From 4844417eabab0a64657b14e4267367fea0f27c36 Mon Sep 17 00:00:00 2001
From: Aura <kyradiscord@gmail.com>
Date: Sat, 23 Nov 2024 00:25:20 +0100
Subject: [PATCH] feat: add `windows` (#836)

---
 packages/iterator-utilities/package.json      | 10 ++++
 packages/iterator-utilities/src/index.ts      |  1 +
 .../iterator-utilities/src/lib/windows.ts     | 39 ++++++++++++++++
 .../iterator-utilities/tests/windows.test.ts  | 46 +++++++++++++++++++
 4 files changed, 96 insertions(+)
 create mode 100644 packages/iterator-utilities/src/lib/windows.ts
 create mode 100644 packages/iterator-utilities/tests/windows.test.ts

diff --git a/packages/iterator-utilities/package.json b/packages/iterator-utilities/package.json
index dc5b581045..a0bf39438b 100644
--- a/packages/iterator-utilities/package.json
+++ b/packages/iterator-utilities/package.json
@@ -945,6 +945,16 @@
 				"default": "./dist/cjs/lib/unzip.cjs"
 			}
 		},
+		"./windows": {
+			"import": {
+				"types": "./dist/esm/lib/windows.d.mts",
+				"default": "./dist/esm/lib/windows.mjs"
+			},
+			"require": {
+				"types": "./dist/cjs/lib/windows.d.cts",
+				"default": "./dist/cjs/lib/windows.cjs"
+			}
+		},
 		"./zip": {
 			"import": {
 				"types": "./dist/esm/lib/zip.d.mts",
diff --git a/packages/iterator-utilities/src/index.ts b/packages/iterator-utilities/src/index.ts
index 365d94f2d0..f75ee96613 100644
--- a/packages/iterator-utilities/src/index.ts
+++ b/packages/iterator-utilities/src/index.ts
@@ -84,4 +84,5 @@ export * from './lib/toIterableIterator';
 export * from './lib/union';
 export * from './lib/unique';
 export * from './lib/unzip';
+export * from './lib/windows';
 export * from './lib/zip';
diff --git a/packages/iterator-utilities/src/lib/windows.ts b/packages/iterator-utilities/src/lib/windows.ts
new file mode 100644
index 0000000000..818d7adad0
--- /dev/null
+++ b/packages/iterator-utilities/src/lib/windows.ts
@@ -0,0 +1,39 @@
+import { from, type IterableResolvable } from './from';
+import { assertPositive } from './shared/_assertPositive';
+import { makeIterableIterator } from './shared/_makeIterableIterator';
+import { toIntegerOrInfinityOrThrow } from './shared/_toIntegerOrInfinityOrThrow';
+
+/**
+ * Creates an iterable with arrays of `count` elements representing a sliding window.
+ *
+ * @param iterable The iterator to take values from.
+ * @param count The maximum number of values in the window.
+ * @returns An iterator that yields windows with `count` values from the provided iterator.
+ *
+ * @example
+ * ```typescript
+ * import { windows } from '@sapphire/iterator-utilities';
+ *
+ * const iterable = [1, 2, 3, 4, 5];
+ * console.log([...windows(iterable, 2)]);
+ * // Output: [[1, 2], [2, 3], [3, 4], [4, 5]]
+ * ```
+ */
+export function windows<const ElementType>(iterable: IterableResolvable<ElementType>, count: number): IterableIterator<ElementType[]> {
+	count = assertPositive(toIntegerOrInfinityOrThrow(count), count);
+
+	const buffer = [] as ElementType[];
+	const resolvedIterable = from(iterable);
+	return makeIterableIterator<ElementType[]>(() => {
+		while (buffer.length !== count) {
+			const result = resolvedIterable.next();
+			if (result.done) return { done: true, value: undefined };
+
+			buffer.push(result.value);
+		}
+
+		const value = buffer.slice();
+		buffer.shift();
+		return { done: false, value };
+	});
+}
diff --git a/packages/iterator-utilities/tests/windows.test.ts b/packages/iterator-utilities/tests/windows.test.ts
new file mode 100644
index 0000000000..78f485ea84
--- /dev/null
+++ b/packages/iterator-utilities/tests/windows.test.ts
@@ -0,0 +1,46 @@
+import { windows } from '../src';
+
+describe('windows', () => {
+	test('GIVEN iterable and limit greater than iterable length THEN returns an empty iterable', () => {
+		const iterable = [1, 2, 3];
+		const limit = 5;
+		const result = [...windows(iterable, limit)];
+		expect(result).toEqual([]);
+	});
+
+	test('GIVEN iterable and limit equal to iterable length THEN returns an array with the contents of the iterable', () => {
+		const iterable = [1, 2, 3];
+		const limit = 3;
+		const result = [...windows(iterable, limit)];
+		expect(result).toEqual([[1, 2, 3]]);
+	});
+
+	test('GIVEN iterable and limit less than iterable length THEN returns multiple windows', () => {
+		const iterable = [1, 2, 3];
+		const limit = 2;
+		const result = [...windows(iterable, limit)];
+		expect(result).toEqual([
+			[1, 2],
+			[2, 3]
+		]);
+	});
+
+	test('GIVEN empty iterable THEN returns empty iterable', () => {
+		const iterable: number[] = [];
+		const limit = 5;
+		const result = [...windows(iterable, limit)];
+		expect(result).toEqual([]);
+	});
+
+	test('GIVEN iterable and limit equal to 0 THEN throws RangeError', () => {
+		const iterable = [1, 2, 3];
+		const limit = 0;
+		expect(() => windows(iterable, limit)).toThrowError(new RangeError('0 must be a positive number'));
+	});
+
+	test('GIVEN iterable and limit less than 0 THEN throws RangeError', () => {
+		const iterable = [1, 2, 3];
+		const limit = -1;
+		expect(() => windows(iterable, limit)).toThrowError(new RangeError('-1 must be a positive number'));
+	});
+});