feat: add TrustedSenderService to scan Sent folder for trusted contacts

src/SpamGuard/Services/TrustedSenderService.cs

@@ -0,0 +1,97 @@
+// src/SpamGuard/Services/TrustedSenderService.cs
+namespace SpamGuard.Services;
+
+using MailKit;
+using MailKit.Search;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using MimeKit;
+using SpamGuard.Configuration;
+using SpamGuard.State;
+
+public sealed class TrustedSenderService : BackgroundService
+{
+    private readonly ImapClientFactory _imapFactory;
+    private readonly TrustedSenderStore _store;
+    private readonly SpamGuardOptions _options;
+    private readonly ILogger<TrustedSenderService> _logger;
+
+    public TrustedSenderService(
+        ImapClientFactory imapFactory,
+        TrustedSenderStore store,
+        IOptions<SpamGuardOptions> options,
+        ILogger<TrustedSenderService> logger)
+    {
+        _imapFactory = imapFactory;
+        _store = store;
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("TrustedSenderService started");
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await ScanSentFolderAsync(stoppingToken);
+                _store.Save();
+                _logger.LogInformation("Trusted sender scan complete. {Count} trusted senders", _store.Count);
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Error scanning sent folder");
+            }
+
+            await Task.Delay(TimeSpan.FromMinutes(_options.Monitoring.TrustedSenderRefreshMinutes), stoppingToken);
+        }
+    }
+
+    private async Task ScanSentFolderAsync(CancellationToken ct)
+    {
+        using var client = await _imapFactory.CreateConnectedClientAsync(ct);
+
+        var sentFolder = client.GetFolder(MailKit.SpecialFolder.Sent)
+                         ?? throw new InvalidOperationException("Could not find Sent folder");
+
+        await sentFolder.OpenAsync(FolderAccess.ReadOnly, ct);
+
+        var uids = await sentFolder.SearchAsync(SearchQuery.All, ct);
+        _logger.LogDebug("Found {Count} messages in Sent folder", uids.Count);
+
+        var addresses = new List<string>();
+        foreach (var uid in uids)
+        {
+            var headers = await sentFolder.GetHeadersAsync(uid, ct);
+            ExtractAddresses(headers, addresses);
+        }
+
+        _store.AddRange(addresses);
+        await client.DisconnectAsync(true, ct);
+    }
+
+    private static void ExtractAddresses(HeaderList headers, List<string> addresses)
+    {
+        foreach (var headerName in new[] { "To", "Cc" })
+        {
+            var value = headers[headerName];
+            if (string.IsNullOrEmpty(value)) continue;
+
+            if (InternetAddressList.TryParse(value, out var list))
+            {
+                foreach (var address in list.Mailboxes)
+                {
+                    if (!string.IsNullOrEmpty(address.Address))
+                        addresses.Add(address.Address);
+                }
+            }
+        }
+    }
+}