PHP license key client: Quick script tutorial

script.php

<?php

use LicenseKeys\Utility\Api;
use LicenseKeys\Utility\Client;
use LicenseKeys\Utility\LicenseRequest;

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// NO WORDPRESS -> START

/**
 * Saves and updates the license string.
 * @param string $key     The key used as filename
 * @param string $license License string.
 */
function update_option( $key, $license ) {
    $filename = $key . '.key';
    // Delete if license is null
    if ( $license === null && is_file( $filename ) ) {
        return unlink( $filename );
    }
    // Open or create and save
    $file = fopen( $filename, 'w' ) or die( 'Unable to open or create file:  '.$filename );
    fwrite( $file , $license );
    fclose( $file );
}
/**
 * Returns license string found.
 * @param string $key The key used as filename
 */
function get_option( $key ) {
    $filename = $key . '.key';
    // If no file return null
    if ( ! is_file( $filename ) ) return;
    // Read and return
    $file = fopen( $filename, 'r' ) or die( 'Unable to open file:  ' . $filename );
    $license = fread( $file, filesize( $filename ) );
    fclose( $file );
    return $license;
}

// NO WORDPRESS -> END
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define( 'PHOTOMEME_OPTION_KEY', '_photomeme_string' );

/**
 * Method used to activate the product. Returns true or false.
 * @param string $license_key A customer license key.
 * @return bool
 */
function photomeme_activate( $license_key ) {
    $response = Api::activate(
        Client::instance(),
        function() use( $license_key ) {
            return LicenseRequest::create(
                'https://tutorials.net/wp-admin/admin-ajax.php',
                'fake007',
                'PHOTOMEME',
                $license_key ,
                LicenseRequest::DAILY_FREQUENCY
            );
        },
        function( $license ) {
           update_option( PHOTOMEME_OPTION_KEY, $license, true );
        }
    );
    return $response->error === false;
}

/**
 * Returns true or false.
 * @return bool
 */
function photomeme_is_valid() {
    return Api::validate(
        Client::instance(),
        function() {
            return new LicenseRequest( get_option( PHOTOMEME_OPTION_KEY) );
        },
        function( $license ) {
           update_option( PHOTOMEME_OPTION_KEY, $license );
        }
    );
}

/**
 * Returns true or false.
 * @return bool
 */
function photomeme_deactivate() {
    $response = Api::deactivate(
        Client::instance(),
        function() {
            return new LicenseRequest( get_option( PHOTOMEME_OPTION_KEY) );
        },
        function( $license ) {
           if ($license === null)
               update_option( PHOTOMEME_OPTION_KEY, null );
        }
    );
    return $response->error === false;
}