Log post history in comments - WordPress

post-versioning-via-comments.php

function add_comment_on_post_update( $post_id, $post_after, $post_before ) {

    // If this is just a revision, don't send the email.
    if ( wp_is_post_revision( $post_id ) )
        return;
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE)
        return;
    if (isset($post_before->post_status) && 'auto-draft' == $post_before->post_status) {
        return;
    }

    if ('post' == $_POST['post_type']) {
        $current_user = wp_get_current_user();
        $comment = 'Edited by '.$current_user->user_login;

        $time = current_time('mysql');

        $data = array(
            'comment_post_ID' => $post_id,
            'comment_author' => 'admin',
            'comment_author_email' => 'admin@admin.com',
            'comment_author_url' => 'http://www.xyz.com',
            'comment_content' => $comment,
            'user_id' => $current_user->ID,
            'comment_date' => $time,
            'comment_approved' => 1,
            'comment_type' => 'custom-comment-class'
        );
        wp_insert_comment($data);
    }

}
add_action( 'post_updated', 'add_comment_on_post_update', 10 , 3 );