Based on the description, first thing you realize is that its a graph problem. So you need to traverse the graph and get writings from some nodes(rooms). Because you have multiple dones, the goal is to guide them to traverse the graph asynchronously.
Since the problem is not about looking for shortest path, it doesnt really matter if the traversal is Depth First Search or Breath First Search. I will use DFS here. this.rooms is a stack to hold discovered rooms, this.visited is a set to hold rooms have been visited.
The first step is to call endpoint /start to get a roomId as the root and drones in startMission(). The idea is to assign drones to visit each node asynchronously. Because visiting each node is an asynchronous action here and each asynchronous operation returns a promise, we can use Promise.all to combine all the promises so they can be executed in parallel.
When assigning a drone to explore a room, first check if the stack is empty or not. After popping a room from the top of the stack, first check if the roomId is undefined or not because the graph is being traversed asynchronously, there might chances that all the rooms have been assigned to drones to explore but no new connections have been discovered within the while loop. If the stack is empty at that moment, popped roomId will be undefined. Besides checking whether its undefined, be sure to check if the room has been visited or not.
When visiting each room/node, in deployDroneToRoom(droneId, roomId), make a POST request with roomId to explore and read. In handleExplorationResult(), push newly discovered rooms onto the stack and store new writings to array this.writings is the order is not -1.
After visiting all the rooms, turning writings in this.writings into a string and make a POST request to /report in report() method.