add memory usage check

app/Sensor/MemInfo.php

@@ -48,6 +48,13 @@ class MemInfo extends AbstractSensor
 
     public function status(array $records) : int
     {
+        foreach ($records as $record) {
+            $mem = $this->parseMeminfo($record->memory);
+            if ($mem->usedRatio() > 0.8) {
+                return  \App\Status::WARNING;
+            }
+        }
+
         return \App\Status::OK;
     }
 

app/Sensor/Memory.php

@@ -19,15 +19,21 @@ class Memory
     public $free;
     public $cached;
 
-    public function __construct($total, $free, $cached)
+    public function __construct(int $total, int $free, int $cached)
     {
         $this->total = $total;
         $this->free = $free;
         $this->cached = $cached;
     }
 
-    public function used()
+    public function used() : int
     {
         return $this->total - $this->free - $this->cached;
     }
+
+
+    public function usedRatio() : float
+    {
+        return $this->used() / $this->total;
+    }
 }