feat(asyncTakeOnce): add asyncTakeOnce function

Author: djcsdy

index.test.ts

@@ -10,6 +10,7 @@ import {
     asyncPushOnce,
     asyncSliceOnce,
     asyncTailOnce,
+    asyncTakeOnce,
     asyncToArrayOnce,
     asyncUnshiftOnce
 } from "./index";
@@ -160,3 +161,13 @@ test("asyncSliceOnce", async t => {
     t.deepEqual(await asyncToArrayOnce(asyncSliceOnce(asyncIterator([1, 2, 3]), 2, 0)), []);
     t.deepEqual(await asyncToArrayOnce(asyncSliceOnce(asyncIterator([1, 2, 3]), 1, 1)), []);
 });
+
+test("asyncTakeOnce", async t => {
+    t.deepEqual(await asyncToArrayOnce(asyncTakeOnce(asyncIterator([]), 3)), []);
+    t.deepEqual(await asyncToArrayOnce(asyncTakeOnce(asyncIterator([1, 2]), 3)), [1, 2]);
+    t.deepEqual(
+        await asyncToArrayOnce(asyncTakeOnce(asyncIterator([1, 2, 3, 4, 5]), 3)),
+        [1, 2, 3]
+    );
+    t.deepEqual(await asyncToArrayOnce(asyncTakeOnce(asyncIterator([1, 2, 3, 4, 5]), 0)), []);
+});

index.ts

@@ -247,3 +247,31 @@ export function asyncSliceOnceFn<T>(
 ): (iterator: AsyncIteratorLike<T>) => AsyncIterator<T> {
     return iterator => asyncSliceOnce(iterator, start, end);
 }
+
+export function asyncTakeOnce<T>(
+    iterator: AsyncIteratorLike<T>,
+    count: number | Promise<number>
+): AsyncIterator<T> {
+    const it = asyncIterator(iterator);
+    let i = 0;
+    const done: IteratorResult<T> = {done: true, value: undefined};
+    const during = async (): Promise<IteratorResult<T>> => {
+        const element = await it.next();
+        const c = await count;
+        if (i++ < c && element.done !== true) {
+            return element;
+        } else {
+            next = after;
+            return done;
+        }
+    };
+    const after = async (): Promise<IteratorResult<T>> => done;
+    let next = during;
+    return {next: async () => next()};
+}
+
+export function asyncTakeOnceFn<T>(
+    count: number | Promise<number>
+): (iterator: AsyncIteratorLike<T>) => AsyncIterator<T> {
+    return iterator => asyncTakeOnce(iterator, count);
+}