From 3e8aef7c006e1434842bcc9a57646fa7cdfcac4a Mon Sep 17 00:00:00 2001
From: Alisue <lambdalisue@gmail.com>
Date: Wed, 21 Aug 2024 00:21:40 +0900
Subject: [PATCH] feat(ensurePromise): add `ensurePromise` function

---
 deno.jsonc             |  2 ++
 ensure_promise.ts      | 20 ++++++++++++++++++++
 ensure_promise_test.ts | 12 ++++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 ensure_promise.ts
 create mode 100644 ensure_promise_test.ts

diff --git a/deno.jsonc b/deno.jsonc
index 67aa3d3..2d12f52 100644
--- a/deno.jsonc
+++ b/deno.jsonc
@@ -5,6 +5,7 @@
     ".": "./mod.ts",
     "./async-value": "./async_value.ts",
     "./barrier": "./barrier.ts",
+    "./ensure-promise": "./ensure_promise.ts",
     "./lock": "./lock.ts",
     "./mutex": "./mutex.ts",
     "./notify": "./notify.ts",
@@ -34,6 +35,7 @@
     "@core/asyncutil": "./mod.ts",
     "@core/asyncutil/async-value": "./async_value.ts",
     "@core/asyncutil/barrier": "./barrier.ts",
+    "@core/asyncutil/ensure-promise": "./ensure_promise.ts",
     "@core/asyncutil/lock": "./lock.ts",
     "@core/asyncutil/mutex": "./mutex.ts",
     "@core/asyncutil/notify": "./notify.ts",
diff --git a/ensure_promise.ts b/ensure_promise.ts
new file mode 100644
index 0000000..5dde7da
--- /dev/null
+++ b/ensure_promise.ts
@@ -0,0 +1,20 @@
+/**
+ * Ensure that a value is a promise.
+ *
+ * It returns the value if it is already a promise, otherwise it returns a
+ * promise that resolves to the value.
+ *
+ * @param value - The value to ensure as a promise.
+ * @returns A promise that resolves to the value.
+ *
+ * ```ts
+ * import { assertEquals } from "@std/assert";
+ * import { ensurePromise } from "@core/asyncutil/ensure-promise";
+ *
+ * assertEquals(await ensurePromise(42), 42);
+ * assertEquals(await ensurePromise(Promise.resolve(42)), 42);
+ * ```
+ */
+export function ensurePromise<T>(value: T): Promise<T> {
+  return value instanceof Promise ? value : Promise.resolve(value);
+}
diff --git a/ensure_promise_test.ts b/ensure_promise_test.ts
new file mode 100644
index 0000000..3c63b9a
--- /dev/null
+++ b/ensure_promise_test.ts
@@ -0,0 +1,12 @@
+import { test } from "@cross/test";
+import { assertEquals } from "@std/assert";
+import { ensurePromise } from "./ensure_promise.ts";
+
+test("ensurePromise() returns the value if it is already a promise", async () => {
+  const p = Promise.resolve(42);
+  assertEquals(await ensurePromise(p), 42);
+});
+
+test("ensurePromise() returns a promise that resolves to the value", async () => {
+  assertEquals(await ensurePromise(42), 42);
+});