using Windows.ApplicationModel.DataTransfer;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace ClientSoft.UI.Controls.TreeView
{
    public sealed class TreeView : ListView
    {
        #region Fields
        private TreeViewCollection _collection;
        #endregion


        public TreeView()
        {
            IsItemClickEnabled = true;
            ItemClick += TreeView_ItemClick;
            DragItemsStarting += TreeView_DragItemsStarting;
            DragItemsCompleted += TreeView_DragItemsCompleted;

            CanDragItems = true;
            CanReorderItems = true;
            AllowDrop = true;
        }


        #region Properties
        /// <summary>
        /// Buffer for dragged TreeViewItem.
        /// </summary>
        internal TreeViewItem DraggedItem { get; set; }

        /// <summary>
        /// Items collection.
        /// </summary>
        internal TreeViewCollection Collection =>
            _collection ?? (_collection = (TreeViewCollection)ItemsSource);
        #endregion


        private void TreeView_ItemClick(object sender, ItemClickEventArgs e)
        {
            var targetNode = (TreeNode)e.ClickedItem;
            if (targetNode.IsRootNode)
            {
                if (targetNode.IsExpanded)
                {
                    targetNode.Collapse();
                }
                else
                {
                    targetNode.Expand();
                }
            }
        }

        private void TreeView_DragItemsCompleted(ListViewBase sender, DragItemsCompletedEventArgs args)
        {
            DraggedItem = null;
        }

        private void TreeView_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
        {
            DraggedItem = (TreeViewItem)ContainerFromItem(e.Items[0]);
        }

        #region Overridden methods
        protected override DependencyObject GetContainerForItemOverride() => new TreeViewItem();

        protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
        {
            ((UIElement)element).AllowDrop = ((TreeNode)item).IsRootNode;
            base.PrepareContainerForItemOverride(element, item);
        }

        protected override void OnDrop(DragEventArgs e)
        {
            if (e.AcceptedOperation == DataPackageOperation.Move)
            {
                MoveItem(e);
            }

            base.OnDrop(e);
        }
        #endregion


        #region Private methods
        private void MoveItem(DragEventArgs e)
        {
            var position = e.GetPosition(ItemsPanelRoot);
            if (ItemsPanelRoot is IInsertionPanel panel)
            {
                panel.GetInsertionIndexes(position, out var aboveIndex, out var belowIndex);
                var targetNode = (TreeNode)ItemFromContainer(DraggedItem);

                if (aboveIndex >= 0 && belowIndex >= 0 && belowIndex != Collection.Count)
                {
                    var aboveNode = Collection[aboveIndex];
                    var belowNode = Collection[belowIndex];
                    RemoveNode(targetNode);

                    if (belowNode.RootNode == aboveNode)
                    {
                        aboveNode.Insert(0, targetNode);
                    }
                    else
                    {
                        if (aboveNode.RootNode == null)
                        {
                            var insertionIndex = aboveIndex - Collection.IndexOf(aboveNode.RootNode);

                            Collection.AddNodeToView(insertionIndex, targetNode);
                            Collection.AddNodeDescadentsToView(targetNode, insertionIndex, 0);
                        }
                        else
                        {
                            aboveNode.RootNode.Insert(aboveIndex, targetNode);
                        }
                    }
                }
                else if (aboveIndex >= 0 && (belowIndex == -1 || belowIndex == Collection.Count))
                {
                    RemoveNode(targetNode);

                    var insertionIndex = Collection.Count;
                    Collection.AddNodeToView(insertionIndex, targetNode);
                    Collection.AddNodeDescadentsToView(targetNode, insertionIndex, 0);
                }
                else if (aboveIndex == -1 && belowIndex >= 0)
                {
                    RemoveNode(targetNode);
                    Collection.AddNodeToView(0, targetNode);
                }
            }

            e.Handled = true;
        }

        private void RemoveNode(TreeNode targetNode)
        {
            if (targetNode.RootNode != null)
            {
                targetNode.RootNode.Remove(targetNode);
            }
            else
            {
                Collection.RemoveNodeAndDescadentsFromView(targetNode);
            }
        }
        #endregion
    }
}