refactor: Enable more lints

lib/views/widgets/audio_player.dart

@@ -27,10 +27,10 @@ class AudioPlayer extends StatefulWidget {
   _AudioPlayerState createState() => _AudioPlayerState();
 }
 
-enum AudioPlayerStatus { NOT_DOWNLOADED, DOWNLOADING, DOWNLOADED }
+enum AudioPlayerStatus { notDownloaded, downloading, downloaded }
 
 class _AudioPlayerState extends State<AudioPlayer> {
-  AudioPlayerStatus status = AudioPlayerStatus.NOT_DOWNLOADED;
+  AudioPlayerStatus status = AudioPlayerStatus.notDownloaded;
 
   final FlutterSoundPlayer flutterSound = FlutterSoundPlayer();
 
@@ -70,14 +70,14 @@ class _AudioPlayerState extends State<AudioPlayer> {
   }
 
   Future<void> _downloadAction() async {
-    if (status != AudioPlayerStatus.NOT_DOWNLOADED) return;
-    setState(() => status = AudioPlayerStatus.DOWNLOADING);
+    if (status != AudioPlayerStatus.notDownloaded) return;
+    setState(() => status = AudioPlayerStatus.downloading);
     try {
       final matrixFile =
           await widget.event.downloadAndDecryptAttachmentCached();
       setState(() {
         audioFile = matrixFile.bytes;
-        status = AudioPlayerStatus.DOWNLOADED;
+        status = AudioPlayerStatus.downloaded;
       });
       _playAction();
     } catch (e, s) {
@@ -126,7 +126,7 @@ class _AudioPlayerState extends State<AudioPlayer> {
             });
             AudioPlayer.currentId = null;
           } else if (e != null) {
-            var txt =
+            final txt =
                 '${e.position.inMinutes.toString().padLeft(2, '0')}:${(e.position.inSeconds % 60).toString().padLeft(2, '0')}';
             setState(() {
               maxPosition = e.duration.inMilliseconds.toDouble();
@@ -158,7 +158,7 @@ class _AudioPlayerState extends State<AudioPlayer> {
       children: <Widget>[
         Container(
           width: 30,
-          child: status == AudioPlayerStatus.DOWNLOADING
+          child: status == AudioPlayerStatus.downloading
               ? CircularProgressIndicator(strokeWidth: 2)
               : IconButton(
                   icon: Icon(
@@ -171,7 +171,7 @@ class _AudioPlayerState extends State<AudioPlayer> {
                       ? L10n.of(context).audioPlayerPause
                       : L10n.of(context).audioPlayerPlay,
                   onPressed: () {
-                    if (status == AudioPlayerStatus.DOWNLOADED) {
+                    if (status == AudioPlayerStatus.downloaded) {
                       _playAction();
                     } else {
                       _downloadAction();
@@ -184,7 +184,7 @@ class _AudioPlayerState extends State<AudioPlayer> {
             value: currentPosition,
             onChanged: (double position) => flutterSound
                 .seekToPlayer(Duration(milliseconds: position.toInt())),
-            max: status == AudioPlayerStatus.DOWNLOADED ? maxPosition : 0,
+            max: status == AudioPlayerStatus.downloaded ? maxPosition : 0,
             min: 0,
           ),
         ),

lib/views/widgets/avatar.dart

@@ -25,7 +25,7 @@ class Avatar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    var thumbnail = mxContent?.getThumbnail(
+    final thumbnail = mxContent?.getThumbnail(
       client ?? Matrix.of(context).client,
       width: size * MediaQuery.of(context).devicePixelRatio,
       height: size * MediaQuery.of(context).devicePixelRatio,

lib/views/widgets/chat_settings_popup_menu.dart

@@ -38,7 +38,7 @@ class _ChatSettingsPopupMenuState extends State<ChatSettingsPopupMenu> {
         .listen(
           (u) => setState(() => null),
         );
-    var items = <PopupMenuEntry<String>>[
+    final items = <PopupMenuEntry<String>>[
       widget.room.pushRuleState == PushRuleState.notify
           ? PopupMenuItem<String>(
               value: 'mute',
@@ -66,7 +66,7 @@ class _ChatSettingsPopupMenuState extends State<ChatSettingsPopupMenu> {
       onSelected: (String choice) async {
         switch (choice) {
           case 'leave':
-            var confirmed = await showOkCancelAlertDialog(
+            final confirmed = await showOkCancelAlertDialog(
               context: context,
               useRootNavigator: false,
               title: L10n.of(context).areYouSure,

lib/views/widgets/dialogs/key_verification_dialog.dart

@@ -248,7 +248,7 @@ class _KeyVerificationPageState extends State<KeyVerificationDialog> {
         ));
         break;
       case KeyVerificationState.waitingSas:
-        var acceptText = widget.request.sasTypes.contains('emoji')
+        final acceptText = widget.request.sasTypes.contains('emoji')
             ? L10n.of(context).waitingPartnerEmoji
             : L10n.of(context).waitingPartnerNumbers;
         body = Column(

lib/views/widgets/dialogs/recording_dialog.dart

@@ -36,7 +36,7 @@ class _RecordingDialogState extends State<RecordingDialog> {
       _recordedPath = '${tempDir.path}/recording${ext[codec.index]}';
 
       // delete any existing file
-      var outputFile = File(_recordedPath);
+      final outputFile = File(_recordedPath);
       if (outputFile.existsSync()) {
         await outputFile.delete();
       }

lib/views/widgets/list_items/message.dart

@@ -45,9 +45,9 @@ class Message extends StatelessWidget {
       return StateMessage(event, unfold: unfold);
     }
 
-    var client = Matrix.of(context).client;
+    final client = Matrix.of(context).client;
     final ownMessage = event.senderId == client.userID;
-    var alignment = ownMessage ? Alignment.topRight : Alignment.topLeft;
+    final alignment = ownMessage ? Alignment.topRight : Alignment.topLeft;
     var color = Theme.of(context).secondaryHeaderColor;
     final sameSender = nextEvent != null &&
             [EventTypes.Message, EventTypes.Sticker].contains(nextEvent.type)
@@ -58,7 +58,7 @@ class Message extends StatelessWidget {
         : Theme.of(context).brightness == Brightness.dark
             ? Colors.white
             : Colors.black;
-    var rowMainAxisAlignment =
+    final rowMainAxisAlignment =
         ownMessage ? MainAxisAlignment.end : MainAxisAlignment.start;
 
     final displayEvent = event.getDisplayEvent(timeline);
@@ -72,7 +72,7 @@ class Message extends StatelessWidget {
           : Theme.of(context).primaryColor;
     }
 
-    var rowChildren = <Widget>[
+    final rowChildren = <Widget>[
       Expanded(
         child: Container(
           alignment: alignment,

lib/views/widgets/list_items/participant_list_item.dart

@@ -12,7 +12,7 @@ class ParticipantListItem extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    var membershipBatch = <Membership, String>{
+    final membershipBatch = <Membership, String>{
       Membership.join: '',
       Membership.ban: L10n.of(context).banned,
       Membership.invite: L10n.of(context).invited,

lib/views/widgets/matrix.dart

@@ -238,7 +238,7 @@ class MatrixState extends State<Matrix> with WidgetsBindingObserver {
 
   Future<void> initConfig() async {
     try {
-      var configJsonString =
+      final configJsonString =
           utf8.decode((await http.get('config.json')).bodyBytes);
       final configJson = json.decode(configJsonString);
       AppConfig.loadFromJson(configJson);

lib/views/widgets/user_bottom_sheet.dart

@@ -90,7 +90,7 @@ class UserBottomSheet extends StatelessWidget {
   Widget build(BuildContext context) {
     final client = user.room.client;
     final presence = client.presences[user.id];
-    var items = <PopupMenuEntry<String>>[];
+    final items = <PopupMenuEntry<String>>[];
 
     if (onMention != null) {
       items.add(