Adding a taxonomy tag to wordpress post by writing it in comment with hashtag

Question

In wordpress, I have a post with some tags. A user should be able to add a tag to the post by writing the tag with a hashtag in the comment, e.g. 'This is a comment that adds #orange' should add the tag orange.

That is my code:

function add_tag_from_comment( $comment_ID ) {
    $comment = get_comment($comment_ID);
    $search_text = strip_tags( str_replace( array( "\n", "\r"), $comment->comment_content));
    preg_match_all('/#([\d\w-_]+)[\b|]{0,3}/', $search_text, $matches, PREG_PATTERN_ORDER);
    foreach($matches[1] as $match) {
        wp_set_post_tags( $comment->comment_post_ID, $match, true );
    }
}
add_action( 'comment_post', 'add_tag_from_comment', 10, 2 );

If I replace $comment->comment_content with a text like 'This is a comment that adds #oranges', then it works. But it does not work when I write the actual comment and I don't know the reason. Can somebody help me?

Answer 1

I found a solution based on Sco's Answer:

add_action('comment_post', 'tag_comment_insert', 2);
function tag_comment_insert($comment) {
    $comment_text = get_comment_text($comment);
    $current_comment = get_comment( $comment );
    $comment_post_id = $current_comment->comment_post_ID;
    preg_match_all('/#([\d\w-_]+)[\b|]{0,3}/', $comment_text, $matches, PREG_PATTERN_ORDER);
    wp_set_post_tags( $comment_post_id, $matches[1], true );
}

add_action('comment_text', 'tag_comment', 2);
function tag_comment($comment) {
    $comment = preg_replace('/#([0-9a-zA-Z]+)/i', '<a class="hashtag" href="'.get_home_url().'/tag/$1">#$1</a>', $comment);
    return $comment;
}

The problem before was that the post_ID was not set. My solution seems to be a bit complicated, so any shortening is appreciated. Thank you all for the help.