Speed up payment/refund processing on the supervisor dashboard

Reconciling a Yoco payment and sending payment links blocked the HTTP
response on ticket-PDF generation and email/WhatsApp sends; they now
run in the background like the other payment flows already did.
Registration/payment option loops (pricing, stock checks, ticket
generation) now resolve concurrently instead of sequentially. The
Payments page dropped a per-registration N+1 fetch and now refreshes
its lists in parallel after each action. Added missing indexes for
dashboard stats and donation-leg lookups, and made GET
/api/registrations optionally paginated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/utils/ticketUtils.js

@@ -54,42 +54,43 @@ const generateTicketsForRegistration = async (registrationId) => {
       byOption.get(key).push(ro);
     }
 
-    // For each group with duplicates, merge into the one that has tickets (or the first)
-    for (const [, group] of byOption) {
-      if (group.length <= 1) continue;
+    // For each group with duplicates, merge into the one that has tickets (or the first).
+    // Different (eventOptionId, variantId) groups touch disjoint rows, so process groups
+    // concurrently instead of one at a time.
+    await Promise.all(Array.from(byOption.values()).map(async (group) => {
+      if (group.length <= 1) return;
 
       // Prefer the option that already has tickets
       const withTickets = group.filter(ro => (ro.tickets || []).length > 0);
       const primary = withTickets.length > 0 ? withTickets[0] : group[0];
       const duplicates = group.filter(ro => ro.id !== primary.id);
 
-      // Move all tickets from duplicates to primary, then delete duplicate options
-      for (const dup of duplicates) {
-        for (const t of (dup.tickets || [])) {
-          await prisma.ticket.update({ where: { id: t.id }, data: { registrationOptionId: primary.id, updatedAt: new Date() } });
-        }
-        const totalMergedQty = duplicates.reduce((s, d) => s + (d.quantity || 0), 0);
-        await prisma.registrationOption.update({
-          where: { id: primary.id },
-          data: { quantity: (primary.quantity || 0) + totalMergedQty, }
-        });
-        await prisma.registrationOption.delete({ where: { id: dup.id } });
-      }
+      // Move all tickets from duplicates to primary (independent rows — safe to parallelize)
+      await Promise.all(duplicates.map(dup => Promise.all(
+        (dup.tickets || []).map(t =>
+          prisma.ticket.update({ where: { id: t.id }, data: { registrationOptionId: primary.id, updatedAt: new Date() } })
+        )
+      )));
 
-      // Re-load the primary's current quantity after merge
+      // Single write of the merged quantity, then delete the now-empty duplicate options
+      const totalMergedQty = duplicates.reduce((s, d) => s + (d.quantity || 0), 0);
+      await prisma.registrationOption.update({
+        where: { id: primary.id },
+        data: { quantity: (primary.quantity || 0) + totalMergedQty }
+      });
+      await Promise.all(duplicates.map(dup => prisma.registrationOption.delete({ where: { id: dup.id } })));
+
+      // Re-load the primary's current quantity + tickets after merge
       const updated = await prisma.registrationOption.findUnique({ where: { id: primary.id } });
       primary.quantity = updated?.quantity ?? primary.quantity;
-      // Reload tickets
       primary.tickets = await prisma.ticket.findMany({
         where: { registrationOptionId: primary.id },
         include: { usages: true },
         orderBy: { createdAt: 'asc' }
       });
-    }
+    }));
 
     // ── Step 2: For each unique option, ensure exactly one ticket with correct qty ──
-    const generatedTickets = [];
-
     // Re-read fresh list (some options may have been deleted above)
     const freshOptions = await prisma.registrationOption.findMany({
       where: { registrationId },
@@ -98,13 +99,14 @@ const generateTicketsForRegistration = async (registrationId) => {
       }
     });
 
-    for (const option of freshOptions) {
+    // Each option owns disjoint tickets, so resolve them concurrently instead of one at a time.
+    const perOptionResults = await Promise.all(freshOptions.map(async (option) => {
       const targetQty = option.quantity || 1;
       const existingTickets = option.tickets || [];
 
       if (existingTickets.length === 0) {
         // Create one ticket
-        const ticket = await prisma.ticket.create({
+        return prisma.ticket.create({
           data: {
             id: uuidv4(),
             qrCode: uuidv4(),
@@ -115,27 +117,28 @@ const generateTicketsForRegistration = async (registrationId) => {
             updatedAt: new Date()
           }
         });
-        generatedTickets.push(ticket);
-        continue;
       }
 
       // Pick primary: prefer scanned, otherwise oldest
       const withUsages = existingTickets.filter(t => (t.usages || []).length > 0);
       const primary = withUsages.length > 0 ? withUsages[0] : existingTickets[0];
 
+      const updates = [];
       // Update quantity on primary if needed
       if (primary.quantity !== targetQty) {
-        await prisma.ticket.update({ where: { id: primary.id }, data: { quantity: targetQty, updatedAt: new Date() } });
+        updates.push(prisma.ticket.update({ where: { id: primary.id }, data: { quantity: targetQty, updatedAt: new Date() } }));
       }
 
       // Delete unscanned duplicates
       const dups = existingTickets.filter(t => t.id !== primary.id && (t.usages || []).length === 0);
       if (dups.length > 0) {
-        await prisma.ticket.deleteMany({ where: { id: { in: dups.map(t => t.id) } } });
+        updates.push(prisma.ticket.deleteMany({ where: { id: { in: dups.map(t => t.id) } } }));
       }
-    }
+      if (updates.length > 0) await Promise.all(updates);
+      return null;
+    }));
 
-    return generatedTickets;
+    return perOptionResults.filter(Boolean);
   } catch (error) {
     console.error('Error generating tickets:', error);
     throw error;