INBOX-2: extract provider-agnostic OpenAiChatClient from SaleAdService (shared AI wire, public surface unchanged)

GerbilManagerWebAPI/Ai/OpenAiChatClient.cs

@@ -0,0 +1,99 @@
+using System.Net.Http.Headers;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using GerbilManagerWebAPI.SaleAd;
+using Microsoft.Extensions.Options;
+
+namespace GerbilManagerWebAPI.Ai
+{
+    public enum AiCallStatus
+    {
+        Ok,
+        /// <summary>AI section not (fully) configured -> callers map to 503 "AiKeyMissing".</summary>
+        NotConfigured,
+        /// <summary>Provider call failed -> callers map to 502 "AiUpstreamError".</summary>
+        UpstreamError,
+    }
+
+    public sealed record AiCallResult(AiCallStatus Status, string? Text, string? Error = null);
+
+    /// <summary>
+    /// INBOX-2: provider-agnostic chat client, extracted from SaleAdService so the
+    /// reply-draft (and future AI features) reuse the SAME wire implementation:
+    /// plain JSON POST to {AI:BaseUrl}/chat/completions with a Bearer key — covers
+    /// Gemini (compat endpoint), Groq, Mistral, local Ollama; no vendor SDK.
+    /// Configuration stays the single AI section (AiOptions, env-only).
+    /// </summary>
+    public sealed class OpenAiChatClient(HttpClient http, IOptions<AiOptions> options)
+    {
+        private static readonly JsonSerializerOptions JsonOptions = new()
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        };
+
+        public async Task<AiCallResult> CompleteAsync(
+            string systemPrompt, string userPrompt, CancellationToken ct = default)
+        {
+            var ai = options.Value;
+            if (!ai.IsConfigured)
+            {
+                return new AiCallResult(AiCallStatus.NotConfigured, null,
+                    "KI-Anbieter ist nicht konfiguriert (AI__BaseUrl / AI__ApiKey / AI__Model).");
+            }
+
+            var payload = new ChatRequest(
+                Model: ai.Model!,
+                Messages:
+                [
+                    new ChatMessage("system", systemPrompt),
+                    new ChatMessage("user", userPrompt),
+                ],
+                Temperature: 0.7);
+
+            using var httpRequest = new HttpRequestMessage(HttpMethod.Post, BuildCompletionsUri(ai.BaseUrl!))
+            {
+                Content = new StringContent(JsonSerializer.Serialize(payload, JsonOptions),
+                    Encoding.UTF8, "application/json"),
+            };
+            httpRequest.Headers.Authorization = new AuthenticationHeaderValue("Bearer", ai.ApiKey);
+
+            try
+            {
+                using var response = await http.SendAsync(httpRequest, ct);
+                var body = await response.Content.ReadAsStringAsync(ct);
+                if (!response.IsSuccessStatusCode)
+                {
+                    return new AiCallResult(AiCallStatus.UpstreamError, null,
+                        $"KI-Anbieter antwortete mit HTTP {(int)response.StatusCode}.");
+                }
+
+                var completion = JsonSerializer.Deserialize<ChatResponse>(body, JsonOptions);
+                var text = completion?.Choices?.FirstOrDefault()?.Message?.Content?.Trim();
+                return string.IsNullOrWhiteSpace(text)
+                    ? new AiCallResult(AiCallStatus.UpstreamError, null,
+                        "KI-Antwort enthielt keinen Text.")
+                    : new AiCallResult(AiCallStatus.Ok, text);
+            }
+            catch (Exception ex) when (ex is HttpRequestException or TaskCanceledException or JsonException)
+            {
+                return new AiCallResult(AiCallStatus.UpstreamError, null,
+                    $"KI-Anbieter nicht erreichbar: {ex.Message}");
+            }
+        }
+
+        /// <summary>{BaseUrl}/chat/completions — tolerant of a trailing slash on BaseUrl.</summary>
+        internal static Uri BuildCompletionsUri(string baseUrl) =>
+            new($"{baseUrl.TrimEnd('/')}/chat/completions");
+
+        // ── OpenAI-compatible wire records (request + the slice of the response we read) ──
+        internal sealed record ChatRequest(string Model, List<ChatMessage> Messages, double? Temperature);
+
+        internal sealed record ChatMessage(string Role, string Content);
+
+        internal sealed record ChatResponse(List<ChatChoice>? Choices);
+
+        internal sealed record ChatChoice(ChatMessage? Message);
+    }
+}