implement save and get all in flat file carrier repo

src/Carrier/FlatFileCarrierRepository.php

@@ -4,6 +4,15 @@ namespace FreightQuote\Carrier;
 
 class FlatFileCarrierRepository implements CarrierRepository
 {
+    private string $pathToCarrierFile = __DIR__.'/../../storage/carriers.json';
+
+    private function getCarrierData(): array
+    {
+        $json = file_get_contents($this->pathToCarrierFile);
+
+        return json_decode($json, true);
+    }
+
     public function find(int $id): ?Carrier
     {
         return null;
@@ -11,6 +20,56 @@ class FlatFileCarrierRepository implements CarrierRepository
 
     public function save(Carrier $carrier): Carrier
     {
-        return new Carrier(null, 'fake@email.com');
+        $data = $this->getCarrierData();
+        foreach ($data as $jsonCarrier) {
+            if ($jsonCarrier['id'] === $carrier->getId()) {
+                file_put_contents(
+                    $this->pathToCarrierFile,
+                    json_encode($data, JSON_PRETTY_PRINT)
+                );
+                return new Carrier(
+                    $jsonCarrier['id'],
+                    $jsonCarrier['email'],
+                    $jsonCarrier['companyName'],
+                );
+            }
+        }
+        $newCarrier = [
+            'id' => $this->autoIncrementId($data),
+            'email' => $carrier->getEmail(),
+            'companyName' => $carrier->getCompanyName(),
+        ];
+        $data[] = $newCarrier;
+        file_put_contents(
+            $this->pathToCarrierFile,
+            json_encode($data, JSON_PRETTY_PRINT)
+        );
+        return new Carrier(
+            $newCarrier['id'],
+            $newCarrier['email'],
+            $newCarrier['companyName'],
+        );
+    }
+
+    /**
+     * @return Carrier[]
+     */
+    public function getAll(): array
+    {
+        return array_map(function ($carrier) {
+            return new Carrier(
+                $carrier['id'],
+                $carrier['email'],
+                $carrier['companyName']
+            );
+        }, $this->getCarrierData());
+    }
+
+    /**
+     * @param array<int,mixed> $data
+     */
+    private function autoIncrementId(array $data): int
+    {
+        return count($data);
     }
 }