																																																																																	values for related fields, etc. For example, you might have a function like this to validate
																																																																																																																																																																																	a start date field:

																																																																																																																																																																																	function datePickerClosed(dateField)
																																																																																																																																																																																	{
																																																																																																																																																																																	  var dateObj = getFieldDate(dateField.value);
																																																																																																																																																																																	    var today = new Date();
																																																																																																																																																																																		  today = new Date(today.getFullYear(), today.getMonth(), today.getDate());
																																																																																																																																																																																		    
																																																																																																																																																																																			  if (dateField.name == "StartDate") {
																																																																																																																																																																																			      if (dateObj < today) {
																																																																																																																																																																																				        // if the date is before today, alert the user and display the datepicker again
																																																																																																																																																																																						      alert("Please enter a date that is today or later");
																																																																																																																																																																																							        dateField.value = "";
																																																																																																																																																																																									      document.getElementById(datePickerDivID).style.visibility = "visible";
																																																																																																																																																																																										        adjustiFrame();
																																																																																																																																																																																												    } else {
																																																																																																																																																																																													      // if the date is okay, set the EndDate field to 7 days after the StartDate
																																																																																																																																																																																														        dateObj.setTime(dateObj.getTime() + (7 * 24 * 60 * 60 * 1000));
																																																																																																																																																																																																      var endDateField = document.getElementsByName("EndDate").item(0);
																																																																																																																																																																																																	        endDateField.value = getDateString(dateObj);
																																																																																																																																																																																																			    }
																																																																																																																																																																																																				  }
																																																																																																																																																																																																				  }

																																																																																																																																																																																																				  */
																																																																																																																																																																																																				  function updateDateField(dateFieldName, dateString)
																																																																																																																																																																																																				  {
																																																																																																																																																																																																				    var targetDateField = document.getElementsByName(dateFieldName).item(0);
																																																																																																																																																																																																					  if (dateString)
																																																																																																																																																																																																					      targetDateField.value = dateString;
																																																																																																																																																																																																						    document.getElementById(datePickerDivID).style.visibility = "hidden";
																																																																																																																																																																																																							  adjustiFrame();
																																																																																																																																																																																																							    targetDateField.focus();
																																																																																																																																																																																																								  
																																																																																																																																																																																																								    // after the datepicker has closed, optionally run a user-defined function called
																																																																																																																																																																																																									  // datePickerClosed, passing the field that was just updated as a parameter
																																																																																																																																																																																																									    // (note that this will only run if the user actually selected a date from the datepicker)
																																																																																																																																																																																																										  if ((dateString) && (typeof(datePickerClosed) == "function"))
																																																																																																																																																																																																										      datePickerClosed(targetDateField);
																																																																																																																																																																																																											  }


																																																																																																																																																																																																											  /**
																																																																																																																																																																																																											  Use an "iFrame shim" to deal with problems where the datepicker shows up behind
																																																																																																																																																																																																											  selection list elements, if they're below the datepicker. The problem and solution are
																																																																																																																																																																																																											  described at:

																																																																																																																																																																																																											  http://dotnetjunkies.com/WebLog/jking/archive/2003/07/21/488.aspx
																																																																																																																																																																																																											  http://dotnetjunkies.com/WebLog/jking/archive/2003/10/30/2975.aspx
																																																																																																																																																																																																											  */
																																																																																																																																																																																																											  function adjustiFrame(pickerDiv, iFrameDiv)
																																																																																																																																																																																																											  {
																																																																																																																																																																																																											    if (!document.getElementById(iFrameDivID)) {
																																																																																																																																																																																																												    // don't use innerHTML to update the body, because it can cause global variables
																																																																																																																																																																																																													    // that are currently pointing to objects on the page to have bad references
																																																																																																																																																																																																														    //document.body.innerHTML += "<iframe id='" + iFrameDivID + "' src='javascript:false;' scrolling='no' frameborder='0'>";
																																																																																																																																																																																																															    var newNode = document.createElement("iFrame");
																																																																																																																																																																																																																    newNode.setAttribute("id", iFrameDivID);
																																																																																																																																																																																																																	    newNode.setAttribute("src", "javascript:false;");
																																																																																																																																																																																																																		    newNode.setAttribute("scrolling", "no");
																																																																																																																																																																																																																			    newNode.setAttribute("frameborder", "0");
																																																																																																																																																																																																																				    document.body.appendChild(newNode);
																																																																																																																																																																																																																					  }
																																																																																																																																																																																																																					    
																																																																																																																																																																																																																						  if (!pickerDiv)
																																																																																																																																																																																																																						      pickerDiv = document.getElementById(datePickerDivID);
																																																																																																																																																																																																																							    if (!iFrameDiv)
																																																																																																																																																																																																																								    iFrameDiv = document.getElementById(iFrameDivID);
																																																																																																																																																																																																																									  
																																																																																																																																																																																																																									    try {
																																																																																																																																																																																																																										    iFrameDiv.style.position = "absolute";
																																																																																																																																																																																																																											    iFrameDiv.style.width = pickerDiv.offsetWidth;
																																																																																																																																																																																																																												    iFrameDiv.style.height = pickerDiv.offsetHeight;
																																																																																																																																																																																																																													    iFrameDiv.style.top = pickerDiv.style.top;
																																																																																																																																																																																																																														    iFrameDiv.style.left = pickerDiv.style.left;
																																																																																																																																																																																																																															    iFrameDiv.style.zIndex = pickerDiv.style.zIndex - 1;
																																																																																																																																																																																																																																    iFrameDiv.style.visibility = pickerDiv.style.visibility;
																																																																																																																																																																																																																																	  } catch(e) {
																																																																																																																																																																																																																																	    }
																																																																																																																																																																																																																																		}