Filter 'the_content', count the words, and add the markup you need. You should not use str_word_count() because it has issues with numbers and utf-8.
So let’s start with a word count function:
/**
* Alternative for str_word_count().
*
* @link http://toscho.de/2012/php-woerter-zaehlen/
* @param string $str
* @return int Number of words
*/
function t5_word_count( $str )
{
// We do not want to count markup
$text = strip_tags( $str );
// no leading and trailing white space
$text = trim( $text );
// take multiple white spaces as one
// Add one space to get an almost exact match
$word_count = preg_match_all( '~\s+~', "$text ", $m );
return (int) $word_count;
}
Now the filter function:
// Hook in very late to let other filters (shortcodes and such)
// do their work first.
add_filter( 'the_content', 't5_content_word_count', 999 );
/**
* Add a <div> with a special class to the content.
*
* @param string $content
* @return string
*/
function t5_content_word_count( $content )
{
$words = t5_word_count( $content );
$class = 'default';
// max 100 words
$words < 101 && $class = '100';
// max 50 words
$words < 51 && $class = '50';
return "<div class='word-count-$class'>$content</div>";
}
Instead of inline styles which are very bad on mobile devices or printed pages I have chosen a class.
In your stylesheet you can now style these classes:
.word-count-default
{
font-size: 1em;
}
.word-count-100
{
font-size: 1.1em;
}
.word-count-50
{
font-size: 1.2em;
}
Be aware that the filter works on single pages of a post only. If you have split a post into multiple parts with <!--nextpage--> you may get different classes for different pages of that post.
Update
To insert the div when a post is saved do not filter 'the_content', but 'wp_insert_post_data'. And you need a third function for this:
add_filter( 'wp_insert_post_data', 't5_count_words_on_insert', 999 );
/**
* Add the font size div on post insert.
*
* @wp-hook wp_insert_post_data
* @param array $data
* @return array
*/
function t5_count_words_on_insert( $data )
{
'' !== $data['post_content']
&& FALSE === strpos(
stripslashes( $data['post_content'] ),
"<div class='word-count-"
)
&& $data['post_content'] = t5_content_word_count( $data['post_content'] );
return $data;
}
See /wp-includes/post.php function wp_insert_post() for details.
I do not recommend this solution. You cannot use <!--nextpage--> now anymore because you would end up with an unclosed <div> on the first page.
