Microsoft.Extensions.AI: chat clients in C#

#:package Microsoft.Extensions.AI@10.10.0
#:package Microsoft.Extensions.Hosting@10.0.12
#:property PublishAot=false
// A ticket summariser that depends only on IChatClient. An app would register the IChatClient of a provider's package;
// this program registers FakeChatClient, which records what it is sent and answers with a fixed sentence, so the run
// needs no network, no key and no model, and prints the same lines every time.
using Microsoft.Extensions.AI;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
builder.Logging.ClearProviders();
FakeChatClient fake = new("Charged twice for order A-1042; wants one payment refunded.");
builder.Services.AddChatClient(fake);
builder.Services.AddSingleton<TicketSummarizer>();
using IHost host = builder.Build();

TicketSummarizer summarizer = host.Services.GetRequiredService<TicketSummarizer>();
string summary = await summarizer.SummarizeAsync(
    "Hello, I paid for order A-1042 on Monday and the money left my account twice. Please refund one payment.");

Console.WriteLine("the chat client was sent:");
foreach (ChatMessage message in fake.Received)
    Console.WriteLine($"  {message.Role}: {message.Text}");
Console.WriteLine($"with Temperature {fake.Options?.Temperature} and MaxOutputTokens {fake.Options?.MaxOutputTokens}");
Console.WriteLine($"summary: {summary}");

// The service: it builds the messages, sets the options and reads the text of the answer. It never names a model.
sealed class TicketSummarizer(IChatClient chat)
{
    public async Task<string> SummarizeAsync(string ticket, CancellationToken cancellationToken = default)
    {
        ChatResponse response = await chat.GetResponseAsync(
            [
                new ChatMessage(ChatRole.System, "Summarise the support ticket in one sentence. Keep order numbers."),
                new ChatMessage(ChatRole.User, ticket),
            ],
            new ChatOptions { Temperature = 0, MaxOutputTokens = 60 },
            cancellationToken);
        return response.Text;
    }
}

// A stand-in for a real client: it keeps the last request and returns its fixed answer.
sealed class FakeChatClient(string answer) : IChatClient
{
    public List<ChatMessage> Received { get; } = [];
    public ChatOptions? Options { get; private set; }

    public Task<ChatResponse> GetResponseAsync(IEnumerable<ChatMessage> messages, ChatOptions? options = null, CancellationToken cancellationToken = default)
    {
        Received.Clear();
        Received.AddRange(messages);
        Options = options;
        return Task.FromResult(new ChatResponse(new ChatMessage(ChatRole.Assistant, answer)));
    }

    public IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(IEnumerable<ChatMessage> messages, ChatOptions? options = null, CancellationToken cancellationToken = default) =>
        throw new NotSupportedException("this fake only answers whole responses");

    public object? GetService(Type serviceType, object? serviceKey = null) => serviceType.IsInstanceOfType(this) ? this : null;

    public void Dispose() { }
}

from session import run

# network: true. summarise.cs names Microsoft.Extensions.AI 10.10.0 and Microsoft.Extensions.Hosting 10.0.12 in its
# #:package lines, and dotnet run restores them from nuget.org into the session's own home folder. The chat client is
# a fake inside the program, so nothing else is reached: no model, no key.
run("""
cd summarise
dotnet run summarise.cs
""", network=True)

$ cd summarise
$ dotnet run summarise.cs
the chat client was sent:
  system: Summarise the support ticket in one sentence. Keep order numbers.
  user: Hello, I paid for order A-1042 on Monday and the money left my account twice. Please refund one payment.
with Temperature 0 and MaxOutputTokens 60
summary: Charged twice for order A-1042; wants one payment refunded.