System.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Runtime.InteropServices;

namespace Foster.Framework;

/// <summary>
/// Core System Module, used for managing Windows and Input
/// </summary>
public abstract class System : AppModule
{
    /// <summary>
    /// Underlying System implementation API Name
    /// </summary>
    public string ApiName { get; protected set; } = "Unknown";

    /// <summary>
    /// Underlying System implementation API Version
    /// </summary>
    public Version ApiVersion { get; protected set; } = new Version(0, 0, 0);

    /// <summary>
    /// Whether the System can support Multiple Windows
    /// </summary>
    public abstract bool SupportsMultipleWindows { get; }

    /// <summary>
    /// A list of all opened Windows
    /// </summary>
    public readonly ReadOnlyCollection<Window> Windows;

    /// <summary>
    /// A list of active Monitors
    /// </summary>
    public readonly ReadOnlyCollection<Monitor> Monitors;

    /// <summary>
    /// System Input
    public abstract Input Input { get; }

    /// <summary>
    /// The User Directory & a safe location to store save data or preferences
    /// </summary>
    public virtual string UserDirectory(string applicationName) => DefaultUserDirectory(applicationName);

    /// <summary>
    /// Called when a Window is Created
    /// </summary>
    public Action<Window>? OnWindowCreated;

    /// <summary>
    /// Internal list of all Windows owned by the System.
    /// </summary>
    internal readonly List<Window> windows = new List<Window>();

    /// <summary>
    /// Internal list of all Monitors owned by the System. The Platform implementation should maintain this.
    /// </summary>
    protected readonly List<Monitor> monitors = new List<Monitor>();

    protected System() : base(100)
    {
        Windows = new ReadOnlyCollection<Window>(windows);
        Monitors = new ReadOnlyCollection<Monitor>(monitors);
    }

    protected internal abstract Window.Platform CreateWindow(string title, int width, int height, WindowFlags flags = WindowFlags.None);

    protected internal override void Startup()
    {
        Log.Info($"{ApiName} {ApiVersion}");
    }

    /// <summary>
    /// Gets the Default UserDirectory
    /// </summary>
    internal static string DefaultUserDirectory(string applicationName)
    {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), applicationName);
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
        {
            var result = Environment.GetEnvironmentVariable("HOME");
            if (!string.IsNullOrEmpty(result))
                return Path.Combine(result, "Library", "Application Support", applicationName);
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux) ||
                 RuntimeInformation.IsOSPlatform(OSPlatform.FreeBSD))
        {
            var result = Environment.GetEnvironmentVariable("XDG_DATA_HOME");
            if (!string.IsNullOrEmpty(result))
            {
                return Path.Combine(result, applicationName);
            }
            else
            {
                result = Environment.GetEnvironmentVariable("HOME");
                if (!string.IsNullOrEmpty(result))
                    return Path.Combine(result, ".local", "share", applicationName);
            }
        }

        return AppDomain.CurrentDomain.BaseDirectory!;
    }
}