Implement parent child ticket hierarchy

app/Http/Controllers/ProjectTicketController.php

@@ -27,13 +27,28 @@ class ProjectTicketController extends Controller
             403,
         );
 
+        $excludedParentIds = [$ticket->id, ...$this->descendantIds($ticket)];
+
         return Inertia::render('projects/Ticket', [
             'canEditTicket' => $this->projectPermissionService->userHasPermission($request->user(), $project, 'edit'),
+            'childTicketTree' => $this->buildChildTicketTree($ticket),
+            'parentTicketOptions' => Ticket::query()
+                ->where('project_id', $project->id)
+                ->whereNotIn('id', $excludedParentIds)
+                ->whereHas('ticketType', fn ($query) => $query->where('system_key', 'parent'))
+                ->orderByDesc('sequence_number')
+                ->get()
+                ->map(fn (Ticket $parentTicket): array => [
+                    'id' => $parentTicket->id,
+                    'ticket_key' => $parentTicket->ticket_key,
+                    'title' => $parentTicket->title,
+                ]),
             'project' => $project,
             'status' => session('status'),
             'ticket' => $ticket->load([
                 'fieldValues.ticketFieldDefinition',
                 'fieldValues.userValue',
+                'parentTicket',
                 'ticketPriority',
                 'ticketType',
                 'worklogEntries.actor',
@@ -71,4 +86,42 @@ class ProjectTicketController extends Controller
         return to_route('projects.tickets.show', [$project, $ticket])
             ->with('status', $statusMessage);
     }
+
+    /**
+     * @return array<int, array{
+     *     children: array<int, mixed>,
+     *     id: int,
+     *     ticket_key: string,
+     *     ticket_type_name: string|null,
+     *     title: string
+     * }>
+     */
+    private function buildChildTicketTree(Ticket $ticket): array
+    {
+        return $ticket->childTickets()
+            ->with('ticketType')
+            ->get()
+            ->map(fn (Ticket $childTicket): array => [
+                'children' => $this->buildChildTicketTree($childTicket),
+                'id' => $childTicket->id,
+                'ticket_key' => $childTicket->ticket_key,
+                'ticket_type_name' => $childTicket->ticketType?->name,
+                'title' => $childTicket->title,
+            ])
+            ->all();
+    }
+
+    /**
+     * @return array<int, int>
+     */
+    private function descendantIds(Ticket $ticket): array
+    {
+        return $ticket->childTickets()
+            ->get()
+            ->flatMap(function (Ticket $childTicket): array {
+                return [$childTicket->id, ...$this->descendantIds($childTicket)];
+            })
+            ->values()
+            ->all();
+    }
 }