Find related pages using Fieldtype Page for tagging. Returns PageArray with added property "score" for later use.

TagsHelper.module

<?php

/**
 * TagsHelper ProcessWire2.+ Module
 *
 *
 * @author Soma
 * modified 2012/08/31
 *
 * ProcessWire 2.x
 * Copyright (C) 2010 by Ryan Cramer
 * Licensed under GNU/GPL v2, see LICENSE.TXT
 *
 * http://www.processwire.com
 * http://www.ryancramer.com
 *
 *
 *
 */


class TagsHelper extends WireData implements Module {

    /**
     * getModuleInfo is a module required by all modules to tell ProcessWire about them
     *
     * @return array
     *
     */
    public static function getModuleInfo() {

        return array(
            'title' => 'Tags Helper',
            'version' => 1,
            'summary' => 'Finds related pages using a Fieltype Page field with multiple tags. Returns PageArray with added [score] property to page objects or null if none found. Usage: $result = $pages->findRelated( Page $page, PageArray $tags, string $field [, string $tmpl, int $limit] );',
            'href' => '',
            'singular' => true,
            'autoload' => true
            );
    }

    public function init() {
        // add method to $pages var
        $this->addHook('Pages::findRelated', $this, 'findRelated');
    }

    /**
     * Find related pages using Page reference field
     *
     * findRelated( Page $page, PageArray $tags, string $field [, string $tmpl, int $limit] );
     *
     * @param  HookEvent $event
     * @return PageArray|null
     */
    public function findRelated( HookEvent $event ) {

        // get arguments
        $page = $event->arguments[0];
        if(!$page->id) throw new WireException("findRelated() Error: first argument page is not found.");
        $tags = $event->arguments[1];
        $field = $event->arguments[2];

        //$tmplq = isset($event->arguments[3]) ? ",template=".$event->arguments[3] : '';

        if(isset($event->arguments[3])){
            $tmpl = $event->arguments[3];
            if(strpos($tmpl,"|") !== false){
                $tmpls = explode("|",$tmpl);
                foreach($tmpls as $t) {
                    if( $tt = wire("templates")->get($t) )
                        $tmplIDs[] = $tt->id;
                    else throw new WireException("findRelated() Error: template '$t' could not be found.");
                }
                $tmplq = " AND pages.templates_id in(" . implode(',',$tmplIDs) . ")";
            } else {
                $tmplID = wire("templates")->get($tmpl)->id;
                $tmplq = " AND pages.templates_id=$tmplID";
            }
        } else {
            $tmplq = '';
        }

        $limit = isset($event->arguments[4]) ? $event->arguments[4] : 100;


        /* mysql plain query method, this way we can sort multiple rows
        ----------------------------------------------------------------- */

        if(count($tags) < 1) return $event->return = null;
        foreach($tags as $tag) $tagIDs .= "$tag->id,";
        $tagIDs = substr($tagIDs,0,-1);

        $query = "
            SELECT data,pages_id,modified, COUNT(pages_id) as score
            FROM field_$field LEFT JOIN pages ON (field_$field.pages_id=pages.id)
            WHERE field_$field.data in($tagIDs)
            AND field_$field.pages_id != $page->id AND pages.status < 2048 $tmplq
            GROUP BY pages_id
            ORDER BY score DESC, modified DESC
            LIMIT $limit";

        $res = $this->db->query($query);
        if(!$res->num_rows) return $event->return = null;

        $pa = new PageArray();
        while($r = $res->fetch_object()){
            $pa->add(wire("pages")->get($r->pages_id)->set("score",$r->score));
        }

        $event->return = $pa;

        /* PW query method, this way we can only sort on one field
        ----------------------------------------------------------------- */

        /*
        foreach($tags as $tag) {
            $found = wire("pages")->find("$field=$tag,id!=$page->id,limit=$limit" . $tmplq);
            foreach($found as $r) $rel[$r->id]++;
        }
        // if none found return
        if(empty($rel)) return $event->return = null;
        // build PageArray and add "score" property
        $pa = new PageArray();
        foreach($rel as $key => $score) {
            $pa->add( wire('pages')->get($key)->set("score",$score) );
        }
        $event->return = $pa;
        */
    }

}