Redirect gid for featured debate if required

Make sure that if the gid for the featured debate has been redirected we
follow it rather than displaying nothing.

Fixes #873

classes/Gid.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace MySociety\TheyWorkForYou;
+
+class Gid {
+
+    public $gid;
+    private $db;
+
+    public function __construct($gid) {
+        $this->gid = $gid;
+        $this->db = new \ParlDB;
+    }
+
+    public function checkForRedirect() {
+        $q = $this->db->query(
+            "SELECT gid_to FROM gidredirect WHERE gid_from = :gid",
+            array(':gid' => $this->gid)
+        );
+
+        if ($q->rows() == 0) {
+            return $this->gid;
+        } else {
+            do {
+                $gid = $q->field(0, 'gid_to');
+                $q = $this->db->query(
+                    "SELECT gid_to FROM gidredirect WHERE gid_from = :gid",
+                    array(':gid' => $gid)
+                );
+            } while ($q->rows() > 0);
+            return $gid;
+        }
+    }
+}

classes/Homepage.php

@@ -98,6 +98,8 @@ protected function getEditorialContent() {
         $debatelist = new \DEBATELIST;
         $featured = new Model\Featured;
         $gid = $featured->get_gid();
+        $gidCheck = new Gid($gid);
+        $gid = $gidCheck->checkForRedirect();
         if ( $gid ) {
             $title = $featured->get_title();
             $context = $featured->get_context();