Append post thumbnail timage to the first content heading tag

I want to add new conditions to the following code:

function add_thumb_after_h2( $content ) {
  if (is_single()) {
    global $post;

    if ( substr_count( $content, '<h2>' ) > 3 ) {
      $thumb = '<div id="post_thumbnail">' . get_the_post_thumbnail( $post->ID, 'fullsize' ) . '</div>';
      $content = str_replace_once("</h2>", "</h2>".$thumb, $content);
    }
  }

  return $content;
}

I also need to include h3, h4 and h5, example:

    if ( substr_count( $content, '<h2>,<h3>,<h4>,<h5>' ) > 3 ) {}

How can I do it? The thumbnail should be added only to the first occurrence of a heading tag, regardless of its type (h2, h3, etc.)

Thanks

Answer

You can achieve this my modifying your function to the following:

function add_thumb_after_h2( $content ) {
  if ( is_single() ) {
    global $post;

    foreach ( array('h2', 'h3', 'h4', 'h5') as $heading ) {
      if ( ! $replaced && substr_count( $content, "<{$heading}>" ) > 3 ) {
        $thumb = '<div id="post_thumbnail">' . get_the_post_thumbnail( $post->ID, 'fullsize' ) . '</div>';
        $content = str_replace_once("</{$heading}>", "</{$heading}>" . $thumb, $content);
        break;
      }
    }
  }

  return $content;
}