task: improve mail service error handling (#454)

* MailService: throw exception of database can't be resettet
* MailService: add own function for loading and saving the database
* MailService: validate database path

src/Service/MailService.php

@@ -8,26 +8,60 @@ class MailService
 
     public function __construct(string $databaseFile)
     {
+        if (!$this->isValidDatabasePath($databaseFile)) {
+            throw new \Exception('Database or path is not writable: ' . $databaseFile);
+        }
         $this->databaseFile = $databaseFile;
     }
 
-    public function addRecipientToDatabase(string $recipient): void
+    private function isValidDatabasePath(string $path): bool
     {
-        if (!file_exists($this->databaseFile)) {
-            $addresses = [];
+        if (is_file($path)) {
+            return is_writable($path);
+        } else {
+            return is_writable(dirname($path));
+        }
+    }
+
+    private function loadDatabase(): array
+    {
+        if (is_file($this->databaseFile)) {
+            $data = file_get_contents($this->databaseFile);
+            $addresses = json_decode($data, true);
+            if ($addresses === null) {
+                throw new \Exception('Failed to decode the database ' . $this->databaseFile);
+            }
         } else {
-            $addresses = json_decode(file_get_contents($this->databaseFile));
+            $addresses = [];
         }
+
+        return $addresses;
+    }
+
+    public function addRecipientToDatabase(string $recipient): void
+    {
+        $addresses = $this->loadDatabase();
+
         if (!in_array($recipient, $addresses)) {
             $addresses[] = $recipient;
+            $this->saveDatabase($addresses);
+        }
+    }
+
+    private function saveDatabase(array $addresses): void
+    {
+        $data = json_encode($addresses);
+        if (file_put_contents($this->databaseFile, $data) === false) {
+            throw new \Exception('Failed to save the database ' . $this->databaseFile);
         }
-        file_put_contents($this->databaseFile, json_encode($addresses));
     }
 
     public function resetDatabase(): void
     {
         if (is_file($this->databaseFile)) {
-            unlink($this->databaseFile);
+            if (!unlink($this->databaseFile)) {
+                throw new \Exception('Failed to reset the database ' . $this->databaseFile);
+            }
         }
     }