reason.cs

using OpenAI;
using OpenAI.Responses;
using System.ClientModel;

static string Require(string? v, string name)
    => string.IsNullOrWhiteSpace(v) ? throw new InvalidOperationException($"{name} is missing") : v;

var endpoint = Require(Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT"), "AZURE_OPENAI_ENDPOINT");
// Example endpoint: https://YOUR-RESOURCE-NAME.openai.azure.com
var apiKey = Require(Environment.GetEnvironmentVariable("AZURE_OPENAI_API_KEY"), "AZURE_OPENAI_API_KEY");
var deployment = Require(Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT"), "AZURE_OPENAI_DEPLOYMENT");

// Azure OpenAI v1 base URL (important)
var v1BaseUrl = $"{endpoint.TrimEnd('/')}/openai/v1/";

var client = new OpenAIClient(
    credential: new ApiKeyCredential(apiKey),
    options: new OpenAIClientOptions { Endpoint = new Uri(v1BaseUrl) }
);

var responsesClient = client.GetResponsesClient(deployment);

// Basic reasoning sample
var systemPrompt = "You are a helpful assistant. Provide a short reasoning summary, then a final answer.";
var userPrompt =
    "If a train travels at 60 mph for 2.5 hours, then slows down to 40 mph for another 1.5 hours, " +
    "what is the total distance traveled and the average speed for the entire journey?";

var options = new CreateResponseOptions
{
    Instructions = systemPrompt,
    ReasoningOptions = new ResponseReasoningOptions
    {
        ReasoningEffortLevel = ResponseReasoningEffortLevel.Medium,
        ReasoningSummaryVerbosity = ResponseReasoningSummaryVerbosity.Auto
    }
};

options.InputItems.Add(ResponseItem.CreateUserMessageItem(userPrompt));

var result = await responsesClient.CreateResponseAsync(options);
var response = result.Value;

// Print reasoning summary (if present)
Console.WriteLine("🧠 REASONING SUMMARY");
Console.WriteLine("────────────────────");
var printed = false;

foreach (var item in response.OutputItems)
{
    if (item is ReasoningResponseItem reasoningItem)
    {
        foreach (var part in reasoningItem.SummaryParts)
        {
            if (part is ReasoningSummaryTextPart textPart)
            {
                Console.WriteLine(textPart.Text);
                printed = true;
            }
        }
    }
}

if (!printed)
{
    Console.WriteLine("(No reasoning summary returned for this request)");
}

// Print final answer
Console.WriteLine();
Console.WriteLine("✅ FINAL ANSWER");
Console.WriteLine("────────────────────");
Console.WriteLine(response.GetOutputText());