Writing a wordpress plugin to filter comments

I’m completely new to wordpress plugin development. I want to write a plugin to delete comments I don’t want based on a keyword list.

Update: WordPress already comes with this feature under Comment Moderation

The code

The code isn’t complex. It first use the preprocess_comment hook to check the comment content. If it contains hyperlinks, a 404 error will be returned and the comment will not be inserted into database.

 
/*
 Plugin Name: Keyword Based Spam Removal
 Plugin URI: http://wp-plugins.headdesk.me
 Description: a plugin to delete spam based on a defined keyword list
 Version: 0.2
 Author: xpk
 Author URI: http://blog.headdesk.me
 License: GPL2
*/

add_filter( 'preprocess_comment', 'examine_comment', '' , 1 );
function examine_comment($commentdata) { 
  if (preg_match('/https?:/i', $commentdata['comment_content'])) { 
    $commentdata['comment_content'] = "Comment contains hyperlink and sanitized."; 
    $commentdata['comment_post_ID'] = 64277; 
    error_log("WPPL-SPAM: Link detected, content removed");     
    wp_die( __( 'ERROR: Bad comments are disabled.' ), '', array( 'response' => 404 ) ); 
  } 
  return ($commentdata);
}

add_action( 'rest_insert_comment', 'drop_rest_comment');
function drop_rest_comment() {
 wp_die( __( 'ERROR: REST comments are disabled.' ), '', array( 'response' => 404 ) );
}

// The following is no longer needed
add_action('comment_post', 'delete_comment',10,3);
function delete_comment($id, $approval, $commentdata) {
	if ($commentdata['comment_post_ID'] == 64277)
		wp_delete_comment($id, $force_delete = true);
}

Thanks to 146.185.223.125 who kept spamming my site and helped improved my code.