TF-3416 Handle download attachment in EML previewer on mobile

core/lib/data/constants/constant.dart

@@ -10,4 +10,7 @@ class Constant {
   static const textVCardMimeType = 'text/x-vcard';
   static const textPlainMimeType = 'text/plain';
   static const emlMimeType = 'message/rfc822';
+  static const mailtoScheme = 'mailto';
+  static const attachmentScheme = 'attachment';
+  static const emlPreviewerScheme = 'eml-previewer';
 }

core/lib/presentation/views/html_viewer/html_content_viewer_widget.dart

@@ -1,12 +1,12 @@
 import 'dart:async';
 import 'dart:math' as math;
 
+import 'package:core/data/constants/constant.dart';
 import 'package:core/presentation/views/loading/cupertino_loading_widget.dart';
 import 'package:core/utils/app_logger.dart';
 import 'package:core/utils/html/html_interaction.dart';
 import 'package:core/utils/html/html_utils.dart';
 import 'package:core/utils/platform_info.dart';
-import 'package:core/utils/preview_eml_file_utils.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -18,6 +18,7 @@ typedef OnScrollHorizontalEndAction = Function(bool leftDirection);
 typedef OnLoadWidthHtmlViewerAction = Function(bool isScrollPageViewActivated);
 typedef OnMailtoDelegateAction = Future<void> Function(Uri? uri);
 typedef OnPreviewEMLDelegateAction = Future<void> Function(Uri? uri);
+typedef OnDownloadAttachmentDelegateAction = Future<void> Function(Uri? uri);
 
 class HtmlContentViewer extends StatefulWidget {
 
@@ -29,6 +30,7 @@ class HtmlContentViewer extends StatefulWidget {
   final OnMailtoDelegateAction? onMailtoDelegateAction;
   final OnScrollHorizontalEndAction? onScrollHorizontalEnd;
   final OnPreviewEMLDelegateAction? onPreviewEMLDelegateAction;
+  final OnDownloadAttachmentDelegateAction? onDownloadAttachmentDelegateAction;
 
   const HtmlContentViewer({
     Key? key,
@@ -39,6 +41,7 @@ class HtmlContentViewer extends StatefulWidget {
     this.onMailtoDelegateAction,
     this.onScrollHorizontalEnd,
     this.onPreviewEMLDelegateAction,
+    this.onDownloadAttachmentDelegateAction,
   }) : super(key: key);
 
   @override
@@ -261,17 +264,23 @@ class _HtmlContentViewState extends State<HtmlContentViewer> {
 
     final requestUri = Uri.parse(url);
     if (widget.onMailtoDelegateAction != null &&
-        requestUri.isScheme('mailto')) {
+        requestUri.isScheme(Constant.mailtoScheme)) {
       await widget.onMailtoDelegateAction?.call(requestUri);
       return NavigationActionPolicy.CANCEL;
     }
 
     if (widget.onPreviewEMLDelegateAction != null &&
-        requestUri.isScheme(PreviewEmlFileUtils.emlPreviewerScheme)) {
+        requestUri.isScheme(Constant.emlPreviewerScheme)) {
       await widget.onPreviewEMLDelegateAction?.call(requestUri);
       return NavigationActionPolicy.CANCEL;
     }
 
+    if (widget.onDownloadAttachmentDelegateAction != null &&
+        requestUri.isScheme(Constant.attachmentScheme)) {
+      await widget.onDownloadAttachmentDelegateAction?.call(requestUri);
+      return NavigationActionPolicy.CANCEL;
+    }
+
     if (await launcher.canLaunchUrl(Uri.parse(url))) {
       await launcher.launchUrl(
         Uri.parse(url),

core/lib/utils/preview_eml_file_utils.dart

@@ -7,8 +7,6 @@ import 'package:html/dom.dart';
 import 'package:html/parser.dart';
 
 class PreviewEmlFileUtils {
-  static const String emlPreviewerScheme = 'eml-previewer';
-
   Element? _createEmailElement({
     required String subjectPrefix,
     required String fromPrefix,