feat(ai): IEmbeddingProvider foundation (#18)

src/InboxIntel.Infrastructure/Ai/AiProviders.cs

@@ -2,6 +2,7 @@ using InboxIntel.Application.Abstractions;
 using InboxIntel.Domain.Enums;
 using InboxIntel.Infrastructure.Configuration;
 using Microsoft.Extensions.Options;
+using System.Linq;
 using System.Net.Http.Json;
 using System.Text.Json;
 
@@ -15,6 +16,53 @@ public class NullAiProvider : IAiProvider
         => Task.FromResult(string.Empty);
 }
 
+/// <summary>No-op embeddings used when AI is disabled. Returns empty vectors so callers fall
+/// back to lexical search.</summary>
+public class NullEmbeddingProvider : IEmbeddingProvider
+{
+    public bool IsAvailable => false;
+    public Task<float[]> EmbedAsync(string text, CancellationToken ct = default)
+        => Task.FromResult(Array.Empty<float>());
+    public Task<IReadOnlyList<float[]>> EmbedBatchAsync(IReadOnlyList<string> texts, CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<float[]>>(Array.Empty<float[]>());
+}
+
+/// <summary>Local embeddings via Ollama's /api/embeddings endpoint (e.g. nomic-embed-text).</summary>
+public class OllamaEmbeddingProvider : IEmbeddingProvider
+{
+    private readonly HttpClient _http;
+    private readonly AiOptions _options;
+
+    public OllamaEmbeddingProvider(IHttpClientFactory factory, IOptions<AiOptions> options)
+    {
+        _options = options.Value;
+        _http = factory.CreateClient("ollama");
+        _http.BaseAddress = new Uri(_options.OllamaBaseUrl);
+    }
+
+    public bool IsAvailable => true;
+
+    public async Task<float[]> EmbedAsync(string text, CancellationToken ct = default)
+    {
+        var payload = new { model = _options.EmbeddingModel, prompt = text };
+        var resp = await _http.PostAsJsonAsync("/api/embeddings", payload, ct);
+        resp.EnsureSuccessStatusCode();
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync(ct));
+        return doc.RootElement.GetProperty("embedding").EnumerateArray()
+            .Select(e => e.GetSingle()).ToArray();
+    }
+
+    // Ollama's /api/embeddings takes one prompt per call, so batch is a sequential loop.
+    // Kept behind the interface so a future batch endpoint is a drop-in swap.
+    public async Task<IReadOnlyList<float[]>> EmbedBatchAsync(IReadOnlyList<string> texts, CancellationToken ct = default)
+    {
+        var results = new List<float[]>(texts.Count);
+        foreach (var t in texts)
+            results.Add(await EmbedAsync(t, ct));
+        return results;
+    }
+}
+
 /// <summary>Local LLM via Ollama's /api/chat endpoint.</summary>
 public class OllamaProvider : IAiProvider
 {