Add API endpoint for getting server resource utilization, closes #900

This endpoint is throttled to 15 requests per minute to avoid destroying the daemon since clients can use it.

app/Transformers/Api/Client/StatsTransformer.php

@@ -0,0 +1,88 @@
+<?php
+
+namespace Pterodactyl\Transformers\Api\Client;
+
+use Pterodactyl\Models\Server;
+use Pterodactyl\Contracts\Repository\Daemon\ServerRepositoryInterface;
+
+class StatsTransformer extends BaseClientTransformer
+{
+    /**
+     * @var \Pterodactyl\Contracts\Repository\Daemon\ServerRepositoryInterface
+     */
+    private $repository;
+
+    /**
+     * Perform dependency injection.
+     *
+     * @param \Pterodactyl\Contracts\Repository\Daemon\ServerRepositoryInterface $repository
+     */
+    public function handle(ServerRepositoryInterface $repository)
+    {
+        $this->repository = $repository;
+    }
+
+    /**
+     * @return string
+     */
+    public function getResourceName(): string
+    {
+        return 'stats';
+    }
+
+    /**
+     * Transform stats from the daemon into a result set that can be used in
+     * the client API.
+     *
+     * @param \Pterodactyl\Models\Server $model
+     * @return array
+     */
+    public function transform(Server $model)
+    {
+        try {
+            $stats = $this->repository->setServer($model)->details();
+        } catch (RequestException $exception) {
+            throw new DaemonConnectionException($exception);
+        }
+
+        $object = json_decode($stats->getBody()->getContents());
+
+        return [
+            'state' => $this->transformState(object_get($object, 'status', 0)),
+            'memory' => [
+                'current' => round(object_get($object, 'proc.memory.total', 0) / 1024 / 1024),
+                'limit' => floatval($model->memory),
+            ],
+            'cpu' => [
+                'current' => object_get($object, 'proc.cpu.total', 0),
+                'cores' => object_get($object, 'proc.cpu.cores', []),
+                'limit' => floatval($model->cpu),
+            ],
+            'disk' => [
+                'current' => round(object_get($object, 'proc.disk.used', 0)),
+                'limit' => floatval($model->disk),
+            ],
+        ];
+    }
+
+    /**
+     * Transform the state returned by the daemon into a human readable string.
+     *
+     * @param int $state
+     * @return string
+     */
+    private function transformState(int $state): string
+    {
+        switch ($state) {
+            case 1:
+                return 'on';
+            case 2:
+                return 'starting';
+            case 3:
+                return 'stopping';
+            case 0:
+            default:
+                return 'off';
+        }
+    }
+}