Ciao Bigdada e grazie per la tua risposta!

Il problema è che non so assolutamente scrivere la regola in php e ho bisogno di qualcuno che la scriva per me.

In pratica ho un modulo di prenotazioni, all'interno del quale vorrei mettere una select menu a discesa per far scegliere all'utente le varie offerte.

Queste offerte sono valide solo se la data di arrivo è entro un certo periodo.

Le date che ho scritto sono tutte identiche ma potrebbero anche essere diverse...

Poichè l'utente deve inserire (oltre ai vari dati) anche la data di arrivo e di partenza, la select con le offerte dovrebbe andare a controllare se la data di arrivo corrisponde ai requisiti per quell'offerta specifica.

Tutto il modulo si appoggia ad un file che esegue le varie validazioni dei campi, e vorrei aggiungere anche questa regola specifica.

Di seguito il codice del file validation.php dove ci sono queste regole di validazione e a cui dovrei aggiungere anche questa.

codice:
<?php
/**
* @version 1.4.0
* @package RSform!Pro 1.4.0
* @copyright (C) 2007-2011 www.rsjoomla.com
* @license GPL, http://www.gnu.org/copyleft/gpl.html
*/

// no direct access
defined( '_JEXEC' ) or die( 'Restricted access' );

class RSFormProValidations
{
	function none($value,$extra=null,$data=null)
	{
		return true;
	}

	function alpha($param,$extra=null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
			
		for($i=0;$i<strlen($param);$i++)
			if(strpos($extra,$param[$i]) === false && preg_match('#([^a-zA-Z ])#', $param[$i]))
				return false;
				
		return true;
	}
	
	function numeric($param,$extra=null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
		
		for($i=0;$i<strlen($param);$i++)
			if (strpos($extra,$param[$i]) === false && !is_numeric($param[$i]))
				return false;
				
		return true;
	}
	
	
		function validBonuscode($param,$extra = null)
{
     if($param !== 'pdcuyd2013') 
       	 return false;
     	 return true;
}

	
	function alphanumeric($param,$extra = null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
		
		for($i=0;$i<strlen($param);$i++)
			if(strpos($extra,$param[$i]) === false && preg_match('#([^a-zA-Z0-9 ])#', $param[$i]))
				return false;
				
		return true;
	}
	
	function alphaaccented($value, $extra=null, $data=null) {
		if (preg_match('#[^[:alpha:] ]#u', $value)) {
			return false;
		}
		return true;
	}
	
	function alphanumericaccented($value, $extra=null, $data=null) {
		if (preg_match('#[^[:alpha:]0-9 ]#u', $value)) {
			return false;
		}
		return true;
	}
	
	function email($email,$extra=null,$data=null)
	{
		jimport('joomla.mail.helper');
		
		$email = trim($email);
		return JMailHelper::isEmailAddress($email);
	}
	
	function emaildns($email,$extra=null,$data=null)
	{
		// Check if it's an email address format
		if (!RSFormProValidations::email($email,$extra,$data))
			return false;
		
		$email = trim($email);
		list($user, $domain) = explode('@', $email, 2);
		
		// checkdnsrr for PHP < 5.3.0
		if (!function_exists('checkdnsrr') && function_exists('exec') && is_callable('exec'))
		{
			@exec('nslookup -type=MX '.escapeshellcmd($domain), $output);
			foreach($output as $line)
				if (preg_match('/^'.preg_quote($domain).'/',$line))
					return true;
			
			return false;
		}
		
		// fallback method...
		if (!function_exists('checkdnsrr') || !is_callable('checkdnsrr'))
			return true;
		
		return checkdnsrr($domain, substr(PHP_OS, 0, 3) == 'WIN' ? 'A' : 'MX');
	}
	
	function uniquefield($value, $extra=null,$data=null)
	{
		$db 	=& JFactory::getDBO();
		$form   = JRequest::getVar('form');
		$formId = (int) @$form['formId'];
		
		$db->setQuery("SELECT `SubmissionValueId` FROM #__rsform_submission_values WHERE FormId='".$formId."' AND `FieldName`='".$db->getEscaped($data['NAME'])."' AND `FieldValue`='".$db->getEscaped($value)."'");
		return $db->loadResult() ? false : true;
	}
	
	function uniquefielduser($value, $extra=null,$data=null)
	{
		$db 	=& JFactory::getDBO();
		$form   = JRequest::getVar('form');
		$formId = (int) @$form['formId'];
		$user	=& JFactory::getUser();
		
		$db->setQuery("SELECT sv.`SubmissionValueId` FROM #__rsform_submission_values sv LEFT JOIN #__rsform_submissions s ON (sv.SubmissionId=s.SubmissionId) WHERE sv.FormId='".$formId."' AND sv.`FieldName`='".$db->getEscaped($data['NAME'])."' AND sv.`FieldValue`='".$db->getEscaped($value)."' AND (".($user->get('guest') ? "s.`UserIp`='".$db->getEscaped($_SERVER['REMOTE_ADDR'])."'" : "s.`UserId`='".(int) $user->get('id')."'").")");
		return $db->loadResult() ? false : true;
	}
	
	function uszipcode($value)
	{
		return preg_match("/^([0-9]{5})(-[0-9]{4})?$/i",$value);
	}
	
	function phonenumber($value)
	{
		return preg_match("/\(?\b[0-9]{3}\)?[-. ]?[0-9]{3}[-. ]?[0-9]{4}\b/i", $value);
	}
	
	function creditcard($value,$extra=null,$data=null)
	{
		$value = preg_replace ('/[^0-9]+/', '', $value);
		if (!$value)
			return false;
		
		if (preg_match("/^([34|37]{2})([0-9]{13})$/", $value)) // Amex
			return true;
		
		if (preg_match("/^([30|36|38]{2})([0-9]{12})$/", $value)) // Diners
			return true;
		
		if (preg_match("/^([6011]{4})([0-9]{12})$/", $value)) // Discover
			return true;
			
		if (preg_match("/^([51|52|53|54|55]{2})([0-9]{14})$/", $value)) // Master
			return true;
			
		if (preg_match("/^([4]{1})([0-9]{12,15})$/", $value)) // Visa
			return true;
		
		return false;
	}

	function custom($param,$extra=null,$data=null)
	{
		if(strpos($param,"\n") !== FALSE) 
			$param = str_replace(array("\r","\n"),'',$param);
		
		for($i=0;$i<strlen($param);$i++)
			if(strpos($extra,$param[$i]) === false)
				return false;
				
		return true;
	}

	function password($param,$extra=null,$data=null)
	{
		if ($data['DEFAULTVALUE'] == $param)
			return true;
		
		return false;
	}
	
	function ipaddress($param,$extra=null,$data=null)
	{
		return preg_match('#\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b#', $param, $match);
	}
	
	function validurl($param,$extra=null,$data=null)
	{
		$format = 
		'/^(https?):\/\/'.                                         // protocol
		'(([a-z0-9$_\.\+!\*\'\(\),;\?&=-]|%[0-9a-f]{2})+'.         // username
		'(:([a-z0-9$_\.\+!\*\'\(\),;\?&=-]|%[0-9a-f]{2})+)?'.      // password
		'@)?(?#'.                                                  // auth requires @
		')((([a-z0-9][a-z0-9-]*[a-z0-9]\.)*'.                      // domain segments AND
		'[a-z][a-z0-9-]*[a-z0-9]'.                                 // top level domain  OR
		'|((\d|[1-9]\d|1\d{2}|2[0-4][0-9]|25[0-5])\.){3}'.
		'(\d|[1-9]\d|1\d{2}|2[0-4][0-9]|25[0-5])'.                 // IP address
		')(:\d+)?'.                                                // port
		')(((\/+([a-z0-9$_\.\+!\*\'\(\),;:@&=-]|%[0-9a-f]{2})*)*'. // path
		'(\?([a-z0-9$_\.\+!\*\'\(\),;:@&=-]|%[0-9a-f]{2})*)'.      // query string
		'?)?)?'.                                                   // path and query string optional
		'(#([a-z0-9$_\.\+!\*\'\(\),;:@&=-]|%[0-9a-f]{2})*)?'.      // fragment
		'$/i';
		
		return preg_match($format, $param, $match);
	}
	
	function regex($value,$pattern=null,$data=null)
	{
		return preg_match($pattern, $value);
	}
<?php
/**
* @version 1.4.0
* @package RSform!Pro 1.4.0
* @copyright (C) 2007-2011 www.rsjoomla.com
* @license GPL, http://www.gnu.org/copyleft/gpl.html
*/

// no direct access
defined( '_JEXEC' ) or die( 'Restricted access' );

class RSFormProValidations
{
	function none($value,$extra=null,$data=null)
	{
		return true;
	}

	function alpha($param,$extra=null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
			
		for($i=0;$i<strlen($param);$i++)
			if(strpos($extra,$param[$i]) === false && preg_match('#([^a-zA-Z ])#', $param[$i]))
				return false;
				
		return true;
	}
	
	function numeric($param,$extra=null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
		
		for($i=0;$i<strlen($param);$i++)
			if (strpos($extra,$param[$i]) === false && !is_numeric($param[$i]))
				return false;
				
		return true;
	}
	
	
		function validBonuscode($param,$extra = null)
{
     if($param !== 'pdcuyd2013') 
       	 return false;
     	 return true;
}

	
	function alphanumeric($param,$extra = null,$data=null)
	{
		if(strpos($param,"\n") !== false) 
			$param = str_replace(array("\r","\n"),'',$param);
		
		for($i=0;$i<strlen($param);$i++)
			if(strpos($extra,$param[$i]) === false && preg_match('#([^a-zA-Z0-9 ])#', $param[$i]))
				return false;
				
		return true;
	}
	
	function alphaaccented($value, $extra=null, $data=null) {
		if (preg_match('#[^[:alpha:] ]#u', $value)) {
			return false;
		}
		return true;
	}
	
	function alphanumericaccented($value, $extra=null, $data=null) {
		if (preg_match('#[^[:alpha:]0-9 ]#u', $value)) {
			return false;
		}
		return true;
	}
	
	function email($email,$extra=null,$data=null)
	{
		jimport('joomla.mail.helper');
		
		$email = trim($email);
		return JMailHelper::isEmailAddress($email);
	}
	
	function emaildns($email,$extra=null,$data=null)
	{
		// Check if it's an email address format
		if (!RSFormProValidations::email($email,$extra,$data))
			return false;
		
		$email = trim($email);
		list($user, $domain) = explode('@', $email, 2);
		
		// checkdnsrr for PHP < 5.3.0
		if (!function_exists('checkdnsrr') && function_exists('exec') && is_callable('exec'))
		{
			@exec('nslookup -type=MX '.escapeshellcmd($domain), $output);
			foreach($output as $line)
				if (preg_match('/^'.preg_quote($domain).'/',$line))
					return true;
			
			return false;
		}
		
		// fallback method...
		if (!function_exists('checkdnsrr') || !is_callable('checkdnsrr'))
			return true;
		
		return checkdnsrr($domain, substr(PHP_OS, 0, 3) == 'WIN' ? 'A' : 'MX');
	}
	
	function uniquefield($value, $extra=null,$data=null)
	{
		$db 	=& JFactory::getDBO();
		$form   = JRequest::getVar('form');
		$formId = (int) @$form['formId'];
		
		$db->setQuery("SELECT `SubmissionValueId` FROM #__rsform_submission_values WHERE FormId='".$formId."' AND `FieldName`='".$db->getEscaped($data['NAME'])."' AND `FieldValue`='".$db->getEscaped($value)."'");
		return $db->loadResult() ? false : true;
	}
	
	function uniquefielduser($value, $extra=null,$data=null)
	{
		$db 	=& JFactory::getDBO();
		$form   = JRequest::getVar('form');
		$formId = (int) @$form['formId'];
		$user	=& JFactory::getUser();
		
		$db->setQuery("SELECT sv.`SubmissionValueId` FROM #__rsform_submission_values sv LEFT JOIN #__rsform_submissions s ON (sv.SubmissionId=s.SubmissionId) WHERE sv.FormId='".$formId."' AND sv.`FieldName`='".$db->getEscaped($data['NAME'])."' AND sv.`FieldValue`='".$db->getEscaped($value)."' AND (".($user->get('guest') ? "s.`UserIp`='".$db->getEscaped($_SERVER['REMOTE_ADDR'])."'" : "s.`UserId`='".(int) $user->get('id')."'").")");
		return $db->loadResult() ? false : true;
	}
	
	function uszipcode($value)
	{
		return preg_match("/^([0-9]{5})(-[0-9]{4})?$/i",$value);
	}
	
	function phonenumber($value)
	{
		return preg_match("/\(?\b[0-9]{3}\)?[-. ]?[0-9]{3}[-. ]?[0-9]{4}\b/i", $value);
	}
Grazie per il tuo aiuto!