$(function() {
	var DATEPICKER_FORMAT = 'yyyy-m-d';
	var TIMEPICKER_FORMAT = 'g:ia';
	var DATE_FORMAT = 'Y-n-j'; // for this format see http://php.net/manual/function.date.php

	$('.datepair input.date').each(function(){
		var $this = $(this);

		$this.datepicker({
			'format': DATEPICKER_FORMAT,
			'autoclose': true
		});

		if ($this.hasClass('start') || $this.hasClass('end')) {
			$this.on('change', doDatepair);
		}

	});

	$('.datepair input.time').each(function() {
		var $this = $(this);

		$this.timepicker({
			'showDuration': true,
			'timeFormat': TIMEPICKER_FORMAT,
			'scrollDefaultNow': true
		});

		if ($this.hasClass('start') || $this.hasClass('end')) {
			$this.on('change', doDatepair);
		}

		if ($this.hasClass('end')) {
			$this.on('focus', function(){$('.ui-timepicker-with-duration').scrollTop(0);});
		}

	});

	$('.datepair').each(initDatepair);

	function initDatepair()
	{
		var container = $(this);

		var startDateInput = container.find('input.start.date');
		var endDateInput = container.find('input.end.date');
		var dateDelta = 0;

		if (startDateInput.length && endDateInput.length) {
			var startDate = parseDate(startDateInput.val(), DATEPICKER_FORMAT);
			var endDate =  parseDate(endDateInput.val(), DATEPICKER_FORMAT);

			dateDelta = endDate.getTime() - startDate.getTime();
			container.data('dateDelta', dateDelta);
		}

		var startTimeInput = container.find('input.start.time');
		var endTimeInput = container.find('input.end.time');

		if (startTimeInput.length && endTimeInput.length) {
			var startInt = startTimeInput.timepicker('getSecondsFromMidnight');
			var endInt = endTimeInput.timepicker('getSecondsFromMidnight');

			container.data('timeDelta', endInt - startInt);

			if (dateDelta < 86400000) {
				endTimeInput.timepicker('option', 'minTime', startInt);
			}
		}
	}

	function doDatepair()
	{
		var target = $(this);
		if (target.val() == '') {
			return;
		}

		var container = target.closest('.datepair');

		if (target.hasClass('date')) {
			updateDatePair(target, container);

		} else if (target.hasClass('time')) {
			updateTimePair(target, container);
		}
	}

	function updateDatePair(target, container)
	{
		var start = container.find('input.start.date');
		var end = container.find('input.end.date');
		if (!start.length || !end.length) {
			return;
		}

		var startDate = parseDate(start.val(), DATEPICKER_FORMAT);
		var endDate =  parseDate(end.val(), DATEPICKER_FORMAT);

		var oldDelta = container.data('dateDelta');

		if (!isNaN(oldDelta) && oldDelta !== null && target.hasClass('start')) {
			var newEnd = new Date(startDate.getTime()+oldDelta);
			end.val(newEnd.format(DATE_FORMAT));
			end.datepicker('update');
			return;

		} else {
			var newDelta = endDate.getTime() - startDate.getTime();

			if (newDelta < 0) {
				newDelta = 0;

				if (target.hasClass('start')) {
					end.val(start.val());
					end.datepicker('update');
				} else if (target.hasClass('end')) {
					start.val(end.val());
					start.datepicker('update');
				}
			}

			if (newDelta < 86400000) {
				var startTimeVal = container.find('input.start.time').val();

				if (startTimeVal) {
					container.find('input.end.time').timepicker('option', {'minTime': startTimeVal});
				}
			} else {
				container.find('input.end.time').timepicker('option', {'minTime': null});
			}

			container.data('dateDelta', newDelta);
		}
	}

	function updateTimePair(target, container)
	{
		var start = container.find('input.start.time');
		var end = container.find('input.end.time');

		if (!start.length || !end.length) {
			return;
		}

		var startInt = start.timepicker('getSecondsFromMidnight');
		var dateDelta = container.data('dateDelta');
		var oldDelta = container.data('timeDelta');

		if (target.hasClass('start') && (!dateDelta || dateDelta + oldDelta < 86400000)) {
			end.timepicker('option', 'minTime', startInt);
		} else {
			end.timepicker('option', 'minTime', null);
		}

		var endInt = end.timepicker('getSecondsFromMidnight');

		var endDateAdvance = 0;
		var newDelta;

		if (oldDelta && target.hasClass('start')) {
			// lock the duration and advance the end time

			var newEnd = (startInt+oldDelta)%86400;

			if (newEnd < 0) {
				newEnd += 86400;
			}

			end.timepicker('setTime', newEnd);
			newDelta = newEnd - startInt;
		} else if (startInt !== null && endInt !== null) {
			newDelta = endInt - startInt;
		} else {
			return;
		}

		container.data('timeDelta', newDelta);

		if (newDelta < 0 && (!oldDelta || oldDelta > 0)) {
			// overnight time span. advance the end date 1 day
			endDateAdvance = 86400000;

		} else if (newDelta > 0 && oldDelta < 0) {
			// switching from overnight to same-day time span. decrease the end date 1 day
			endDateAdvance = -86400000;
		}

		var startInput = container.find('.start.date');
		var endInput = container.find('.end.date');

		if (startInput.val() && !endInput.val()) {
			endInput.val(startInput.val());
			endInput.datepicker('update');
			dateDelta = 0;
			container.data('dateDelta', 0);
		}

		if (endDateAdvance != 0) {
			if (dateDelta || dateDelta === 0) {
				var endDate =  parseDate(endInput.val(), DATEPICKER_FORMAT);
				var newEnd = new Date(endDate.getTime() + endDateAdvance);
				endInput.val(newEnd.format(DATE_FORMAT));
				endInput.datepicker('update');
				container.data('dateDelta', dateDelta + endDateAdvance);
			}
		}
	}
});

function parseDate(input, format) {
	if (input == '')
		return new Date('');

	format = format || 'yyyy-mm-dd'; // default format
	var parts = input.match(/(\d+)/g), i = 0, fmt = {};
	// extract date-part indexes from the format
	format.replace(/(yyyy|dd?|mm?)/g, function(part) { fmt[part] = i++; });

	return new Date(parts[fmt['yyyy']], parts[fmt['mm'] == undefined ? fmt['m'] : fmt['mm']]-1, parts[fmt['dd'] == undefined ? fmt['d'] : fmt['dd']]);
}

// Simulates PHP's date function
Date.prototype.format=function(format){var returnStr='';var replace=Date.replaceChars;for(var i=0;i<format.length;i++){var curChar=format.charAt(i);if(replace[curChar]){returnStr+=replace[curChar].call(this);}else{returnStr+=curChar;}}return returnStr;};Date.replaceChars={shortMonths:['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'],longMonths:['January','February','March','April','May','June','July','August','September','October','November','December'],shortDays:['Sun','Mon','Tue','Wed','Thu','Fri','Sat'],longDays:['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'],d:function(){return(this.getDate()<10?'0':'')+this.getDate();},D:function(){return Date.replaceChars.shortDays[this.getDay()];},j:function(){return this.getDate();},l:function(){return Date.replaceChars.longDays[this.getDay()];},N:function(){return this.getDay()+1;},S:function(){return(this.getDate()%10==1&&this.getDate()!=11?'st':(this.getDate()%10==2&&this.getDate()!=12?'nd':(this.getDate()%10==3&&this.getDate()!=13?'rd':'th')));},w:function(){return this.getDay();},z:function(){return"Not Yet Supported";},W:function(){return"Not Yet Supported";},F:function(){return Date.replaceChars.longMonths[this.getMonth()];},m:function(){return(this.getMonth()<9?'0':'')+(this.getMonth()+1);},M:function(){return Date.replaceChars.shortMonths[this.getMonth()];},n:function(){return this.getMonth()+1;},t:function(){return"Not Yet Supported";},L:function(){return(((this.getFullYear()%4==0)&&(this.getFullYear()%100!=0))||(this.getFullYear()%400==0))?'1':'0';},o:function(){return"Not Supported";},Y:function(){return this.getFullYear();},y:function(){return(''+this.getFullYear()).substr(2);},a:function(){return this.getHours()<12?'am':'pm';},A:function(){return this.getHours()<12?'AM':'PM';},B:function(){return"Not Yet Supported";},g:function(){return this.getHours()%12||12;},G:function(){return this.getHours();},h:function(){return((this.getHours()%12||12)<10?'0':'')+(this.getHours()%12||12);},H:function(){return(this.getHours()<10?'0':'')+this.getHours();},i:function(){return(this.getMinutes()<10?'0':'')+this.getMinutes();},s:function(){return(this.getSeconds()<10?'0':'')+this.getSeconds();},e:function(){return"Not Yet Supported";},I:function(){return"Not Supported";},O:function(){return(-this.getTimezoneOffset()<0?'-':'+')+(Math.abs(this.getTimezoneOffset()/60)<10?'0':'')+(Math.abs(this.getTimezoneOffset()/60))+'00';},P:function(){return(-this.getTimezoneOffset()<0?'-':'+')+(Math.abs(this.getTimezoneOffset()/60)<10?'0':'')+(Math.abs(this.getTimezoneOffset()/60))+':'+(Math.abs(this.getTimezoneOffset()%60)<10?'0':'')+(Math.abs(this.getTimezoneOffset()%60));},T:function(){var m=this.getMonth();this.setMonth(0);var result=this.toTimeString().replace(/^.+ \(?([^\)]+)\)?$/,'$1');this.setMonth(m);return result;},Z:function(){return-this.getTimezoneOffset()*60;},c:function(){return this.format("Y-m-d")+"T"+this.format("H:i:sP");},r:function(){return this.toString();},U:function(){return this.getTime()/1000;}};