JosephBurnett.com

<?php
/**
 * Plugin name: Simple Nav
 * Author: Joseph Burnett
 * Author URI: http://www.josephburnett.com
 * Plugin URI: http://www.josephburnett.com
 * Version: 1.0
 * Description: Adds a widget which will provide simple navigation links to adjacent posts (or pages).
 **/

class SimpleNav extends WP_Widget {

    private static $class_initialized = false;
    private static $simple_nav_category = null;
    private static $is_single = false;
    private static $is_category = false;

    private static $nav_initialized = false;
    private static $next_link = null;
    private static $next_count = 0;
    private static $prev_link = null;
    private static $prev_count = 0;
    
    # Initialize members used by entire class
    private static function init() {
        global $wp;

        error_log("DEBUG initializing");
        if (SimpleNav::$class_initialized == false) {
            if (is_single()) {
                SimpleNav::$is_single = true;
                SimpleNav::$is_category = false;
                SimpleNav::$simple_nav_category = SimpleNav::determine_post_category();
            }
            if (is_category() or !empty($wp->query_vars['s'])) {
                SimpleNav::$is_single = false;
                SimpleNav::$is_category = true;
                SimpleNav::$simple_nav_category = SimpleNav::determine_category();
            }
            SimpleNav::$class_initialized = true;
       }
    }

    # Initialize members used in rendering navigation
    private static function init_nav() {
        error_log("DEBUG initializing links");
        if ( !SimpleNav::$nav_initialized ) {
            error_log("DEBUG rendering links and finding counts");
            SimpleNav::$next_link = SimpleNav::get_link(false);
            SimpleNav::$next_count = SimpleNav::get_count(false);
            SimpleNav::$prev_link = SimpleNav::get_link(true);
            SimpleNav::$prev_count = SimpleNav::get_count(true);
            SimpleNav::$nav_initialized = true;
        }
    }

    # Widget constructor
    function SimpleNav() {
        parent::WP_Widget(false, $name = 'Simple Nav');
    }

    # Render the widget
    function widget($args, $instance) {

        SimpleNav::init();
        SimpleNav::init_nav();

        $prev_text = "Previous";
        $next_text = "Next";

        $right_arrow = "»";
        $left_arrow = "«";

        $prev_class = "simple_nav_prev";
        $next_class = "simple_nav_next";

        echo "<div class=\"simple_nav\">\n";

        if ( SimpleNav::$is_single ) {

            if ( !empty( SimpleNav::$prev_link ) )
                echo "<span class=\"$prev_class\"><a href=\"" . SimpleNav::$prev_link . "\">$left_arrow $prev_text (" . SimpleNav::$prev_count . ")</a></span>";

            if ( !empty( SimpleNav::$next_link ) )
                echo "<span class=\"$next_class\"><a href=\"" . SimpleNav::$next_link . "\">$next_text (" . SimpleNav::$next_count . ") $right_arrow</a></span>";
        }

        if ( SimpleNav::$is_category ) {

            if ( !empty( SimpleNav::$prev_link ) ) {
                if ( SimpleNav::$prev_count == 1 )
                    echo "<span class=\"$prev_class\"><a href=\"" . SimpleNav::$prev_link . "\">$left_arrow $prev_text (" . SimpleNav::$prev_count . " page)</a></span>";
                else
                    echo "<span class=\"$prev_class\"><a href=\"" . SimpleNav::$prev_link . "\">$left_arrow $prev_text (" . SimpleNav::$prev_count . " pages)</a></span>";
            }

            if ( !empty( SimpleNav::$next_link ) ) {
                if ( SimpleNav::$next_count == 1 )
                    echo "<span class=\"$next_class\"><a href=\"" . SimpleNav::$next_link . "\">$next_text (" . SimpleNav::$next_count . " page) $right_arrow</a></span>";
                else
                    echo "<span class=\"$next_class\"><a href=\"" . SimpleNav::$next_link . "\">$next_text (" . SimpleNav::$next_count . " pages) $right_arrow</a></span>";
            }
        }

        echo "</div>\n";
    }

    # Update the instance of the widget
    function update($new_instance, $old_instance) {				
        return $old_instance; // nothing to do
    }

    # Print the form to configure the widget
    function form($instance) {
        echo "<p>A simple set of navigation links to the adjacent posts (or pages). ";
        echo "The number of posts (or pages) in either direction is given in parenthesis.</p>";
    }

    # Determine which category we're viewing
    private static function determine_category() {
        global $wp;
        return $wp->query_vars['category_name'];
    }

    # Determine which single category (of possibily many) we are navigating within
    private static function determine_post_category() {
        global $post, $wp;

        # Get the current post id
        $post_id = $wp->query_vars['p'];

        if ( empty( $post_id ) ) {
            error_log("DEBUG couldn't get current post id");
            return '';
        }

        # Get categories for the current post
        error_log("DEBUG finding categories for post " . $post_id);
        $post_categories = wp_get_post_categories( $post_id );
        $cats = array();
        $cat_slugs = array();
        foreach($post_categories as $c){
            $cat = get_category( $c );
            $cats[] = array( 'name' => $cat->name, 'slug' => $cat->slug, 'id' => $cat->term_id );
            $cat_slugs[] = $cat->slug;
            error_log("DEBUG adding category: " . $cat->slug);
        }

        if (count($cats) < 1) {
            # Post has no categories, so can't have a simple previous and next
            error_log("DEBUG post has no categories, returning empty");
            return '';
        }

        # What's the category we should be working in?
        $simple_nav_category = $wp->query_vars['simple_nav_category'];
        
        if ( !in_array($simple_nav_category, $cat_slugs) ) {
            # Current post doesn't have the given category, so we ignore it
            error_log("DEBUG post doesn't have given category, ignoring " . $simple_nav_category);
            $simple_nav_category = '';
        }
        
        if ( empty( $simple_nav_category ) ) {
            # No category was specified, so choose the first one
            $simple_nav_category = $cats[0]['slug'];
            error_log("DEBUG no simple_nav_category given, choosing " . $simple_nav_category);
        }

        error_log("DEBUG returning simple nav category: " . $simple_nav_category);
        return $simple_nav_category;
    }

    # Get a link to an adjacent object
    private static function get_link($prev = true) {

        $link = null;

        if ( SimpleNav::$is_single ) {
            $post = SimpleNav::adjacent_post( $prev, false );
            if ( !empty( $post ) )
                $link = get_permalink( $post->ID );
        }

        if ( SimpleNav::$is_category ) {
            $link = SimpleNav::adjacent_page_link( $prev );
        }

        return $link;
    }

    # Get a count of adjacent objects
    private static function get_count($prev = true) {

        $count = null;

        if ( SimpleNav::$is_single )
            $count = SimpleNav::adjacent_post( $prev, true );

        if ( SimpleNav::$is_category )
            $count = SimpleNav::adjacent_page_count( $prev ); 

        return $count;
    }

    # Get link to adjacent page of posts
    private static function adjacent_page_link($previous = true, $count_only = false) {
        global $wp_query;

        $current_page = max( 1, get_query_var('paged') );
        $last_page = max( 1, $wp_query->max_num_pages );

        error_log("DEBUG current page: " . $current_page);
        error_log("DEBUG last page: " . $last_page);

        $link = null;

        if ( $previous ) {

            if ( $current_page > 1 )
                $link = get_pagenum_link( $current_page - 1 );

        } else {

            if ( ($last_page - $current_page + 1) > 1 )
                $link = get_pagenum_link( $current_page + 1 );

        }

        error_log("DEBUG returning adjacent page link: " . $link);
        return $link;
    }

    # Get count of adjacent pages of posts
    private static function adjacent_page_count($previous = true, $count_only = false) {
        global $wp_query;

        $current_page = max( 1, get_query_var('paged') );
        $last_page = max( 1, $wp_query->max_num_pages );

        error_log("DEBUG current page: " . $current_page);
        error_log("DEBUG last page: " . $last_page);

        $count = 0;

        if ( $previous ) {

            if ( $current_page > 1 )
                $count = $current_page - 1;

        } else {

            if ( ($last_page - $current_page + 1) > 1 )
                $count = $last_page - $current_page;

        }

        error_log("DEBUG return adjacent page count: " . $count);
        return $count;
    }

    # Get information about adjacent posts
    private static function adjacent_post($previous = true, $count_only = false) {
        global $post, $wpdb;

        if ( empty( SimpleNav::$simple_nav_category ) ) {
            error_log("DEBUG couldn't determine simple_nav_category");
            return null;
        }

        # Build the SQL query
        $op = $previous ? '<' : '>';
        $current_post_date = $post->post_date;
        $order = $previous ? 'DESC' : 'ASC';

        $query  = "SELECT " . ($count_only ? "count(*)" : "p.*") . " FROM $wpdb->posts AS p ";
        $query .= "INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id ";
        $query .= "INNER JOIN $wpdb->term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id ";
        $query .= "INNER JOIN $wpdb->terms AS t ON tt.term_id = t.term_id ";
        $query .= "WHERE p.post_date $op '%s' ";
        $query .= "AND p.post_type = 'post' ";
        $query .= "AND p.post_status = 'publish' ";
        $query .= "AND tt.taxonomy = 'category' ";
        $query .= "AND t.slug = '%s' ";
        if (!$count_only) {
            $query .= "ORDER BY p.post_date $order ";
            $query .= "LIMIT 1";
        }
        
        $prepared_query = $wpdb->prepare($query, $current_post_date, SimpleNav::$simple_nav_category);

        error_log("DEBUG " . $prepared_query);

        # Look for a cache hit
        $query_key = 'adjacent_post_' . md5($query);
        $result = wp_cache_get($query_key, 'counts');
        if ( false !== $result )
            return $result;

        # Cache miss
        if ($count_only) {
            $result = $wpdb->get_var($prepared_query);
            if ( empty( $result ) )
                $result = 0; // empty results means a count of zero
        } else {
            $result = $wpdb->get_row($prepared_query);
        }
        if ( null === $result ) {
            error_log("DEBUG nothing returned from query");
            $result = '';
        }

        # Cache the result
        wp_cache_set($query_key, $result, 'counts');
        return $result;
    }
    
    # Update a post link with the current simple nav category
    public static function post_link($permalink) {

        SimpleNav::init();

        if ( empty( SimpleNav::$simple_nav_category ) ) {
            error_log("DEBUG not adding simple_nav_category to permalink");
            return $permalink;
        } else {
            error_log("DEBUG adding simple_nav_category to permalink: " . SimpleNav::$simple_nav_category);
            return $permalink . "&simple_nav_category=" . SimpleNav::$simple_nav_category;
        }
    }
}

# Register the widget
add_action('widgets_init', create_function('', 'register_widget("SimpleNav");'));

# Add the simple_nav_category url parameter
add_filter('query_vars', 'add_simple_nav_category');
function add_simple_nav_category( $qvars ) {
    $qvars[] = 'simple_nav_category';
    return $qvars;
}

# Hook into the post_link filter
add_action('post_link', array('SimpleNav', 'post_link'));

?>