throttled

Home.razor

@page "/"
@rendermode InteractiveServer

<input value="@query" @oninput="OnInput" />

@if (isGetItems)
{
    <div style="font-style: italic;">поиск...</div>
}
else
{
    @if (items.Count == 0)
    {
        <div style="font-weight: bold;">found nothing</div>
    }
    else
    {
        <h6>@items.Count</h6>
        <ul>
    @foreach (var item in items)
            {
                <li>@item.name</li>
            }
        </ul>
    }
}

@code {
    List<Item> items = new();
    string query = "United States";
    CancellationTokenSource cts = new CancellationTokenSource();
    SemaphoreSlim mutex = new SemaphoreSlim(1);
    bool isGetItems;
    async Task OnInput(ChangeEventArgs args)
    {
        query = args.Value?.ToString() ?? string.Empty;
        cts.Cancel();
        isGetItems = false;
        cts = new CancellationTokenSource();
        await InvokeAsync(async () => await Task.Delay(1000, cts.Token)
        .ContinueWith(async x => await mutex.WaitAsync(cts.Token))
        .ContinueWith(async x => await GetItems(cts.Token)));
    }

    async Task GetItems(CancellationToken token)
    {
        try
        {
            isGetItems = true;
            using (var http = new HttpClient())
            {
                items.Clear();
                var url = string.Format("http://universities.hipolabs.com/search?country={0}", System.Net.WebUtility.UrlEncode(query));
                var res = await http.GetFromJsonAsync<List<Item>>(url, token);
                if (res != null)
                    items.AddRange(res);
            }
        }
        finally
        {
            isGetItems = false;
            mutex.Release();
            await InvokeAsync(StateHasChanged);
        }
    }

    public record Item(string name);
}