Through a date given as input, it returns the same date or the first date to make a payment by a deadline. A check is performed on the specified date, to see if the same appears as Italian festivity.

date_payments.php

<?php

	//	Check if var is a valid date
	function validateDate($date, $format = 'Y-m-d H:i:s') {

		$d = DateTime::createFromFormat($format, $date);
		return $d && $d->format($format) == $date;

	}

	/**
	 * Check day of week for specified date
	 * -----------------------------------------------------------
	 * N is ISO-8601 numeric representation of the day of the week
	 * 1 (for Monday) through 7 (for Sunday)
	 * -----------------------------------------------------------
	 */
	function checkWeek($check_data) {

		$res_d = "";

		$check_d = date('N', strtotime($check_data));
		$prtd = explode("-", $check_data);

		if ($check_d == 6)	//	Saturday
			$res_d = date("Y-m-d", mktime(0,0,0,$prtd[1],($prtd[2]+2),$prtd[0]));
		elseif ($check_d == 7)	//	Sunday
			$res_d = date("Y-m-d", mktime(0,0,0,$prtd[1],($prtd[2]+1),$prtd[0]));
		else
			$res_d = $check_data;

		return $res_d;

	}

	//	Return label with utils date
	function parseDate($good_day) {

		//	Label for week days
		$week_days = array('','Luned&igrave;','Marted&igrave;','Mercoled&igrave;','Gioved&igrave;','Venerd&igrave;','Sabato','Domenica');

		//	Label for month
		$month_lab = array('', 'Gennaio', 'Febbraio', 'Marzo', 'Aprile', 'Maggio', 'Giugno', 'Luglio', 'Agosto', 'Settembre', 'Ottobre', 'Novembre', 'Dicembre');

		$wk_d = date('N', strtotime($good_day));
		$pzd = explode("-", $good_day);

		$data_parsed = $week_days[$wk_d].", ".$pzd[2]." ".$month_lab[intval($pzd[1])]." ".$pzd[0];

		return sprintf("Data utile: %s", $data_parsed);

	}

	function getPayDay($day_deadline='') {

		$bl_data = "";

		//	Only for Italy - Fix date
		$festivity = array(
			"01-01",	//	Capodanno
			"01-06",	//	Epifania
			"04-25",	//	Liberazione dal nazifascismo (1945)
			"05-01",	//	Festa del lavoro
			"06-02",	//	Festa della Repubblica
			"08-15",	//	Assunzione di Maria
			"11-01",	//	Ognissanti
			"12-08",	//	Immacolata Concezione
			"12-25",	//	Natale di Gesu'
			"12-26"	//	Santo Stefano
		);

		//	Check if var isn't empty and if a valid date
		if (isset($day_deadline) && !empty($day_deadline) && validateDate($day_deadline, 'Y-m-d')) {

			//	Check day of week for specified date
			$bl_data = checkWeek($day_deadline);
			$przd = explode("-", $bl_data);

			//	Calculate Easter Day
			$east_d = easter_days($przd[0]);
			$easter_day = date("Y-m-d", mktime(0,0,0,"03",("21"+$east_d),$przd[0]));

			//	Calculate Next Monday
			//	Lunedi' dell'Angelo - Pasquetta
			$east_d_m = easter_days($przd[0])+1;
			$monday_easter_day = date("Y-m-d", mktime(0,0,0,"03",("21"+$east_d_m),$przd[0]));

			//	If exists list of festivity, add Easter day and next Monday of Easter
			if (isset($festivity) && !empty($festivity) && is_array($festivity)) {

				array_push($festivity, substr($easter_day, 5), substr($monday_easter_day, 5));

				//	Check if date declared, is a festivity
				if (in_array(substr($bl_data, 5), $festivity) !== false)
					$bl_data = date("Y-m-d", mktime(0,0,0,$przd[1],($przd[2]+1),$przd[0]));

			} else {

				if ($bl_data == $easter_day)
					$bl_data = date("Y-m-d", mktime(0,0,0,$przd[1],($przd[2]+2),$przd[0]));
				elseif ($bl_data == $monday_easter_day)
					$bl_data = date("Y-m-d", mktime(0,0,0,$przd[1],($przd[2]+1),$przd[0]));

			}

			//	Check again day of week for date
			$bl_data = checkWeek($bl_data);

		}

		return (!empty($bl_data)) ? parseDate($bl_data) : "Error!";

	}

	//	Init Script
	echo getPayDay("2015-05-01");