using System;
using gaemstone.Utility;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

public class Term
{
	public Identifier ID { get; set; }
	public TermID? Source { get; set; }
	public TermID? Relation { get; set; }
	public TermID? Target { get; set; }
	public TermInOutKind InOut { get; set; }
	public TermOperKind Oper { get; set; }
	public IdentifierFlags Flags { get; set; }

	public Term() {  }
	public Term(Identifier id) => ID = id;
	public Term(TermID relation, TermID target)
		{ Relation = relation; Target = target; }

	public static implicit operator Term(EntityRef entity) => new(entity);
	public static implicit operator Term(Entity    entity) => new(entity);
	public static implicit operator Term(IdentifierRef id) => new(id);
	public static implicit operator Term(Identifier    id) => new(id);

	public Term None { get { InOut = TermInOutKind.None; return this; } }
	public Term In   { get { InOut = TermInOutKind.In;   return this; } }
	public Term Out  { get { InOut = TermInOutKind.Out;  return this; } }

	public Term Or       { get { Oper = TermOperKind.Or;       return this; } }
	public Term Not      { get { Oper = TermOperKind.Not;      return this; } }
	public Term Optional { get { Oper = TermOperKind.Optional; return this; } }

	public ecs_term_t ToFlecs(IAllocator allocator) => new() {
		id       = ID,
		src      = Source?.ToFlecs(allocator) ?? default,
		first    = Relation?.ToFlecs(allocator) ?? default,
		second   = Target?.ToFlecs(allocator) ?? default,
		inout    = (ecs_inout_kind_t)InOut,
		oper     = (ecs_oper_kind_t)Oper,
		id_flags = (ecs_id_t)(ulong)Flags,
	};
}

public enum TermInOutKind
{
	Default = ecs_inout_kind_t.EcsInOutDefault,
	None    = ecs_inout_kind_t.EcsInOutNone,
	InOut   = ecs_inout_kind_t.EcsInOut,
	In      = ecs_inout_kind_t.EcsIn,
	Out     = ecs_inout_kind_t.EcsOut,
}

public enum TermOperKind
{
	And      = ecs_oper_kind_t.EcsAnd,
	Or       = ecs_oper_kind_t.EcsOr,
	Not      = ecs_oper_kind_t.EcsNot,
	Optional = ecs_oper_kind_t.EcsOptional,
	AndFrom  = ecs_oper_kind_t.EcsAndFrom,
	OrFrom   = ecs_oper_kind_t.EcsOrFrom,
	NotFrom  = ecs_oper_kind_t.EcsNotFrom,
}

public class TermID
{
	public static TermID This { get; } = new("$This");

	public Entity ID { get; }
	public string? Name { get; }
	public Entity Traverse { get; set; }
	public TermTraversalFlags Flags { get; set; }

	public TermID(Entity id)
		=> ID = id;
	public TermID(string name)
	{
		if (name[0] == '$') {
			Name  = name[1..];
			Flags = TermTraversalFlags.IsVariable;
		} else Name = name;
	}

	public static implicit operator TermID(EntityRef entity) => new(entity);
	public static implicit operator TermID(Entity    entity) => new(entity);
	public static implicit operator TermID(string name) => new(name);

	public ecs_term_id_t ToFlecs(IAllocator allocator) => new() {
		id    = ID,
		name  = allocator.AllocateCString(Name),
		trav  = Traverse,
		flags = (ecs_flags32_t)(uint)Flags
	};
}

[Flags]
public enum TermTraversalFlags : uint
{
	/// <summary> Match on self. </summary>
	Self       = EcsSelf,
	/// <summary> Match by traversing upwards. </summary>
	Up         = EcsUp,
	/// <summary> Match by traversing downwards (derived, cannot be set). </summary>
	Down       = EcsDown,
	/// <summary> Sort results breadth first. </summary>
	Cascade    = EcsCascade,
	/// <summary> Short for up(ChildOf). </summary>
	Parent     = EcsParent,
	/// <summary> Term id is a variable. </summary>
	IsVariable = EcsIsVariable,
	/// <summary> Term id is an entity. </summary>
	IsEntity   = EcsIsEntity,
	/// <summary> Prevent observer from triggering on term. </summary>
	Filter     = EcsFilter,
}