feat: reverse shares (#86)

* add first concept

* add reverse share funcionality to frontend

* allow creator to limit share expiration

* moved reverse share in seperate module

* add table to manage reverse shares

* delete complete share if reverse share was deleted

* optimize function names

* add db migration

* enable reverse share email notifications

* fix config variable descriptions

* fix migration for new installations

backend/src/reverseShare/guards/reverseShareOwner.guard.ts

@@ -0,0 +1,22 @@
+import { CanActivate, ExecutionContext, Injectable } from "@nestjs/common";
+import { User } from "@prisma/client";
+import { Request } from "express";
+import { PrismaService } from "src/prisma/prisma.service";
+
+@Injectable()
+export class ReverseShareOwnerGuard implements CanActivate {
+  constructor(private prisma: PrismaService) {}
+
+  async canActivate(context: ExecutionContext) {
+    const request: Request = context.switchToHttp().getRequest();
+    const { reverseShareId } = request.params;
+
+    const reverseShare = await this.prisma.reverseShare.findUnique({
+      where: { id: reverseShareId },
+    });
+
+    if (!reverseShare) return false;
+
+    return reverseShare.creatorId == (request.user as User).id;
+  }
+}