added connectivity service

lib/features/core/widgets/mcg_scaffold.dart

@@ -0,0 +1,71 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+import '../data/constants/const_durations.dart';
+import '../services/connection_service.dart';
+
+class McgScaffold extends StatelessWidget {
+  const McgScaffold({
+    this.appBar,
+    this.bodyBuilderCompleter,
+    this.body,
+    this.waitingWidget,
+    this.forceInternetCheck = false,
+    super.key,
+  });
+
+  final AppBar? appBar;
+
+  /// Awaits an external signal (complete) before building the body.
+  final Completer? bodyBuilderCompleter;
+  final Widget? body;
+
+  /// Custom widget to be used while awaiting [bodyBuilderCompleter].
+  ///
+  /// Defaults to using [PlatformCircularProgressIndicator].
+  final Widget? waitingWidget;
+
+  /// Enabling listing to [ConnectionState], showing a small text at the top, when connectivity is lost.
+  final bool forceInternetCheck;
+
+  @override
+  Widget build(BuildContext context) {
+    final Widget loginOptionsBody = bodyBuilderCompleter != null
+        ? FutureBuilder(
+            future: bodyBuilderCompleter!.future,
+            builder: (context, snapshot) {
+              switch (snapshot.connectionState) {
+                case ConnectionState.none:
+                case ConnectionState.waiting:
+                case ConnectionState.active:
+                  return Center(child: waitingWidget ?? const CircularProgressIndicator());
+                case ConnectionState.done:
+                  return body ?? const SizedBox.shrink();
+              }
+            },
+          )
+        : body ?? const SizedBox.shrink();
+
+    return Scaffold(
+      appBar: appBar,
+      body: forceInternetCheck
+          ? SingleChildScrollView(
+              child: ValueListenableBuilder<bool>(
+                valueListenable: ConnectionService.locate.hasInternetConnectionListenable,
+                builder: (context, hasInternetConnection, _) => Column(
+                  children: [
+                    AnimatedSwitcher(
+                      duration: ConstDurations.defaultAnimationDuration,
+                      child: !hasInternetConnection ? Text('No internet') : const SizedBox.shrink(),
+                    ),
+                    loginOptionsBody,
+                  ],
+                ),
+              ),
+            )
+          : loginOptionsBody,
+    );
+  }
+}