package iterator

import "fmt"

type Iterator[T any] struct {
	data []T
	index int
}

func New[T any](items []T) Iterator[T] {
	return Iterator[T]{ data: items, index: 0 }
}

func (i Iterator[T]) Index() int {
	return i.index
}

func (i Iterator[T]) IsDone() bool {
	return i.index == len(i.data)
}

func (i Iterator[T]) Peek() (T, error) {
	var null T

	if i.IsDone() {
		return null, fmt.Errorf("Iterator is exhausted.")
	}

	return i.data[i.index], nil
}

func (i *Iterator[T]) Next() (T, error) {
	if val, err := i.Peek(); err != nil {
		return val, err
	} else {
		i.index++
		return val, nil
	}
}