/*
Package "iterator"
*/
package iterator

import "fmt"

// An iterator over slices.
type Iterator[T any] struct {
	items []T
	index int
}

// Create a new iterator, over a set of items.
func Of[T any](items []T) *Iterator[T] {
	return &Iterator[T]{items: items, index: 0}
}

// Returns the current position of the iterator.
func (i Iterator[T]) Index() int {
	return i.index
}

func (i Iterator[T]) Copy() *Iterator[T] {
	return &Iterator[T]{items: i.items, index: i.index}
}

func (i *Iterator[T]) Sync(o *Iterator[T]) {
	i.index = o.index
}

// Create a new iterator, over a set of items.
func (i Iterator[T]) Get() (T, error) {
	var null T
	if i.Done() {
		return null, fmt.Errorf("iterator is exhausted")
	}

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

func (i Iterator[T]) MustGet() T {
	var null T
	if i.Done() {
		return null
	}

	return i.items[i.index]
}

func (i *Iterator[T]) Forward() {
	if !i.Done() {
		i.index++
	}
}

// Create a new iterator, over a set of items.
func (i *Iterator[T]) Next() (T, error) {
	item, err := i.Get()
	if err == nil {
		i.index++
	}

	return item, err
}

// Create a new iterator, over a set of items.
func (i *Iterator[T]) Back() {
	i.index = max(i.index-1, 0)
}

// Returns the current position of the iterator.
func (i Iterator[T]) Done() bool {
	return i.index == len(i.items)
}

func Do[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
	i2 := i.Copy()

	out, err := fn(i2)
	if err == nil {
		i.Sync(i2)
	}

	return out, err
}