Ticket 2141: bugs with weighted popularity lists across year boundary.

Consolidated several separate implementations of the same weighting algorithm into common_sql_weight() and fixed some bugs...
For MySQL, now using timestampdiff() instead of subtraction for the comparison, so we get sane results when the year doesn't match, and utc_timestamp() rather than now() so we don't get negative ages for recent items with local server timezone.
Unknown whether the same problems affect PostgreSQL, but note that it lacks the timestampdiff() SQL function.

1 files changed, 8 insertions, 7 deletions

diff --git a/actions/publictagcloud.php b/actions/publictagcloud.php
index e7f6ee36c..9e4478dbb 100644
--- a/actions/publictagcloud.php
+++ b/actions/publictagcloud.php
@@ -105,12 +105,8 @@ class PublictagcloudAction extends Action
 
         #Add the aggregated columns...
         $tags->selectAdd('max(notice_id) as last_notice_id');
-        if(common_config('db','type')=='pgsql') {
-            $calc='sum(exp(-extract(epoch from (now()-created))/%s)) as weight';
-        } else {
-            $calc='sum(exp(-(now() - created)/%s)) as weight';
-        }
-        $tags->selectAdd(sprintf($calc, common_config('tag', 'dropoff')));
+        $calc = common_sql_weight('created', common_config('tag', 'dropoff'));
+        $tags->selectAdd($calc . ' as weight');
         $tags->groupBy('tag');
         $tags->orderBy('weight DESC');
 
@@ -136,7 +132,12 @@ class PublictagcloudAction extends Action
             $this->elementStart('dd');
             $this->elementStart('ul', 'tags xoxo tag-cloud');
             foreach ($tw as $tag => $weight) {
-                $this->showTag($tag, $weight, $weight/$sum);
+                if ($sum) {
+                    $weightedSum = $weight/$sum;
+                } else {
+                    $weightedSum = 0.5;
+                }
+                $this->showTag($tag, $weight, $weightedSum);
             }
             $this->elementEnd('ul');
             $this->elementEnd('dd');