[DefaultValue(TreeListAllowedDropTarget.Internal)]
[Parameter]
public TreeListAllowedDropTarget AllowedDropTarget { get; set; }

<DxTreeList @ref="PlannedTasksTreeList"
            Data="PlannedTasks"
            KeyFieldName="Id"
            ParentKeyFieldName="ParentId"
            AllowDragRows="true"
            AllowedDropTarget="TreeListAllowedDropTarget.All"
            ItemsDropped="TreeList_ItemsDropped">
    <Columns>
        <DxTreeListDataColumn FieldName="Name" Caption="Task" />
        <DxTreeListDataColumn FieldName="Priority" Width="100px" CaptionAlignment="TreeListTextAlignment.Center" TextAlignment="TreeListTextAlignment.Center">
            <CellDisplayTemplate>
                @GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
            </CellDisplayTemplate>
        </DxTreeListDataColumn>
    </Columns>
    <DragHintTextTemplate>
        @if(context.DataItems[0] != null) {
            var employeeTask = (EmployeeTask)context.DataItems[0];
            <span class="dxbl-text">@(employeeTask.Name)</span>
            <span class="dxbl-text">@GetEmployeeTaskPriorityIconHtml(employeeTask)</span>
        }
    </DragHintTextTemplate>
</DxTreeList>

<DxGrid Data="PendingTasks"
        TextWrapEnabled="false"
        AllowDragRows="true"
        AllowedDropTarget="GridAllowedDropTarget.External"
        ItemsDropped="Grid_ItemsDropped">
    <Columns>
        <DxGridDataColumn FieldName="Name" Caption="Task" />
        <DxGridDataColumn FieldName="Priority" Width="100px" CaptionAlignment="GridTextAlignment.Center" TextAlignment="GridTextAlignment.Center">
            <CellDisplayTemplate>
                @GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
            </CellDisplayTemplate>
        </DxGridDataColumn>
    </Columns>
    <DragHintTextTemplate>
        @if(context.DataItems.Count == 1) {
            var employeeTask = (EmployeeTask)context.DataItems[0];
            <span class="dxbl-text">@(employeeTask.Name)</span>
            <span class="dxbl-text">@GetEmployeeTaskPriorityIconHtml(employeeTask)</span>
        }
        else {
            <span class="dxbl-text">@(context.DataItems.Count) tasks</span>
        }
    </DragHintTextTemplate>
</DxGrid>

@code {
    ITreeList PlannedTasksTreeList { get; set; }

    ObservableCollection<EmployeeTask> PlannedTasks { get; set; }
    ObservableCollection<EmployeeTask> PendingTasks { get; set; }

    protected override async Task OnInitializedAsync() {
        var employeeTasks = EmployeeTaskDataProvider.GenerateData();
        PlannedTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority <= 0));
        PendingTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority > 0));
    }

    void TreeList_ItemsDropped(TreeListItemsDroppedEventArgs evt) {
        var sourceTasks = GetTaskCollection(evt.SourceComponent);
        RemoveDroppedItems(sourceTasks, evt.DroppedItems);

        var targetTask = (EmployeeTask)evt.TargetItem;
        var index = targetTask != null
            ? PlannedTasks.IndexOf(targetTask) + (evt.DropPosition == TreeListItemDropPosition.After ? 1 : 0)
            : PlannedTasks.Count;

        var droppedTasks = evt.DroppedItems.OfType<EmployeeTask>();
        foreach(var droppedTask in droppedTasks) {
            droppedTask.ParentId = evt.DropPosition == TreeListItemDropPosition.Inside
                ? targetTask.Id
                : targetTask.ParentId;
        }

        InsertDroppedItems(PlannedTasks, evt.DroppedItems, index);
    }

    void Grid_ItemsDropped(GridItemsDroppedEventArgs evt) {
        var sourceTasks = GetTaskCollection(evt.SourceComponent);
        RemoveDroppedItems(sourceTasks, evt.DroppedItems);

        var targetTask = (EmployeeTask)evt.TargetItem;
        var index = targetTask != null
            ? PendingTasks.IndexOf(targetTask) + (evt.DropPosition == GridItemDropPosition.After ? 1 : 0)
            : PendingTasks.Count;

        InsertDroppedItems(PendingTasks, evt.DroppedItems, index);
    }

    void RemoveDroppedItems(IList<EmployeeTask> employeeTasks, IEnumerable<object> droppedItems) {
        foreach(var item in droppedItems)
            employeeTasks.Remove((EmployeeTask)item);
    }

    void InsertDroppedItems(IList<EmployeeTask> employeeTasks, IEnumerable<object> droppedItems, int index) {
        foreach(var item in droppedItems.Reverse())
            employeeTasks.Insert(index, (EmployeeTask)item);
    }

    ObservableCollection<EmployeeTask> GetTaskCollection(object grid) {
        return grid == PlannedTasksTreeList ? PlannedTasks : PendingTasks;
    }

    MarkupString GetEmployeeTaskPriorityIconHtml(EmployeeTask employeeTask) {
        var displayText = TreeListRenderHelper.EmployeeTaskPriorityToString(employeeTask);
        var badgeClass = employeeTask.Priority switch {
            -1 => "bg-success",
            0 => "bg-info",
            1 => "bg-warning",
            _ => throw new ArgumentException()
        };

        string html = string.Format("<span class='badge {0} py-1 px-2' title='{1} priority'>{1}</span>", badgeClass, displayText);
        return new MarkupString(html);
    }
}