save length and history when value done changing

src/App/Pages/Generator/GeneratorPage.xaml

@@ -105,6 +105,7 @@
                             VerticalOptions="CenterAndExpand"
                             HorizontalTextAlignment="End" />
                         <controls:ExtendedSlider
+                            ValueChanged="LengthSlider_ValueChanged"
                             Value="{Binding Length}"
                             StyleClass="box-value"
                             VerticalOptions="CenterAndExpand"

src/App/Pages/Generator/GeneratorPage.xaml.cs

@@ -23,6 +23,8 @@ namespace Bit.App.Pages
             }
         }
 
+        public DateTime LastLengthSliderChange { get; set; } = DateTime.MinValue;
+
         public async Task InitAsync()
         {
             await _vm.InitAsync();
@@ -57,5 +59,13 @@ namespace Bit.App.Pages
             var page = new GeneratorHistoryPage();
             await Navigation.PushModalAsync(new NavigationPage(page));
         }
+
+        private void LengthSlider_ValueChanged(object sender, ValueChangedEventArgs e)
+        {
+            if(e.NewValue != e.OldValue)
+            {
+                LastLengthSliderChange = DateTime.UtcNow;
+            }
+        }
     }
 }

src/App/Pages/Generator/GeneratorPageViewModel.cs

@@ -3,7 +3,9 @@ using Bit.App.Utilities;
 using Bit.Core.Abstractions;
 using Bit.Core.Models.Domain;
 using Bit.Core.Utilities;
+using System;
 using System.Collections.Generic;
+using System.Threading;
 using System.Threading.Tasks;
 using Xamarin.Forms;
 
@@ -29,6 +31,7 @@ namespace Bit.App.Pages
         private string _wordSeparator;
         private int _typeSelectedIndex;
         private bool _doneIniting;
+        private CancellationTokenSource _sliderCancellationTokenSource;
 
         public GeneratorPageViewModel()
         {
@@ -67,7 +70,7 @@ namespace Bit.App.Pages
                 if(SetProperty(ref _length, value))
                 {
                     _options.Length = value;
-                    var task = SaveOptionsAsync();
+                    var task = SaveOptionsSliderAsync();
                 }
             }
         }
@@ -207,8 +210,7 @@ namespace Bit.App.Pages
         {
             _options = await _passwordGenerationService.GetOptionsAsync();
             LoadFromOptions();
-            Password = await _passwordGenerationService.GeneratePasswordAsync(_options);
+            await RegenerateAsync();
-            await _passwordGenerationService.AddHistoryAsync(Password);
             _doneIniting = true;
         }
 
@@ -234,6 +236,39 @@ namespace Bit.App.Pages
             }
         }
 
+        public async Task SaveOptionsSliderAsync()
+        {
+            if(!_doneIniting)
+            {
+                return;
+            }
+            SetOptions();
+            _passwordGenerationService.NormalizeOptions(_options);
+            LoadFromOptions();
+            Password = await _passwordGenerationService.GeneratePasswordAsync(_options);
+
+            var page = Page as GeneratorPage;
+            var previousCts = _sliderCancellationTokenSource;
+            var cts = new CancellationTokenSource();
+            var task = Task.Run(async () =>
+            {
+                await Task.Delay(500);
+                if(DateTime.UtcNow - page.LastLengthSliderChange < TimeSpan.FromMilliseconds(450))
+                {
+                    return;
+                }
+                else
+                {
+                    previousCts?.Cancel();
+                }
+                cts.Token.ThrowIfCancellationRequested();
+                await _passwordGenerationService.SaveOptionsAsync(_options);
+                cts.Token.ThrowIfCancellationRequested();
+                await _passwordGenerationService.AddHistoryAsync(Password, cts.Token);
+            }, cts.Token);
+            _sliderCancellationTokenSource = cts;
+        }
+
         public async Task CopyAsync()
         {
             await _platformUtilsService.CopyToClipboardAsync(Password);

src/Core/Abstractions/IPasswordGenerationService.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Threading;
 using System.Threading.Tasks;
 using Bit.Core.Models.Domain;
 
@@ -6,7 +7,7 @@ namespace Bit.Core.Abstractions
 {
     public interface IPasswordGenerationService
     {
-        Task AddHistoryAsync(string password);
+        Task AddHistoryAsync(string password, CancellationToken token = default(CancellationToken));
         Task ClearAsync();
         Task<string> GeneratePassphraseAsync(PasswordGenerationOptions options);
         Task<string> GeneratePasswordAsync(PasswordGenerationOptions options);

src/Core/Services/PasswordGenerationService.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace Bit.Core.Services
@@ -240,7 +241,7 @@ namespace Bit.Core.Services
             return _history ?? new List<GeneratedPasswordHistory>();
         }
 
-        public async Task AddHistoryAsync(string password)
+        public async Task AddHistoryAsync(string password, CancellationToken token = default(CancellationToken))
         {
             var hasKey = await _cryptoService.HasKeyAsync();
             if(!hasKey)
@@ -253,6 +254,7 @@ namespace Bit.Core.Services
             {
                 return;
             }
+            token.ThrowIfCancellationRequested();
             currentHistory.Insert(0, new GeneratedPasswordHistory { Password = password, Date = DateTime.UtcNow });
             // Remove old items.
             if(currentHistory.Count > MaxPasswordsInHistory)
@@ -260,6 +262,7 @@ namespace Bit.Core.Services
                 currentHistory.RemoveAt(currentHistory.Count - 1);
             }
             var newHistory = await EncryptHistoryAsync(currentHistory);
+            token.ThrowIfCancellationRequested();
             await _storageService.SaveAsync(Keys_History, newHistory);
         }