Hy2026/backend/Infrastructure/Llm/OpenAiCompatibleLlmProvider.cs

using System.Net.Http.Json;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using TarninaHub.Application.Matchmaking;

namespace TarninaHub.Infrastructure.Llm;

/// <summary>
/// OpenAI-compatible chat completion provider. Interchangeable behind
/// <see cref="ILlmProvider"/> (ADR-0005). The API key is read from
/// configuration/secrets and never logged.
/// </summary>
public sealed class OpenAiCompatibleLlmProvider : ILlmProvider
{
    private readonly HttpClient _httpClient;
    private readonly LlmSettings _settings;
    private readonly ILogger<OpenAiCompatibleLlmProvider> _logger;

    public OpenAiCompatibleLlmProvider(
        HttpClient httpClient,
        IOptions<LlmSettings> settings,
        ILogger<OpenAiCompatibleLlmProvider> logger)
    {
        _httpClient = httpClient;
        _settings = settings.Value;
        _logger = logger;
    }

    public bool IsConfigured => _settings.IsConfigured;

    public async Task<string?> CompleteAsync(
        string systemPrompt,
        string userPrompt,
        CancellationToken cancellationToken)
    {
        if (!IsConfigured)
        {
            return null;
        }

        var endpoint = _settings.BaseUrl.TrimEnd('/') + "/chat/completions";
        var payload = new
        {
            model = _settings.Model,
            max_tokens = _settings.MaxTokens,
            messages = new object[]
            {
                new { role = "system", content = systemPrompt },
                new { role = "user", content = userPrompt },
            },
        };

        try
        {
            using var request = new HttpRequestMessage(HttpMethod.Post, endpoint)
            {
                Content = JsonContent.Create(payload),
            };
            request.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue(
                "Bearer",
                _settings.ApiKey);

            using var response = await _httpClient.SendAsync(request, cancellationToken);

            if (!response.IsSuccessStatusCode)
            {
                _logger.LogWarning("LLM provider returned status {Status}.", (int)response.StatusCode);

                return null;
            }

            var document = await response.Content.ReadFromJsonAsync<JsonElement>(cancellationToken);

            return document
                .GetProperty("choices")[0]
                .GetProperty("message")
                .GetProperty("content")
                .GetString();
        }
        catch (Exception exception) when (exception is not OperationCanceledException)
        {
            _logger.LogWarning(exception, "LLM completion failed; falling back to template rationale.");

            return null;
        }
    }
}