using System.Collections.Specialized;

namespace JD.AssetBrowser.Model
{
    /// <summary>
    /// Provides a common implementation of a tree node model that supports three-state checking.
    /// </summary>
    public class ThreeStateCheckableTreeNodeModel : CheckableTreeNodeModel
    {

        private bool _isUpdatingIsChecked;
        private ThreeStateCheckableTreeNodeModel _parent;

        /// <summary>
        /// Initializes a new instance of the <see cref="ThreeStateCheckableTreeNodeModel"/> class.
        /// </summary>
        public ThreeStateCheckableTreeNodeModel()
        {
            Children.CollectionChanged += OnChildrenCollectionChanged;
        }

        /// <summary>
        /// Occurs when the collection is changed.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The <see cref="NotifyCollectionChangedEventArgs"/> containing data related to this event.</param>
        private void OnChildrenCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e != null)
            {
                if (e.OldItems != null)
                {
                    foreach (var oldItem in e.OldItems)
                    {
                        if (oldItem is ThreeStateCheckableTreeNodeModel oldChild)
                            oldChild.Parent = null;
                    }
                }

                if (e.NewItems != null)
                {
                    foreach (var newItem in e.NewItems)
                    {
                        if (newItem is ThreeStateCheckableTreeNodeModel newChild)
                            newChild.Parent = this;
                    }
                }
            }
        }

        /// <summary>
        /// Applies recursive updates based on the checked state.
        /// </summary>
        private void ApplyRecursiveUpdates()
        {
            if (!IsChecked.HasValue)
                return;

            foreach (var child in Children)
            {
                if (child is ThreeStateCheckableTreeNodeModel checkableChild)
                    ApplyRecursiveUpdates(checkableChild, IsChecked);
            }

            var ancestor = _parent;
            while (ancestor != null)
            {
                var allChildrenChecked = true;
                var allChildrenUnchecked = true;

                foreach (var child in ancestor.Children)
                {
                    if (child is ThreeStateCheckableTreeNodeModel checkableChild)
                    {
                        switch (checkableChild.IsChecked)
                        {
                            case true:
                                allChildrenUnchecked = false;
                                break;
                            case false:
                                allChildrenChecked = false;
                                break;
                            default:
                                allChildrenChecked = false;
                                allChildrenUnchecked = false;
                                break;
                        }
                    }
                }

                if (allChildrenChecked)
                    ancestor.SetIsCheckedWithoutRecursion(true);
                else if (allChildrenUnchecked)
                    ancestor.SetIsCheckedWithoutRecursion(false);
                else
                    ancestor.SetIsCheckedWithoutRecursion(null);

                ancestor = ancestor.Parent;
            }
        }

        /// <summary>
        /// Applies recursive updates based on the checked state.
        /// </summary>
        /// <param name="node">The node to update.</param>
        /// <param name="newValue">The new value.</param>
        private void ApplyRecursiveUpdates(ThreeStateCheckableTreeNodeModel node, bool? newValue)
        {
            if ((node != null) && (node.IsChecked != newValue))
            {
                node.SetIsCheckedWithoutRecursion(newValue);

                foreach (var child in node.Children)
                {
                    if (child is ThreeStateCheckableTreeNodeModel checkableChild)
                        ApplyRecursiveUpdates(checkableChild, newValue);
                }
            }
        }

        protected override void OnPropertyChanged(string propertyName = null)
        {
            base.OnPropertyChanged(propertyName);

            switch (propertyName)
            {
                case nameof(IsChecked):
                    if (!_isUpdatingIsChecked)
                        ApplyRecursiveUpdates();
                    break;
            }
        }

        /// <summary>
        /// Gets the parent node, whose reference is needed for check updates that affect the ancestor nodes.
        /// </summary>
        /// <value>The parent node, whose reference is needed for check updates that affect the ancestor nodes.</value>
        public ThreeStateCheckableTreeNodeModel Parent
        {
            get { return _parent; }
            set { SetProperty(ref _parent, value); }
        }

        /// <summary>
        /// Sets the <c>IsChecked</c> property without recursion.
        /// </summary>
        /// <param name="newValue">The new value.</param>
        public void SetIsCheckedWithoutRecursion(bool? newValue)
        {
            try
            {
                _isUpdatingIsChecked = true;
                IsChecked = newValue;
            }
            finally
            {
                _isUpdatingIsChecked = false;
            }
        }

    }
}