implement backend components for push notifications

go/internal/network/reader.go

@@ -16,6 +16,9 @@ type Reader interface {
 	ListForHuman(ctx context.Context, humanId string) ([]*Network, error)
 	// IsMember returns ErrInvalidHumanId if humanId is empty.
 	IsMember(ctx context.Context, networkID, humanId string) (bool, error)
+	// ListMembers returns all human IDs belonging to the network.
+  // Returns an empty slice if the network doesn't exist.
+	ListMembers(ctx context.Context, networkID string) ([]string, error)
 	// ListAll returns all networks with their members
 	ListAll(ctx context.Context) ([]*Network, error)
 	// ListAllMemberships returns humanId -> networkIds for every human with at
@@ -69,6 +72,12 @@ func (r *readerImpl) IsMember(ctx context.Context, networkID, humanId string) (b
 	return r.repo.isMember(ctx, networkID, humanId)
 }
 
+func (r *readerImpl) ListMembers(ctx context.Context, networkID string) ([]string, error) {
+	// Admin is guaranteed to be in network_members: Create() calls AddMembers
+	// for the admin, and RemoveMemberFromNetwork rejects admin removal.
+	return r.repo.getMemberHumanIds(ctx, networkID)
+}
+
 func (r *readerImpl) ListAll(ctx context.Context) ([]*Network, error) {
 	return r.repo.listAll(ctx)
 }

go/internal/network/visibility.go

@@ -0,0 +1,41 @@
+package network
+
+import "strings"
+
+// ResolveVisibility expands a stream particle's visible_to entries into the set
+// of human IDs that should see (and thus be notified about) activity in that
+// stream. Entries are formatted as `human:{id}` for a specific human or
+// `network:{id}` to expand to every member of the surrounding network.
+//
+// networkMembers must contain every human currently in the network (members +
+// admin). visible_to entries that point to humans no longer in the network are
+// dropped — they may have been removed since the stream was created.
+//
+// Returns a deduped slice; ordering is not stable.
+func ResolveVisibility(visibleTo []string, networkMembers []string) []string {
+	memberSet := make(map[string]bool, len(networkMembers))
+	for _, id := range networkMembers {
+		memberSet[id] = true
+	}
+
+	result := make(map[string]bool)
+	for _, entry := range visibleTo {
+		switch {
+		case strings.HasPrefix(entry, "human:"):
+			id := strings.TrimPrefix(entry, "human:")
+			if memberSet[id] {
+				result[id] = true
+			}
+		case strings.HasPrefix(entry, "network:"):
+			for id := range memberSet {
+				result[id] = true
+			}
+		}
+	}
+
+	out := make([]string, 0, len(result))
+	for id := range result {
+		out = append(out, id)
+	}
+	return out
+}