Have a go at some error handling

Still not happy with how this is all fitting together. But good enough
for now

src/Api/ExceptionHandler.php

@@ -0,0 +1,75 @@
+<?php namespace Flarum\Api;
+
+use Exception;
+use Illuminate\Foundation\Exceptions\Handler;
+use Illuminate\Http\Response;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Database\Eloquent\ModelNotFoundException;
+use Flarum\Core\Exceptions\ValidationFailureException;
+use Flarum\Core\Exceptions\PermissionDeniedException;
+use Symfony\Component\HttpKernel\Exception\HttpException;
+use Config;
+
+class ExceptionHandler extends Handler
+{
+    /**
+     * A list of the exception types that should not be reported.
+     *
+     * @var array
+     */
+    protected $dontReport = [
+        'Symfony\Component\HttpKernel\Exception\HttpException'
+    ];
+
+    /**
+     * Render an exception into an HTTP response.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Exception  $e
+     * @return \Illuminate\Http\Response
+     */
+    public function render($request, Exception $e)
+    {
+        if ($request->is('api/*')) {
+            if ($e instanceof ValidationFailureException) {
+                return $this->renderValidationException($e);
+            }
+            if ($e instanceof PermissionDeniedException) {
+                return new Response(null, 401);
+            }
+
+            $error = [];
+            if (Config::get('app.debug')) {
+                $error['code'] = (new \ReflectionClass($e))->getShortName();
+            }
+            if ($detail = $e->getMessage()) {
+                $error['detail'] = $detail;
+            }
+            $statusCode = $e instanceof HttpException ? $e->getStatusCode() : 500;
+            if (count($error)) {
+                return $this->renderErrors([$error], $statusCode);
+            } else {
+                return new Response(null, $statusCode);
+            }
+        }
+
+        return parent::render($request, $e);
+    }
+
+    protected function renderErrors($errors, $httpCode = 500)
+    {
+        return new JsonResponse(['errors' => $errors], $httpCode);
+    }
+
+    protected function renderValidationException(ValidationFailureException $e)
+    {
+        $errors = [];
+        foreach ($e->getErrors()->getMessages() as $field => $messages) {
+            $errors[] = [
+                'detail' => implode("\n", $messages),
+                'path' => $field
+            ];
+        }
+        return $this->renderErrors($errors, 422);
+    }
+}