using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using CommunityToolkit.Mvvm.Messaging;
using MoreLinq;
using Nito.AsyncEx;
using Serilog;
using Wino.Core.Domain;
using Wino.Core.Domain.Entities.Mail;
using Wino.Core.Domain.Entities.Shared;
using Wino.Core.Domain.Enums;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.Folders;
using Wino.Core.Domain.Models.MailItem;
using Wino.Core.Domain.Models.Menus;
using Wino.Core.Domain.Models.Navigation;
using Wino.Core.Domain.Models.Reader;
using Wino.Core.Domain.Models.Synchronization;
using Wino.Core.Services;
using Wino.Mail.ViewModels.Collections;
using Wino.Mail.ViewModels.Data;
using Wino.Mail.ViewModels.Helpers;
using Wino.Mail.ViewModels.Messages;
using Wino.Messaging.Client.Mails;
using Wino.Messaging.Server;
using Wino.Messaging.UI;

namespace Wino.Mail.ViewModels;

public partial class MailListPageViewModel : MailBaseViewModel,
    IRecipient<MailItemNavigationRequested>,
    IRecipient<ActiveMailFolderChangedEvent>,
    IRecipient<AccountSynchronizationCompleted>,
    IRecipient<NewMailSynchronizationRequested>,
    IRecipient<AccountSynchronizerStateChanged>,
    IRecipient<AccountCacheResetMessage>,
    IRecipient<ThumbnailAdded>
{
    private bool isChangingFolder = false;

    private Guid? trackingSynchronizationId = null;
    private int completedTrackingSynchronizationCount = 0;

    /* [Bug] Unread folder reads All emails automatically with setting "Mark as Read: When Selected" enabled 
     * https://github.com/bkaankose/Wino-Mail/issues/162
     * We store the UniqueIds of the mails that are marked as read in Gmail Unread folder
     * to prevent them from being removed from the list when they are marked as read.
     */

    private readonly HashSet<Guid> gmailUnreadFolderMarkedAsReadUniqueIds = [];

    private ThrottledEventHandler _selectionChangedThrottler;

    public event EventHandler ThrottledSelectionChanged;
    public GroupedEmailCollection MailCollection { get; set; } = new GroupedEmailCollection();
    //public ObservableCollection<MailItemViewModel> SelectedItems { get; set; } = [];
    public ObservableCollection<FolderPivotViewModel> PivotFolders { get; set; } = [];
    public ObservableCollection<MailOperationMenuItem> ActionItems { get; set; } = [];

    private readonly SemaphoreSlim listManipulationSemepahore = new SemaphoreSlim(1);
    private CancellationTokenSource listManipulationCancellationTokenSource = new CancellationTokenSource();

    public INavigationService NavigationService { get; }
    public IStatePersistanceService StatePersistenceService { get; }
    public IPreferencesService PreferencesService { get; }
    public INewThemeService ThemeService { get; }

    private readonly IAccountService _accountService;
    private readonly IMailDialogService _mailDialogService;
    private readonly IMailService _mailService;
    private readonly IFolderService _folderService;
    private readonly IContextMenuItemService _contextMenuItemService;
    private readonly IWinoRequestDelegator _winoRequestDelegator;
    private readonly IKeyPressService _keyPressService;
    private readonly IWinoLogger _winoLogger;
    private MailItemViewModel _activeMailItem;

    public List<SortingOption> SortingOptions { get; } =
    [
        new(Translator.SortingOption_Date, SortingOptionType.ReceiveDate),
        new(Translator.SortingOption_Name, SortingOptionType.Sender),
    ];

    public List<FilterOption> FilterOptions { get; } =
    [
        new (Translator.FilteringOption_All, FilterOptionType.All),
        new (Translator.FilteringOption_Unread, FilterOptionType.Unread),
        new (Translator.FilteringOption_Flagged, FilterOptionType.Flagged),
        new (Translator.FilteringOption_Files, FilterOptionType.Files)
    ];

    private FolderPivotViewModel _selectedFolderPivot;

    [ObservableProperty]
    private bool isMultiSelectionModeEnabled;

    [ObservableProperty]
    public partial string SearchQuery { get; set; }

    [ObservableProperty]
    private FilterOption _selectedFilterOption;
    private SortingOption _selectedSortingOption;

    // Indicates state when folder is initializing. It can happen after folder navigation, search or filter change applied or loading more items.
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(IsEmpty))]
    [NotifyPropertyChangedFor(nameof(IsFolderEmpty))]
    [NotifyPropertyChangedFor(nameof(IsProgressRing))]
    private bool isInitializingFolder;

    [ObservableProperty]
    private InfoBarMessageType barSeverity;

    [ObservableProperty]
    private string barMessage;

    [ObservableProperty]
    private double mailListLength = 420;

    [ObservableProperty]
    private double maxMailListLength = 1200;

    [ObservableProperty]
    private string barTitle;

    [ObservableProperty]
    private bool isBarOpen;

    /// <summary>
    /// Current folder that is being represented from the menu.
    /// </summary>
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(CanSynchronize))]
    [NotifyPropertyChangedFor(nameof(IsFolderSynchronizationEnabled))]
    private IBaseFolderMenuItem activeFolder;

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(CanSynchronize))]
    private bool isAccountSynchronizerInSynchronization;

    public MailListPageViewModel(IMailDialogService dialogService,
                                 INavigationService navigationService,
                                 IAccountService accountService,
                                 IMailDialogService mailDialogService,
                                 IMailService mailService,
                                 IStatePersistanceService statePersistenceService,
                                 IFolderService folderService,
                                 IContextMenuItemService contextMenuItemService,
                                 IWinoRequestDelegator winoRequestDelegator,
                                 IKeyPressService keyPressService,
                                 IPreferencesService preferencesService,
                                 INewThemeService themeService,
                                 IWinoLogger winoLogger)
    {
        PreferencesService = preferencesService;
        ThemeService = themeService;
        _winoLogger = winoLogger;
        StatePersistenceService = statePersistenceService;
        NavigationService = navigationService;
        _accountService = accountService;
        _mailDialogService = mailDialogService;
        _mailService = mailService;
        _folderService = folderService;
        _contextMenuItemService = contextMenuItemService;
        _winoRequestDelegator = winoRequestDelegator;
        _keyPressService = keyPressService;

        SelectedFilterOption = FilterOptions[0];
        SelectedSortingOption = SortingOptions[0];

        mailListLength = statePersistenceService.MailListPaneLength;

        _selectionChangedThrottler = new ThrottledEventHandler(100, () =>
        {
            _ = ExecuteUIThread(() =>
            {
                if (MailCollection.SelectedVisibleCount == 1)
                {
                    ActiveMailItemChanged(MailCollection.SelectedVisibleItems.ElementAt(0));
                }
                else
                {
                    // At this point, either we don't have any item selected 
                    // or we have multiple item selected. In either case
                    // there should be no active item.

                    ActiveMailItemChanged(null);
                }

                NotifyItemSelected();
                SetupTopBarActions();
            });

            ThrottledSelectionChanged?.Invoke(this, EventArgs.Empty);
        });
    }

    public override void OnNavigatedTo(NavigationMode mode, object parameters)
    {
        base.OnNavigatedTo(mode, parameters);

        MailCollection.SelectionChanged += SelectedItemsChanged;
    }

    public override void OnNavigatedFrom(NavigationMode mode, object parameters)
    {
        base.OnNavigatedFrom(mode, parameters);

        MailCollection.SelectionChanged -= SelectedItemsChanged;
        MailCollection.Dispose();

        _selectionChangedThrottler?.Dispose();
        _selectionChangedThrottler = null;
    }

    private void SelectedItemsChanged(object sender, EventArgs e)
    {
        _selectionChangedThrottler?.Trigger();
    }

    private void SetupTopBarActions()
    {
        ActionItems.Clear();
        var actions = GetAvailableMailActions(MailCollection.SelectedVisibleItems);
        actions.ForEach(a => ActionItems.Add(a));
    }

    #region Properties

    /// <summary>
    /// Selected internal folder. This can be either folder's own name or Focused-Other.
    /// </summary>
    public FolderPivotViewModel SelectedFolderPivot
    {
        get => _selectedFolderPivot;
        set
        {
            if (_selectedFolderPivot != null)
                _selectedFolderPivot.SelectedItemCount = 0;

            SetProperty(ref _selectedFolderPivot, value);
        }
    }

    /// <summary>
    /// Selected sorting option.
    /// </summary>
    public SortingOption SelectedSortingOption
    {
        get => _selectedSortingOption;
        set
        {
            if (SetProperty(ref _selectedSortingOption, value))
            {
                if (value != null && MailCollection != null)
                {
                    MailCollection.GroupingType = value.Type == SortingOptionType.ReceiveDate ? EmailGroupingType.ByDate : EmailGroupingType.ByFromName;
                }
            }
        }
    }

    public bool CanSynchronize => !IsAccountSynchronizerInSynchronization && IsFolderSynchronizationEnabled;
    public bool IsFolderSynchronizationEnabled => ActiveFolder?.IsSynchronizationEnabled ?? false;
    public bool IsArchiveSpecialFolder => ActiveFolder?.SpecialFolderType == SpecialFolderType.Archive;

    public string SelectedMessageText => MailCollection.SelectedVisibleCount > 0 ? string.Format(Translator.MailsSelected, MailCollection.SelectedVisibleCount) : Translator.NoMailSelected;

    /// <summary>
    /// Indicates current state of the mail list. Doesn't matter it's loading or no.
    /// </summary>
    public bool IsEmpty => MailCollection.Count == 0;

    /// <summary>
    /// Progress ring only should be visible when the folder is initializing and there are no items. We don't need to show it when there are items.
    /// </summary>
    public bool IsProgressRing => IsInitializingFolder && IsEmpty;
    public bool IsFolderEmpty => !IsInitializingFolder && IsEmpty;

    public bool HasNoOnlineSearchResult { get; private set; }

    [ObservableProperty]
    public partial bool IsInSearchMode { get; set; }

    [ObservableProperty]
    public partial bool IsOnlineSearchButtonVisible { get; set; }

    [ObservableProperty]
    public partial bool IsOnlineSearchEnabled { get; set; }

    [ObservableProperty]
    public partial bool AreSearchResultsOnline { get; set; }

    #endregion

    private async void ActiveMailItemChanged(MailItemViewModel selectedMailItemViewModel)
    {
        if (_activeMailItem == selectedMailItemViewModel) return;

        // Don't update active mail item if Ctrl key is pressed or multi selection is enabled.
        // User is probably trying to select multiple items.
        // This is not the same behavior in Windows Mail,
        // but it's a trash behavior.

        var isCtrlKeyPressed = _keyPressService.IsCtrlKeyPressed();

        bool isMultiSelecting = isCtrlKeyPressed || IsMultiSelectionModeEnabled;

        if (isMultiSelecting && StatePersistenceService.IsReaderNarrowed)
        {
            return;
        }

        _activeMailItem = selectedMailItemViewModel;

        Messenger.Send(new ActiveMailItemChangedEvent(_activeMailItem));

        if (_activeMailItem == null || _activeMailItem.IsRead) return;

        // Automatically set mark as read or not based on preferences.

        var markAsPreference = PreferencesService.MarkAsPreference;

        if (markAsPreference == MailMarkAsOption.WhenSelected)
        {
            //var operation = MailOperation.MarkAsRead;
            //var package = new MailOperationPreperationRequest(operation, _activeMailItem.MailCopy);

            //if (ActiveFolder?.SpecialFolderType == SpecialFolderType.Unread &&
            //    !gmailUnreadFolderMarkedAsReadUniqueIds.Contains(_activeMailItem.UniqueId))
            //{
            //    gmailUnreadFolderMarkedAsReadUniqueIds.Add(_activeMailItem.UniqueId);
            //}

            //await ExecuteMailOperationAsync(package);
        }
        else if (markAsPreference == MailMarkAsOption.AfterDelay && PreferencesService.MarkAsDelay >= 0)
        {
            // TODO: Start a timer then queue.
        }
    }

    public void NotifyItemSelected()
    {
        OnPropertyChanged(nameof(SelectedMessageText));
        //OnPropertyChanged(nameof(HasSingleItemSelection));
        //OnPropertyChanged(nameof(HasSelectedItems));
        //OnPropertyChanged(nameof(SelectedItemCount));
        //OnPropertyChanged(nameof(HasMultipleItemSelections));

        SelectedFolderPivot?.SelectedItemCount = MailCollection.SelectedItemsCount;
    }

    private void NotifyItemFoundState()
    {
        OnPropertyChanged(nameof(IsEmpty));
        OnPropertyChanged(nameof(IsFolderEmpty));
    }

    private async void UpdateBarMessage(InfoBarMessageType severity, string title, string message)
    {
        await ExecuteUIThread(() =>
        {
            BarSeverity = severity;
            BarTitle = title;
            BarMessage = message;

            IsBarOpen = true;
        });
    }

    private async Task UpdateFolderPivotsAsync()
    {
        if (ActiveFolder == null) return;

        PivotFolders.Clear();
        SelectedFolderPivot = null;

        if (IsInSearchMode)
        {
            var isFocused = SelectedFolderPivot?.IsFocused;

            PivotFolders.Add(new FolderPivotViewModel(Translator.SearchPivotName, isFocused));
        }
        else
        {
            // Merged folders don't support focused feature.

            if (ActiveFolder is IMergedAccountFolderMenuItem)
            {
                PivotFolders.Add(new FolderPivotViewModel(ActiveFolder.FolderName, null));
            }
            else if (ActiveFolder is IFolderMenuItem singleFolderMenuItem)
            {
                var parentAccount = singleFolderMenuItem.ParentAccount;

                bool isFocusedInboxEnabled = await _accountService.IsAccountFocusedEnabledAsync(parentAccount.Id);
                bool isInboxFolder = ActiveFolder.SpecialFolderType == SpecialFolderType.Inbox;

                // Folder supports Focused - Other
                if (isInboxFolder && isFocusedInboxEnabled)
                {
                    // Can be passed as empty string. Focused - Other will be used regardless.
                    var focusedItem = new FolderPivotViewModel(string.Empty, true);
                    var otherItem = new FolderPivotViewModel(string.Empty, false);

                    PivotFolders.Add(focusedItem);
                    PivotFolders.Add(otherItem);
                }
                else
                {
                    // If the account and folder doesn't support focused feature, just add itself.
                    PivotFolders.Add(new FolderPivotViewModel(singleFolderMenuItem.FolderName, null));
                }
            }
        }



        // This will trigger refresh.
        SelectedFolderPivot = PivotFolders.FirstOrDefault();
    }

    #region Commands

    [RelayCommand]
    public Task ExecuteHoverAction(MailOperationPreperationRequest request) => ExecuteMailOperationAsync(request);

    [RelayCommand]
    private async Task ExecuteTopBarAction(MailOperationMenuItem menuItem)
    {
        if (menuItem == null || MailCollection.SelectedVisibleCount == 0) return;

        await HandleMailOperation(menuItem.Operation, MailCollection.SelectedVisibleItems);
    }

    /// <summary>
    /// Executes the requested mail operation for currently selected items.
    /// </summary>
    /// <param name="operation">Action to execute for selected items.</param>
    [RelayCommand]
    private async Task ExecuteMailOperation(MailOperation mailOperation)
    {
        if (!MailCollection.SelectedVisibleItems.Any()) return;

        await HandleMailOperation(mailOperation, MailCollection.SelectedVisibleItems);
    }

    private async Task HandleMailOperation(MailOperation mailOperation, IEnumerable<MailItemViewModel> mailItems)
    {
        if (!mailItems.Any()) return;

        var package = new MailOperationPreperationRequest(mailOperation, mailItems.Select(a => a.MailCopy));

        await ExecuteMailOperationAsync(package);
    }

    /// <summary>
    /// Sens a new message to synchronize current folder.
    /// </summary>
    [RelayCommand]
    private void SyncFolder()
    {
        if (!CanSynchronize) return;

        // Only synchronize listed folders.

        // When doing linked inbox sync, we need to save the sync id to report progress back only once.
        // Otherwise, we will report progress for each folder and that's what we don't want.

        trackingSynchronizationId = Guid.NewGuid();
        completedTrackingSynchronizationCount = 0;

        foreach (var folder in ActiveFolder.HandlingFolders)
        {
            var options = new MailSynchronizationOptions()
            {
                AccountId = folder.MailAccountId,
                Type = MailSynchronizationType.CustomFolders,
                SynchronizationFolderIds = [folder.Id],
                GroupedSynchronizationTrackingId = trackingSynchronizationId
            };

            Messenger.Send(new NewMailSynchronizationRequested(options));
        }
    }

    [RelayCommand]
    private async Task SelectedPivotChanged()
    {
        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    private async Task SelectedSortingChanged(SortingOption option)
    {
        SelectedSortingOption = option;

        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    private async Task SelectedFilterChanged(FilterOption option)
    {
        SelectedFilterOption = option;

        if (isChangingFolder) return;

        await InitializeFolderAsync();
    }

    [RelayCommand]
    public async Task PerformSearchAsync()
    {
        IsOnlineSearchEnabled = false;
        AreSearchResultsOnline = false;
        IsInSearchMode = !string.IsNullOrEmpty(SearchQuery);

        if (IsInSearchMode)
        {
            IsOnlineSearchButtonVisible = false;
        }

        await UpdateFolderPivotsAsync();
    }

    [RelayCommand]
    private async Task EnableFolderSynchronizationAsync()
    {
        if (ActiveFolder == null) return;

        foreach (var folder in ActiveFolder.HandlingFolders)
        {
            await _folderService.ChangeFolderSynchronizationStateAsync(folder.Id, true);
        }
    }

    [RelayCommand]
    private async Task LoadMoreItemsAsync()
    {
        if (IsInitializingFolder || IsOnlineSearchEnabled) return;

        await ExecuteUIThread(() => { IsInitializingFolder = true; });

        var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
                                                                      SelectedFilterOption.Type,
                                                                      SelectedSortingOption.Type,
                                                                      PreferencesService.IsThreadingEnabled,
                                                                      SelectedFolderPivot.IsFocused,
                                                                      IsInSearchMode ? SearchQuery : string.Empty,
                                                                      MailCollection.MailCopyIdHashSet);

        var items = await _mailService.FetchMailsAsync(initializationOptions).ConfigureAwait(false);

        var viewModels = PrepareMailViewModels(items);

        await ExecuteUIThread(() => { MailCollection.AddEmails(viewModels); });
        await ExecuteUIThread(() => { IsInitializingFolder = false; });
    }

    #endregion

    public Task ExecuteMailOperationAsync(MailOperationPreperationRequest package) => _winoRequestDelegator.ExecuteAsync(package);

    public IEnumerable<MailOperationMenuItem> GetAvailableMailActions(IEnumerable<MailItemViewModel> contextMailItems)
        => _contextMenuItemService.GetMailItemContextMenuActions(contextMailItems.Select(a => a.MailCopy));

    private bool ShouldPreventItemAdd(MailCopy mailItem)
    {
        bool condition = mailItem.IsRead
                          && SelectedFilterOption.Type == FilterOptionType.Unread
                          || !mailItem.IsFlagged
                          && SelectedFilterOption.Type == FilterOptionType.Flagged;

        return condition;
    }

    protected override async void OnMailAdded(MailCopy addedMail)
    {
        base.OnMailAdded(addedMail);

        if (addedMail.AssignedAccount == null || addedMail.AssignedFolder == null) return;

        try
        {
            if (ActiveFolder == null) return;

            // At least one of the accounts we are listing must match with the account of the added mail.
            if (!ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == addedMail.AssignedAccount.Id)) return;

            // Messages coming to sent or draft folder must be inserted regardless of the filter.
            bool shouldPreventIgnoringFilter = addedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Draft ||
                                               addedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Sent;

            // Item does not belong to this folder and doesn't have special type to be inserted.
            if (!shouldPreventIgnoringFilter && !ActiveFolder.HandlingFolders.Any(a => a.Id == addedMail.AssignedFolder.Id)) return;

            // Item should be prevented from being added to the list due to filter.
            if (!shouldPreventIgnoringFilter && ShouldPreventItemAdd(addedMail)) return;

            await listManipulationSemepahore.WaitAsync();

            await ExecuteUIThread(() =>
            {
                MailCollection.AddEmail(new MailItemViewModel(addedMail));
                NotifyItemFoundState();
            });
        }
        catch { }
        finally
        {
            listManipulationSemepahore.Release();
        }
    }

    protected override async void OnMailUpdated(MailCopy updatedMail)
    {
        base.OnMailUpdated(updatedMail);

        Debug.WriteLine($"Updating {updatedMail.Id}-> {updatedMail.UniqueId}");

        // TODO
        // await MailCollection.UpdateMailCopy(updatedMail);

        await ExecuteUIThread(() => { SetupTopBarActions(); });
    }

    protected override async void OnMailRemoved(MailCopy removedMail)
    {
        base.OnMailRemoved(removedMail);

        if (removedMail.AssignedAccount == null || removedMail.AssignedFolder == null) return;

        // We should delete the items only if:
        // 1. They are deleted from the active folder.
        // 2. Deleted from draft or sent folder.
        // 3. Removal is not caused by Gmail Unread folder action.
        // Delete/sent are special folders that can list their items in other folders.

        bool removedFromActiveFolder = ActiveFolder.HandlingFolders.Any(a => a.Id == removedMail.AssignedFolder.Id);
        bool removedFromDraftOrSent = removedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Draft ||
                                      removedMail.AssignedFolder.SpecialFolderType == SpecialFolderType.Sent;

        bool isDeletedByGmailUnreadFolderAction = ActiveFolder.SpecialFolderType == SpecialFolderType.Unread &&
                                                  gmailUnreadFolderMarkedAsReadUniqueIds.Contains(removedMail.UniqueId);

        if ((removedFromActiveFolder || removedFromDraftOrSent) && !isDeletedByGmailUnreadFolderAction)
        {
            bool isDeletedMailSelected = MailCollection.SelectedVisibleItems.Any(a => a.MailCopy.UniqueId == removedMail.UniqueId);

            // Automatically select the next item in the list if the setting is enabled.
            MailItemViewModel nextItem = null;

            if (isDeletedMailSelected && PreferencesService.AutoSelectNextItem)
            {
                await ExecuteUIThread(() =>
                {
                    nextItem = MailCollection.GetNextItem(removedMail);
                });
            }

            // Remove the deleted item from the list.
            await ExecuteUIThread(() =>
            {
                MailCollection.RemoveEmailByMailCopy(removedMail);
            });

            if (nextItem != null)
                WeakReferenceMessenger.Default.Send(new SelectMailItemContainerEvent(nextItem, ScrollToItem: true));
            else if (isDeletedMailSelected)
            {
                // There are no next item to select, but we removed the last item which was selected.
                // Clearing selected item will dispose rendering page.

                await ExecuteUIThread(() =>
                {
                    MailCollection.ClearSelections();
                });
            }

            await ExecuteUIThread(() => { NotifyItemFoundState(); });
        }
        else if (isDeletedByGmailUnreadFolderAction)
        {
            // Remove the entry from the set so we can listen to actual deletes next time.
            gmailUnreadFolderMarkedAsReadUniqueIds.Remove(removedMail.UniqueId);
        }
    }

    protected override async void OnDraftCreated(MailCopy draftMail, MailAccount account)
    {
        base.OnDraftCreated(draftMail, account);

        try
        {
            // If the draft is created in another folder, we need to wait for that folder to be initialized.
            // Otherwise the draft mail item will be duplicated on the next add execution.
            await listManipulationSemepahore.WaitAsync();

            await ExecuteUIThread(() =>
            {
                // Create the item. Draft folder navigation is already done at this point.
                MailCollection.AddEmail(new MailItemViewModel(draftMail));

                // New draft is created by user. Select the item.
                Messenger.Send(new MailItemNavigationRequested(draftMail.UniqueId, ScrollToItem: true));

                NotifyItemFoundState();
            });
        }
        finally
        {
            listManipulationSemepahore.Release();
        }
    }

    private IEnumerable<MailItemViewModel> PrepareMailViewModels(IEnumerable<MailCopy> mailItems)
    {
        return mailItems.Select(a => new MailItemViewModel(a));
    }

    [RelayCommand]
    private async Task PerformOnlineSearchAsync()
    {
        IsOnlineSearchButtonVisible = false;
        IsOnlineSearchEnabled = true;

        await InitializeFolderAsync();
    }

    private async Task InitializeFolderAsync()
    {
        if (SelectedFilterOption == null || SelectedFolderPivot == null || SelectedSortingOption == null)
            return;

        try
        {
            MailCollection.Clear();

            if (ActiveFolder == null)
                return;

            await ExecuteUIThread(() => { IsInitializingFolder = true; });

            // Folder is changed during initialization.
            // Just cancel the existing one and wait for new initialization.

            if (!listManipulationCancellationTokenSource.IsCancellationRequested)
            {
                listManipulationCancellationTokenSource.Cancel();
            }

            listManipulationCancellationTokenSource = new CancellationTokenSource();

            var cancellationToken = listManipulationCancellationTokenSource.Token;

            await listManipulationSemepahore.WaitAsync(cancellationToken);

            // Here items are sorted and filtered.

            List<MailCopy> items = null;

            bool isDoingSearch = !string.IsNullOrEmpty(SearchQuery);
            bool isDoingOnlineSearch = false;

            if (isDoingSearch)
            {
                isDoingOnlineSearch = PreferencesService.DefaultSearchMode == SearchMode.Online || IsOnlineSearchEnabled;

                // Perform online search.
                if (isDoingOnlineSearch)
                {
                    // TODO: Burak: Handle online search.
                    //WinoServerResponse<OnlineSearchResult> onlineSearchResult = null;
                    //string onlineSearchFailedMessage = null;

                    //try
                    //{
                    //    var accountIds = ActiveFolder.HandlingFolders.Select(a => a.MailAccountId).ToList();
                    //    var folders = ActiveFolder.HandlingFolders.ToList();
                    //    var searchRequest = new OnlineSearchRequested(accountIds, SearchQuery, folders);

                    //    onlineSearchResult = await _winoServerConnectionManager.GetResponseAsync<OnlineSearchResult, OnlineSearchRequested>(searchRequest, cancellationToken);

                    //    if (onlineSearchResult.IsSuccess)
                    //    {
                    //        await ExecuteUIThread(() => { AreSearchResultsOnline = true; });

                    //        onlineSearchItems = onlineSearchResult.Data.SearchResult;
                    //    }
                    //    else
                    //    {
                    //        onlineSearchFailedMessage = onlineSearchResult.Message;
                    //    }
                    //}
                    //catch (OperationCanceledException)
                    //{
                    //    throw;
                    //}
                    //catch (Exception ex)
                    //{
                    //    Log.Warning(ex, "Failed to perform online search.");
                    //    onlineSearchFailedMessage = ex.Message;
                    //}

                    //if (onlineSearchResult != null && !onlineSearchResult.IsSuccess)
                    //{
                    //    // Query or server error.
                    //    var serverErrorMessage = string.Format(Translator.OnlineSearchFailed_Message, onlineSearchResult.Message);
                    //    _mailDialogService.InfoBarMessage(Translator.GeneralTitle_Error, serverErrorMessage, InfoBarMessageType.Warning);

                    //}
                    //else if (!string.IsNullOrEmpty(onlineSearchFailedMessage))
                    //{
                    //    // Fatal error.
                    //    var serverErrorMessage = string.Format(Translator.OnlineSearchFailed_Message, onlineSearchFailedMessage);
                    //    _mailDialogService.InfoBarMessage(Translator.GeneralTitle_Error, serverErrorMessage, InfoBarMessageType.Warning);
                    //}
                }
            }

            var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
                                                                          SelectedFilterOption.Type,
                                                                          SelectedSortingOption.Type,
                                                                          PreferencesService.IsThreadingEnabled,
                                                                          SelectedFolderPivot.IsFocused,
                                                                          SearchQuery,
                                                                          MailCollection.MailCopyIdHashSet);

            items = await _mailService.FetchMailsAsync(initializationOptions, cancellationToken).ConfigureAwait(false);

            if (!listManipulationCancellationTokenSource.IsCancellationRequested)
            {
                // Here they are already threaded if needed.
                // We don't need to insert them one by one.
                // Just create VMs and do bulk insert.

                var viewModels = PrepareMailViewModels(items);

                await ExecuteUIThread(() =>
                {
                    MailCollection.AddEmails(viewModels);

                    if (isDoingSearch && !isDoingOnlineSearch)
                    {
                        IsOnlineSearchButtonVisible = true;
                    }
                });
            }
        }
        catch (OperationCanceledException)
        {
            Debug.WriteLine("Initialization of mails canceled.");
        }
        catch (Exception ex)
        {
            Debugger.Break();

            if (IsInSearchMode)
                Log.Error(ex, "Failed to perform search.");
            else
                Log.Error(ex, "Failed to refresh listed mails.");
        }
        finally
        {
            listManipulationSemepahore.Release();

            await ExecuteUIThread(() =>
            {
                IsInitializingFolder = false;

                OnPropertyChanged(nameof(CanSynchronize));
                NotifyItemFoundState();
            });
        }
    }

    #region Receivers

    async void IRecipient<ActiveMailFolderChangedEvent>.Receive(ActiveMailFolderChangedEvent message)
    {
        NotifyItemSelected();

        isChangingFolder = true;

        ActiveFolder = message.BaseFolderMenuItem;
        gmailUnreadFolderMarkedAsReadUniqueIds.Clear();

        trackingSynchronizationId = null;
        completedTrackingSynchronizationCount = 0;

        // Notify change for archive-unarchive app bar button.
        OnPropertyChanged(nameof(IsArchiveSpecialFolder));

        IsInSearchMode = false;
        IsOnlineSearchButtonVisible = false;
        AreSearchResultsOnline = false;

        // Prepare Focused - Other or folder name tabs.
        await UpdateFolderPivotsAsync();

        // Reset filters and sorting options.
        ResetFilters();

        await InitializeFolderAsync();

        // TODO: This should be done in a better way.
        while (IsInitializingFolder)
        {
            await Task.Delay(100);
        }

        // Check whether the account synchronizer that this folder belongs to is already in synchronization.
        await CheckIfAccountIsSynchronizingAsync();

        // Let awaiters know about the completion of mail init.
        message.FolderInitLoadAwaitTask?.TrySetResult(true);

        await Task.Yield();

        isChangingFolder = false;

        void ResetFilters()
        {
            // Expected that FilterOptions and SortingOptions have default value in 0 index.
            SelectedFilterOption = FilterOptions[0];
            SelectedSortingOption = SortingOptions[0];
            SearchQuery = string.Empty;
            IsInSearchMode = false;
            IsOnlineSearchEnabled = false;
        }
    }

    public void Receive(AccountSynchronizationCompleted message)
    {
        if (ActiveFolder == null) return;

        bool isLinkedInboxSyncResult = message.SynchronizationTrackingId == trackingSynchronizationId;

        if (isLinkedInboxSyncResult)
        {
            var isCompletedAccountListed = ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId);

            if (isCompletedAccountListed) completedTrackingSynchronizationCount++;

            // Group sync is started but not all folders are synchronized yet. Don't report progress.
            if (completedTrackingSynchronizationCount < ActiveFolder.HandlingFolders.Count()) return;
        }

        bool isReportingActiveAccountResult = ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId);

        if (!isReportingActiveAccountResult) return;

        // At this point either all folders or a single folder sync is completed.
        switch (message.Result)
        {
            case SynchronizationCompletedState.Success:
                UpdateBarMessage(InfoBarMessageType.Success, ActiveFolder.FolderName, Translator.SynchronizationFolderReport_Success);
                break;
            case SynchronizationCompletedState.Failed:
                UpdateBarMessage(InfoBarMessageType.Error, ActiveFolder.FolderName, Translator.SynchronizationFolderReport_Failed);
                break;
            default:
                break;
        }
    }

    void IRecipient<MailItemNavigationRequested>.Receive(MailItemNavigationRequested message)
    {
        Debug.WriteLine($"Mail item navigation requested");
        // Find mail item and add to selected items.

        MailItemViewModel navigatingMailItem = null;
        ThreadMailItemViewModel threadMailItemViewModel = null;

        for (int i = 0; i < 3; i++)
        {
            var mailContainer = MailCollection.GetMailItemContainer(message.UniqueMailId);

            if (mailContainer != null)
            {
                navigatingMailItem = mailContainer.ItemViewModel;
                threadMailItemViewModel = mailContainer.ThreadViewModel;

                break;
            }
        }

        if (threadMailItemViewModel != null)
            threadMailItemViewModel.IsThreadExpanded = true;

        if (navigatingMailItem != null)
            WeakReferenceMessenger.Default.Send(new SelectMailItemContainerEvent(navigatingMailItem, message.ScrollToItem));
    }

    #endregion

    public async void Receive(NewMailSynchronizationRequested message)
        => await ExecuteUIThread(() => { OnPropertyChanged(nameof(CanSynchronize)); });

    protected override async void OnFolderSynchronizationEnabled(IMailItemFolder mailItemFolder)
    {
        if (ActiveFolder?.EntityId != mailItemFolder.Id) return;

        await ExecuteUIThread(() =>
        {
            ActiveFolder.UpdateFolder(mailItemFolder);

            OnPropertyChanged(nameof(CanSynchronize));
            OnPropertyChanged(nameof(IsFolderSynchronizationEnabled));
        });

        SyncFolderCommand?.Execute(null);
    }

    public async void Receive(AccountSynchronizerStateChanged message)
        => await CheckIfAccountIsSynchronizingAsync();

    private async Task CheckIfAccountIsSynchronizingAsync()
    {
        bool isAnyAccountSynchronizing = false;

        // Check each account that this page is listing folders from.
        // If any of the synchronizers are synchronizing, we disable sync.

        if (ActiveFolder != null)
        {
            var accountIds = ActiveFolder.HandlingFolders.Select(a => a.MailAccountId);

            foreach (var accountId in accountIds)
            {
                if (SynchronizationManager.Instance.IsAccountSynchronizing(accountId))
                {
                    isAnyAccountSynchronizing = true;
                    break;
                }
            }
        }

        await ExecuteUIThread(() => { IsAccountSynchronizerInSynchronization = isAnyAccountSynchronizing; });
    }

    public void Receive(AccountCacheResetMessage message)
    {
        if (message.Reason == AccountCacheResetReason.ExpiredCache &&
            ActiveFolder.HandlingFolders.Any(a => a.MailAccountId == message.AccountId))
        {
            var handlingFolder = ActiveFolder.HandlingFolders.FirstOrDefault(a => a.MailAccountId == message.AccountId);

            if (handlingFolder == null) return;

            _ = ExecuteUIThread(() =>
            {
                MailCollection.Clear();

                _mailDialogService.InfoBarMessage(Translator.AccountCacheReset_Title, Translator.AccountCacheReset_Message, InfoBarMessageType.Warning);
            });
        }
    }

    public void Receive(ThumbnailAdded message)
    {
        Dispatcher.ExecuteOnUIThread(() =>
        {
            MailCollection.UpdateThumbnailsForAddress(message.Email);
        });
    }

    protected override void RegisterRecipients()
    {
        base.RegisterRecipients();

        Messenger.Register<MailItemNavigationRequested>(this);
        Messenger.Register<ActiveMailFolderChangedEvent>(this);
        Messenger.Register<AccountSynchronizationCompleted>(this);
        Messenger.Register<NewMailSynchronizationRequested>(this);
        Messenger.Register<AccountSynchronizerStateChanged>(this);
        Messenger.Register<AccountCacheResetMessage>(this);
        Messenger.Register<ThumbnailAdded>(this);
    }

    protected override void UnregisterRecipients()
    {
        base.UnregisterRecipients();

        Messenger.Unregister<MailItemNavigationRequested>(this);
        Messenger.Unregister<ActiveMailFolderChangedEvent>(this);
        Messenger.Unregister<AccountSynchronizationCompleted>(this);
        Messenger.Unregister<NewMailSynchronizationRequested>(this);
        Messenger.Unregister<AccountSynchronizerStateChanged>(this);
        Messenger.Unregister<AccountCacheResetMessage>(this);
        Messenger.Unregister<ThumbnailAdded>(this);
    }
}