ids.go

package id

type IdType int

const (
	IdTypeUnknown IdType = -1

	IdType1 IdType = iota
	IdType2
)

type Id struct {
	string
	// pointer to next element in the chain of ids
	nextId *Id
}

var ZeroId = Id{}

// NewId is a test helper for creating a chain of ids.
func NewId(values ...string) (id Id) {
	if len(values) == 0 {
		return ZeroId
	}

	// push front values, so Next iterated over them in the original order
	for i := len(values) - 1; i >= 0; i-- {
		nextId := id
		id = Id{string: values[i]}
		if nextId != ZeroId {
			id.nextId = &nextId
		}
	}
	return id
}

func (id Id) Next() (nextId Id, ok bool) {
	if id.nextId == nil {
		return ZeroId, false
	}
	return *id.nextId, true
}

func (id Id) String() string {
	if id.nextId == nil {
		return id.string
	}
	s := strings.Builder{}
	s.WriteString(id.string)
	for nextId := id.nextId; nextId != nil; nextId = nextId.nextId {
		s.WriteByte(',')
		s.WriteString(nextId.string)
	}
	return s.String()
}

func (id Id) Value() string {
	return id.string
}

func (id Id) Values() (values []string) {
	if id.string == "" {
		return nil
	}
	values = append(values, id.string)
	for nextId := id.nextId; nextId != nil; nextId = nextId.nextId {
		values = append(values, nextId.string)
	}
	return values
}

// Ids is the collection of several hashes device IDs obtained from a request.
type Ids map[IdType]Id

type idsIterator struct {
	ids    Ids
	keys   []IdType
	n      int
	idType IdType
	id     Id
}

func newIdsIterator(ids Ids) *idsIterator {
	it := &idsIterator{
		keys: make([]IdType, 0, len(ids)),
	}
	it.Reset(ids)
	return it
}

func (it *idsIterator) Reset(ids Ids) {
	it.ids = ids
	it.keys = it.keys[:0]
	it.n = 0
	it.idType = IdTypeUnknown
	it.id = ZeroId
}

func (it *idsIterator) lazyInit() {
	if len(it.keys) != 0 {
		return
	}
	for idType := range it.ids {
		it.keys = append(it.keys, idType)
	}
}

func (it *idsIterator) Next() bool {
	it.lazyInit()

	if it.n >= len(it.keys) {
		return false
	}

	if id, ok := it.id.Next(); ok {
		it.id = id
		return true
	}

	it.idType = it.keys[it.n]
	it.id = it.ids[it.idType]
	it.n++

	return true
}

func (it *idsIterator) Id() (IdType, Id) {
	return it.idType, it.id
}

func ExampleIds() {
	ids := Ids{
		IdType1: NewId("id1val1", "id1val2", "id1val3"),
		IdType2: NewId("id2val1"),
	}
	
	it := newIdsIterator(ids)
	for it.Next() {
		idType, id := it.Id()
		// do something
		_, _ = idType, id
	}	
}