using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using Chernobyl.App.Core;

namespace Chernobyl.App.Layout
{
    /// <summary>
    /// A view model representing a view of some data and the actions that can be performed on that
    /// data.
    /// </summary>
    public class ContentTabsViewModel : ViewModel
    {
        /// <param name="available">The content vailable for viewing.</param>
        public ContentTabsViewModel(ObservableCollection<Content> available)
            : this(available, Enumerable.Empty<object>())
        {}

        /// <param name="available">The content vailable for viewing.</param>
        /// <param name="tools">Tools that are common to all tabs.</param>
        public ContentTabsViewModel(ObservableCollection<Content> available, IEnumerable<object> tools)
        {
            _constantTools = tools;
            _tools = _constantTools.Cast<object>();

            Available = available;
            Current = Available.FirstOrDefault();

            // Select the first piece of content once it is added.
            if (Current == null)
            {
                Available.CollectionChanged += (sender, args) =>
                {
                    if (args.Action == NotifyCollectionChangedAction.Add && (args.OldItems == null || args.OldItems.Count == 0))
                        Current = Available.FirstOrDefault();
                };
            }
        }

        /// <summary>
        /// The tools or information available for use when interacting with the content.
        /// </summary>
        public IEnumerable<object> Tools
        {
            get => _tools;
            private set
            {
                if (_tools != value)
                {
                    _tools = value;
                    RaisePropertyChanged();
                }
            }
        }

        /// <summary>
        /// The currently selected tab content being displayed.
        /// </summary>
        public Content Current
        {
            get => _current;
            set
            {
                if (_current != value)
                {
                    _current = value;
                    RaisePropertyChanged();

                    if (_current != null)
                        Tools = _constantTools.Cast<object>().Concat(_current.Tools.Cast<object>());
                }
            }
        }

        /// <summary>
        /// The content vailable for viewing.
        /// </summary>
        public ObservableCollection<Content> Available { get; }

        readonly IEnumerable _constantTools;
        IEnumerable<object> _tools;
        Content _current;
    }
}