pagination

lib/chat/models/window_state.dart

@@ -0,0 +1,27 @@
+import 'package:fast_immutable_collections/fast_immutable_collections.dart';
+import 'package:flutter/foundation.dart';
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'window_state.freezed.dart';
+
+@freezed
+class WindowState<T> with _$WindowState<T> {
+  const factory WindowState({
+    // List of objects in the window
+    required IList<T> window,
+    // Total number of objects (windowTail max)
+    required int length,
+    // One past the end of the last element
+    required int windowTail,
+    // The total number of elements to try to keep in the window
+    required int windowCount,
+    // If we should have the tail following the array
+    required bool follow,
+  }) = _WindowState;
+}
+
+extension WindowStateExt<T> on WindowState<T> {
+  int get windowEnd => (length == 0) ? -1 : (windowTail - 1) % length;
+  int get windowStart =>
+      (length == 0) ? 0 : (windowTail - window.length) % length;
+}