using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using gaemstone.ECS.Internal;
using gaemstone.ECS.Utility;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

public unsafe class Iterator<TContext> : Iterator
	, IEnumerable<Iterator<TContext>>
{
	public new World<TContext> World => new(base.World);

	public Iterator(ecs_iter_t* handle) : base(handle) {  }
	public Iterator(ecs_iter_t value)   : base(value) {  }

	public static TermIterator<TContext> FromTerm(World world, Term term)
	{
		using var alloc = TempAllocator.Use();
		var flecsTerm = term.ToFlecs(alloc);
		var flecsIter = ecs_term_iter(world, &flecsTerm);
		return new(flecsIter);
	}

	public new Entity<TContext>? GetVar(Variable var)
		=> Entity<TContext>.GetOrNull(World, base.GetVar(var));
	public new Iterator<TContext> SetVar(Variable var, Entity entity)
		=> (Iterator<TContext>)base.SetVar(var, entity);

	public new Entity<TContext>? First()
		=> Entity<TContext>.GetOrNull(World, base.First());
	public new IEnumerable<Entity<TContext>> GetAllEntities()
		=> base.GetAllEntities().Select(e => Entity<TContext>.GetOrInvalid(World, e));

	public new Id<TContext> FieldId(int index)
		=> Id<TContext>.GetUnsafe(World, base.FieldId(index));

	public new Entity<TContext> Entity(int index)
		=> Entity<TContext>.GetOrInvalid(World, base.Entity(index));

	// IEnumerable implementation
	public virtual IEnumerator<Iterator<TContext>> GetEnumerator()
		{ while (Next()) yield return this; }
	IEnumerator IEnumerable.GetEnumerator()
		=> GetEnumerator();
}

[Flags]
public enum IteratorFlags : uint
{
	/// <summary> Does iterator contain valid result. </summary>
	IsValid        = EcsIterIsValid,
	/// <summary> Does iterator provide (component). </summary>
	NoData         = EcsIterNoData,
	/// <summary> Is iterator instanced. </summary>
	IsInstanced    = EcsIterIsInstanced,
	/// <summary> Does result have shared terms. </summary>
	HasShared      = EcsIterHasShared,
	/// <summary> Result only populates table. </summary>
	TableOnly      = EcsIterTableOnly,
	/// <summary> Treat terms with entity subject as optional. </summary>
	EntityOptional = EcsIterEntityOptional,
	/// <summary> Iterator has no results. </summary>
	NoResults      = EcsIterNoResults,
	/// <summary> Only evaluate non-this terms. </summary>
	IgnoreThis     = EcsIterIgnoreThis,
	/// <summary> Does iterator have conditionally set fields. </summary>
	MatchVar       = EcsIterMatchVar,
	/// <summary>  </summary>
	HasCondSet     = EcsIterHasCondSet,
	/// <summary> Profile iterator performance. </summary>
	Profile        = EcsIterProfile,
}

public class Variable
{
	public int Index { get; }
	public string Name { get; }
	public Variable(int index, string name)
		{ Index = index; Name = name; }
}

public unsafe class TermIterator<TContext>
	: Iterator<TContext>
{
	internal TermIterator(ecs_iter_t value)
		: base(value) {  }
	public override bool Next()
		=> ecs_term_next(Handle);
}