lightbox [nfc]: Go through MessageTimestampStyle for timestamp

Author: chrisbobbe

lib/widgets/lightbox.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
-import 'package:intl/intl.dart';
 import 'package:video_player/video_player.dart';
 
 import '../api/core.dart';
@@ -12,6 +11,7 @@ import '../model/binding.dart';
 import 'actions.dart';
 import 'content.dart';
 import 'dialog.dart';
+import 'message_list.dart';
 import 'page.dart';
 import 'store.dart';
 import 'user.dart';
@@ -176,11 +176,8 @@ class _LightboxPageLayoutState extends State<_LightboxPageLayout> {
 
     PreferredSizeWidget? appBar;
     if (_headerFooterVisible) {
-      // TODO(#45): Format with e.g. "Yesterday at 4:47 PM"
-      final timestampText = DateFormat
-        .yMMMd(/* TODO(#278): Pass selected language here, I think? */)
-        .add_Hms()
-        .format(DateTime.fromMillisecondsSinceEpoch(widget.message.timestamp * 1000));
+      final timestampText = MessageTimestampStyle.lightbox
+        .format(widget.message.timestamp);
 
       // We use plain [AppBar] instead of [ZulipAppBar], even though this page
       // has a [PerAccountStore], because:

lib/widgets/message_list.dart

@@ -1987,6 +1987,9 @@ enum MessageTimestampStyle {
   none,
   timeOnly,
 
+  // TODO(#45): E.g. "Yesterday at 4:47 PM"; see details in #45
+  lightbox,
+
   /// The longest format, with full date and time as numbers, not "Today"/etc.
   ///
   /// For UI contexts focused just on the one message,
@@ -2002,6 +2005,7 @@ enum MessageTimestampStyle {
   ;
 
   static final _timeOnlyFormat = DateFormat('h:mm aa', 'en_US');
+  static final _lightboxFormat = DateFormat.yMMMd().add_Hms();
   static final _fullFormat = DateFormat.yMMMd().add_jm();
 
   /// Format a [Message.timestamp] for this mode.
@@ -2013,6 +2017,7 @@ enum MessageTimestampStyle {
     switch (this) {
       case none:     return null;
       case timeOnly: return _timeOnlyFormat.format(asDateTime);
+      case lightbox: return _lightboxFormat.format(asDateTime);
       case full: return _fullFormat.format(asDateTime);
     }
   }