@*Set initial Gantt state*@

@using Telerik.DataSource

<TelerikGantt @ref="@GanttRef"
              Data="@GanttData"
              OnStateInit="@( (GanttStateEventArgs<GanttTask> args) => OnStateInitHandler(args) )"
              Sortable="true"
              FilterMode="@GanttFilterMode.FilterRow"
              IdField="Id"
              ParentIdField="ParentId"
              ColumnResizable="true"
              TreeListWidth="50%"
              Width="1000px"
              Height="600px"
              OnUpdate="@OnTaskUpdate"
              OnDelete="@OnTaskDelete">
    <GanttColumns>
        <GanttColumn Field="Title"
                     Expandable="true"
                     Width="160px"
                     Title="Task Title">
        </GanttColumn>
        <GanttColumn Field="PercentComplete"
                     Title="Status"
                     Width="100px">
        </GanttColumn>
        <GanttColumn Field="Start"
                     Width="100px"
                     DisplayFormat="{0:d}">
        </GanttColumn>
        <GanttColumn Field="End"
                     Width="100px"
                     DisplayFormat="{0:d}">
        </GanttColumn>
    </GanttColumns>
    <GanttViews>
        <GanttDayView></GanttDayView>
        <GanttWeekView></GanttWeekView>
        <GanttMonthView></GanttMonthView>
    </GanttViews>
</TelerikGantt>

@code {
    private TelerikGantt<GanttTask> GanttRef;

    private List<GanttTask> GanttData { get; set; }

    private async Task OnStateInitHandler(GanttStateEventArgs<GanttTask> args)
    {
        var filterDescriptorCollection = new FilterDescriptorCollection();

        filterDescriptorCollection.Add(new FilterDescriptor(nameof(GanttTask.PercentComplete), FilterOperator.IsLessThan, 0.5) { MemberType = typeof(double) });

        var state = new GanttState<GanttTask>
        {
            ExpandedItems = GanttData.Where(i => i.Id == 1).ToList(), //set the items you need to expand

            View = GanttView.Week,
        };

        args.State = state;
    }

    class GanttTask
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Title { get; set; }
        public double PercentComplete { get; set; }
        public DateTime Start { get; set; }
        public DateTime End { get; set; }
    }

    private int LastId { get; set; } = 1;

    protected override void OnInitialized()
    {
        GanttData = new List<GanttTask>();

        var random = new Random();

        for (int i = 1; i < 6; i++)
        {
            var newItem = new GanttTask()
                {
                    Id = LastId,
                    Title = "Task  " + i.ToString(),
                    Start = new DateTime(2021, 7, 5 + i),
                    End = new DateTime(2021, 7, 11 + i),
                    PercentComplete = Math.Round(random.NextDouble(), 2)
                };

            GanttData.Add(newItem);
            var parentId = LastId;
            LastId++;

            for (int j = 0; j < 5; j++)
            {
                GanttData.Add(new GanttTask()
                    {
                        Id = LastId,
                        ParentId = parentId,
                        Title = "    Task " + i + " : " + j.ToString(),
                        Start = new DateTime(2021, 7, 5 + j),
                        End = new DateTime(2021, 7, 6 + i + j),
                        PercentComplete = Math.Round(random.NextDouble(), 2)
                    });

                LastId++;
            }
        }

        base.OnInitialized();
    }

    private void OnTaskUpdate(GanttUpdateEventArgs args)
    {
        var item = args.Item as GanttTask;

        var foundItem = GanttData.FirstOrDefault(i => i.Id.Equals(item.Id));

        if (foundItem != null)
        {
            foundItem.Title = item.Title;
            foundItem.Start = item.Start;
            foundItem.End = item.End;
            foundItem.PercentComplete = item.PercentComplete;
        }
    }

    private void OnTaskDelete(GanttDeleteEventArgs args)
    {
        var item = GanttData.FirstOrDefault(i => i.Id.Equals((args.Item as GanttTask).Id));

        RemoveChildRecursive(item);
    }

    private void RemoveChildRecursive(GanttTask item)
    {
        var children = GanttData.Where(i => item.Id.Equals(i.ParentId)).ToList();

        foreach (var child in children)
        {
            RemoveChildRecursive(child);
        }

        GanttData.Remove(item);
    }
}