ReCaptcha.php

<?php

/**
 * Class ReCaptcha
 *
 * USAGE:
 *
 *  CLIENT SIDE:
 * Create the tags like its explained on the google site when you obtain the keys or before the </head> tag
 * <?= ReCaptcha::getHeadTag() ?> and where you want to put the verification <?= ReCaptcha::getFormTag() ?>
 *
 *  SERVER SIDE:
 * Just need an if(ReCaptcha::check($_POST['g-recaptcha-response']) an it returns true when verified, and false
 * when not verified, if you want to check the errors just do a ReCaptcha::getErrors()
 *
 */
class ReCaptcha {

    public $status = false;
    public $errors = [];

    const SITE_KEY = '';
    const SECRET_KEY = '';

    const URL_SCRIPT = 'https://www.google.com/recaptcha/api.js';
    const URL_VERIFY = 'https://www.google.com/recaptcha/api/siteverify';

    private static $INSTANCE;

    private function __construct($status = false, $errors = []){
        $this->status = $status;
        $this->errors = $errors;
    }

    public static function check($response, $remoteIp = null){
        if(empty($response)){
            self::$INSTANCE = new self(false, ['No input given']);
            return false;
        }
        if(empty($remoteIp)){
            $remoteIp = $_SERVER['REMOTE_ADDR'];
        }
        $HTTPData = self::getHTTPData($response, $remoteIp);
        if($HTTPData->success){
            return true;
        }else{
            self::$INSTANCE = new self(false, $HTTPData->error-codes);
            return false;
        }
    }

    public static function getErrors(){
        if(empty(self::$INSTANCE)){
            return "Not checked yet";
        }else{
            return implode(', ', self::$INSTANCE->errors);
        }
    }

    private static function submitHTTP($response, $remoteIp){
        return file_get_contents(self::URL_VERIFY.'?'.http_build_query([
                'secret' => self::SECRET_KEY,
                'response' => $response,
                'remoteip' => $remoteIp
            ]));
    }

    private static function getHTTPData($response, $remoteIp){
        $httpResponse = self::submitHTTP($response, $remoteIp);
        if($httpResponse === false){
            return null;
        }else{
            return json_decode($httpResponse);
        }
    }

    public static function getFormTag(){
        return '<div class="g-recaptcha" data-sitekey="'.self::SITE_KEY.'"></div>';
    }

    public static function getHeadTag(){
        return '<script src="'.self::URL_SCRIPT.'"></script>';
    }

}