/**

	the script only works on "input [type=text]"

**/

// don't declare anything out here in the global namespace

(function($) { // create private scope (inside you can use $ instead of jQuery)

    // functions and vars declared here are effectively 'singletons'.  there will be only a single

    // instance of them.  so this is a good place to declare any immutable items or stateless

    // functions.  for example:

	var today = new Date(); // used in defaults

    var months = 'January,February,March,April,May,June,July,August,September,October,November,December'.split(',');

	var monthlengths = '31,28,31,30,31,30,31,31,30,31,30,31'.split(',');

  	var dateRegEx = /^\d{1,2}\/\d{1,2}\/\d{2}|\d{4}$/;

	var yearRegEx = /^\d{4,4}$/;

    // next, declare the plugin function

    $.fn.simpleDatepicker = function(options) {

        // functions and vars declared here are created each time your plugn function is invoked

        // you could probably refactor your 'build', 'load_month', etc, functions to be passed

        // the DOM element from below

		var opts = jQuery.extend({}, jQuery.fn.simpleDatepicker.defaults, options);

		// replaces a date string with a date object in opts.startdate and opts.enddate, if one exists

		// populates two new properties with a ready-to-use year: opts.startyear and opts.endyear

		setupYearRange();

		/** extracts and setup a valid year range from the opts object **/

		function setupYearRange () {

			var startyear, endyear;  

			if (opts.startdate.constructor == Date) {

				startyear = opts.startdate.getFullYear();

			} else if (opts.startdate) {

				if (yearRegEx.test(opts.startdate)) {

				startyear = opts.startdate;

				} else if (dateRegEx.test(opts.startdate)) {

					opts.startdate = new Date(opts.startdate);

					startyear = opts.startdate.getFullYear();

				} else {

				startyear = today.getFullYear();

				}

			} else {

				startyear = today.getFullYear();

			}

			opts.startyear = startyear;

			if (opts.enddate.constructor == Date) {

				endyear = opts.enddate.getFullYear();

			} else if (opts.enddate) {

				if (yearRegEx.test(opts.enddate)) {

					endyear = opts.enddate;

				} else if (dateRegEx.test(opts.enddate)) {

					opts.enddate = new Date(opts.enddate);

					endyear = opts.enddate.getFullYear();

				} else {

					endyear = today.getFullYear();

				}

			} else {

				endyear = today.getFullYear();

			}

			opts.endyear = endyear;	

		}

		/** HTML factory for the actual datepicker table element **/

		// has to read the year range so it can setup the correct years in our HTML <select>

		function newDatepickerHTML () {

			var years = [];

			// process year range into an array

			for (var i = 0; i <= opts.endyear - opts.startyear; i ++) years[i] = opts.startyear + i;

			// build the table structure

			var table = jQuery('<table class="datepicker" cellpadding="0" cellspacing="0"></table>');

			table.append('<thead></thead>');

			table.append('<tfoot></tfoot>');

			table.append('<tbody></tbody>');

				// month select field

				var monthselect = '<select name="month">';

				for (var i in months) monthselect += '<option value="'+i+'">'+months[i]+'</option>';

				monthselect += '</select>';

				// year select field

				var yearselect = '<select name="year">';

				for (var i in years) yearselect += '<option>'+years[i]+'</option>';

				yearselect += '</select>';

			jQuery("thead",table).append('<tr class="controls"><th colspan="7"><span class="prevMonth">&laquo;</span>&nbsp;'+monthselect+yearselect+'&nbsp;<span class="nextMonth">&raquo;</span></th></tr>');

			jQuery("thead",table).append('<tr class="days"><th>S</th><th>M</th><th>T</th><th>W</th><th>T</th><th>F</th><th>S</th></tr>');

			jQuery("tfoot",table).append('<tr><td colspan="2"><span class="today">today</span></td><td colspan="3">&nbsp;</td><td colspan="2"><span class="close">close</span></td></tr>');

			for (var i = 0; i < 6; i++) jQuery("tbody",table).append('<tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr>');	

			return table;

		}

		/** get the real position of the input (well, anything really) **/

		//http://www.quirksmode.org/js/findpos.html

		function findPosition (obj) {

			var curleft = curtop = 0;

			if (obj.offsetParent) {

				do { 

					curleft += obj.offsetLeft;

					curtop += obj.offsetTop;

				} while (obj = obj.offsetParent);

				return [curleft,curtop];

			} else {

				return false;

			}

		}

		/** load the initial date and handle all date-navigation **/

		// initial calendar load (e is null)

		// prevMonth & nextMonth buttons

		// onchange for the select fields

		function loadMonth (e, el, datepicker, chosendate) {

			// reference our years for the nextMonth and prevMonth buttons

			var mo = jQuery("select[name=month]", datepicker).get(0).selectedIndex;

			var yr = jQuery("select[name=year]", datepicker).get(0).selectedIndex;

			var yrs = jQuery("select[name=year] option", datepicker).get().length;

			// first try to process buttons that may change the month we're on

			if (e && jQuery(e.target).hasClass('prevMonth')) {				

				if (0 == mo && yr) {

					yr -= 1; mo = 11;

					jQuery("select[name=month]", datepicker).get(0).selectedIndex = 11;

					jQuery("select[name=year]", datepicker).get(0).selectedIndex = yr;

				} else {

					mo -= 1;

					jQuery("select[name=month]", datepicker).get(0).selectedIndex = mo;

				}

			} else if (e && jQuery(e.target).hasClass('nextMonth')) {

				if (11 == mo && yr + 1 < yrs) {

					yr += 1; mo = 0;

					jQuery("select[name=month]", datepicker).get(0).selectedIndex = 0;

					jQuery("select[name=year]", datepicker).get(0).selectedIndex = yr;

				} else { 

					mo += 1;

					jQuery("select[name=month]", datepicker).get(0).selectedIndex = mo;

				}

			}

			// maybe hide buttons

			if (0 == mo && !yr) jQuery("span.prevMonth", datepicker).hide(); 

			else jQuery("span.prevMonth", datepicker).show(); 

			if (yr + 1 == yrs && 11 == mo) jQuery("span.nextMonth", datepicker).hide(); 

			else jQuery("span.nextMonth", datepicker).show(); 

			// clear the old cells

			var cells = jQuery("tbody td", datepicker).unbind().empty().removeClass('date');

			// figure out what month and year to load

			var m = jQuery("select[name=month]", datepicker).val();

			var y = jQuery("select[name=year]", datepicker).val();

			var d = new Date(y, m, 1);

			var startindex = d.getDay();

			var numdays = monthlengths[m];

			// http://en.wikipedia.org/wiki/Leap_year

			if (1 == m && ((y%4 == 0 && y%100 != 0) || y%400 == 0)) numdays = 29;

			// test for end dates (instead of just a year range)

			if (opts.startdate.constructor == Date) {

				var startMonth = opts.startdate.getMonth();

				var startDate = opts.startdate.getDate();

			}

			if (opts.enddate.constructor == Date) {

				var endMonth = opts.enddate.getMonth();

				var endDate = opts.enddate.getDate();

			}

			// walk through the index and populate each cell, binding events too

			for (var i = 0; i < numdays; i++) {

				var cell = jQuery(cells.get(i+startindex)).removeClass('chosen');

				// test that the date falls within a range, if we have a range

				if ( 

					(yr || ((!startDate && !startMonth) || ((i+1 >= startDate && mo == startMonth) || mo > startMonth))) &&

					(yr + 1 < yrs || ((!endDate && !endMonth) || ((i+1 <= endDate && mo == endMonth) || mo < endMonth)))) {

					cell

						.text(i+1)

						.addClass('date')

						.hover(

							function () { jQuery(this).addClass('over'); },

							function () { jQuery(this).removeClass('over'); })

						.click(function () {

							var chosenDateObj = new Date(jQuery("select[name=year]", datepicker).val(), jQuery("select[name=month]", datepicker).val(), jQuery(this).text());

							closeIt(el, datepicker, chosenDateObj);

						});

					// highlight the previous chosen date

					if (i+1 == chosendate.getDate() && m == chosendate.getMonth() && y == chosendate.getFullYear()) cell.addClass('chosen');

				}

			}

		}

		/** closes the datepicker **/

		// sets the currently matched input element's value to the date, if one is available

		// remove the table element from the DOM

		// indicate that there is no datepicker for the currently matched input element

		function closeIt (el, datepicker, dateObj) { 

			if (dateObj && dateObj.constructor == Date)

				el.val(jQuery.fn.simpleDatepicker.formatOutput(dateObj));

			datepicker.remove();

			datepicker = null;

			jQuery.data(el.get(0), "simpleDatepicker", { hasDatepicker : false });

		}

        // iterate the matched nodeset

        return this.each(function() {

            // functions and vars declared here are created for each matched element. so if

            // your functions need to manage or access per-node state you can defined them

            // here and use $this to get at the DOM element

			if ( jQuery(this).is('input') && 'text' == jQuery(this).attr('type')) {

				var datepicker; 

				jQuery.data(jQuery(this).get(0), "simpleDatepicker", { hasDatepicker : false });

				// open a datepicker on the click event

				jQuery(this).click(function (ev) {

					var $this = jQuery(ev.target);

					if (false == jQuery.data($this.get(0), "simpleDatepicker").hasDatepicker) {

						// store data telling us there is already a datepicker

						jQuery.data($this.get(0), "simpleDatepicker", { hasDatepicker : true });

						// validate the form's initial content for a date

						var initialDate = $this.val();

						if (initialDate && dateRegEx.test(initialDate)) {

							var chosendate = new Date(initialDate);

						} else if (opts.chosendate.constructor == Date) {

							var chosendate = opts.chosendate;

						} else if (opts.chosendate) {

							var chosendate = new Date(opts.chosendate);

						} else {

							var chosendate = today;

						}

						// insert the datepicker in the DOM

						datepicker = newDatepickerHTML();

						jQuery("body").prepend(datepicker);

						// position the datepicker

						var elPos = findPosition($this.get(0));

						var x = (parseInt(opts.x) ? parseInt(opts.x) : 0) + elPos[0];

						var y = (parseInt(opts.y) ? parseInt(opts.y) : 0) + elPos[1];

						jQuery(datepicker).css({ position: 'absolute', left: x, top: y });

						// bind events to the table controls

						jQuery("span", datepicker).css("cursor","pointer");

						jQuery("select", datepicker).bind('change', function () { loadMonth (null, $this, datepicker, chosendate); });

						jQuery("span.prevMonth", datepicker).click(function (e) { loadMonth (e, $this, datepicker, chosendate); });

						jQuery("span.nextMonth", datepicker).click(function (e) { loadMonth (e, $this, datepicker, chosendate); });

						jQuery("span.today", datepicker).click(function () { closeIt($this, datepicker, new Date()); });

						jQuery("span.close", datepicker).click(function () { closeIt($this, datepicker); });

						// set the initial values for the month and year select fields

						// and load the first month

						jQuery("select[name=month]", datepicker).get(0).selectedIndex = chosendate.getMonth();

						jQuery("select[name=year]", datepicker).get(0).selectedIndex = Math.max(0, chosendate.getFullYear() - opts.startyear);

						loadMonth(null, $this, datepicker, chosendate);

					}

				});

			}

        });

    };

    // finally, I like to expose default plugin options as public so they can be manipulated.  one

    // way to do this is to add a property to the already-public plugin fn

	jQuery.fn.simpleDatepicker.formatOutput = function (dateObj) {

		return (dateObj.getMonth() + 1) + "/" + dateObj.getDate() + "/" + dateObj.getFullYear();	

	};

	jQuery.fn.simpleDatepicker.defaults = {

		// date string matching /^\d{1,2}\/\d{1,2}\/\d{2}|\d{4}$/

		chosendate : today,

		// date string matching /^\d{1,2}\/\d{1,2}\/\d{2}|\d{4}$/

		// or four digit year

		startdate : today.getFullYear(), 

		enddate : today.getFullYear() + 1,

		// offset from the top left corner of the input element

		x : 18, // must be in px

		y : 18 // must be in px

	};

})(jQuery);