package wfa

type PositiveSlice[T any] struct {
	data         []T
	valid        []bool
	defaultValue T
}

func (a *PositiveSlice[T]) TranslateIndex(idx int) int {
	return idx
}

func (a *PositiveSlice[T]) Valid(idx int) bool {
	actualIdx := a.TranslateIndex(idx)
	return 0 <= actualIdx && actualIdx < len(a.valid) && a.valid[actualIdx]
}

func (a *PositiveSlice[T]) Get(idx int) T {
	actualIdx := a.TranslateIndex(idx)
	if 0 <= actualIdx && actualIdx < len(a.valid) && a.valid[actualIdx] { // idx is in the slice
		return a.data[actualIdx]
	} else { // idx is out of the slice
		return a.defaultValue
	}
}

func (a *PositiveSlice[T]) Set(idx int, value T) {
	actualIdx := a.TranslateIndex(idx)
	if actualIdx < 0 || actualIdx >= len(a.valid) { // idx is outside the slice
		// expand data array to actualIdx
		newData := make([]T, 2*actualIdx+1)
		copy(newData, a.data)
		a.data = newData

		// expand valid array to actualIdx
		newValid := make([]bool, 2*actualIdx+1)
		copy(newValid, a.valid)
		a.valid = newValid
	}

	a.data[actualIdx] = value
	a.valid[actualIdx] = true
}

func (a *PositiveSlice[T]) Preallocate(hi int) {
	size := hi

	// expand data array to actualIdx
	newData := make([]T, size+1)
	a.data = newData

	// expand valid array to actualIdx
	newValid := make([]bool, size+1)
	a.valid = newValid
}