如何在wordpress帖子中设置最小字数

I am planning to create a code filter and set a minimum word count in saving/submitting the wordpress post. I tried this code.

function minWord($content)
{
    global $post;
    $content = $post->post_content;
    if (str_word_count($content) < 300 ) //set this to the minimum number of words
    wp_die( __('Error: your post is below the minimum word count. It needs to be longer than 300 words.') );
}
add_action('publish_post', 'minWord');

but the issue, when I input < 300 words the post still saves it on the database. My question now is what should I do that if the content will have < 300 words it won't save to the database?