chore: clean up admin panel

CannedNet.Admin/Services/AdminConfigService.cs

@@ -0,0 +1,46 @@
+using System.Text.Json;
+
+namespace CannedNet.Admin.Services;
+
+public class AdminConfigService
+{
+    private const string ConfigFile = "admin_config.json";
+    private static readonly JsonSerializerOptions Indented = new() { WriteIndented = true };
+
+    public AdminConfigData Config { get; private set; }
+
+    public string ServerBaseUrl => Config.ServerBaseUrl;
+    public string ImagesBaseUrl => Config.ServerBaseUrl.TrimEnd('/') + "/img";
+
+    public AdminConfigService()
+    {
+        Config = Load();
+    }
+
+    public bool IsConfigured =>
+        !string.IsNullOrWhiteSpace(Config.ServerBaseUrl);
+
+    private static AdminConfigData Load()
+    {
+        if (!File.Exists(ConfigFile))
+        {
+            var empty = new AdminConfigData();
+            File.WriteAllText(ConfigFile, JsonSerializer.Serialize(empty, Indented));
+            return empty;
+        }
+
+        var json = File.ReadAllText(ConfigFile);
+        return JsonSerializer.Deserialize<AdminConfigData>(json) ?? new AdminConfigData();
+    }
+
+    public void Save(AdminConfigData updated)
+    {
+        Config = updated;
+        File.WriteAllText(ConfigFile, JsonSerializer.Serialize(Config, Indented));
+    }
+
+    public class AdminConfigData
+    {
+        public string ServerBaseUrl { get; set; } = "";
+    }
+}