// Package voc implements a generic vocabulary. Vocabularies may be nested
// and are searched upwards using the parent vocabulary until this is nil.
// Individual entries contain slices of values; the last item in a
// slice is the current value.
package voc

type VocData[V any] map[string][]V

type Vocabulary[V any] struct {
	parent *Vocabulary[V]
	data   VocData[V]
}

func NewVoc[V any](parent *Vocabulary[V]) *Vocabulary[V] {
	return &Vocabulary[V]{
		parent: parent,
		data:   VocData[V]{},
	}
}

func (voc *Vocabulary[V]) Parent() *Vocabulary[V] {
	return voc.parent
}

func (voc *Vocabulary[V]) Register(name string, it V) {
	vi, ok := voc.data[name]
	if ok {
		voc.data[name] = append(vi, it)
	} else {
		voc.data[name] = []V{it}
	}
}

func (voc *Vocabulary[V]) Lookup(name string) (V, bool) {
	vi, ok := voc.data[name]
	if ok {
		return vi[len(vi)-1], true
	}
	if voc.parent != nil {
		return voc.parent.Lookup(name)
	}
	var r V
	return r, false
}