feat: game lobby service

lobby/internal/service/shared/roster.go

@@ -0,0 +1,33 @@
+package shared
+
+import (
+	"context"
+
+	"galaxy/lobby/internal/domain/common"
+	"galaxy/lobby/internal/domain/membership"
+	"galaxy/lobby/internal/ports"
+)
+
+// CountActiveMemberships returns the number of memberships in
+// membership.StatusActive attached to gameID. It is used by the
+// application services (submitapplication, approveapplication) to
+// evaluate the max_players + start_gap_players roster cap and the
+// gap-window activation threshold without each service re-implementing
+// the same scan + filter.
+func CountActiveMemberships(
+	ctx context.Context,
+	store ports.MembershipStore,
+	gameID common.GameID,
+) (int, error) {
+	records, err := store.GetByGame(ctx, gameID)
+	if err != nil {
+		return 0, err
+	}
+	count := 0
+	for _, record := range records {
+		if record.Status == membership.StatusActive {
+			count++
+		}
+	}
+	return count, nil
+}