feat(admin): add instance wide dashboard with storage and bandwidth usage

* add DashboardCard component
* add instance wide podcasts and episodes numbers
* add app.storageLimit environment variable
* divide bytes by 1000 instead of 1024 in stats sql queries

closes #216

modules/Admin/Controllers/DashboardController.php

@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright  2020 Ad Aures
+ * @license    https://www.gnu.org/licenses/agpl-3.0.en.html AGPL3
+ * @link       https://castopod.org/
+ */
+
+namespace Modules\Admin\Controllers;
+
+use App\Models\EpisodeModel;
+use App\Models\MediaModel;
+use App\Models\PodcastModel;
+use CodeIgniter\I18n\Time;
+
+class DashboardController extends BaseController
+{
+    public function index(): string
+    {
+        $podcastsData = [];
+        $podcastsCount = (new PodcastModel())->builder()
+            ->countAll();
+        $podcastsLastPublishedAt = (new PodcastModel())->builder()
+            ->select('MAX(published_at) as last_published_at')
+            ->where('`published_at` <= UTC_TIMESTAMP()', null, false)
+            ->get()
+            ->getResultArray()[0]['last_published_at'];
+        $podcastsData['number_of_podcasts'] = (int) $podcastsCount;
+        $podcastsData['last_published_at'] = $podcastsLastPublishedAt === null ? null : new Time(
+            $podcastsLastPublishedAt
+        );
+
+        $episodesData = [];
+        $episodesCount = (new EpisodeModel())->builder()
+            ->countAll();
+        $episodesLastPublishedAt = (new EpisodeModel())->builder()
+            ->select('MAX(published_at) as last_published_at')
+            ->where('`published_at` <= UTC_TIMESTAMP()', null, false)
+            ->get()
+            ->getResultArray()[0]['last_published_at'];
+        $episodesData['number_of_episodes'] = (int) $episodesCount;
+        $episodesData['last_published_at'] = $episodesLastPublishedAt === null ? null : new Time(
+            $episodesLastPublishedAt
+        );
+
+        $totalUploaded = (new MediaModel())->builder()
+            ->selectSum('file_size')
+            ->get()
+            ->getResultArray()[0];
+
+        $appStorageLimit = config('App')
+            ->storageLimit;
+        if ($appStorageLimit === null || $appStorageLimit < 0) {
+            $storageLimitBytes = disk_free_space('./');
+        } else {
+            $storageLimitBytes = $appStorageLimit * 1000000000;
+        }
+
+        $storageData = [
+            'limit' => formatBytes((int) $storageLimitBytes),
+            'percentage' => round((((int) $totalUploaded['file_size']) / $storageLimitBytes) * 100, 0),
+            'total_uploaded' => formatBytes((int) $totalUploaded['file_size']),
+        ];
+
+        $onlyPodcastId = null;
+        if ($podcastsData['number_of_podcasts'] === 1) {
+            $onlyPodcastId = (new PodcastModel())->first()
+                ->id;
+        }
+
+        $data = [
+            'podcastsData' => $podcastsData,
+            'episodesData' => $episodesData,
+            'storageData' => $storageData,
+            'onlyPodcastId' => $onlyPodcastId,
+        ];
+
+        return view('dashboard', $data);
+    }
+}