From 17d946bfb0009f39b5e46bf5c46459cab5175805 Mon Sep 17 00:00:00 2001
From: Jerel Miller <jmiller@newrelic.com>
Date: Thu, 11 Jun 2020 12:06:22 -0700
Subject: [PATCH] feat: Add a splitWhen utility

---
 src/utils/__tests__/splitWhen.js | 28 ++++++++++++++++++++++++++++
 src/utils/splitWhen.js           | 15 +++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 src/utils/__tests__/splitWhen.js
 create mode 100644 src/utils/splitWhen.js

diff --git a/src/utils/__tests__/splitWhen.js b/src/utils/__tests__/splitWhen.js
new file mode 100644
index 000000000..ac3c27088
--- /dev/null
+++ b/src/utils/__tests__/splitWhen.js
@@ -0,0 +1,28 @@
+import splitWhen from '../splitWhen';
+
+test('splits the list into 2 chunks where the predicate is true', () => {
+  const list = [1, 2, 3, 4, 5];
+
+  const result = splitWhen(list, (num) => num === 3);
+
+  expect(result).toEqual([
+    [1, 2],
+    [3, 4, 5],
+  ]);
+});
+
+test('returns empty list if there are no items', () => {
+  const list = [];
+
+  const result = splitWhen(list, () => true);
+
+  expect(result).toEqual([]);
+});
+
+test('handles list where no items satisfy the predicate', () => {
+  const list = [1, 2, 3];
+
+  const result = splitWhen(list, (num) => num === 10);
+
+  expect(result).toEqual([[1, 2, 3], []]);
+});
diff --git a/src/utils/splitWhen.js b/src/utils/splitWhen.js
new file mode 100644
index 000000000..5f9febb60
--- /dev/null
+++ b/src/utils/splitWhen.js
@@ -0,0 +1,15 @@
+const splitWhen = (list, predicate) => {
+  if (list.length === 0) {
+    return [];
+  }
+
+  const idx = list.findIndex((item) => predicate(item));
+
+  if (idx === -1) {
+    return [list, []];
+  }
+
+  return [list.slice(0, idx), list.slice(idx)];
+};
+
+export default splitWhen;