gaemstone/src/gaemstone/Universe+Modules.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using gaemstone.ECS;
using gaemstone.Utility;
using static gaemstone.Flecs.Core;
using Module = gaemstone.Flecs.Core.Module;

namespace gaemstone;

public class ModuleManager
{
	private readonly Dictionary<Entity, ModuleInfo> _modules = new();

	public Universe Universe { get; }
	public ModuleManager(Universe universe)
		=> Universe = universe;

	internal ModuleInfo? Lookup(Entity entity)
		=> _modules.GetValueOrDefault(entity);

	public EntityRef Register<T>()
		where T : class, IModule, new()
	{
		var moduleType = typeof(T);
		if (moduleType.IsGenericType) throw new Exception(
			$"Module {moduleType} must be a non-generic class");

		var module = new ModuleInfo<T>(Universe);
		_modules.Add(module.Entity, module);
		TryEnableModule(module);
		return module.Entity;
	}

	private void TryEnableModule(ModuleInfo module)
	{
		if (module.UnmetDependencies.Count > 0) return;

		Console.WriteLine($"Enabling module {module.Entity.GetFullPath()} ...");
		module.Enable();

		// Find other modules that might be missing this module as a dependency.
		foreach (var other in _modules.Values) {
			if (other.IsActive) continue;
			if (!other.UnmetDependencies.Contains(module.Entity)) continue;

			// Move the just enabled module from unmet to met depedencies.
			other.UnmetDependencies.Remove(module.Entity);
			other.MetDependencies.Add(module);

			TryEnableModule(other);
		}
	}

	internal abstract class ModuleInfo
	{
		public abstract EntityRef Entity { get; }
		public abstract bool IsActive { get; }

		public HashSet<ModuleInfo> MetDependencies { get; } = new();
		public HashSet<Entity> UnmetDependencies { get; } = new();

		public abstract void Enable();
	}

	internal class ModuleInfo<T> : ModuleInfo
		where T : IModule, new()
	{
		public override EntityRef Entity { get; }
		public override bool IsActive => (Instance != null);
		public T? Instance { get; internal set; }

		public ModuleInfo(Universe universe)
		{
			var builder = universe.New(T.ModulePath).Add<Module>();

			foreach (var dependsPath in T.Dependencies) {
				var dependency = universe.LookupByPath(dependsPath) ??
					universe.New(dependsPath).Add<Module>().Disable().Build();

				var depModule = universe.Modules.Lookup(dependency);
				if (depModule?.IsActive == true) MetDependencies.Add(depModule);
				else { UnmetDependencies.Add(dependency); builder.Disable(); }

				builder.Add<DependsOn>(dependency);
			}

			Entity = builder.Build().CreateLookup<T>();

			// Ensure all parent entities have Module set.
			for (var p = Entity.Parent; p != null; p = p.Parent)
				p.Add<Module>();
		}

		public override void Enable()
		{
			Entity.Enable();
			Instance = new T();
			(Instance as IModuleAutoRegisterComponents)?.RegisterComponents(Entity);
			(Instance as IModuleInitializer)?.Initialize(Entity);
			RegisterMethods(Instance);
		}

		private void RegisterMethods(object? instance)
		{
			var world = Entity.World;
			foreach (var method in typeof(T).GetMethods(
				BindingFlags.Public | BindingFlags.NonPublic |
				BindingFlags.Static | BindingFlags.Instance
			)) {
				if (method.Has<SystemAttribute>())
					world.InitSystem(instance, method).ChildOf(Entity);
				if (method.Has<ObserverAttribute>())
					world.InitObserver(instance, method).ChildOf(Entity);
			}
		}
	}
}