From dc11d294e99ddecdccaa41cc30d0de8aec31a094 Mon Sep 17 00:00:00 2001
From: Gao Sun <gao@silverhand.io>
Date: Fri, 23 Dec 2022 18:29:09 +0800
Subject: [PATCH] feat: get()

---
 src/utilities/get.test.ts | 19 ++++++++++++++
 src/utilities/get.ts      | 52 +++++++++++++++++++++++++++++++++++++++
 src/utilities/index.ts    |  1 +
 3 files changed, 72 insertions(+)
 create mode 100644 src/utilities/get.test.ts
 create mode 100644 src/utilities/get.ts

diff --git a/src/utilities/get.test.ts b/src/utilities/get.test.ts
new file mode 100644
index 0000000..7390c3e
--- /dev/null
+++ b/src/utilities/get.test.ts
@@ -0,0 +1,19 @@
+import { get, getValue } from './get.js';
+
+describe('get()', () => {
+  const object = { aaa: 'asdasd', bbb: { ccc: 123, ddd: { eee: [true] } } };
+
+  it('should return proper value with even nested keys', () => {
+    expect(get(object, 'aaa')).toStrictEqual('asdasd');
+    expect(get(object, 'bbb')).toStrictEqual({ ccc: 123, ddd: { eee: [true] } });
+    expect(get(object, 'bbb.ccc')).toStrictEqual(123);
+    expect(getValue(object, 'bbb.ddd')).toStrictEqual({ eee: [true] });
+    expect(getValue(object, 'bbb.ddd.eee')).toStrictEqual([true]);
+  });
+
+  it('should return undefined of throw TypeError when accessing non-existing value', () => {
+    // eslint-disable-next-line unicorn/no-useless-undefined
+    expect(get(object, 'ddd')).toStrictEqual(undefined);
+    expect(() => get(object, 'ddd.ccc')).toThrowError(TypeError);
+  });
+});
diff --git a/src/utilities/get.ts b/src/utilities/get.ts
new file mode 100644
index 0000000..5089b51
--- /dev/null
+++ b/src/utilities/get.ts
@@ -0,0 +1,52 @@
+type ValidKeys<T> = keyof T extends string ? keyof T : never;
+
+export type KeySerial<T extends Record<string, unknown>> =
+  | ValidKeys<T>
+  | {
+      [key in ValidKeys<T>]: T[key] extends unknown[]
+        ? never
+        : T[key] extends Record<string, unknown>
+        ? `${key}.${KeySerial<T[key]>}`
+        : never;
+    }[ValidKeys<T>];
+
+export type ExtractKeySerialType<
+  T extends Record<string, unknown>,
+  Serial extends string
+> = Serial extends `${infer Key}.${infer Rest}`
+  ? T[Key] extends Record<string, unknown>
+    ? ExtractKeySerialType<T[Key], Rest>
+    : never
+  : T[Serial];
+
+/* eslint-disable @silverhand/fp/no-let, @silverhand/fp/no-mutation */
+type Get = {
+  <T extends Record<string, unknown>, Serial extends KeySerial<T>>(
+    object: T,
+    keySerial: Serial
+  ): ExtractKeySerialType<T, Serial>;
+  // eslint-disable-next-line @typescript-eslint/ban-types
+  <T extends object>(object: T, keySerial: unknown): unknown;
+};
+
+export const get: Get = <T extends Record<string, unknown>, Serial extends KeySerial<T>>(
+  object: T,
+  keySerial: Serial
+): ExtractKeySerialType<T, Serial> => {
+  let result: unknown = object;
+
+  for (const key of keySerial.split('.')) {
+    // @ts-expect-error for performance
+    result = result[key];
+  }
+
+  // eslint-disable-next-line no-restricted-syntax
+  return result as ExtractKeySerialType<T, Serial>;
+};
+
+/** Same to `get()` but with the strict type definition only to enable IntelliSense. */
+export const getValue = <T extends Record<string, unknown>, Serial extends KeySerial<T>>(
+  object: T,
+  keySerial: Serial
+): ExtractKeySerialType<T, Serial> => get(object, keySerial);
+/* eslint-enable @silverhand/fp/no-let, @silverhand/fp/no-mutation */
diff --git a/src/utilities/index.ts b/src/utilities/index.ts
index fe606c8..2766cc5 100644
--- a/src/utilities/index.ts
+++ b/src/utilities/index.ts
@@ -7,3 +7,4 @@ export * from './function.js';
 export * from './pick.js';
 export * from './string.js';
 export * from './types.js';
+export * from './get.js';