velocity-pay-flutter/lib/screens/gateway/gateway_web_screen.dart

import 'package:flutter/material.dart';
import 'package:flutter_dotenv/flutter_dotenv.dart';
import 'package:go_router/go_router.dart';
import 'package:qpay/models/responsive_policy.dart';
import 'package:qpay/screens/gateway/gateway_controller.dart';
import 'package:web/web.dart' as web;

class GatewayWebScreen extends StatefulWidget {
  const GatewayWebScreen({super.key});

  @override
  State<GatewayWebScreen> createState() => _GatewayWebScreenState();
}

class _GatewayWebScreenState extends State<GatewayWebScreen> {
  late GatewayController controller;
  late String url;

  bool integrationStarted = false;
  bool redirecting = false;

  @override
  void initState() {
    super.initState();
    controller = GatewayController(context);

    url = controller.transactionController.model.receiptData?['targetUrl'];
  }

  void _redirectToGateway() {
    if (redirecting) return;

    setState(() {
      redirecting = true;
    });

    bool simulate = bool.parse(
      dotenv.env['SIMULATE_PAYMENT_SUCCESS'] ?? 'false',
    );
    if (simulate) {
      // In simulation mode, just go to polling
      WidgetsBinding.instance.addPostFrameCallback((_) {
        context.go('/poll');
      });
      return;
    }

    // Save the transaction ID to localStorage so index.html can redirect
    // the user back to /poll/:id when the gateway returns to this app.
    final transactionId =
        controller.transactionController.model.confirmationData['id'];
    if (transactionId != null) {
      web.window.localStorage.setItem(
        'pendingTransactionId',
        transactionId.toString(),
      );
    }

    // Navigate the current browser tab to the payment gateway URL.
    // After payment, the gateway will redirect back to this app's host.
    // index.html then reads the saved transaction ID and navigates to
    // /poll/:id so the app can immediately start polling for the result.
    web.window.location.href = url;
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Complete your payment'),
        leading: context.canPop()
            ? IconButton(
                onPressed: () {
                  context.pop();
                },
                icon: const Icon(Icons.arrow_back),
              )
            : const SizedBox.shrink(),
      ),
      body: ListenableBuilder(
        listenable: controller,
        builder: (context, child) {
          return Center(
            child: LayoutBuilder(
              builder: (context, constraints) {
                return SizedBox(
                  width: constraints.maxWidth > ResponsivePolicy.md
                      ? ResponsivePolicy.md.toDouble()
                      : constraints.maxWidth.toDouble(),
                  child: SingleChildScrollView(
                    child: Padding(
                      padding: const EdgeInsets.all(20.0),
                      child: Column(
                        mainAxisAlignment: MainAxisAlignment.center,
                        crossAxisAlignment: CrossAxisAlignment.center,
                        children: [
                          const SizedBox(height: 40),

                          // Info icon
                          Icon(
                            Icons.lock_outline,
                            size: 64,
                            color: Theme.of(context).colorScheme.primary,
                          ),
                          const SizedBox(height: 24),

                          Text(
                            'You are about to leave this app to complete your payment on a secure payment gateway.',
                            style: const TextStyle(fontSize: 18),
                            textAlign: TextAlign.center,
                          ),
                          const SizedBox(height: 16),

                          Text(
                            'After completing payment, you will be automatically redirected back to this app to see your transaction status.',
                            style: TextStyle(
                              fontSize: 14,
                              color: Colors.grey[600],
                            ),
                            textAlign: TextAlign.center,
                          ),

                          const SizedBox(height: 40),

                          Image.asset(
                            'assets/velocity-animation.gif',
                            width: 150,
                          ),

                          const SizedBox(height: 40),

                          SizedBox(
                            width: double.infinity,
                            child: ElevatedButton(
                              onPressed: redirecting
                                  ? null
                                  : _redirectToGateway,
                              style: ElevatedButton.styleFrom(
                                padding: const EdgeInsets.symmetric(
                                  vertical: 16,
                                ),
                              ),
                              child: Text(
                                redirecting
                                    ? 'Redirecting...'
                                    : 'Proceed to Payment Gateway',
                                style: const TextStyle(fontSize: 16),
                              ),
                            ),
                          ),

                          const SizedBox(height: 16),

                          TextButton(
                            onPressed: () {
                              context.go('/poll');
                            },
                            child: const Text('Check transaction status'),
                          ),
                        ],
                      ),
                    ),
                  ),
                );
              },
            ),
          );
        },
      ),
    );
  }
}