Add proof of concept config system

Signed-off-by: David Mehren <git@herrmehren.de>
Co-authored-by: Yannick Bungers <git@innay.de>

src/config/app.config.ts

@@ -0,0 +1,60 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { registerAs } from '@nestjs/config';
+import * as Joi from 'joi';
+
+export interface AppConfig {
+  port: number;
+  media: {
+    backend: {
+      use: string;
+      filesystem: {
+        uploadPath: string;
+      };
+    };
+  };
+}
+
+const schema = Joi.object({
+  port: Joi.number(),
+  media: {
+    backend: {
+      use: Joi.string().valid('filesystem'),
+      filesystem: {
+        uploadPath: Joi.when('...use', {
+          is: Joi.valid('filesystem'),
+          then: Joi.string(),
+          otherwise: Joi.optional(),
+        }),
+      },
+    },
+  },
+});
+
+export default registerAs('appConfig', async () => {
+  const appConfig = schema.validate(
+    {
+      port: parseInt(process.env.PORT) || undefined,
+      media: {
+        backend: {
+          use: process.env.HD_MEDIA_BACKEND,
+          filesystem: {
+            uploadPath: process.env.HD_MEDIA_BACKEND_FILESYSTEM_UPLOAD_PATH,
+          },
+        },
+      },
+    },
+    {
+      abortEarly: false,
+      presence: 'required',
+    },
+  );
+  if (appConfig.error) {
+    throw new Error(appConfig.error.toString());
+  }
+  return appConfig.value;
+});