package selsl

import "fmt"

type Slots map[string]Object

func (s Slots) Set(name string, inst Object) Slots {
	s[name] = inst
	return s
}

func (s Slots) Get(name string) Object {
	res, ok := s[name]
	if !ok {
		return Nil
	}
	return res
}

func (s Slots) Clone() Slots {
	clone := Slots{}
	for k, v := range s {
		clone[k] = v.Clone()
	}
	return clone
}

// Constants for special object slot names
const (
	ParentSlot = "*parent"
	SelfSlot   = "*self"
	MeSlot     = "*me"
	ArgsSlot   = "*args"
)

// Effect is the effect an object has on return from a Run
type Effect int

// Constants for effects
const (
	EffectNone   Effect = 0
	EffectBreak  Effect = 1
	EffectReturn Effect = 2
	EffectThrow  Effect = 4
)

// Object is the interface for all objects in SELSL.
type Object interface {
	Name() string
	Slots() Slots
	Run(env Object) Object
	Effect() Effect
	Clone() Object
}

var Nil Object = NewInstance("nil")

func ParentOf(val Object) Object {
	return val.Slots().Get(ParentSlot)
}

type Environment struct {
	Instance
}

func NewEnvironment(parent, me, to Object, args ...Object) *Environment {
	name := "_env"
	if parent != nil {
		name = parent.Name() + "_env"
	}
	res := &Environment{Instance{name: name, slots: Slots{}}}
	res.Set(ParentSlot, parent)
	res.Set(SelfSlot, to)
	res.Set(ArgsSlot, List(args))
	res.Set(MeSlot, me)
	return res
}

func Send(to Object, message string, me, here Object, args ...Object) Object {
	env := NewEnvironment(here, me, to, args...)
	lookup := to
	value := lookup.Slots().Get(message)
	for value == Nil {
		lookup = ParentOf(lookup)
		if lookup == Nil || lookup == nil {
			panic("Object does not support message " + message)
		}
		value = lookup.Slots().Get(message)
	}
	return value.Run(env)
}

type Instance struct {
	name  string
	slots Slots
}

func (i Instance) Name() string {
	return i.name
}

func (i Instance) Slots() Slots {
	return i.slots
}

func (i Instance) Effect() Effect {
	return EffectNone
}

func (i Instance) Run(env Object) Object {
	return i
}

func (i *Instance) Set(name string, inst Object) *Instance {
	i.slots.Set(name, inst)
	return i
}

func (i Instance) DeepCopy() Instance {
	return Instance{name: i.name + "", slots: i.slots.Clone()}
}

func (i Instance) Clone() Object {
	return i.DeepCopy()
}

func NewInstance(name string) *Instance {
	return &Instance{name: name, slots: Slots{}}
}

type Primitive func(env Object) Object

func (p Primitive) Name() string {
	return "primitive"
}

func (p Primitive) Slots() Slots {
	emptySlots := Slots{}
	return emptySlots
}

func (p Primitive) Effect() Effect {
	return EffectNone
}

func (p Primitive) Run(env Object) Object {
	return p(env)
}

func (p Primitive) Clone() Object {
	return p
}

func Self(o Object) Object {
	return o.Slots().Get(SelfSlot)
}

func Me(o Object) Object {
	return o.Slots().Get(MeSlot)
}

func Args(o Object) List {
	list := o.Slots().Get(ArgsSlot)
	if list == Nil {
		return List{}
	}
	return list.(List)
}

func Unary(unary func(target Object) Object) Primitive {
	return func(env Object) Object {
		return unary(Self(env))
	}
}

func Nullary(nullary func() Object) Primitive {
	return func(env Object) Object {
		return nullary()
	}
}

type String string

func (s String) Name() string {
	return string(s)
}

var StringType Object = NewInstance("String").
	Set(ParentSlot, RootType)

var StringSlots Slots = Slots{}.Set(ParentSlot, StringType)

func (s String) Slots() Slots {
	return StringSlots
}

func (s String) Effect() Effect {
	return EffectNone
}

func (s String) Run(env Object) Object {
	return s
}

func (s String) Clone() Object {
	return String(s + "")
}

func NameOf(o Object) Object {
	return String(o.Name())
}

func NameString(o Object) func() Object {
	return func() Object {
		return NameOf(o)
	}
}

var RootType Object = NewInstance("Type").Set("name", Unary(NameOf))

type List []Object

func (l List) Name() string {
	res := fmt.Sprintf("list: ")
	sep := ""
	for _, o := range l {
		res = fmt.Sprintf("%s %s %s", res, sep, o.Name())
		sep = "and"
	}
	res += ";"
	return res
}

var ListType Object = NewInstance("List").
	Set(ParentSlot, RootType)

var ListSlots Slots = Slots{}.Set(ParentSlot, ListType)

func (l List) Slots() Slots {
	return ListSlots
}

func (l List) Effect() Effect {
	return EffectNone
}

func (l List) Run(env Object) Object {
	return l
}

func (l List) DeepCopy() List {
	res := List{}
	for _, o := range l {
		res = append(res, o.Clone())
	}
	return res
}

func (l List) Clone() Object {
	return l.DeepCopy()
}

/*
var RootType Object = NewInstance("Type").Slot("string")
var InstanceType Type = NewType("Instance", &RootType, nil)
var ErrorType Type = NewType("Error", &InstanceType, nil)
var StringType Type = NewType("String", &InstanceType, nil)
var IntType Type = NewType("Int", &InstanceType, nil)
var ListType Type = NewType("List", &InstanceType, nil)
var MethodType Type = NewType("Method", &InstanceType, nil)


type Error struct {
	Instance
	Object error
}

func (s Error) String() string {
	return fmt.Sprintf("%s", s.Object)
}

func NewError(name string, Slots Slots, Object error) Error {
	return Error{Instance: NewInstance(name, ErrorType, Slots),
		Object: Object}
}


type Int struct {
	Instance
	Object int64
}

func NewInt(name string, Slots Slots, Object int64) Int {
	return Int{Instance: NewInstance(name, IntType, Slots),
		Object: Object}
}

func (i Int) String() string {
	return fmt.Sprintf("%d", i.Object)
}

type List struct {
	Instance
	Object []Object
}

func NewList(name string, Slots Slots, Object ...Object) List {
	return List{Instance: NewInstance(name, ListType, Slots),
		Object: Object}
}

func (l List) String() string {
	return fmt.Sprintf("[%v]", l.Object)
}

type Method struct {
	Instance
	Signature List
	Object    func(env Object, self Object, args ...Object) List
}

func NewMethod(name string, Slots Slots, signature List,
	Object func(env Object, self Object, args ...Object) List) Method {
	return Method{Instance: NewInstance(name, MethodType, Slots),
		Signature: signature, Object: Object}
}

func (m Method) String() string {
	return fmt.Sprintf("Method: %s", m.Name())
}

var _ Object = RootType
var _ Object = InstanceType
var _ Object = Error{}
var _ Object = String{}
var _ Object = Int{}
var _ Object = List{}
var _ Object = Method{}
*/