From fa0377f72e55a83eb1779cb2098e39a216a07526 Mon Sep 17 00:00:00 2001
From: Omry Nachman <omry@wix.com>
Date: Wed, 19 Jul 2023 22:46:20 +0300
Subject: [PATCH] chore: updated iterables

---
 packages/common/src/chain.ts               |  4 ++++
 packages/common/src/iterables-gen.ts       |  5 +++++
 packages/common/src/iterables.ts           |  3 +--
 packages/common/src/test/chain.unit.ts     | 13 ++++++++++++-
 packages/common/src/test/iterables.unit.ts | 17 +++++++++++++++--
 5 files changed, 37 insertions(+), 5 deletions(-)
 create mode 100644 packages/common/src/iterables-gen.ts

diff --git a/packages/common/src/chain.ts b/packages/common/src/chain.ts
index 16d646e3..d823ea1f 100644
--- a/packages/common/src/chain.ts
+++ b/packages/common/src/chain.ts
@@ -123,6 +123,9 @@ function chainIter<T>(iterable: Iterable<T>): IterableChain<T> {
     return {
         value: iterable,
         iterable,
+        get array() {
+            return [...iterable];
+        },
         ...boundToIter,
         ...boundToElm,
         forEach: (mapping: Mapping<T, unknown>) => {
@@ -168,4 +171,5 @@ export type Chain<T> = {
     skip: (count: number) => IterableChain<T>;
     reduce: <A>(reducer: (acc: A, item: T) => A, initial: A) => ValueChain<A>;
     iterable: Iterable<T>;
+    get array(): T[];
 };
diff --git a/packages/common/src/iterables-gen.ts b/packages/common/src/iterables-gen.ts
new file mode 100644
index 00000000..d0ce7a92
--- /dev/null
+++ b/packages/common/src/iterables-gen.ts
@@ -0,0 +1,5 @@
+export function* times(count: number, start = 0, step = 1) {
+    for (let i = start; i < count; i += step) {
+        yield i;
+    }
+}
diff --git a/packages/common/src/iterables.ts b/packages/common/src/iterables.ts
index 195011a6..492698c5 100644
--- a/packages/common/src/iterables.ts
+++ b/packages/common/src/iterables.ts
@@ -58,8 +58,7 @@ export function size(iterable: Nullable<Iterable<unknown>>): number {
 export function at<T>(iterable: Nullable<Iterable<T>>, index: number): T | undefined {
     if (iterable) {
         if (index < 0) {
-            const iterAsArray = Array.from(iterable);
-            return iterAsArray[iterAsArray.length + index];
+            return Array.from(iterable).at(index);
         }
         let i = 0;
         for (const v of iterable) {
diff --git a/packages/common/src/test/chain.unit.ts b/packages/common/src/test/chain.unit.ts
index 3c69c52c..13088e1b 100644
--- a/packages/common/src/test/chain.unit.ts
+++ b/packages/common/src/test/chain.unit.ts
@@ -2,11 +2,12 @@ import { expect } from 'chai';
 import { chain } from '../chain';
 // @ts-expect-error no types
 import gc from 'expose-gc/function';
+import { times } from '../iterables-gen';
 const forceGc = gc as () => void;
 
 const timer = typeof performance !== 'undefined' ? performance : Date;
 
-describe('performance', () => {
+describe('chain', () => {
     it('it faster than the array equivalent function for large iterables', () => {
         const veryLargeArray = Array.from(new Array(2 ** 18)).map((_, i) => i % 2 ** 32);
         forceGc();
@@ -40,4 +41,14 @@ describe('performance', () => {
         expect([...result]).to.eql([...iterResult]);
         expect(iterTime).to.be.lessThan(arrayTime);
     });
+
+    it('can chain all of the iterable functions', () => {
+        expect(
+            chain(times(10))
+                .skip(2)
+                .map((i) => [i, 2 * i])
+                .flatMap((i) => i)
+                .filter((i) => i < 10).array
+        ).to.eql([2, 4, 3, 6, 4, 8, 5, 6, 7, 8, 9]);
+    });
 });
diff --git a/packages/common/src/test/iterables.unit.ts b/packages/common/src/test/iterables.unit.ts
index 8ea59d3f..b6649c53 100644
--- a/packages/common/src/test/iterables.unit.ts
+++ b/packages/common/src/test/iterables.unit.ts
@@ -102,8 +102,21 @@ describe('iterables', () => {
         expect(isEmpty([1])).to.eql(false);
     });
     it(`size`, () => {
-        expect(size([])).to.eql(0);
-        expect(size([0, 1])).to.eql(2);
+        expect(size([]), 'size of empty array').to.eql(0);
+        expect(size([0, 1]), 'size of array').to.eql(2);
+        expect(size(undefined), 'size of undefined').to.eql(0);
+        expect(size(null), 'size of null').to.eql(0);
+        expect(size(''), 'size of empty string').to.eql(0);
+        expect(size('hello'), 'size of string string').to.eql(5);
+        expect(
+            size(
+                (function* () {
+                    yield 1;
+                    yield 1;
+                })()
+            ),
+            'generated iterator'
+        ).to.eql(2);
     });
     it(`map`, () => {
         expect([...map([0, 1, 2], (i) => i ** 2)]).to.eql([0, 1, 4]);