typedef struct Scope Scope;
typedef struct Checker Checker;
typedef struct Type Type;
typedef enum BuiltinProcId BuiltinProcId;
typedef enum ImplicitValueId ImplicitValueId;

#define ENTITY_KINDS \
	ENTITY_KIND(Invalid) \
	ENTITY_KIND(Constant) \
	ENTITY_KIND(Variable) \
	ENTITY_KIND(TypeName) \
	ENTITY_KIND(Procedure) \
	ENTITY_KIND(Builtin) \
	ENTITY_KIND(ImportName) \
	ENTITY_KIND(Nil) \
	ENTITY_KIND(ImplicitValue) \
	ENTITY_KIND(Count)

typedef enum EntityKind {
#define ENTITY_KIND(k) GB_JOIN2(Entity_, k),
	ENTITY_KINDS
#undef ENTITY_KIND
} EntityKind;

String const entity_strings[] = {
#define ENTITY_KIND(k) {cast(u8 *)#k, gb_size_of(#k)-1},
	ENTITY_KINDS
#undef ENTITY_KIND
};

typedef enum EntityFlag {
	EntityFlag_Visited    = 1<<0,
	EntityFlag_Used       = 1<<1,
	EntityFlag_Anonymous  = 1<<2,
	EntityFlag_Field      = 1<<3,
	EntityFlag_Param      = 1<<4,
	EntityFlag_VectorElem = 1<<5,
} EntityFlag;

typedef enum OverloadKind {
	Overload_No      = -1,
	Overload_Unknown = 0,
	Overload_Yes     = +1,
} OverloadKind;

typedef struct Entity Entity;
struct Entity {
	EntityKind kind;
	u32        flags;
	Token      token;
	Scope *    scope;
	Type *     type;
	AstNode *  identifier; // Can be NULL

	// TODO(bill): Cleanup how `using` works for entities
	Entity *   using_parent;
	AstNode *  using_expr;

	union {
		struct {
			ExactValue value;
		} Constant;
		struct {
			i32  field_index;
			i32  field_src_index;
			bool is_immutable;
		} Variable;
		i32 TypeName;
		struct {
			bool         is_foreign;
			String       foreign_name;
			String       link_name;
			u64          tags;
			OverloadKind overload_kind;
		} Procedure;
		struct {
			BuiltinProcId id;
		} Builtin;
		struct {
			String path;
			String name;
			Scope *scope;
			bool   used;
		} ImportName;
		i32 Nil;
		struct {
			// TODO(bill): Should this be a user-level construct rather than compiler-level?
			ImplicitValueId id;
			Entity *        backing;
		} ImplicitValue;
	};
};


Entity *alloc_entity(gbAllocator a, EntityKind kind, Scope *scope, Token token, Type *type) {
	Entity *entity = gb_alloc_item(a, Entity);
	entity->kind   = kind;
	entity->scope  = scope;
	entity->token  = token;
	entity->type   = type;
	return entity;
}

Entity *make_entity_variable(gbAllocator a, Scope *scope, Token token, Type *type) {
	Entity *entity = alloc_entity(a, Entity_Variable, scope, token, type);
	return entity;
}

Entity *make_entity_using_variable(gbAllocator a, Entity *parent, Token token, Type *type) {
	GB_ASSERT(parent != NULL);
	Entity *entity = alloc_entity(a, Entity_Variable, parent->scope, token, type);
	entity->using_parent = parent;
	entity->flags |= EntityFlag_Anonymous;
	return entity;
}


Entity *make_entity_constant(gbAllocator a, Scope *scope, Token token, Type *type, ExactValue value) {
	Entity *entity = alloc_entity(a, Entity_Constant, scope, token, type);
	entity->Constant.value = value;
	return entity;
}

Entity *make_entity_type_name(gbAllocator a, Scope *scope, Token token, Type *type) {
	Entity *entity = alloc_entity(a, Entity_TypeName, scope, token, type);
	return entity;
}

Entity *make_entity_param(gbAllocator a, Scope *scope, Token token, Type *type, bool anonymous) {
	Entity *entity = make_entity_variable(a, scope, token, type);
	entity->flags |= EntityFlag_Used;
	entity->flags |= EntityFlag_Anonymous*(anonymous != 0);
	entity->flags |= EntityFlag_Param;
	return entity;
}

Entity *make_entity_field(gbAllocator a, Scope *scope, Token token, Type *type, bool anonymous, i32 field_src_index) {
	Entity *entity = make_entity_variable(a, scope, token, type);
	entity->Variable.field_src_index = field_src_index;
	entity->Variable.field_index = field_src_index;
	entity->flags |= EntityFlag_Field;
	entity->flags |= EntityFlag_Anonymous*(anonymous != 0);
	return entity;
}

Entity *make_entity_vector_elem(gbAllocator a, Scope *scope, Token token, Type *type, i32 field_src_index) {
	Entity *entity = make_entity_variable(a, scope, token, type);
	entity->Variable.field_src_index = field_src_index;
	entity->Variable.field_index = field_src_index;
	entity->flags |= EntityFlag_Field;
	entity->flags |= EntityFlag_VectorElem;
	return entity;
}

Entity *make_entity_procedure(gbAllocator a, Scope *scope, Token token, Type *signature_type, u64 tags) {
	Entity *entity = alloc_entity(a, Entity_Procedure, scope, token, signature_type);
	entity->Procedure.tags = tags;
	return entity;
}

Entity *make_entity_builtin(gbAllocator a, Scope *scope, Token token, Type *type, BuiltinProcId id) {
	Entity *entity = alloc_entity(a, Entity_Builtin, scope, token, type);
	entity->Builtin.id = id;
	return entity;
}

Entity *make_entity_import_name(gbAllocator a, Scope *scope, Token token, Type *type,
                                String path, String name, Scope *import_scope) {
	Entity *entity = alloc_entity(a, Entity_ImportName, scope, token, type);
	entity->ImportName.path = path;
	entity->ImportName.name = name;
	entity->ImportName.scope = import_scope;
	return entity;
}

Entity *make_entity_nil(gbAllocator a, String name, Type *type) {
	Token token = make_token_ident(name);
	Entity *entity = alloc_entity(a, Entity_Nil, NULL, token, type);
	return entity;
}

Entity *make_entity_implicit_value(gbAllocator a, String name, Type *type, ImplicitValueId id) {
	Token token = make_token_ident(name);
	Entity *entity = alloc_entity(a, Entity_ImplicitValue, NULL, token, type);
	entity->ImplicitValue.id = id;
	return entity;
}


Entity *make_entity_dummy_variable(gbAllocator a, Scope *scope, Token token) {
	token.string = str_lit("_");
	return make_entity_variable(a, scope, token, NULL);
}