Handle signal.me links

ts/util/isValidE164.ts

@@ -0,0 +1,22 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+/**
+ * Returns `true` if the input looks like a valid E164, and `false` otherwise. Note that
+ * this may return false positives, as it is a fairly naïve check.
+ *
+ * See <https://www.twilio.com/docs/glossary/what-e164#regex-matching-for-e164> and
+ * <https://stackoverflow.com/a/23299989>.
+ */
+export function isValidE164(
+  value: unknown,
+  mustStartWithPlus: boolean
+): value is string {
+  if (typeof value !== 'string') {
+    return false;
+  }
+
+  const regex = mustStartWithPlus ? /^\+[1-9]\d{1,14}$/ : /^\+?[1-9]\d{1,14}$/;
+
+  return regex.test(value);
+}