import 'dart:async';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:sharedinbox/core/utils/html_utils.dart';
import 'package:url_launcher/url_launcher.dart';
import 'package:webview_flutter/webview_flutter.dart';
/// Builds the full HTML document string for rendering an email body.
///
/// Forces `color-scheme: light` so that emails with black text remain readable
/// when the device is in dark mode — the WebView would otherwise apply a dark
/// background while leaving the email's own text colours unchanged.
@visibleForTesting
String buildEmailHtml(String htmlBody, {bool loadRemoteImages = false}) {
final imgSrc = loadRemoteImages ? 'https: http: data: blob:' : 'data: blob:';
// script-src 'none' blocks page scripts; JS mode stays unrestricted so the
// controller can call runJavaScriptReturningResult for height measurement.
const cspBase = "default-src 'none'; "
"style-src 'unsafe-inline'; "
"script-src 'none'; "
"object-src 'none'; "
"font-src 'none'";
final csp = '$cspBase; img-src $imgSrc';
return '''
$htmlBody
''';
}
/// Renders an HTML email body securely.
///
/// On Android the content is displayed in a WebView with JavaScript blocked
/// via CSP and remote images blocked until the user opts in. Link taps show
/// a confirmation dialog that highlights the registered domain to aid phishing
/// detection.
///
/// On Linux (where webview_flutter has no platform support) the HTML is
/// converted to plain text and shown in a [SelectableText] widget.
class SecureEmailWebView extends StatefulWidget {
const SecureEmailWebView({
super.key,
required this.htmlBody,
this.loadRemoteImages = false,
});
final String htmlBody;
final bool loadRemoteImages;
@override
State createState() => _SecureEmailWebViewState();
}
class _SecureEmailWebViewState extends State {
// Null on Linux where WebView is unavailable.
WebViewController? _controller;
double _height = 300;
@override
void initState() {
super.initState();
if (!Platform.isLinux) {
final c = WebViewController();
unawaited(c.setJavaScriptMode(JavaScriptMode.unrestricted));
unawaited(c.setBackgroundColor(Colors.transparent));
unawaited(
c.setNavigationDelegate(
NavigationDelegate(
onNavigationRequest: _handleNavigation,
onPageFinished: _measureHeight,
),
),
);
unawaited(c.loadHtmlString(_buildHtml()));
_controller = c;
}
}
@override
void didUpdateWidget(SecureEmailWebView old) {
super.didUpdateWidget(old);
if (old.htmlBody != widget.htmlBody ||
old.loadRemoteImages != widget.loadRemoteImages) {
if (_controller != null) {
unawaited(_controller!.loadHtmlString(_buildHtml()));
}
}
}
String _buildHtml() => buildEmailHtml(
widget.htmlBody,
loadRemoteImages: widget.loadRemoteImages,
);
Future _measureHeight(String _) async {
final result = await _controller!.runJavaScriptReturningResult(
'document.documentElement.scrollHeight',
);
final h = double.tryParse(result.toString());
if (h != null && h > 0 && mounted) {
setState(() => _height = h);
}
}
NavigationDecision _handleNavigation(NavigationRequest req) {
final url = req.url;
if (url == 'about:blank' || url.startsWith('data:')) {
return NavigationDecision.navigate;
}
unawaited(_showLinkDialog(url));
return NavigationDecision.prevent;
}
Future _showLinkDialog(String url) async {
final uri = Uri.tryParse(url);
if (uri == null || !mounted) return;
final host = uri.host;
final parts = host.split('.');
// Bold the registered domain (last two DNS labels) to aid phishing detection.
final boldStart = (parts.length >= 2
? host.length -
parts.last.length -
1 -
parts[parts.length - 2].length
: 0)
.clamp(0, host.length);
final confirmed = await showDialog(
context: context,
builder: (ctx) => AlertDialog(
title: const Text('Open link?'),
content: Column(
mainAxisSize: MainAxisSize.min,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text.rich(
TextSpan(
style: const TextStyle(fontFamily: 'monospace', fontSize: 13),
children: [
TextSpan(text: host.substring(0, boldStart)),
TextSpan(
text: host.substring(boldStart),
style: const TextStyle(fontWeight: FontWeight.bold),
),
],
),
),
const SizedBox(height: 4),
Text(
url,
style: const TextStyle(fontSize: 11, color: Colors.grey),
maxLines: 3,
overflow: TextOverflow.ellipsis,
),
],
),
actions: [
TextButton(
onPressed: () => Navigator.pop(ctx, false),
child: const Text('Cancel'),
),
TextButton(
onPressed: () => Navigator.pop(ctx, true),
child: const Text('Open in browser'),
),
],
),
);
if (confirmed == true && mounted) {
final launched =
await launchUrl(uri, mode: LaunchMode.externalApplication);
if (!launched && mounted) {
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(content: Text('Could not open: $url')),
);
}
}
}
@override
Widget build(BuildContext context) {
// Linux has no webview_flutter platform implementation — show plain text.
if (Platform.isLinux) {
return SelectableText(
htmlToPlain(widget.htmlBody),
style: Theme.of(context).textTheme.bodyMedium,
);
}
return SizedBox(
height: _height,
child: WebViewWidget(controller: _controller!),
);
}
}