SF-74: Client — CustomImagesService (in-memory cache, GET /api/CustomImages), DI registration

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/CustomImagesService.cs

@@ -0,0 +1,55 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+
+namespace EnvelopeGenerator.Server.Client.Services;
+
+/// <summary>
+/// Fetches and caches the CustomImages configuration (signFLOW + company logos)
+/// from GET /api/CustomImages.
+///
+/// Config changes rarely (deployment-time only), so results are cached in-memory
+/// for the lifetime of the service (WASM app session). No TTL needed.
+/// </summary>
+public class CustomImagesService(IHttpClientFactory clientFactory)
+{
+    private static readonly JsonSerializerOptions _json = new(JsonSerializerDefaults.Web);
+    private const string Endpoint = "/api/CustomImages";
+
+    private CustomImagesDto? _cached;
+
+    /// <summary>
+    /// Returns logo configuration. Fetches once from server; all subsequent calls
+    /// are served from memory with zero network overhead.
+    /// Returns defaults (empty Src) on auth failure (401) — components must handle gracefully.
+    /// </summary>
+    public async Task<CustomImagesDto> GetAsync(CancellationToken ct = default)
+    {
+        if (_cached is not null)
+            return _cached;
+
+        try
+        {
+            var client = clientFactory.CreateClient("EnvelopeGenerator.Server");
+            var response = await client.GetAsync(Endpoint, ct);
+
+            if (!response.IsSuccessStatusCode)
+            {
+                // Not authenticated yet (login page) — return defaults silently.
+                _cached = new CustomImagesDto();
+                return _cached;
+            }
+
+            _cached = await response.Content.ReadFromJsonAsync<CustomImagesDto>(_json, ct)
+                      ?? new CustomImagesDto();
+            return _cached;
+        }
+        catch (Exception)
+        {
+            // Network error or server unavailable — return defaults so UI still renders.
+            return new CustomImagesDto();
+        }
+    }
+
+    /// <summary>Call after logout to force re-fetch on next login.</summary>
+    public void Invalidate() => _cached = null;
+}