From 044cb83e7339d77cea322050fd181eea4b9af09a Mon Sep 17 00:00:00 2001
From: Federico Biccheddu <433819+FedericoBiccheddu@users.noreply.github.com>
Date: Wed, 19 Feb 2025 18:05:07 +0100
Subject: [PATCH] feat: add Array.window (#4477)

---
 .changeset/tender-kangaroos-kiss.md  |  5 +++++
 packages/effect/dtslint/Array.tst.ts | 12 +++++++++++
 packages/effect/src/Array.ts         | 31 ++++++++++++++++++++++++++++
 packages/effect/test/Array.test.ts   | 12 +++++++++++
 4 files changed, 60 insertions(+)
 create mode 100644 .changeset/tender-kangaroos-kiss.md

diff --git a/.changeset/tender-kangaroos-kiss.md b/.changeset/tender-kangaroos-kiss.md
new file mode 100644
index 00000000000..74ab03a9c47
--- /dev/null
+++ b/.changeset/tender-kangaroos-kiss.md
@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Add `Array.window` function
diff --git a/packages/effect/dtslint/Array.tst.ts b/packages/effect/dtslint/Array.tst.ts
index 50d980b6f4e..aeec35bb786 100644
--- a/packages/effect/dtslint/Array.tst.ts
+++ b/packages/effect/dtslint/Array.tst.ts
@@ -942,6 +942,18 @@ describe("Array", () => {
       .type.toBe<[[string, ...Array<string>], ...Array<[string, ...Array<string>]>]>()
   })
 
+  it("window", () => {
+    // Array
+    expect(Array.window(strings, 2)).type.toBe<Array<Array<string>>>()
+    expect(pipe(strings, Array.window(2))).type.toBe<Array<Array<string>>>()
+    expect(Array.window(2)(strings)).type.toBe<Array<Array<string>>>()
+
+    // NonEmptyArray
+    expect(Array.window(nonEmptyStrings, 2)).type.toBe<Array<Array<string>>>()
+    expect(pipe(nonEmptyStrings, Array.window(2))).type.toBe<Array<Array<string>>>()
+    expect(Array.window(2)(nonEmptyStrings)).type.toBe<Array<Array<string>>>()
+  })
+
   it("reverse", () => {
     // Array
     expect(Array.reverse(strings)).type.toBe<Array<string>>()
diff --git a/packages/effect/src/Array.ts b/packages/effect/src/Array.ts
index 0b280500ae5..dfadc3a5e8d 100644
--- a/packages/effect/src/Array.ts
+++ b/packages/effect/src/Array.ts
@@ -1969,6 +1969,37 @@ export const chunksOf: {
   return []
 })
 
+/**
+ * Creates sliding windows of size `n` from an `Iterable`.
+ * If the number of elements is less than `n` or if `n` is not greater than zero,
+ * an empty array is returned.
+ *
+ * @example
+ * ```ts
+ * import { Array } from "effect"
+ *
+ * const numbers = [1, 2, 3, 4, 5]
+ * assert.deepStrictEqual(Array.window(numbers, 3), [[1, 2, 3], [2, 3, 4], [3, 4, 5]])
+ * assert.deepStrictEqual(Array.window(numbers, 6), [])
+ * ```
+ *
+ * @category splitting
+ * @since 3.13.2
+ */
+export const window: {
+  (n: number): <A>(self: Iterable<A>) => Array<Array<A>>
+  <A>(self: Iterable<A>, n: number): Array<Array<A>>
+} = dual(2, <A>(self: Iterable<A>, n: number): Array<Array<A>> => {
+  const input = fromIterable(self)
+  if (n > 0 && isNonEmptyReadonlyArray(input)) {
+    return Array.from(
+      { length: input.length - (n - 1) },
+      (_, index) => input.slice(index, index + n)
+    )
+  }
+  return []
+})
+
 /**
  * Group equal, consecutive elements of a `NonEmptyReadonlyArray` into `NonEmptyArray`s using the provided `isEquivalent` function.
  *
diff --git a/packages/effect/test/Array.test.ts b/packages/effect/test/Array.test.ts
index 5d749a33090..4af94093cb0 100644
--- a/packages/effect/test/Array.test.ts
+++ b/packages/effect/test/Array.test.ts
@@ -956,6 +956,18 @@ describe("Array", () => {
     assertSingleChunk(Arr.make(1, 2), 3)
   })
 
+  it("window", () => {
+    deepStrictEqual(Arr.window(2)([]), [])
+
+    deepStrictEqual(Arr.window(2)([1, 2, 3, 4, 5]), [[1, 2], [2, 3], [3, 4], [4, 5]])
+    deepStrictEqual(Arr.window(3)([1, 2, 3, 4, 5]), [[1, 2, 3], [2, 3, 4], [3, 4, 5]])
+
+    // n out of bounds
+    deepStrictEqual(Arr.window([1, 2, 3, 4, 5], 6), [])
+    deepStrictEqual(Arr.window([1, 2, 3, 4, 5], 0), [])
+    deepStrictEqual(Arr.window([1, 2, 3, 4, 5], -1), [])
+  })
+
   it("min", () => {
     deepStrictEqual(Arr.min(Num.Order)([2, 1, 3]), 1)
     deepStrictEqual(Arr.min(Num.Order)([3]), 3)