from django.db import transaction
from .models import Item, StockLocation, StockLedger

class StockMovementType:
    ISSUE = "ISSUE"         # going out (consume, dispense, use)
    RECEIPT = "RECEIPT"     # coming in (receive)
    ADJUSTMENT = "ADJUSTMENT"
    TRANSFER = "TRANSFER"

@transaction.atomic
def record_stock_movement(*, tenant, item_id, location_id, qty: float, movement_type: str, reference=None, performed_by=None, note:str=""):
    item = Item.objects.select_for_update().get(id=item_id, tenant=tenant)
    loc  = StockLocation.objects.select_for_update().get(id=location_id, tenant=tenant)

    # Update on-hand (you likely store per-location balances; adjust to your schema)
    if movement_type == StockMovementType.ISSUE:
        loc.on_hand = (loc.on_hand or 0) - qty
    elif movement_type == StockMovementType.RECEIPT:
        loc.on_hand = (loc.on_hand or 0) + qty
    # ADJUSTMENT or TRANSFER handled similarly (or with from/to locations)
    loc.save(update_fields=["on_hand"])

    StockLedger.objects.create(
        tenant=tenant, item=item, location=loc, qty=qty, movement_type=movement_type,
        reference=str(reference) if reference else "", note=note, performed_by=performed_by
    )
    return loc.on_hand