diff --git a/src/tasks/service.ts b/src/tasks/service.ts
index e582543..9b8f2cb 100644
--- a/src/tasks/service.ts
+++ b/src/tasks/service.ts
@@ -1,36 +1,52 @@
 import { db } from '../db';
-import type { Task, TaskAssignment } from './model';
+
+type CreateTaskInput = {
+  description: string;
+  due_date?: string | null; // Expect 'YYYY-MM-DD' or null
+  group_id?: string | null; // Full JID (e.g., 'xxx@g.us') or null
+  created_by: string;       // Normalized user ID
+};
+
+type CreateAssignmentInput = {
+  user_id: string;    // Normalized user ID
+  assigned_by: string; // Normalized user ID (typically created_by)
+};
 
 export class TaskService {
-  static createTask(task: Omit<Task, 'id'>, assignments: Omit<TaskAssignment, 'task_id'>[]) {
-    return db.transaction(() => {
+  static createTask(task: CreateTaskInput, assignments: CreateAssignmentInput[] = []): number {
+    const runTx = db.transaction(() => {
       const insertTask = db.prepare(`
-        INSERT INTO tasks (description, due_date, group_id)
-        VALUES (?, ?, ?)
+        INSERT INTO tasks (description, due_date, group_id, created_by)
+        VALUES (?, ?, ?, ?)
         RETURNING id
       `);
-      
+
       const taskResult = insertTask.get(
         task.description,
-        task.due_date?.toISOString(),
-        task.group_id
+        task.due_date ?? null,
+        task.group_id ?? null,
+        task.created_by
       ) as { id: number };
-      
-      const insertAssignment = db.prepare(`
-        INSERT INTO task_assignments (task_id, user_id, assigned_by)
-        VALUES (?, ?, ?)
-      `);
-      
-      assignments.forEach(assignment => {
-        insertAssignment.run(
-          taskResult.id,
-          assignment.user_id,
-          assignment.assigned_by
-        );
-      });
-      
+
+      if (assignments.length > 0) {
+        const insertAssignment = db.prepare(`
+          INSERT INTO task_assignments (task_id, user_id, assigned_by)
+          VALUES (?, ?, ?)
+        `);
+
+        // Evitar duplicados por (task_id, user_id)
+        const seen = new Set<string>();
+        for (const a of assignments) {
+          if (seen.has(a.user_id)) continue;
+          seen.add(a.user_id);
+          insertAssignment.run(taskResult.id, a.user_id, a.assigned_by);
+        }
+      }
+
       return taskResult.id;
     });
+
+    return runTx();
   }
 
   // We'll add more methods here as we progress