FileTime2/src/AppCommon/FileTime.App.Core/Services/CommandHandler/NavigationCommandHandler.cs

using System.Reactive.Linq;
using FileTime.App.Core.Command;
using FileTime.App.Core.Extensions;
using FileTime.App.Core.ViewModels;
using FileTime.Core.Models;

namespace FileTime.App.Core.Services.CommandHandler
{
    public class NavigationCommandHandler : CommandHanderBase
    {
        private readonly IAppState _appState;
        private ITabViewModel? _selectedTab;
        private IContainer? _currentLocation;
        private IItemViewModel? _currentSelectedItem;
        private IEnumerable<IItemViewModel> _currentItems = Enumerable.Empty<IItemViewModel>();

        public NavigationCommandHandler(IAppState appState)
        {
            _appState = appState;

            _appState.SelectedTab.Subscribe(t => _selectedTab = t);
            _appState.SelectedTab.Select(t => t == null ? Observable.Return<IContainer?>(null) : t.CurrentLocation).Switch().Subscribe(l => _currentLocation = l);
            _appState.SelectedTab.Select(t => t == null ? Observable.Return<IItemViewModel?>(null) : t.CurrentSelectedItem).Switch().Subscribe(l => _currentSelectedItem = l);
            _appState.SelectedTab.Select(t => t?.CurrentItemsCollectionObservable ?? Observable.Return((IEnumerable<IItemViewModel>?)Enumerable.Empty<IItemViewModel>())).Switch().Subscribe(i => _currentItems = i ?? Enumerable.Empty<IItemViewModel>());

            AddCommandHandlers(new (Commands, Func<Task>)[]
            {
                (Commands.GoUp, GoUp),
                (Commands.MoveCursorDown, MoveCursorDown),
                (Commands.MoveCursorUp, MoveCursorUp),
                (Commands.Open, OpenContainer),
            });
        }

        private Task OpenContainer()
        {
            if (_currentSelectedItem is not IContainerViewModel containerViewModel || containerViewModel.Container is null) return Task.CompletedTask;

            _selectedTab?.Tab?.SetCurrentLocation(containerViewModel.Container);
            return Task.CompletedTask;
        }

        private async Task GoUp()
        {
            if (_currentLocation?.Parent is not IAbsolutePath parentPath || await parentPath.ResolveAsyncSafe() is not IContainer newContainer) return;
            _selectedTab?.Tab?.SetCurrentLocation(newContainer);
        }

        private Task MoveCursorDown()
        {
            SelectNewSelectedItem(i => i.SkipWhile(i => !i.EqualsTo(_currentSelectedItem)).Skip(1).FirstOrDefault());
            return Task.CompletedTask;
        }

        private Task MoveCursorUp()
        {
            SelectNewSelectedItem(i => i.TakeWhile(i => !i.EqualsTo(_currentSelectedItem)).LastOrDefault());
            return Task.CompletedTask;
        }

        private void SelectNewSelectedItem(Func<IEnumerable<IItemViewModel>, IItemViewModel?> getNewSelected)
        {
            if (_selectedTab is null || _currentLocation is null) return;

            var newSelectedItem = getNewSelected(_currentItems);
            if (newSelectedItem == null) return;

            _selectedTab.Tab?.SetSelectedItem(newSelectedItem.ToAbsolutePath());
        }
    }
}