Roll your own PHP validator

test-validator.php

<?php                                                                                                                       
error_reporting(-1);                                                                                                        
require_once("vendor/autoload.php");                                                                               
use \Utils\Validator as V;                                                                                                  
                                                                                                                            
main();                                                                                                                     
function main()                                                                                                             
{                                                                                                                           
    V::validate([                                                                                                           
        ['field' => 'http://www.google.com', 'alias' => 'URL', 'rules' => [V::IS_URL]],                                     
        ['field' => 'v1', 'alias' => 'value', 'rules' => [V::IN_ARRAY], 'array' => ['v1', 'val2']]                          
    ]);                                                                                                                     
}  

Validator.php

<?php                                                                                                                    
namespace Utils;                                                                                                         
                                                                                                                         
class Validator {                                                                                                        
    const IS_URL = 1;                                                                                                  
    const IN_ARRAY = 2;
    //other constants
                                                                                                                         
    public static function validate($fields) {                                                                           
        foreach ($fields as $f) {                                                                                        
            //we need field, alias and rules for each value to be checked                                                
            if (!array_key_exists('field', $f)) {                                                                           
                throw new \Exception('No field specified');                                                                                                               }                                                                                                               
                                                                                                                            
            if (!array_key_exists('alias', $f)) {                                                                           
                throw new \Exception('No alias specified');                                                                                                               }                                                                                                               
                                                                                                                            
            if (!array_key_exists('rules', $f)) {                                                                           
                throw new \Exception('No rules specified');                                                                 
            }                                                                                                                                                                                                                                                                           
                                                                                                                         
            foreach ($f['rules'] as $r) {                                                                                
                static::check($f, $r);                                                                                   
            }                                                                                                            
        }                                                                                                                
    }                                                                                                                    
                                                                                                                         
    private static function check($f, $rule) {                                                                           
        switch ($rule) {                                                                                                 
        case static::IS_URL:                                                                                             
            $url = filter_var($f['field'], FILTER_VALIDATE_URL);                                                         
                                                                                                                         
            if (!$url) {                                                                                                 
                throw new \Exception("Please provide valid {$f['alias']}");                                              
            }                                                                                                            
            break; 
            
        case static::IN_ARRAY:                                                                                           
            if (!array_key_exists('array', $f)) {                                                                                   
                throw new \Exception("No array specified");                                                              
            }                                                                                                            
                                                                                                                         
            if (!in_array($f['field'], $f['array'])) {                                                                   
                throw new \Exception("Please specify valid value for {$f['alias']}!");                                   
            }                                                                                                            
                                                                                                                         
            break; 
         //other rules
        }
    }
}