From c91c817ad03c1eab1a2a5e04d911a287e64f3eaf Mon Sep 17 00:00:00 2001
From: khalilrached <khalilrached058@gmail.com>
Date: Tue, 23 Apr 2024 22:50:09 +0100
Subject: [PATCH] pass current depth to transform function.

---
 README.md    | 28 ++++++++++++++++++++++++++++
 index.d.ts   |  2 +-
 index.js     |  4 ++--
 test/test.js | 22 ++++++++++++++++++++++
 4 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 325581c..6b5b0f6 100644
--- a/README.md
+++ b/README.md
@@ -207,6 +207,34 @@ unflatten({
 // }
 ```
 
+### transformKey with currentDepth
+
+Transform each part of a flat key before and after flattening with condition of the current depth .
+
+```javascript
+import { flatten, unflatten } from 'flat'
+
+flatten({
+    key1: {
+        keyA: 'valueI'
+    },
+    key2: {
+        keyB: 'valueII'
+    },
+    key3: { a: { b: { c: 2 } } }
+}, {
+    transformKey: function(key, depth){
+      return depth > 2 ? '[' + key + ']' : key;
+    }
+})
+
+// {
+//   'key1.keyA': 'valueI',
+//   'key2.keyB': 'valueII',
+//   'key3.a.[b].[c]': 2
+// }
+```
+
 ## Command Line Usage
 
 `flat` is also available as a command line tool. You can run it with [`npx`](https://docs.npmjs.com/cli/v8/commands/npx):
diff --git a/index.d.ts b/index.d.ts
index 1442ce4..9ed1c47 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -2,7 +2,7 @@ export interface FlattenOptions {
   delimiter?: string;
   maxDepth?: number;
   safe?: boolean;
-  transformKey?: (key: string) => string;
+  transformKey?: (key: string, currentDepth?: number) => string;
 }
 
 export function flatten<T, R>(target: T, options?: FlattenOptions): R;
diff --git a/index.js b/index.js
index 42e1ddc..ae77aa7 100644
--- a/index.js
+++ b/index.js
@@ -30,8 +30,8 @@ export function flatten (target, opts) {
       )
 
       const newKey = prev
-        ? prev + delimiter + transformKey(key)
-        : transformKey(key)
+        ? prev + delimiter + transformKey(key, currentDepth)
+        : transformKey(key, currentDepth)
 
       if (!isarray && !isbuffer && isobject && Object.keys(value).length &&
         (!opts.maxDepth || currentDepth < maxDepth)) {
diff --git a/test/test.js b/test/test.js
index ef01c9b..800f7a4 100644
--- a/test/test.js
+++ b/test/test.js
@@ -194,6 +194,28 @@ describe('Flatten', function () {
       '__lorem__.__ipsum__.__dolor__': 'good evening'
     })
   })
+   
+  test('Transformed Keys with current depth', function () {
+    assert.deepStrictEqual(flatten({
+      hello: {
+        world: {
+          again: 'good morning'
+        }
+      },
+      lorem: {
+        ipsum: {
+          dolor: 'good evening'
+        }
+      }
+    }, {
+      transformKey: function (key, depth) {
+        return depth > 2 ? '[' + key + ']' : key
+      }
+    }), {
+      'hello.world.[again]': 'good morning',
+      'lorem.ipsum.[dolor]': 'good evening'
+    })
+  })
 
   test('Should keep number in the left when object', function () {
     assert.deepStrictEqual(flatten({