merged from gramsrv upstream

internal/app/users/service_sparse.go

@@ -0,0 +1,58 @@
+package users
+
+import (
+	"context"
+	"fmt"
+
+	"telesrv/internal/domain"
+)
+
+// ByIDsForViewerUserIDs projects an actual sparse viewer->owner graph. Base
+// users are loaded once for the union; unlike ByIDsForViewers, owners belonging
+// to one viewer are never implicitly projected for every other viewer.
+func (s *Service) ByIDsForViewerUserIDs(ctx context.Context, userIDsByViewer map[int64][]int64) (map[int64][]domain.User, error) {
+	requested := make(map[int64][]int64, len(userIDsByViewer))
+	union := make([]int64, 0)
+	seenUnion := make(map[int64]struct{})
+	pairs := 0
+	for viewerID, userIDs := range userIDsByViewer {
+		if viewerID == 0 {
+			continue
+		}
+		ids := uniqueUserIDs(userIDs, 0)
+		if !sparseViewerProjectionPairsAllowed(pairs, len(ids)) {
+			return nil, fmt.Errorf("%w: got more than %d sparse pairs", ErrBatchViewerCells, maxBatchViewerProjectionCells)
+		}
+		pairs += len(ids)
+		requested[viewerID] = ids
+		for _, id := range ids {
+			if _, ok := seenUnion[id]; ok {
+				continue
+			}
+			seenUnion[id] = struct{}{}
+			union = append(union, id)
+			if len(union) > maxBatchUsers {
+				return nil, ErrBatchUsersLimit
+			}
+		}
+	}
+	if len(requested) == 0 || len(union) == 0 {
+		return map[int64][]domain.User{}, nil
+	}
+	base, err := s.loadBaseUsersByIDs(ctx, union)
+	if err != nil {
+		return nil, err
+	}
+	base, err = requireBatchBaseUsers(union, base)
+	if err != nil {
+		return nil, err
+	}
+	return s.projector.ForViewerUserIDs(ctx, requested, base)
+}
+
+func sparseViewerProjectionPairsAllowed(current, additional int) bool {
+	if current < 0 || additional < 0 || current > maxBatchViewerProjectionCells {
+		return false
+	}
+	return additional <= maxBatchViewerProjectionCells-current
+}