import uuid

# In-memory storage for tasks
tasks_db = {}

def create_task(title, description=""):
    task_id = str(uuid.uuid4())
    task = {
        "id": task_id,
        "title": title,
        "description": description,
        "completed": False
    }
    tasks_db[task_id] = task
    return task

def get_all_tasks():
    return list(tasks_db.values())

def get_task_by_id(task_id):
    return tasks_db.get(task_id)

def complete_task(task_id):
    task = tasks_db.get(task_id)
    if task:
        task["completed"] = True
        return task
    return None