package list

import (
	"fmt"
	"strings"
)


type IList interface {
	Conj(data any) IList
	First() any
	Rest() IList
	String() string
	IsEmpty() bool
}

type EmptyList struct{}

type List struct {
	Value any
	next  IList
}

func Empty() IList {
	return new(EmptyList)
}

var emptyList = Empty()

func New(val any) *List {
	this := new(List)
	this.Value = val
	this.next = emptyList
	return this
}

func (this *List) Conj(val any) IList {
	new_head := New(val)
	new_head.next = this
	return new_head

}

func (this *EmptyList) Conj(val any) IList {
	return Conj(nil, val)
}

func Conj(this IList, val any) IList {
	if this == nil {
		return New(val)
	} else {
		return this.Conj(val)
	}
}

func Rest(this IList) IList {
	if this == nil {
		return emptyList
	}
	return this.Rest()
}

func (this *List) Rest() IList {
	if this == nil {
		return emptyList
	}
	return this.next
}

func (this *EmptyList) Rest() IList {
	return emptyList
}

func First(this *List) any {
	if this == nil {
		return nil
	}
	return this.Value
}

func (this *List) First() any {
	return First(this)
}

func (this *EmptyList) First() any {
	return nil
}

func IsEmpty(this IList) bool {
	return this == nil || this.IsEmpty()
}

func (this *List) IsEmpty() bool {
	return false
}

func (this *EmptyList) IsEmpty() bool {
	return true
}

func String(this *List) string {
	if IsEmpty(this) {
		return "()"
	}

	var sb strings.Builder
	sb.WriteRune('(')
	// Iterate and print elements
	var e IList
	for e = this; !IsEmpty(e); e = Rest(e) {
		sb.WriteString(fmt.Sprint(e.First()))
		sb.WriteRune(' ')
	}
	return sb.String()[:sb.Len()-1] + ")"
}

func (this *List) String() string {
	return String(this)
}

func (this *EmptyList) String() string {
	return "()"
}