Conservation de l'état connecté entre 2 rafraichissement de page

L'état de connexion est conservé dans le sessionStorage et réutilisé par
défaut lors du rafraichissement de la page.

Si une erreur 401 survient lors d'un appel à l'API alors l'utilisateur
est redirigé vers la page d'accueil.

client/src/util/apollo.ts

@@ -0,0 +1,74 @@
+
+import { ApolloClient, InMemoryCache, HttpLink, from } from '@apollo/client';
+import { Config } from '../config';
+import { WebSocketLink } from "@apollo/client/link/ws";
+import { RetryLink } from "@apollo/client/link/retry";
+import { onError } from "@apollo/client/link/error";
+import { SubscriptionClient } from "subscriptions-transport-ws";
+import { User } from '../types/user';
+
+export function createClient(setLoggedIn: (boolean) => void) {
+  const subscriptionClient = new SubscriptionClient(Config.subscriptionEndpoint, {
+    reconnect: true,
+  });
+  
+  const errorLink = onError(({ operation }) => {
+    const { response } = operation.getContext();
+    if (response.status === 401) setLoggedIn(false);
+  });
+  
+  const retryLink = new RetryLink({attempts: {max: 2}}).split(
+    (operation) => operation.operationName === 'subscription',
+    new WebSocketLink(subscriptionClient),
+    new HttpLink({ 
+      uri: Config.graphQLEndpoint, 
+      credentials: 'include',
+    })
+  );
+  
+  const cache = new InMemoryCache({
+    typePolicies: {
+      Workgroup: {
+        fields: {
+          members: {
+            merge: mergeArrayByField<User>("id"),
+          }
+        }
+      }
+    }
+  });
+  
+  return new ApolloClient<any>({
+    cache: cache,
+    link: from([
+      errorLink,
+      retryLink
+    ]),
+  });
+}
+
+export function mergeArrayByField<T>(fieldName: string) {
+  return (existing: T[] = [], incoming: T[], { readField, mergeObjects }) => {
+    const merged: any[] = existing ? existing.slice(0) : [];
+    
+    const objectFieldToIndex: Record<string, number> = Object.create(null);
+    if (existing) {
+      existing.forEach((obj, index) => {
+        objectFieldToIndex[readField(fieldName, obj)] = index;
+      });
+    }
+
+    incoming.forEach(obj => {
+      const field = readField(fieldName, obj);
+      const index = objectFieldToIndex[field];
+      if (typeof index === "number") {
+        merged[index] = mergeObjects(merged[index], obj);
+      } else {
+        objectFieldToIndex[name] = merged.length;
+        merged.push(obj);
+      }
+    });
+    
+    return merged;
+  }
+}