MX WC with admin

<?php
/*
Plugin Name: MX Woocommerce HRK currency + PayPal + HNB conversion
Plugin URI: http://media-x.hr
Description: Plugin for enabling PayPal gateway with HRK set as store currency + HNB conversion
Version: 1.0
Author: Media X
Author URI: http://media-x.hr
License: GPLv3
*/

add_filter('woocommerce_paypal_args', 'convert_hrk_to_eur');
function get_currency() {
        $eur_rate = get_transient( 'eur_rate' );
        if ( empty( $eur_rate ) ){
                $response = wp_remote_get( 'http://hnbex.eu/api/v1/rates/daily');
                if ( is_wp_error( $response ) || 200 != wp_remote_retrieve_response_code( $response ) )
                        $eur_rate = get_option('mxwc_option')['mxwc_eur_rate_input'];
                try {
                        $result = wp_remote_retrieve_body( $response );
                        $currency_list = json_decode( $result, true);
                        foreach ($currency_list as $item) {
                                if ($item['currency_code'] === 'EUR') {
                                        $eur_rate = $item['median_rate'];
                                }
                        }
                        set_transient( 'eur_rate', $eur_rate, 6 * HOUR_IN_SECONDS );
                } catch ( Exception $ex ) {
                        error_log( 'HNBEX API REQUEST ERROR : ' . $ex->getMessage() );
                       $eur_rate = get_option('mxwc_option')['mxwc_eur_rate_input'];
                }
        }
        return $eur_rate;
}

add_filter( 'woocommerce_paypal_supported_currencies', 'add_hrk_paypal_valid_currency' );
    function add_hrk_paypal_valid_currency( $currencies ) {
     array_push ( $currencies , 'HRK' );
     return $currencies;
    }
add_filter('woocommerce_paypal_args', 'convert_hrk_to_eur');

function convert_hrk_to_eur($paypal_args){
        if ( $paypal_args['currency_code'] == 'HRK'){
        $convert_rate = get_currency();
        $paypal_args['currency_code'] = 'EUR';
                $i = 1;

        while (isset($paypal_args['amount_' . $i])) {
            $paypal_args['amount_' . $i] = round( $paypal_args['amount_' . $i] / $convert_rate, 2);
            ++$i;
        }

                if ( $paypal_args['discount_amount_cart'] > 0 ) {
                        $paypal_args['discount_amount_cart'] = round( $paypal_args['discount_amount_cart'] / $convert_rate, 2);
                }
                }

return $paypal_args;
}
/* Plugin admin option */

class MXWC_SettingsPage
{
    /**
     * Holds the values to be used in the fields callbacks
     */
    private $options;

    /**
     * Start up
     */
    public function __construct()
    {
        add_action( 'admin_menu', array( $this, 'add_mxwc_plugin_page' ) );
        add_action( 'admin_init', array( $this, 'page_init' ) );
    }

    /**
     * Add options page
     */
    public function add_mxwc_plugin_page()
    {
        // This page will be under "Settings"
        add_options_page(
            'MX WC Plugin Page',
            'MX WC fallback rate',
            'manage_options',
            'mxwc_section',
            array( $this, 'create_mxwc_admin_page' )
        );
    }

    /**
     * Options page callback
     */
    public function create_mxwc_admin_page()
    {
        // Set class property
        $this->options = get_option( 'mxwc_option' );
        ?>
        <div class="wrap">
            <h2>MX WC Plugin Page</h2>
            <form method="post" action="options.php">
            <?php
                // This prints out all hidden setting fields
                settings_fields( 'mxwc_options' );
                do_settings_sections( 'mxwc_section' );
                submit_button('Pohrani izmjene');
            ?>
            </form>
        </div>
        <?php
    }

    /**
     * Register and add settings
     */
    public function page_init()
    {
        register_setting(
            'mxwc_options', // Option group
            'mxwc_option', // Option name
            array( $this, 'sanitize' ) // Sanitize
        );

        add_settings_section(
            'mxwc_section_id', // ID
            'MX WC fallback rate', // Title
            array( $this, 'print_section_info' ), // Callback
            'mxwc_section' // Page
        );

        add_settings_field(
            'mxwc_eur_rate_input',
            'Upišite stopu konverzije',
            array( $this, 'eur_rate_callback' ),
            'mxwc_section',
            'mxwc_section_id'
        );
    }

    /**
     * Sanitize each setting field as needed
     *
     * @param array $input Contains all settings fields as array keys
     */
    public function sanitize( $input )
    {
        $new_input = array();

        if( isset( $input['mxwc_eur_rate_input'] ) )
            $new_input['mxwc_eur_rate_input'] = floatval( $input['mxwc_eur_rate_input'] );

        return $new_input;
    }

    /**
     * Print the Section text
     */
    public function print_section_info()
    {
        print 'Dolje unesite stopu konverzije HRK u EUR koja će se koristiti u slučaju da nije moguće dohvatiti HNB tečajnicu.';
    }

    /**
     * Get the settings option array and print one of its values
     */
    public function eur_rate_callback()
    {
        printf(
            '<input type="text" id="mxwc_eur_rate_input" name="mxwc_option[mxwc_eur_rate_input]" value="%s" />',
            isset( $this->options['mxwc_eur_rate_input'] ) ? esc_attr( $this->options['mxwc_eur_rate_input']) : ''
        );
    }
}

if( is_admin() )
    $mxwc_settingspage = new MXWC_SettingsPage();
?>