// Do implements plan.Plan Do interface.
func (r *selectIndexDefaultPlan) Do(ctx context.Context, f plan.RowIterFunc) (err error) {
	var x kv.Index
	switch ix := r.x.(type) {
	case *column.IndexedCol:
		x = ix.X
	default:
		panic("should never happen")
	}

	txn, err := ctx.GetTxn(false)
	if err != nil {
		return err
	}
	en, err := x.SeekFirst(txn)
	if err != nil {
		return types.EOFAsNil(err)
	}
	defer en.Close()

	var id int64
	for {
		k, _, err := en.Next()
		if err != nil {
			return types.EOFAsNil(err)
		}

		id++
		if more, err := f(id, k); !more || err != nil {
			return err
		}
	}
}

// ScanIndexData scans the index handles and values in a limited number, according to the index information.
// It returns data and the next startVals until it doesn't have data, then returns data is nil and
// the next startVals is the values which can't get data. If startVals = nil and limit = -1,
// it returns the index data of the whole.
func ScanIndexData(txn kv.Transaction, kvIndex kv.Index, startVals []interface{}, limit int64) (
	[]*RecordData, []interface{}, error) {
	it, _, err := kvIndex.Seek(txn, startVals)
	if err != nil {
		return nil, nil, errors.Trace(err)
	}
	defer it.Close()

	var idxRows []*RecordData
	var curVals []interface{}
	for limit != 0 {
		val, h, err1 := it.Next()
		if terror.ErrorEqual(err1, io.EOF) {
			return idxRows, nextIndexVals(curVals), nil
		} else if err1 != nil {
			return nil, nil, errors.Trace(err1)
		}
		idxRows = append(idxRows, &RecordData{Handle: h, Values: val})
		limit--
		curVals = val
	}

	nextVals, _, err := it.Next()
	if terror.ErrorEqual(err, io.EOF) {
		return idxRows, nextIndexVals(curVals), nil
	} else if err != nil {
		return nil, nil, errors.Trace(err)
	}

	return idxRows, nextVals, nil
}

// GetIndexRecordsCount returns the total number of the index records from startVals.
// If startVals = nil, returns the total number of the index records.
func GetIndexRecordsCount(txn kv.Transaction, kvIndex kv.Index, startVals []interface{}) (int64, error) {
	it, _, err := kvIndex.Seek(txn, startVals)
	if err != nil {
		return 0, errors.Trace(err)
	}
	defer it.Close()

	var cnt int64
	for {
		_, _, err := it.Next()
		if terror.ErrorEqual(err, io.EOF) {
			break
		} else if err != nil {
			return 0, errors.Trace(err)
		}
		cnt++
	}

	return cnt, nil
}