Provide a hook to pause ongoing backups

lib/events/photo_upload_event.dart

@@ -2,6 +2,12 @@ class PhotoUploadEvent {
   final int completed;
   final int total;
   final bool hasError;
+  final bool wasStopped;
 
-  PhotoUploadEvent({this.completed, this.total, this.hasError = false});
+  PhotoUploadEvent({
+    this.completed,
+    this.total,
+    this.hasError = false,
+    this.wasStopped = false,
+  });
 }

lib/photo_sync_manager.dart

@@ -24,6 +24,7 @@ class PhotoSyncManager {
   final _uploader = FileUploader();
   final _downloader = DiffFetcher();
   bool _isSyncInProgress = false;
+  bool _syncStopRequested = false;
   Future<void> _existingSync;
   SharedPreferences _prefs;
 
@@ -46,6 +47,7 @@ class PhotoSyncManager {
   }
 
   Future<void> sync() async {
+    _syncStopRequested = false;
     if (_isSyncInProgress) {
       _logger.warning("Sync already in progress, skipping.");
       return _existingSync;
@@ -64,6 +66,15 @@ class PhotoSyncManager {
     return _existingSync;
   }
 
+  void stopSync() {
+    _logger.info("Sync stop requested");
+    _syncStopRequested = true;
+  }
+
+  bool shouldStopSync() {
+    return _syncStopRequested;
+  }
+
   bool hasScannedDisk() {
     return _prefs.containsKey(_dbUpdationTimeKey);
   }
@@ -198,11 +209,13 @@ class PhotoSyncManager {
     List<File> filesToBeUploaded =
         await _db.getFilesToBeUploadedWithinFolders(foldersToBackUp);
     for (int i = 0; i < filesToBeUploaded.length; i++) {
+      if (_syncStopRequested) {
+        _syncStopRequested = false;
+        Bus.instance.fire(PhotoUploadEvent(wasStopped: true));
+        return;
+      }
       File file = filesToBeUploaded[i];
       try {
-        if (!foldersToBackUp.contains(file.deviceFolder)) {
-          continue;
-        }
         var uploadedFile;
         if (Configuration.instance.hasOptedForE2E()) {
           uploadedFile = await _uploader.encryptAndUploadFile(file);

lib/ui/sync_indicator.dart

@@ -1,8 +1,10 @@
 import 'dart:async';
+import 'dart:developer';
 
 import 'package:flutter/material.dart';
 import 'package:photos/core/event_bus.dart';
 import 'package:photos/events/photo_upload_event.dart';
+import 'package:photos/photo_sync_manager.dart';
 import 'package:pull_to_refresh/pull_to_refresh.dart';
 
 class SyncIndicator extends StatefulWidget {
@@ -17,6 +19,7 @@ class SyncIndicator extends StatefulWidget {
 class _SyncIndicatorState extends State<SyncIndicator> {
   PhotoUploadEvent _event;
   StreamSubscription<PhotoUploadEvent> _subscription;
+  String _completeText = "Sync completed.";
 
   @override
   void initState() {
@@ -40,10 +43,58 @@ class _SyncIndicatorState extends State<SyncIndicator> {
       idleText: "Pull down to sync.",
       refreshingText: _getRefreshingText(),
       releaseText: "Release to sync.",
-      completeText: "Sync completed.",
+      completeText: _completeText,
       failedText: "Sync unsuccessful.",
       completeDuration: const Duration(milliseconds: 1000),
       refreshStyle: RefreshStyle.UnFollow,
+      refreshingIcon: Container(
+        width: 24,
+        height: 24,
+        child: GestureDetector(
+          onTap: () {
+            AlertDialog alert = AlertDialog(
+              title: Text("Pause?"),
+              content: Text(
+                  "Are you sure that you want to pause backing up your memories?"),
+              actions: [
+                FlatButton(
+                  child: Text("NO"),
+                  onPressed: () {
+                    Navigator.of(context).pop();
+                  },
+                ),
+                FlatButton(
+                  child: Text("YES"),
+                  onPressed: () {
+                    Navigator.of(context).pop();
+                    PhotoSyncManager.instance.stopSync();
+                    _completeText = "Sync stopped.";
+                    setState(() {});
+                    widget.refreshController.refreshCompleted();
+                  },
+                ),
+              ],
+            );
+
+            showDialog(
+              context: context,
+              builder: (BuildContext context) {
+                return alert;
+              },
+            );
+          },
+          child: Stack(
+            children: [
+              Icon(
+                Icons.pause_circle_outline,
+                size: 24,
+                color: Colors.pink,
+              ),
+              CircularProgressIndicator(strokeWidth: 2),
+            ],
+          ),
+        ),
+      ),
     );
   }
 
@@ -55,6 +106,8 @@ class _SyncIndicatorState extends State<SyncIndicator> {
       if (_event.hasError) {
         widget.refreshController.refreshFailed();
         s = "Upload failed.";
+      } else if (_event.wasStopped) {
+        s = "Sync stopped.";
       } else {
         s = "Backing up " +
             _event.completed.toString() +