[C#] アプリケーションの設定をJSON形式で保存する - JsonSerializer

public sealed class AppSettingsStore
{
    public sealed class SettingsDto
    {
        public string Theme { get; set; } = "Light";
        public int FontSize { get; set; } = 12;
        public bool EnableNotifications { get; set; } = true;
    }

    private readonly string _settingsPath;

    public AppSettingsStore(string appName)
    {
        var root = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
        var dir = Path.Combine(root, appName);
        Directory.CreateDirectory(dir);
        _settingsPath = Path.Combine(dir, "settings.json");
    }

    public SettingsDto Load()
    {
        if (!File.Exists(_settingsPath))
        {
            return new SettingsDto(); // デフォルト値
        }
        var json = File.ReadAllText(_settingsPath);
        return JsonSerializer.Deserialize<SettingsDto>(json) ?? new SettingsDto();
    }

    public void Save(SettingsDto settings)
    {
        var json = JsonSerializer.Serialize(settings,
            new JsonSerializerOptions { WriteIndented = true });
        File.WriteAllText(_settingsPath, json);
    }
}

var appSettingsStore = new AppSettingsStore("SampleJson");

// 1. 初回読み込み（ファイルがない場合はデフォルト値）
Console.WriteLine("\n[1. 初回読み込み]");
var currentSettings = appSettingsStore.Load();
Console.WriteLine($"Theme: {currentSettings.Theme}");
Console.WriteLine($"FontSize: {currentSettings.FontSize}");
Console.WriteLine($"EnableNotifications: {currentSettings.EnableNotifications}");

// 2. 設定を変更
Console.WriteLine("\n[2. 設定を変更]");
currentSettings.Theme = "Dark";
currentSettings.FontSize = 16;
currentSettings.EnableNotifications = false;
Console.WriteLine($"変更後 - Theme: {currentSettings.Theme}, 
    FontSize: {currentSettings.FontSize},
    EnableNotifications: {currentSettings.EnableNotifications}"
);

// 3. 保存
Console.WriteLine("\n[3. 保存]");
appSettingsStore.Save(currentSettings);
Console.WriteLine("設定を保存しました。");

// 4. 再読み込みして確認
Console.WriteLine("\n[4. 再読み込みして確認]");
var reloadedSettings = appSettingsStore.Load();
Console.WriteLine($"Theme: {reloadedSettings.Theme}");
Console.WriteLine($"FontSize: {reloadedSettings.FontSize}");
Console.WriteLine($"EnableNotifications: {reloadedSettings.EnableNotifications}");
Console.WriteLine($"保存先: {Path.Combine(
    Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
    "SampleJson", "settings.json"
)}");