JQ UI Date picker - Force users to choose a delivery date in the future and take into account weekends

delivery_date.js

function days_between(date1, date2) {
	var one_day       = 1000 * 60 * 60 * 24,
		date1_ms      = date1.getTime(),
		date2_ms      = date2.getTime(),
		difference_ms = Math.abs(date1_ms - date2_ms);
	
	return Math.round(difference_ms / one_day);
}


function disable_specific_days(date) {
	var now                    = new Date(),
		arr                    = [],			
		disable_monday         = false,
		is_weekend             = (now.getDay() === 0 || now.getDay() === 6),
		no_of_delivery_days    = is_weekend ? 2 : 1,
		dp_date_is_weekend     = (date.getDay() === 0 || date.getDay() === 6),				
		is_friday              = (now.getDay() === 5),
		date_in_the_past       = (date.getTime() - now.getTime()) < 0,
		past_2_pm              = (now.getHours() >= 14),
		dp_is_today            = (date.toDateString() === now.toDateString()),
		days_between_dates     = (function(days) {	 
									return past_2_pm ? days -1 : days;              // 1 days grace for delivery unless after 2pm (then remove 1 day)
								 }(days_between(now, date)));
								
		
	disable_monday = (function() {
							   
		if (is_weekend) {															// only used when hitting this page on a weekend
			return (date.getDay() === 1 && days_between_dates < 4);  				// if weekend dont disable all mondays. Just the next one 
		} else if (is_friday) {														// only used when hitting this page on a friday
			return (date.getDay() === 1 && days_between_dates < 4 && past_2_pm);	// if less than 4 days until the closet monday and after 2pm? then disable all mondays.
		}
		
	}());
	
	
	var disable_date = disable_monday || 
		dp_date_is_weekend || 
		(days_between_dates < no_of_delivery_days) || 
		(days_between_dates <= no_of_delivery_days && past_2_pm && is_friday) ||
		date_in_the_past,
		enable_date = !disable_date;                                                // duhhhh!

		
	arr.push(enable_date);
	arr.push("");	
	
	return arr;
}


$(function() {
	   
	var $delivery_date = $("#delivery_date");
	
	$delivery_date.datepicker({
		dateFormat:'dd-mm-yy',
		numberOfMonths: 2,
		showOn: "button",			
		beforeShowDay: disable_specific_days // http://docs.jquery.com/UI/Datepicker#event-beforeShowDay
	}); 
	
	(function() { 
			  
		// set the value of the delivery_date textbox to the first available date. If a delivery date has been 
		// chosen previously, (i.e. user comes back to the page to amend details) do nothing.
			  
		var prepopulate_delivery_date = <%= cstr(cbool(GlobalRegistry.OrderInProgress.DeliveryDate < now)).toLower() %>,	  
			dateIsDeliverable,
			initialDate = new Date();
		
		if (prepopulate_delivery_date) {
		
			do {
				
				dateIsDeliverable = disable_specific_days(initialDate)[0];	
				
				if (!dateIsDeliverable) {
					initialDate.setDate(initialDate.getDate() + 1);				
				} else {
					$delivery_date.val(initialDate.toCSDate());
				}
				
			} while (!dateIsDeliverable);
		
		}
		
	}());
	
});