from django.db import transaction
from .models import Account, Transaction
 
def transfer_funds(source_id, target_id, amount):
    try:
        with transaction.atomic():
            source = Account.objects.select_for_update().get(id=source_id)
            target = Account.objects.select_for_update().get(id=target_id)
            if source.balance < amount:
                raise ValueError('Insufficient funds')
            source.balance -= amount
            target.balance += amount
            source.save()
            target.save()
            Transaction.objects.create(
                account=source,
                amount=-amount,
                transaction_type='TRANSFER'
            )
            Transaction.objects.create(
                account=target,
                amount=amount,
                transaction_type='TRANSFER'
            )
    except ValueError:
        return False
    return True