Wino-Mail/Wino.Calendar.ViewModels/Data/GroupedAccountCalendarViewModel.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using CommunityToolkit.Mvvm.ComponentModel;
using Wino.Core.Domain.Entities.Shared;

namespace Wino.Calendar.ViewModels.Data;

public partial class GroupedAccountCalendarViewModel : ObservableObject
{
    public event EventHandler CollectiveSelectionStateChanged;
    public event EventHandler<AccountCalendarViewModel> CalendarSelectionStateChanged;

    public MailAccount Account { get; }
    public ObservableCollection<AccountCalendarViewModel> AccountCalendars { get; }

    public GroupedAccountCalendarViewModel(MailAccount account, IEnumerable<AccountCalendarViewModel> calendarViewModels)
    {
        Account = account;
        AccountCalendars = new ObservableCollection<AccountCalendarViewModel>(calendarViewModels);

        ManageIsCheckedState();

        foreach (var calendarViewModel in calendarViewModels)
        {
            calendarViewModel.PropertyChanged += CalendarPropertyChanged;
        }

        AccountCalendars.CollectionChanged += CalendarListUpdated;
    }

    private void CalendarListUpdated(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (AccountCalendarViewModel calendar in e.NewItems)
            {
                calendar.PropertyChanged += CalendarPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (AccountCalendarViewModel calendar in e.OldItems)
            {
                calendar.PropertyChanged -= CalendarPropertyChanged;
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Reset)
        {
            foreach (AccountCalendarViewModel calendar in e.OldItems)
            {
                calendar.PropertyChanged -= CalendarPropertyChanged;
            }
        }
    }

    private void CalendarPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        if (sender is AccountCalendarViewModel viewModel)
        {
            if (e.PropertyName == nameof(AccountCalendarViewModel.IsChecked))
            {
                ManageIsCheckedState();
                UpdateCalendarCheckedState(viewModel, viewModel.IsChecked, true);
            }
        }
    }

    [ObservableProperty]
    private bool _isExpanded = true;

    [ObservableProperty]
    private bool? isCheckedState = true;

    private bool _isExternalPropChangeBlocked = false;

    private void ManageIsCheckedState()
    {
        if (_isExternalPropChangeBlocked) return;

        _isExternalPropChangeBlocked = true;

        if (AccountCalendars.All(c => c.IsChecked))
        {
            IsCheckedState = true;
        }
        else if (AccountCalendars.All(c => !c.IsChecked))
        {
            IsCheckedState = false;
        }
        else
        {
            IsCheckedState = null;
        }

        _isExternalPropChangeBlocked = false;
    }

    partial void OnIsCheckedStateChanged(bool? newValue)
    {
        if (_isExternalPropChangeBlocked) return;

        // Update is triggered by user on the three-state checkbox.
        // We should not report all changes one by one.

        _isExternalPropChangeBlocked = true;

        if (newValue == null)
        {
            // Only primary calendars must be checked.

            foreach (var calendar in AccountCalendars)
            {
                UpdateCalendarCheckedState(calendar, calendar.IsPrimary);
            }
        }
        else
        {
            foreach (var calendar in AccountCalendars)
            {
                UpdateCalendarCheckedState(calendar, newValue.GetValueOrDefault());
            }
        }

        _isExternalPropChangeBlocked = false;

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

    private void UpdateCalendarCheckedState(AccountCalendarViewModel accountCalendarViewModel, bool newValue, bool ignoreValueCheck = false)
    {
        var currentValue = accountCalendarViewModel.IsChecked;

        if (currentValue == newValue && !ignoreValueCheck) return;

        accountCalendarViewModel.IsChecked = newValue;

        // No need to report.
        if (_isExternalPropChangeBlocked == true) return;

        CalendarSelectionStateChanged?.Invoke(this, accountCalendarViewModel);
    }
}