I have an Appointment doctype where i need to verify if the Seller already has an appointment when trying to add another one for the same seller, but i have no idea how to do that. I am using a appointment_calendar.js and a appointment.py files.

appointment_calendar.js

frappe.views.calendar["Appointment"] = {
field_map: {
    start: "start_date",
    end: "end_date",
    id: "name",
    allDay: 0,
    title: "client_name",
    status: "status",
},
order_by: "start_date",
get_events_method: "scheduling_system.scheduling_system.doctype.appointment.appointment.get_appointments"};

appointment.py:

   from frappe.model.document import Document
   from datetime import datetime, timedelta
   from frappe.utils import get_datetime

import frappe 

class Appointment(Document):
    pass

@frappe.whitelist()
def get_appointments(start, end):
    appointments = frappe.get_all(
        "Appointment", 
        filters={"start_date": ["between", [start, end]]},
        fields=["name", "start_date", "duration", "client_name", "status"]
    )

    for app in appointments:
        if not app["start_date"]:
            continue  # Pula registros inválidos
        
        if isinstance(app["start_date"], str):
            start_date = datetime.strptime(app["start_date"], "%Y-%m-%d %H:%M:%S")
        else:
            start_date = app["start_date"]

        duration = app.get("duration", "00:00:00")  # Evita erro caso `duration` seja None
        if isinstance(duration, str):
            h, m, s = map(int, duration.split(":"))
            duration = timedelta(hours=h, minutes=m, seconds=s)

        end_date = start_date + duration
        app["start_date"] = start_date.strftime("%Y-%m-%d %H:%M:%S")
        app["end_date"] = end_date.strftime("%Y-%m-%d %H:%M:%S")

    return appointments