Changes

api/Services/Rag/OpenAiRagClient.cs

@@ -0,0 +1,104 @@
+using System.Net.Http.Headers;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Api.Settings;
+using Microsoft.Extensions.Options;
+
+namespace Api.Services.Rag;
+
+public interface IOpenAiRagClient
+{
+    Task<float[]> CreateEmbeddingAsync(string input, CancellationToken ct);
+    Task<string> CreateChatCompletionAsync(string systemPrompt, string userPrompt, CancellationToken ct);
+}
+
+public sealed class OpenAiRagClient : IOpenAiRagClient
+{
+    private readonly HttpClient _httpClient;
+    private readonly OpenAiSettings _settings;
+    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
+    {
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
+    };
+
+    public OpenAiRagClient(HttpClient httpClient, IOptions<OpenAiSettings> options)
+    {
+        _httpClient = httpClient;
+        _settings = options.Value;
+
+        if (!string.IsNullOrWhiteSpace(_settings.ApiKey))
+        {
+            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", _settings.ApiKey);
+        }
+
+        _httpClient.Timeout = TimeSpan.FromSeconds(Math.Max(15, _settings.TimeoutSeconds));
+        _httpClient.BaseAddress = new Uri("https://api.openai.com/v1/");
+    }
+
+    public async Task<float[]> CreateEmbeddingAsync(string input, CancellationToken ct)
+    {
+        EnsureConfigured();
+        var payload = new { model = _settings.EmbeddingModel, input };
+        using var response = await _httpClient.PostAsync("embeddings", ToJson(payload), ct);
+        var json = await response.Content.ReadAsStringAsync(ct);
+        if (!response.IsSuccessStatusCode)
+        {
+            throw new InvalidOperationException($"OpenAI embeddings request failed: {(int)response.StatusCode} {json}");
+        }
+
+        using var document = JsonDocument.Parse(json);
+        var embedding = document.RootElement.GetProperty("data")[0].GetProperty("embedding");
+        var result = new float[embedding.GetArrayLength()];
+        var i = 0;
+        foreach (var value in embedding.EnumerateArray())
+        {
+            result[i++] = value.GetSingle();
+        }
+        return result;
+    }
+
+    public async Task<string> CreateChatCompletionAsync(string systemPrompt, string userPrompt, CancellationToken ct)
+    {
+        EnsureConfigured();
+        var payload = new
+        {
+            model = _settings.ChatModel,
+            temperature = 0.2,
+            response_format = new { type = "json_object" },
+            messages = new[]
+            {
+                new { role = "system", content = systemPrompt },
+                new { role = "user", content = userPrompt }
+            }
+        };
+
+        using var response = await _httpClient.PostAsync("chat/completions", ToJson(payload), ct);
+        var json = await response.Content.ReadAsStringAsync(ct);
+        if (!response.IsSuccessStatusCode)
+        {
+            throw new InvalidOperationException($"OpenAI chat request failed: {(int)response.StatusCode} {json}");
+        }
+
+        using var document = JsonDocument.Parse(json);
+        return document.RootElement
+            .GetProperty("choices")[0]
+            .GetProperty("message")
+            .GetProperty("content")
+            .GetString() ?? "{}";
+    }
+
+    private void EnsureConfigured()
+    {
+        if (string.IsNullOrWhiteSpace(_settings.ApiKey))
+        {
+            throw new InvalidOperationException("OpenAI API key is not configured. Set OpenAI__ApiKey.");
+        }
+    }
+
+    private static StringContent ToJson<T>(T payload) => new(
+        JsonSerializer.Serialize(payload, JsonOptions),
+        Encoding.UTF8,
+        "application/json"
+    );
+}