@using Telerik.Blazor.ExtensionMethods
@* needed for the .ToODataString() method *@

@SelectedValue
<br />
<TelerikComboBox Data="@Options"
                 OnRead="@ReadItems"
                 Filterable="true"
                 Placeholder="Find what you seek by typing"
                 @bind-Value="@SelectedValue">
</TelerikComboBox>

@code{
    public string SelectedValue { get; set; }
    List<string> Options { get; set; } = new List<string>();

    async Task ReadItems(ComboBoxReadEventArgs args)
    {
        if (args.Request.Filters.Count > 0) // there is user filter input, skips providing data on initialization
        {
            Telerik.DataSource.FilterDescriptor filter = args.Request.Filters[0] as Telerik.DataSource.FilterDescriptor;
            string userInput = filter.Value.ToString();
            string method = filter.Operator.ToString();

            // For the time being, you need to set the field name that needs to be serialized for the filter.
            // When binding to a complex model you should probably use the TextField
            filter.Member = "someField";
            filter.MemberType = Type.GetType("System.String");


            Console.WriteLine(args.Request.ToODataString());


            //new data collection comes down from the service
            Options = await GetOptions(userInput, method);
        }
        else
        {
            // when there is no user input you may still want to provide data
            // in this example we just hardcode a few items, you can either fetch all the data
            // or you can provide some subset of most common items, or something based on the business logic
            Options = new List<string>() { "one", "two", "three" };
        }
    }

    async Task<List<string>> GetOptions(string userInput, string filterOperator)
    {
        await Task.Delay(500); // simulate network delay, remove it for a real app

        //sample logic for getting suggestions - here they are generated, you can call a remote service
        //for brevity, this example does not use the filter operator, but your actual service can
        List<string> optionsData = new List<string>();
        for (int i = 0; i < 5; i++)
        {
            optionsData.Add($"option {i} for input {userInput}");
        }

        return optionsData;
    }
}