From 10b1917ae5750100888899bc1f0645b45d848851 Mon Sep 17 00:00:00 2001
From: Lexus Drumgold <unicornware@flexdevelopment.llc>
Date: Sun, 11 Dec 2022 17:46:18 -0500
Subject: [PATCH] feat(utils): `changeExt`

Signed-off-by: Lexus Drumgold <unicornware@flexdevelopment.llc>
---
 src/utils/__tests__/change-ext.spec.ts | 40 ++++++++++++++++++
 src/utils/change-ext.ts                | 56 ++++++++++++++++++++++++++
 src/utils/index.ts                     |  1 +
 3 files changed, 97 insertions(+)
 create mode 100644 src/utils/__tests__/change-ext.spec.ts
 create mode 100644 src/utils/change-ext.ts

diff --git a/src/utils/__tests__/change-ext.spec.ts b/src/utils/__tests__/change-ext.spec.ts
new file mode 100644
index 00000000..cfca71c3
--- /dev/null
+++ b/src/utils/__tests__/change-ext.spec.ts
@@ -0,0 +1,40 @@
+/**
+ * @file Unit Tests - changeExt
+ * @module pathe/utils/tests/unit/changeExt
+ */
+
+import testSubject from '../change-ext'
+
+describe('unit:utils/changeExt', () => {
+  it('should return path with new file extension', () => {
+    // Arrange
+    const cases: [...Parameters<typeof testSubject>, string][] = [
+      ['file', 'mjs', 'file.mjs'],
+      ['file', 'mts', 'file.mts'],
+      ['file.', '.mjs', 'file.mjs'],
+      ['file.', '.mts', 'file.mts'],
+      ['file.mts', 'd.mts', 'file.d.mts'],
+      ['file.min.cjs', '.mjs', 'file.min.mjs']
+    ]
+
+    // Act + Expect
+    cases.forEach(([path, ext, expected]) => {
+      expect(testSubject(path, ext)).to.equal(expected)
+    })
+  })
+
+  it('should return path without modications if ext is empty', () => {
+    // Arrange
+    const cases: [...Parameters<typeof testSubject>, string][] = [
+      ['file.cjs', '', 'file.cjs'],
+      ['file.cts', ' ', 'file.cts'],
+      ['file.mjs', null, 'file.mjs'],
+      ['file.mts', undefined, 'file.mts']
+    ]
+
+    // Act + Expect
+    cases.forEach(([path, ext, expected]) => {
+      expect(testSubject(path, ext)).to.equal(expected)
+    })
+  })
+})
diff --git a/src/utils/change-ext.ts b/src/utils/change-ext.ts
new file mode 100644
index 00000000..ad4aebb1
--- /dev/null
+++ b/src/utils/change-ext.ts
@@ -0,0 +1,56 @@
+/**
+ * @file Utilities - changeExt
+ * @module pathe/utils/changeExt
+ */
+
+import validateString from '#src/internal/validate-string'
+import extname from '#src/lib/extname'
+import type { Ext } from '#src/types'
+import type { EmptyString, Nullable } from '@flex-development/tutils'
+import addExt from './add-ext'
+import formatExt from './format-ext'
+
+/**
+ * Changes the file extension of the given `path`.
+ *
+ * Does nothing if a file extension isn't provided.
+ *
+ * @example
+ *  changeExt('file') // 'file'
+ * @example
+ *  changeExt('file', 'cjs') // 'file.cjs'
+ * @example
+ *  changeExt('file', '.mjs') // 'file.mjs'
+ * @example
+ *  changeExt('file.mts', '.d.mts') // 'file.d.mts'
+ * @example
+ *  changeExt('file.min.cjs', 'mjs') // 'file.min.mjs'
+ *
+ * @param {string} path - Path to evaluate
+ * @param {Nullable<string>} [ext] - File extension to add
+ * @return {string} `path` unmodified or with new file extension
+ * @throws {TypeError} If `path` is not a string or `ext` is not a string
+ */
+const changeExt = (path: string, ext?: Nullable<string>): string => {
+  validateString(path, 'path')
+
+  // exit early if extension isn't provided or validate ext
+  if (ext === null || ext === undefined) return path
+  else validateString(ext, 'ext')
+
+  // exit early if extension is empty string
+  if (!ext.trim()) return path
+
+  /**
+   * File extension of {@linkcode path}.
+   *
+   * @const {EmptyString | Ext} extension
+   */
+  const extension: EmptyString | Ext = extname((path = path.replace(/\.$/, '')))
+
+  return extension
+    ? path.replace(new RegExp(`\\${extension}$`), formatExt(ext))
+    : addExt(path, ext)
+}
+
+export default changeExt
diff --git a/src/utils/index.ts b/src/utils/index.ts
index b863b619..e2bce538 100644
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -4,5 +4,6 @@
  */
 
 export { default as addExt } from './add-ext'
+export { default as changeExt } from './change-ext'
 export { default as formatExt } from './format-ext'
 export { default as removeExt } from './remove-ext'