feat: add getFirstIdentityFromUser helper function

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/identity/utils.ts

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { User } from '../users/user.entity';
+import { Identity } from './identity.entity';
+import { ProviderType } from './provider-type.enum';
+
+/**
+ * Get the first identity of a given type from the user
+ * @param {User} user - the user to get the identity from
+ * @param {ProviderType} providerType - the type of the identity
+ * @return {Identity | undefined} the first identity of the user or undefined, if such an identity can not be found
+ */
+export async function getFirstIdentityFromUser(
+  user: User,
+  providerType: ProviderType,
+): Promise<Identity | undefined> {
+  const identities = await user.identities;
+  if (identities === undefined) {
+    return undefined;
+  }
+  return identities.find(
+    (aIdentity) => aIdentity.providerType === providerType,
+  );
+}