add storage functionality and appdata model

MetaforceInstaller.Core/Services/StorageService.cs

@@ -0,0 +1,36 @@
+using System.Text.Json;
+using MetaforceInstaller.Core.Intefaces;
+using MetaforceInstaller.Core.Models;
+
+namespace MetaforceInstaller.Core.Services;
+
+public class StorageService : IStorageService
+{
+    private readonly string _storagePath;
+
+    public StorageService()
+    {
+        var appData = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
+        var appDirectory = Path.Combine(appData, "MetaforceInstaller");
+        Directory.CreateDirectory(appDirectory);
+        _storagePath = Path.Combine(appDirectory, "installations.json");
+    }
+
+    public AppData Load()
+    {
+        if (!File.Exists(_storagePath))
+            return new AppData();
+
+        var json = File.ReadAllText(_storagePath);
+        return JsonSerializer.Deserialize<AppData>(json) ?? new AppData();
+    }
+
+    public void Save(AppData data)
+    {
+        var json = JsonSerializer.Serialize(data, new JsonSerializerOptions
+        {
+            WriteIndented = true
+        });
+        File.WriteAllText(_storagePath, json);
+    }
+}