Architecture

Architecture Overview

MVVM

• Models: plain data classes (mods, profiles, settings)
• ViewModels: expose observable state and commands. Use CommunityToolkit.Mvvm source generators ([ObservableProperty], [RelayCommand])
• Views: Avalonia XAML with data bindings

Dependency Injection

All services are singletons registered in App.axaml.cs via Microsoft.Extensions.DependencyInjection. The container is exposed as App.Services for cases like XAML markup extensions.

Service Layer

Every service has an I*Service interface.

Service	Responsibility
ISettingsService	Load/save settings.json
IGameDetectionService	Find game path, detect running game
IModDiscoveryService	Scan mod folders, watch for changes
IModInstallService	Activate, deactivate, install, uninstall, update, rollback
IVersionCacheService	Archive versions, manage cache size
IProfileService	Profile CRUD, import/export, diff computation
IGitHubModsService	Query GitHub Releases API
INexusModsService	Query Nexus Mods GraphQL API
IUpdateService	Orchestrate update checks (GitHub then Nexus)
ILocalizationService	CSV-based i18n with live switching
IDialogService	File pickers, confirmation dialogs

Key Data Flows

Mod Discovery

GameDetectionService finds game path
  -> ModDiscoveryService scans Mods/ and Mods.inactive/
  -> Reads Info.json for each folder (via InfoJsonLocator)
  -> MainWindowViewModel creates ModItemViewModels
  -> UI binds to AvailableMods / ActiveMods

Mod Activation

User clicks Activate -> MainWindowViewModel.ActivateModCommand
  -> ModInstallService.ActivateAsync (moves folder)
  -> ModDiscoveryService detects change via FileSystemWatcher (500ms debounce)
  -> MainWindowViewModel refreshes mod lists
  -> AutoActivateDependenciesAsync runs BFS on Requirements

Profile Application

User selects profile -> MainWindowViewModel.ApplyProfileCommand
  -> ProfileService.ComputeDiff (current mods vs profile)
  -> Executes: activate, deactivate, rollback, download
  -> SettingsService updates ActiveProfileName

Cross-Platform

Concern	Windows	Linux
Game detection	Registry + Steam VDF	~/.steam/steam + ~/.local/share/Steam
Open URL/folder	Process.Start with UseShellExecute	xdg-open
Info.json case	Exact match	Case-insensitive fallback
App data	%APPDATA%	$XDG_CONFIG_HOME or ~/.config
Drag-and-drop	STA thread	Works natively

External Integrations

Integration	Library	Purpose
GitHub API	Octokit 14.0.0	Query releases, download assets
Nexus Mods	HttpClient + GraphQL	Query mod versions
Steam	Registry + VDF parsing	Game detection
Steam launch	steam://launch/588030/dialog	Start game button

Logging

FileLoggerProvider writes rolling daily log files via a BlockingCollection<string> queue and a dedicated background writer thread. Format: [HH:mm:ss.fff] [LVL] [Category] Message.

See Also

• Development Setup
• Contributing Guidelines