From 0bfe98fd463c3504af5ee567b59bfa75302cce07 Mon Sep 17 00:00:00 2001
From: Tyler Holewinski <tyler.holewinski@bryx.com>
Date: Fri, 13 Oct 2023 16:52:33 -0400
Subject: [PATCH] Introduce `maybe(...)` Wrapper (#70)

---
 .changeset/breezy-panthers-breathe.md |  5 ++
 src/maybe.test.ts                     | 68 ++++++++++++++++++++++++++-
 src/maybe.ts                          | 41 ++++++++++++++++
 3 files changed, 113 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/breezy-panthers-breathe.md

diff --git a/.changeset/breezy-panthers-breathe.md b/.changeset/breezy-panthers-breathe.md
new file mode 100644
index 0000000..f8ace9b
--- /dev/null
+++ b/.changeset/breezy-panthers-breathe.md
@@ -0,0 +1,5 @@
+---
+"@bryx-inc/ts-utils": minor
+---
+
+Introduces `maybe(...)` method to provide kotlin-style scope methods
diff --git a/src/maybe.test.ts b/src/maybe.test.ts
index b125c29..74445e5 100644
--- a/src/maybe.test.ts
+++ b/src/maybe.test.ts
@@ -1,4 +1,16 @@
-import { expectMaybe, FormalMaybe, intoMaybe, isNone, isSome, matchMaybe, Maybe, unwrapMaybe, unwrapOrUndef, withSome } from "./maybe";
+import {
+    expectMaybe,
+    FormalMaybe,
+    intoMaybe,
+    isNone,
+    isSome,
+    matchMaybe,
+    maybe,
+    Maybe,
+    unwrapMaybe,
+    unwrapOrUndef,
+    withSome,
+} from "./maybe";
 
 const emptyMaybe: Maybe<string> = null;
 const filledMaybe: Maybe<string> = "foo";
@@ -169,3 +181,57 @@ describe("take()", () => {
         expect(nullableValue.inner()).toBeNull();
     });
 });
+
+describe("maybe()", () => {
+    it("should allow chaining methods and return the wrapped value", () => {
+        const wrappedValue = maybe(42);
+        const result = wrappedValue.let((it) => it * 2);
+
+        expect(result).toBe(84);
+    });
+
+    it("should handle null or undefined values correctly", () => {
+        expect(maybe(null as string | null)?.let((it) => it.length)).toEqual(undefined);
+    });
+
+    it('should handle "takeUnless" method correctly', () => {
+        expect(maybe([1, 2, 3] as number[] | null)?.takeUnless((it) => it.length == 0)).toEqual([1, 2, 3]);
+        expect(maybe([] as number[] | null)?.takeUnless((it) => it.length == 0)).toEqual(null);
+    });
+
+    it('should handle "takeIf" method correctly', () => {
+        expect(maybe([1, 2, 3] as number[] | null)?.takeIf((it) => it.length > 0)).toEqual([1, 2, 3]);
+        expect(maybe([] as number[] | null)?.takeIf((it) => it.length > 0)).toEqual(null);
+    });
+
+    it("should properly eject the wrapped value", () => {
+        const thing = "foo" as Maybe<string>;
+        const thing2 = null as Maybe<string>;
+
+        expect(maybe(thing)?.value()).toEqual("foo");
+        expect(maybe(thing2)?.value).toEqual(undefined);
+    });
+
+    it('should handle "also" method correctly', () => {
+        const thing = "foo" as Maybe<string>;
+        const thing2 = null as Maybe<string>;
+
+        const fn = jest.fn();
+
+        expect(
+            maybe(thing)?.also((it) => {
+                fn(it);
+                return "bar";
+            }),
+        ).toEqual("foo");
+
+        expect(
+            maybe(thing2)?.also((it) => {
+                fn(it);
+                return "bar";
+            }),
+        ).toEqual(undefined);
+
+        expect(fn).toBeCalledTimes(1);
+    });
+});
diff --git a/src/maybe.ts b/src/maybe.ts
index e6ed730..6131996 100644
--- a/src/maybe.ts
+++ b/src/maybe.ts
@@ -391,3 +391,44 @@ export class FormalMaybe<T> {
         return this;
     }
 }
+
+type NullOrUndefined = null | undefined;
+
+type WrappedMaybe<T> = T extends NullOrUndefined
+    ? WrappedMaybe<Exclude<T, NullOrUndefined>> | Extract<T, NullOrUndefined>
+    : {
+          /** Calls the specified function with the wrapped value as its argument and returns the result */
+          let: <E>(fn: (it: T) => E) => E;
+          /** Calls the specified function with the wrapped value as its argument and returns the wrapped value */
+          also: (fn: (it: T) => void) => T;
+          /** Returns the value if it satisfies the given predicate, otherwise returns null */
+          takeIf: (predicate: (it: T) => boolean) => NonNullable<T> | null;
+          /** Returns the value unless it satisfies the given predicate, in which case it returns null */
+          takeUnless: (predicate: (it: T) => boolean) => T | null;
+          /** Returns the `this` value it was called with */
+          value: () => NonNullable<T>;
+      } & NonNullable<T>;
+
+/**
+ * Creates a scoped value for chaining operations on a copy of the given wrapped value.
+ *
+ * @typeParam T The type of the wrapped value.
+ * @param wrapped The value to wrap
+ */
+export function maybe<T>(wrapped: T): WrappedMaybe<T> {
+    if (wrapped !== null && wrapped !== undefined)
+        return {
+            ...wrapped,
+            let: <E>(fn: (it: T) => E) => fn(wrapped),
+            takeIf: (predicate: (it: T) => boolean) => (predicate(wrapped) ? wrapped : null),
+            takeUnless: (predicate: (it: T) => boolean) => (predicate(wrapped) ? null : wrapped),
+            value: () => wrapped,
+            also: (fn: (it: T) => void) => {
+                fn(wrapped);
+                return wrapped;
+            },
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        } as any;
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    else return wrapped as any;
+}