from pymongo import ASCENDING, DESCENDING
import time
from .extensions import mongo
def backfill_orders():
    t=time.time()
    print("Starting backfill process for order serial numbers...")

    # 1. Find the highest existing serial number to know where to start.
    highest_order = mongo.db.orders.find_one(
        {'serial_no': {'$exists': True}},
        sort=[('serial_no', DESCENDING)]
    )
    
    next_serial_to_assign = 1
    if highest_order and 'serial_no' in highest_order:
        next_serial_to_assign = highest_order['serial_no'] + 1
        print(f"Highest existing serial is {highest_order['serial_no']}. New serials will start from {next_serial_to_assign}.")
    else:
        print("No existing serial numbers found. Starting from 1.")

    # 2. Find all orders that are missing a serial number, sorted by creation date.
    orders_to_update = list(mongo.db.orders.find(
        {'serial_no': {'$exists': False}},
        sort=[('created_at', ASCENDING)]
    ))

    if not orders_to_update:
        print("No orders found without a serial number. All good!")
        return

    print(f"Found {len(orders_to_update)} orders to update.")

    # 3. Iterate and assign the new serial numbers.
    for order in orders_to_update:
        mongo.db.orders.update_one(
            {'_id': order['_id']},
            {'$set': {'serial_no': next_serial_to_assign}}
        )
        print(f"  - Updated order {order['_id']} with Serial No: {next_serial_to_assign}")
        next_serial_to_assign += 1

    # 4. Finally, update the global counter to the last assigned value.
    final_serial_value = next_serial_to_assign - 1
    mongo.db.counters.update_one(
        {'_id': 'order_serial'},
        {'$set': {'sequence_value': final_serial_value}},
        upsert=True
    )
    print(time.time()-t)
    print(f"\nBackfill complete. Updated {len(orders_to_update)} orders.")
    print(f"Global order serial counter has been set to {final_serial_value}.")

# --- NEW: Define functions for the AI model ---
def get_next_order_serial():
    """
    Atomically retrieves and increments the global order serial number from the 'counters' collection.
    """
    # find_one_and_update is atomic. upsert=True creates the doc if it doesn't exist.
    # By default, it returns the document *before* the update.
    counter_doc = mongo.db.counters.find_one_and_update(
        {'_id': 'order_serial'},
        {'$inc': {'sequence_value': 1}},
        upsert=True
    )
    # If counter_doc is None, it means the document was just created (upserted) with a value of 1.
    if counter_doc is None:
        return 1
    # Otherwise, it returns the old document, so we add 1 to get the new value.
    else:
        return counter_doc['sequence_value'] + 1