func sortToProto(sort *SortOptions, params *pb.SearchParams) error {
	for _, e := range sort.Expressions {
		spec := &pb.SortSpec{
			SortExpression: proto.String(e.Expr),
		}
		if e.Reverse {
			spec.SortDescending = proto.Bool(false)
		}
		if e.Default != nil {
			switch d := e.Default.(type) {
			case float64:
				spec.DefaultValueNumeric = &d
			case string:
				spec.DefaultValueText = &d
			default:
				return fmt.Errorf("search: invalid Default type %T for expression %q", d, e.Expr)
			}
		}
		params.SortSpec = append(params.SortSpec, spec)
	}

	spec := &pb.ScorerSpec{}
	if sort.Limit > 0 {
		spec.Limit = proto.Int32(int32(sort.Limit))
		params.ScorerSpec = spec
	}
	if sort.Scorer != nil {
		sort.Scorer.toProto(spec)
		params.ScorerSpec = spec
	}

	return nil
}

func (o *autoFacetOpt) setParams(params *pb.SearchParams) error {
	lim := int32(o.facetLimit)
	if lim == 0 {
		lim = defaultAutoFacetLimit
	}
	params.AutoDiscoverFacetCount = &lim
	if o.valueLimit > 0 {
		params.FacetAutoDetectParam = &pb.FacetAutoDetectParam{
			ValueLimit: proto.Int32(int32(o.valueLimit)),
		}
	}
	return nil
}

func refinementsToProto(refinements []Facet, params *pb.SearchParams) error {
	for _, r := range refinements {
		ref := &pb.FacetRefinement{
			Name: proto.String(r.Name),
		}
		switch v := r.Value.(type) {
		case Atom:
			ref.Value = proto.String(string(v))
		case Range:
			rng, err := rangeToProto(v)
			if err != nil {
				return fmt.Errorf("search: refinement for facet %q: %v", r.Name, err)
			}
			// Unfortunately there are two identical messages for identify Facet ranges.
			ref.Range = &pb.FacetRefinement_Range{Start: rng.Start, End: rng.End}
		default:
			return fmt.Errorf("search: unsupported refinement for facet %q of type %T", r.Name, v)
		}
		params.FacetRefinement = append(params.FacetRefinement, ref)
	}
	return nil
}