Refactor error handling internally to follow RFC7807 (#362)

* Refactor error handling internally to follow RFC7807

* style fixes

app/Exceptions/HttpException.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace App\Exceptions;
+
+use Symfony\Component\HttpKernel\Exception\HttpException as SymfonyHttpException;
+
+abstract class HttpException extends SymfonyHttpException
+{
+    /**
+     * Return the RFC 7807 error type (without the URL root)
+     */
+    abstract public function getErrorType(): string;
+
+    /**
+     * Get the detailed error string
+     */
+    abstract public function getErrorDetails(): string;
+
+    /**
+     * Return an array with the error details, merged with the RFC7807 response
+     */
+    abstract public function getErrorMetadata(): array;
+
+    /**
+     * Return the error message as JSON
+     */
+    public function getJson()
+    {
+        $response = [];
+
+        $response['type'] = config('phpvms.error_root').'/'.$this->getErrorType();
+        $response['title'] = $this->getMessage();
+        $response['details'] = $this->getErrorDetails();
+
+        // For backwards compatibility
+        $response['error'] = [
+            'status'  => $this->getStatusCode(),
+            'message' => $this->getErrorDetails(),
+        ];
+
+        return array_merge($response, $this->getErrorMetadata());
+    }
+
+    /**
+     * Return a response object that can be used by Laravel
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function getResponse()
+    {
+        return response()
+            ->json(
+                $this->getJson(),
+                $this->getStatusCode(),
+                [
+                    'content-type' => 'application/problem+json',
+                ]
+            );
+    }
+}