Handle players leaving in GameStart state

- If a player leaves ensure the correct action takes place
- Change the state back to OnePlayer if the player count ever reaches 1

Add tests for changing state on player leaves

If we remove the cap on two players, we should add an additional test for the condition (which checks that there is only one player left before changing back to `OnePlayer` state.
We should also add tests for the number of players on action 'playerLeaves'.

server/machines/lobby.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it, beforeEach, afterEach } from "bun:test";
+import { describe, expect, it } from "bun:test";
 import { lobbyMachine, isNewPlayer, context } from "./lobby";
 import { interpret } from "xstate";
 
@@ -83,6 +83,42 @@ describe("lobbyMachine", () => {
       ).toBe("GameStart");
     });
   });
+
+  describe("On playerLeaves", () => {
+    it("transitions from OnePlayer to Empty state", () => {
+      expect(lobbyMachine.transition("OnePlayer", "playerLeaves").value).toBe(
+        "Empty",
+      );
+    });
+
+    it("transitions from Multiple players to one player when player leaves", () => {
+      expect(
+        lobbyMachine.transition("MultiplePlayers", "playerLeaves").value,
+      ).toBe("OnePlayer");
+    });
+
+    it("transitions from GameStart to OnePlayer if there is only one player left", () => {
+      const actor = interpret(lobbyMachine);
+      actor.start();
+      const player1 = { socketId: "id", name: "a name" };
+      const player2 = { socketId: "id-2", name: "a name 2" };
+
+      const players = [player1, player2];
+
+      players.forEach((player) => {
+        actor.send({
+          type: "playerJoins",
+          player: player,
+        });
+      });
+
+      actor.send({ type: "playerClicksStart" });
+      expect(actor.getSnapshot().value).toBe("GameStart");
+
+      actor.send({ type: "playerLeaves", socketId: "id" });
+      expect(actor.getSnapshot().value).toBe("OnePlayer");
+    });
+  });
 });
 
 describe("isNewPlayer", () => {

server/machines/lobby.ts

@@ -33,9 +33,11 @@ export const isNewPlayer = (
   { player }: { player: Player },
 ) => players.map((player) => player.socketId).indexOf(player.socketId) === -1;
 
+export const isOnlyPlayer = ({ players }: { players: Array<Player> }) =>
+  players.length === 1;
+
 export const lobbyMachine = createMachine(
   {
-    /** @xstate-layout N4IgpgJg5mDOIC5QBsD2AjdBPAdAUQFsAHAFywGIjkBDLMAJwClUBLAO1gG0AGAXUVBFUsFiRao2AkAA9EARgAsANhwAOBQGYA7AFYNSjYoBMSrQBoQWeVpVajcjZo2q53He40BfTxbSZcAPJsYAAKNHT0lOEMzOxcfFJCImISUrIImqo4JhrcDqpG6lpyFlYIcjoqmgqqqloaAJxydbrevhjYOEGh0ZFUtAwAMmDUAG5wPPxIIEmi4pLT6Yoq6tp6BsampYguOBpGRk21utxaqg1ePiB+nQCyAK7IYlQ9A-SwUW8AwsgsAMYAa1gAGUSNR6CRJolhHNUosdg5sgoGg0lNxTlozm5tuVFDglA1uA16nIGnpdEY2tcOrgHk8WC8wm8Pv0IsMxhMEtNZikFqB0sijDhUY4GvZ0R4FDjXCo0RctDUlAojJUyd4rmxUBA4FIbmVBDDeWlEABaJQ4k06YUohouByuJwGKl6-DEMjQ5LzY0ZIzSolqHTnRzKQO5YrOmldYJMiIe2F8mSIXJWwN2ZxGBRaMky6VyIUaQMXBQh1RhhQR-w4OnPZCvCLwbmGr3whBKho4ORKYxGYqGQklSzyPGqQvBpSh07lq4ugDi1AIYFB4JIcaNLZRWSzSgKOmahh0Ch0uYUAaDxfHpcn6s8QA */
     tsTypes: {} as import("./lobby.typegen").Typegen0,
     schema: {
       context: {} as Context,
@@ -73,6 +75,13 @@ export const lobbyMachine = createMachine(
       },
       GameStart: {
         entry: ["setQuestion"],
+        always: {
+          target: "OnePlayer",
+          cond: "isOnlyPlayer",
+        },
+        on: {
+          playerLeaves: { actions: "removePlayer" },
+        },
       },
     },
   },
@@ -94,6 +103,7 @@ export const lobbyMachine = createMachine(
     },
     guards: {
       isNewPlayer,
+      isOnlyPlayer,
     },
   },
 );