Fix gradient avatar colors for users with same-length IDs

packages/stream_chat_flutter/lib/src/avatars/gradient_avatar.dart

@@ -88,7 +88,7 @@ class PolygonGradientPainter extends CustomPainter {
   void paint(Canvas canvas, Size size) {
     final rowUnit = size.width / columnCount;
     final columnUnit = size.height / rowCount;
-    final rand = Random(userId.length);
+    final rand = Random(userId.hashCode);
 
     final squares = <Offset4>[];
     final points = <Offset>{};
@@ -159,7 +159,7 @@ class PolygonGradientPainter extends CustomPainter {
   List<Offset> transformPoints(Set<Offset> points, Size size) {
     final transformedList = <Offset>[];
     final orgList = points.toList();
-    final rand = Random(userId.length);
+    final rand = Random(userId.hashCode);
 
     for (var i = 0; i < points.length; i++) {
       final orgDx = orgList[i].dx;
@@ -235,9 +235,9 @@ class Offset4 {
     final paint = Paint()
       ..color = Color.fromARGB(
         255,
-        Random().nextInt(255),
-        Random().nextInt(255),
-        Random().nextInt(255),
+        Random(row * colSize + column).nextInt(255),
+        Random(row * colSize + column + 1).nextInt(255),
+        Random(row * colSize + column + 2).nextInt(255),
       )
       ..shader = ui.Gradient.linear(
         points[p1],

packages/stream_chat_flutter/test/src/avatars/gradient_avatar_test.dart

@@ -1,3 +1,5 @@
+import 'dart:math';
+
 import 'package:alchemist/alchemist.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -112,4 +114,58 @@ void main() {
       ),
     ),
   );
+
+  group('Gradient Avatar deterministic color tests', () {
+    test('users with same length IDs should have different gradient colors', () {
+      // Create a few user IDs of the same length but different values
+      final userIdsWithSameLength = ['12133', '12134', '12135', '98765', '54321'];
+      final gradientIndices = <int>[];
+
+      for (final userId in userIdsWithSameLength) {
+        // Create a mock random generator using userId.hashCode (the fix)
+        final rand = Random(userId.hashCode);
+        final gradientIndex = rand.nextInt(colorGradients.length);
+        gradientIndices.add(gradientIndex);
+      }
+
+      // Verify that not all gradient indices are the same
+      // (With the old behavior using userId.length, they would all be identical)
+      final uniqueIndices = gradientIndices.toSet();
+      expect(uniqueIndices.length, greaterThan(1), 
+        reason: 'Users with same-length IDs should get different gradient colors');
+    });
+
+    test('same user ID should always get the same gradient color', () {
+      const userId = '12345';
+      final gradientIndices = <int>[];
+
+      // Generate gradient index multiple times for the same user
+      for (int i = 0; i < 5; i++) {
+        final rand = Random(userId.hashCode);
+        final gradientIndex = rand.nextInt(colorGradients.length);
+        gradientIndices.add(gradientIndex);
+      }
+
+      // All indices should be the same for the same user
+      final uniqueIndices = gradientIndices.toSet();
+      expect(uniqueIndices.length, equals(1),
+        reason: 'Same user ID should always get the same gradient color');
+    });
+
+    test('different user IDs should have potential for different colors', () {
+      final userIds = ['user1', 'user2', 'user3', 'user4', 'user5'];
+      final gradientIndices = <int>[];
+
+      for (final userId in userIds) {
+        final rand = Random(userId.hashCode);
+        final gradientIndex = rand.nextInt(colorGradients.length);
+        gradientIndices.add(gradientIndex);
+      }
+
+      // While not guaranteed, different users should very likely get different colors
+      final uniqueIndices = gradientIndices.toSet();
+      expect(uniqueIndices.length, greaterThan(1), 
+        reason: 'Different users should have potential for different gradient colors');
+    });
+  });
 }