WooCommerce 订阅增强：检查用户是否已购买任何产品以限制试用期

public static function limit_trial( $trial_length, $product ) {
    if ( $trial_length <= 0 ) {
        return $trial_length ;
    }

    $user_id = get_current_user_id() ;

    if ( ! $user_id ) {
        return $trial_length ;
    }

    $params = array(
        'posts_per_page' => -1,
        'post_type'      => 'product'
    );

    $products = new WP_Query( $params );

    if ( $products->have_posts() ) {  while ( $products->have_posts() ) {  $products->the_post();

        if ( isset( self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] ) ) {
            return self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] ? 0 : $trial_length ;
        }

        if ( $product->is_type( 'variation' ) ) {
            $parent_product = wc_get_product( $product->get_parent_id() ) ;
        } else {
            $parent_product = wc_get_product( get_the_ID() ) ;
        }

        if ( 'no' !== self::get_product_limitation( $parent_product ) ) {
            self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] = false ;
            return $trial_length ;
        }

        if ( 'yes' !== get_post_meta( $parent_product->get_id(), '_enr_limit_trial_to_one', true ) ) {
            self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] = false ;
            return $trial_length ;
        }

        $subscriptions = wcs_get_users_subscriptions( $user_id ) ;

        foreach ( $subscriptions as $subscription ) {
            if ( $subscription->has_product( get_the_ID() ) && ( '' !== $subscription->get_trial_period() || 0 !== $subscription->get_time( 'trial_end' ) ) ) {
                self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] = true ;
                return 0 ;
            }
        }

        self::$onetime_trial_cache[ $user_id ][ get_the_ID() ] = false ;

    } wp_reset_postdata(); }

    return $trial_length ;
}