Add "today" period with hourly breakdown, and fix timezone issues

This fix ensures that before aggregating daily/hourly statistics, dates
are converted into the local timezone ("flarum-statistics.timezone" in
the settings table).

extensions/statistics/src/Listener/AddStatisticsData.php

@@ -12,20 +12,41 @@
 namespace Flarum\Statistics\Listener;
 
 use DateTime;
+use DateTimeZone;
 use Flarum\Core\Discussion;
 use Flarum\Core\Post;
 use Flarum\Core\User;
 use Flarum\Event\ConfigureWebApp;
+use Flarum\Settings\SettingsRepositoryInterface;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Contracts\Events\Dispatcher;
 
 class AddStatisticsData
 {
+    /**
+     * @var SettingsRepositoryInterface
+     */
+    protected $settings;
+
+    /**
+     * @param SettingsRepositoryInterface $settings
+     */
+    public function __construct(SettingsRepositoryInterface $settings)
+    {
+        $this->settings = $settings;
+    }
+
+    /**
+     * @param Dispatcher $events
+     */
     public function subscribe(Dispatcher $events)
     {
         $events->listen(ConfigureWebApp::class, [$this, 'addStatisticsData']);
     }
 
+    /**
+     * @param ConfigureWebApp $event
+     */
     public function addStatisticsData(ConfigureWebApp $event)
     {
         $event->view->setVariable('statistics', $this->getStatistics());
@@ -49,11 +70,33 @@ class AddStatisticsData
 
     private function getDailyCounts(Builder $query, $column)
     {
+        // Calculate the offset between the server timezone (which is used for
+        // dates stored in the database) and the user's timezone (set via the
+        // settings table). We will use this to adjust dates before aggregating
+        // daily/hourly statistics.
+        $offset = $this->getTimezoneOffset();
+
         return $query
-            ->selectRaw('DATE('.$column.') as date')
+            ->selectRaw(
+                'UNIX_TIMESTAMP(
+                    DATE_FORMAT(
+                        @date := DATE_ADD('.$column.', INTERVAL ? SECOND), -- correct for timezone
+                        IF(@date > ?, \'%Y-%m-%d %H:00:00\', \'%Y-%m-%d\') -- if within the last 48 hours, group by hour
+                    )
+                ) as period',
+                [$offset, new DateTime('-48 hours')]
+            )
             ->selectRaw('COUNT(id) as count')
             ->where($column, '>', new DateTime('-24 months'))
-            ->groupBy('date')
-            ->lists('count', 'date');
+            ->groupBy('period')
+            ->lists('count', 'period');
+    }
+
+    private function getTimezoneOffset()
+    {
+        $dataTimezone = new DateTimeZone(date_default_timezone_get());
+        $displayTimezone = new DateTimeZone($this->settings->get('flarum-statistics.timezone', date_default_timezone_get()));
+
+        return $displayTimezone->getOffset(new DateTime('now', $dataTimezone));
     }
 }