Discriminator in username

ts/util/Username.ts

@@ -0,0 +1,79 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as RemoteConfig from '../RemoteConfig';
+import { parseIntWithFallback } from './parseIntWithFallback';
+
+export function getMaxNickname(): number {
+  return parseIntWithFallback(
+    RemoteConfig.getValue('global.nicknames.max'),
+    32
+  );
+}
+export function getMinNickname(): number {
+  return parseIntWithFallback(RemoteConfig.getValue('global.nicknames.min'), 3);
+}
+
+export function isValidNickname(nickname: string): boolean {
+  if (!/^[a-z_][0-9a-z_]*$/.test(nickname)) {
+    return false;
+  }
+
+  if (nickname.length < getMinNickname()) {
+    return false;
+  }
+
+  if (nickname.length > getMaxNickname()) {
+    return false;
+  }
+
+  return true;
+}
+
+export function isValidUsername(username: string): boolean {
+  const match = username.match(/^([a-z_][0-9a-z_]*)(\.\d+)?$/);
+  if (!match) {
+    return false;
+  }
+
+  const [, nickname] = match;
+  return isValidNickname(nickname);
+}
+
+export function getUsernameFromSearch(searchTerm: string): string | undefined {
+  // Search term contains username if it:
+  // - Is a valid username with or without a discriminator
+  // - Starts with @
+  // - Ends with @
+  const match = searchTerm.match(
+    /^(?:(?<valid>[a-z_][0-9a-z_]*(?:\.\d*)?)|@(?<start>.*?)@?|@?(?<end>.*?)?@)$/
+  );
+  if (!match) {
+    return undefined;
+  }
+
+  const { groups } = match;
+  if (!groups) {
+    return undefined;
+  }
+
+  return (groups.valid || groups.start || groups.end) ?? undefined;
+}
+
+export function getNickname(username: string): string | undefined {
+  const match = username.match(/^(.*?)(?:\.|$)/);
+  if (!match) {
+    return undefined;
+  }
+
+  return match[1];
+}
+
+export function getDiscriminator(username: string): string {
+  const match = username.match(/(\..*)$/);
+  if (!match) {
+    return '';
+  }
+
+  return match[1];
+}