From 20f55ec3539a8e34fe5372c7ba20624fc6d1020e Mon Sep 17 00:00:00 2001
From: Titouan CREACH <titouancreach@users.noreply.github.com>
Date: Fri, 6 Dec 2024 12:49:14 +0100
Subject: [PATCH] add Schema.headNonEmpty on Schema.NonEmptyArray (#3983)

Co-authored-by: Giulio Canti <giulio.canti@gmail.com>
---
 .changeset/violet-spoons-compare.md           |  5 ++++
 packages/effect/src/Schema.ts                 | 13 ++++++++++
 .../Schema/Schema/Array/headNonEmpty.test.ts  | 26 +++++++++++++++++++
 3 files changed, 44 insertions(+)
 create mode 100644 .changeset/violet-spoons-compare.md
 create mode 100644 packages/effect/test/Schema/Schema/Array/headNonEmpty.test.ts

diff --git a/.changeset/violet-spoons-compare.md b/.changeset/violet-spoons-compare.md
new file mode 100644
index 00000000000..f5e26fb5a08
--- /dev/null
+++ b/.changeset/violet-spoons-compare.md
@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Add Schema.headNonEmpty for Schema.NonEmptyArray
diff --git a/packages/effect/src/Schema.ts b/packages/effect/src/Schema.ts
index 88376f6afaa..0e4021023ba 100644
--- a/packages/effect/src/Schema.ts
+++ b/packages/effect/src/Schema.ts
@@ -6014,6 +6014,19 @@ export const head = <A, I, R>(self: Schema<ReadonlyArray<A>, I, R>): SchemaClass
     { strict: true, decode: array_.head, encode: option_.match({ onNone: () => [], onSome: array_.of }) }
   )
 
+/**
+ * Get the first element of a `NonEmptyReadonlyArray`.
+ *
+ * @category NonEmptyReadonlyArray transformations
+ * @since 3.12.0
+ */
+export const headNonEmpty = <A, I, R>(self: Schema<array_.NonEmptyReadonlyArray<A>, I, R>): SchemaClass<A, I, R> =>
+  transform(
+    self,
+    getNumberIndexedAccess(typeSchema(self)),
+    { strict: true, decode: array_.headNonEmpty, encode: array_.of }
+  )
+
 /**
  * Retrieves the first element of a `ReadonlyArray`.
  *
diff --git a/packages/effect/test/Schema/Schema/Array/headNonEmpty.test.ts b/packages/effect/test/Schema/Schema/Array/headNonEmpty.test.ts
new file mode 100644
index 00000000000..51e113134de
--- /dev/null
+++ b/packages/effect/test/Schema/Schema/Array/headNonEmpty.test.ts
@@ -0,0 +1,26 @@
+import * as S from "effect/Schema"
+import * as Util from "effect/test/Schema/TestUtils"
+import { describe, it } from "vitest"
+
+describe("headNonEmpty", () => {
+  it("decoding", async () => {
+    const schema = S.headNonEmpty(S.NonEmptyArray(S.NumberFromString))
+    await Util.expectDecodeUnknownSuccess(schema, ["1"], 1)
+    await Util.expectDecodeUnknownFailure(
+      schema,
+      ["a"],
+      `(readonly [NumberFromString, ...NumberFromString[]] <-> number | number)
+└─ Encoded side transformation failure
+   └─ readonly [NumberFromString, ...NumberFromString[]]
+      └─ [0]
+         └─ NumberFromString
+            └─ Transformation process failure
+               └─ Expected NumberFromString, actual "a"`
+    )
+  })
+
+  it("encoding", async () => {
+    const schema = S.headNonEmpty(S.NonEmptyArray(S.NumberFromString))
+    await Util.expectEncodeSuccess(schema, 1, ["1"])
+  })
+})