So's WordPress Authors Widget: displays a list of blog authors ordered by number of posts

so-authors-widget.php

<?php

/**
 * Description: So's WordPress Authors Widget: displays a list of blog authors ordered by number of posts
 * Author: Ulrich SOSSOU
 * Author URI: http://ulrichsossou.com/
 * Version: 1.0
 * Licence: GPLv2
 * Compatibility: WordPress 3.0+
 *
 */

/*
Copyright (C) 2010  Ulrich SOSSOU

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

class SO_Widget_Authors extends WP_Widget {

	function SO_Widget_Authors() {
		$widget_ops = array( 'classname' => 'so_widget_authors', 'description' => __( 'The authors ordered by number of posts', 'so' ) );
		$this->WP_Widget( 'so_authors', __( 'Authors', 'so' ), $widget_ops);
		$this->alt_option_name = 'so_widget_authors';

		add_action( 'save_post', array(&$this, 'flush_widget_cache' ) );
		add_action( 'transition_post_status', array(&$this, 'flush_widget_cache' ) );
	}

	function flush_widget_cache() {
		wp_cache_delete( 'so_widget_authors', 'widget' );
	}
	
	function widget( $args, $instance ) {
		global $comments, $comment, $wpdb;

		$cache = wp_cache_get( 'so_widget_authors', 'widget' );

		if ( ! is_array( $cache ) )
			$cache = array();

		if ( isset( $cache[$args['widget_id']] ) ) {
			echo $cache[$args['widget_id']];
			return;
		}

 		extract($args, EXTR_SKIP);
 		$output = '';
 		$title = apply_filters( 'widget_title', empty($instance['title']) ? __( 'Authors', 'so' ) : $instance['title']);

		if ( ! $number = (int) $instance['number'] )
 			$number = 5;
 		else if ( $number < 1 )
 			$number = 1;
		
		require_once( ABSPATH . '/wp-admin/includes/user.php' );
		$wp_user_search = new WP_User_Search();

		$wp_user_search->query_from .= " LEFT JOIN $wpdb->posts ON ($wpdb->users.ID = $wpdb->posts.post_author)";
		$wp_user_search->query_where .= " AND (post_type = 'post' OR post_type IS NULL)";
		$wp_user_search->query_orderby = " GROUP BY $wpdb->users.ID ORDER BY COUNT($wpdb->posts.ID) DESC, user_login ASC";
		$wp_user_search->query_limit = " LIMIT 0, $number";
		$wp_user_search->users_per_page = $number;
		
		$users_id = $wp_user_search->get_results();

		$output .= $before_widget;
		if ( $title )
			$output .= $before_title . $title . $after_title;

		$output .= '<ul class="so-authors">';
		if ( $users_id ) {
			foreach ( (array) $users_id as $user_id) {
				$count = count_user_posts( $user_id );
				$count_text = ( $count > 1 ) ? $count . ' posts' : $count . ' post';
				
				if( $count ) {
				    $user_post = get_posts( 'showposts=1&author=' . $user_id );
					$date = mysql2date( get_option('date_format'), $user_post[0]->post_date );
					
					$output .=  '<li>' . get_avatar( $user_id, 40 ) . '<span>' . get_the_author_meta( 'display_name', $user_id ) . '</span> <span>' . $count_text . '</span> <span>latest post - ' . mysql2date( get_option('date_format'), $user_post[0]->post_date ) . '</span></li>';
				}
			}
 		}
		$output .= '</ul>';
		
		$output .= $after_widget;

		echo $output;
		$cache[$args['widget_id']] = $output;
		wp_cache_set( 'so_widget_authors', $cache, 'widget' );
	}

	function update( $new_instance, $old_instance ) {
		$instance = $old_instance;
		$instance['title'] = strip_tags($new_instance['title']);
		$instance['number'] = (int) $new_instance['number'];
		$this->flush_widget_cache();

		$alloptions = wp_cache_get( 'alloptions', 'options' );
		if ( isset($alloptions['so_widget_authors']) )
			delete_option( 'so_widget_authors' );

		return $instance;
	}

	function form( $instance ) {
		$title = isset($instance['title']) ? esc_attr($instance['title']) : '';
		$number = isset($instance['number']) ? absint($instance['number']) : 5;
?>
		<p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
		<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" /></p>

		<p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of authors to show:' ); ?></label>
		<input id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="text" value="<?php echo $number; ?>" size="3" /></p>
<?php
	}
}