chore: flatten payload util (#6531)

https://linear.app/unleash/issue/2-2029/support-filtering-on-nested-properties

This will allow us to support and suggest payload subproperties in the
action filters.

src/lib/util/flattenPayload.test.ts

@@ -0,0 +1,35 @@
+import { flattenPayload } from './flattenPayload';
+
+describe('flattenPayload', () => {
+    it('should flatten a payload', () => {
+        const payload = {
+            a: 1,
+            b: {
+                c: 2,
+                d: [3, 4],
+                e: {
+                    f: 5,
+                },
+            },
+        };
+        expect(flattenPayload(payload)).toEqual({
+            a: 1,
+            'b.c': 2,
+            'b.d[0]': 3,
+            'b.d[1]': 4,
+            'b.e.f': 5,
+        });
+    });
+
+    it('should handle conflicting keys gracefully by prioritizing later keys', () => {
+        const payload = {
+            a: {
+                b: 1,
+            },
+            'a.b': 2,
+        };
+        expect(flattenPayload(payload)).toEqual({
+            'a.b': 2,
+        });
+    });
+});

src/lib/util/flattenPayload.ts

@@ -0,0 +1,32 @@
+export const flattenPayload = (
+    payload = {},
+    parentKey = '',
+): Record<string, unknown> =>
+    Object.entries(payload).reduce((acc, [key, value]) => {
+        const newKey = parentKey ? `${parentKey}.${key}` : key;
+
+        if (
+            typeof value === 'object' &&
+            value !== null &&
+            !Array.isArray(value)
+        ) {
+            // If it's an object, recurse and merge the results
+            Object.assign(acc, flattenPayload(value, newKey));
+        } else if (Array.isArray(value)) {
+            // If it's an array, map through it and handle objects and non-objects differently
+            value.forEach((item, index) => {
+                if (typeof item === 'object' && item !== null) {
+                    Object.assign(
+                        acc,
+                        flattenPayload(item, `${newKey}[${index}]`),
+                    );
+                } else {
+                    acc[`${newKey}[${index}]`] = item;
+                }
+            });
+        } else {
+            acc[newKey] = value;
+        }
+
+        return acc;
+    }, {});