File Upload in WordPress in custom directory

functions.php

<?php

function wp1982_handle_file_upload( $filename, $file_url ) {
    add_filter( 'upload_dir', 'wp1982_customize_upload_dir', 10 );
    $upload_file = wp_upload_bits( $filename, null, file_get_contents( $file_url ) );
    remove_filter( 'upload_dir', 'wp1982_customize_upload_dir' , 10 );

    if ( !$upload_file['error'] ) {
        $wp_filetype = wp_check_filetype( $filename, null );
        $attachment = array(
            'post_mime_type' => $wp_filetype['type'],
            'post_parent' => 0,
            'post_title' => preg_replace( '/\.[^.]+$/', '', $filename ),
            'post_content' => '',
            'post_status' => 'inherit'
        );
        $attachment_id = wp_insert_attachment( $attachment, $upload_file['file'] );

        if (!is_wp_error( $attachment_id )) {
            require_once(ABSPATH . "wp-admin" . '/includes/image.php');
            $attachment_data = wp_generate_attachment_metadata( $attachment_id, $upload_file['file'] );
            wp_update_attachment_metadata( $attachment_id,  $attachment_data );

            return $attachment_id;
        }
    }

    return 0;
}

function wp1982_customize_upload_dir( $upload ) {
    $user_id = get_current_user_id();
    $user = get_user_by( 'id', $user_id );
    $dirname = $user_id . '-' . $user->user_login;

    $upload['subdir'] = '/reserved/' . $dirname;
    $upload['path']   = $upload['basedir'] . $upload['subdir'];
    $upload['url']    = $upload['baseurl'] . $upload['subdir'];
    return $upload;
}

// call upload function

$file_doc = $_FILES['file_name'];
$filename = $file_doc['name'];
$file_url = $file_doc['tmp_name'];

wp1982_handle_file_upload( $filename, $file_url );