From cc4e4efce4b18d5fa525d1b7d46e4f5e33885467 Mon Sep 17 00:00:00 2001
From: ryoppippi <1560508+ryoppippi@users.noreply.github.com>
Date: Sun, 25 Aug 2024 16:16:37 +0100
Subject: [PATCH] feat(reverse): introduce reverse

---
 reverse.ts      | 24 ++++++++++++++++++++++++
 reverse_test.ts | 18 ++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 reverse.ts
 create mode 100644 reverse_test.ts

diff --git a/reverse.ts b/reverse.ts
new file mode 100644
index 0000000..c697b5f
--- /dev/null
+++ b/reverse.ts
@@ -0,0 +1,24 @@
+/**
+  * Returns the elements of an iterable in reverse order.
+  *
+  * @param iterable The iterable to reverse.
+  * @returns The elements of the iterable in reverse order.
+  *
+  * @example
+  * ```ts
+  * import { reverse } from "@core/iterutil/reverse";
+  *
+  * console.log([...reverse([1, 2, 3)]); // [3, 2, 1]
+  * console.log([...reverse([])]); // []
+  * ```
+  */
+export function reverse<T>(iterable: Iterable<T>): Iterable<T> {
+  return {
+    *[Symbol.iterator]() {
+      const array = [...iterable];
+      for (let i = array.length - 1; i >= 0; i--) {
+        yield array[i];
+      }
+    },
+  };
+}
diff --git a/reverse_test.ts b/reverse_test.ts
new file mode 100644
index 0000000..40388fe
--- /dev/null
+++ b/reverse_test.ts
@@ -0,0 +1,18 @@
+import { test } from "@cross/test";
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { reverse } from "./reverse.ts";
+
+await test("reverse with non empty iterable", () => {
+  const result = reverse([1, 2, 3, 4, 5] as const);
+  const expected = [5, 4, 3, 2, 1] as const;
+  assertEquals(result, expected);
+  assertType<IsExact<typeof result, Iterable<[5, 4, 3, 2, 1]>>>(true);
+});
+
+await test("reverse with empty iterable", () => {
+  const result = reverse([] as number[]);
+  const expected = [];
+  assertEquals(result, expected);
+  assertType<IsExact<typeof result, number[]>>(true);
+});