using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using gaemstone.Utility;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

[Entity]
public struct Game {  }

[Component]
public unsafe partial class Universe
{
	// Roles
	public static ecs_id_t ECS_PAIR     { get; } = pinvoke_ECS_PAIR();
	public static ecs_id_t ECS_OVERRIDE { get; } = pinvoke_ECS_OVERRIDE();

	// Relationships
	public static ecs_entity_t EcsIsA       { get; } = pinvoke_EcsIsA();
	public static ecs_entity_t EcsDependsOn { get; } = pinvoke_EcsDependsOn();
	public static ecs_entity_t EcsChildOf   { get; } = pinvoke_EcsChildOf();
	public static ecs_entity_t EcsSlotOf    { get; } = pinvoke_EcsSlotOf();

	// Entity Tags
	public static ecs_entity_t EcsPrefab { get; } = pinvoke_EcsPrefab();


	private readonly Dictionary<Type, ecs_entity_t> _byType = new();

	public ecs_world_t* Handle { get; }

	public UniverseSystems Systems { get; }
	public UniverseModules Modules { get; }

	public Universe(string[]? args = null)
	{
		[UnmanagedCallersOnly]
		static void Abort() => throw new FlecsAbortException();

		ecs_os_set_api_defaults();
		var api = ecs_os_get_api();
		api.abort_ = new FnPtr_Void { Pointer = &Abort };
		ecs_os_set_api(&api);

		if (args?.Length > 0) {
			var argv = Runtime.CStrings.CStringArray(args);
			Handle = ecs_init_w_args(args.Length, argv);
			Runtime.CStrings.FreeCStrings(argv, args.Length);
		} else {
			Handle = ecs_init();
		}

		Systems = new(this);
		Modules = new(this);

		RegisterAll(typeof(Universe).Assembly);
	}

	public bool Progress(TimeSpan delta)
	{
		if (Modules._deferred.Count > 0) throw new Exception(
			"Modules with unmet dependencies:    \n" +
				string.Join("    \n", Modules._deferred.Values.Select(
					m => m.Type + " is missing " + string.Join(", ", m.UnmetDependencies))));
		return ecs_progress(this, (float)delta.TotalSeconds);
	}


	public Entity Lookup<T>()
		=> Lookup(typeof(T));
	public Entity Lookup(Type type)
		=> _byType.TryGetValue(type, out var e) ? new(this, e) : default;

	public Entity Lookup(string path)
		=> new(this, !path.Contains('.') ? ecs_lookup(this, path)
			: ecs_lookup_path_w_sep(this, default, path, ".", default, true));
	public Entity Lookup(ecs_entity_t value)
		=> new(this, ecs_get_alive(this, value));


	public void RegisterAll(Assembly? from = null)
	{
		from ??= Assembly.GetEntryAssembly()!;
		foreach (var type in from.GetTypes()) {
			var isPartOfModule = type.DeclaringType?.Has<ModuleAttribute>() == true;
			if (type.Has<RelationAttribute>()) {
				if (!isPartOfModule) RegisterRelation(type);
			} else if (type.Has<ComponentAttribute>()) {
				if (!isPartOfModule) RegisterComponent(type);
			} else if (type.Has<TagAttribute>()) {
				if (!isPartOfModule) RegisterTag(type);
			} else if (type.Has<EntityAttribute>()) {
				if (!isPartOfModule) RegisterEntity(type);
			} else if (type.Has<ModuleAttribute>())
				RegisterModule(type);
		}
	}

	public Entity RegisterRelation<T>()
		=> RegisterRelation(typeof(T));
	public Entity RegisterRelation(Type type)
		=> throw new NotImplementedException();

	public Entity RegisterComponent<T>()
		=> RegisterComponent(typeof(T));
	public Entity RegisterComponent(Type type)
	{
		var typeInfo = default(ecs_type_info_t);
		if (type.IsValueType) {
			var wrapper = TypeWrapper.For(type);
			if (!wrapper.IsUnmanaged) throw new Exception(
				"Component struct must satisfy the unmanaged constraint. " +
				"(Must not contain any reference types or structs that contain references.)");
			var structLayout = type.StructLayoutAttribute;
			if (structLayout == null || structLayout.Value == LayoutKind.Auto) throw new Exception(
				"Component struct must have a StructLayout attribute with LayoutKind sequential or explicit. " +
				"This is to ensure that the struct fields are not reorganized by the C# compiler.");
			typeInfo.size      = wrapper.Size;
			typeInfo.alignment = structLayout.Pack;
		} else {
			typeInfo.size      = sizeof(nint);
			typeInfo.alignment = sizeof(nint);
		}

		var name = type.GetFriendlyName();
		var entityDesc    = new ecs_entity_desc_t { name = name, symbol = name };
		var componentDesc = new ecs_component_desc_t { entity = Create(entityDesc), type = typeInfo };

		var id = ecs_component_init(Handle, &componentDesc);
		_byType[type] = id;
		// TODO: SetHooks(hooks, id);
		var entity = new Entity(this, id);

		if (type.Has<EntityAttribute>()) {
			if (type.IsValueType) entity.Add(entity);
			else entity.Set(type, Activator.CreateInstance(type)!);
		}

		return entity;
	}

	public Entity RegisterTag<T>()
		where T : unmanaged
		=> RegisterTag(typeof(T));
	public Entity RegisterTag(Type type)
	{
		if (!type.IsValueType || type.IsPrimitive || type.GetFields().Length > 0)
			throw new Exception("Tag must be an empty, used-defined struct.");
		var entity = Create(type.GetFriendlyName());
		_byType.Add(type, entity);
		return entity;
	}

	public Entity RegisterEntity<T>()
		where T : unmanaged
		=> RegisterEntity(typeof(T));
	public Entity RegisterEntity(Type type)
	{
		if (!type.IsValueType || type.IsPrimitive || type.GetFields().Length > 0)
			throw new Exception("Entity must be an empty, used-defined struct.");
		var entity = Create(type.GetFriendlyName());
		_byType.Add(type, entity);
		return entity;
	}


	public Entity Create()
		=> Create(new ecs_entity_desc_t());
	public Entity Create(string name)
		=> Create(new ecs_entity_desc_t { name = name });
	public Entity Create(ecs_entity_desc_t desc)
	{
		var entity = ecs_entity_init(Handle, &desc);
		Debug.Assert(entity.Data != 0, "ECS_INVALID_PARAMETER");
		return new(this, entity);
	}


	public static implicit operator ecs_world_t*(Universe w) => w.Handle;
}