from django.db import models from django.conf import settings from django.core.exceptions import ValidationError from django.db import transaction from decimal import Decimal from django.utils import timezone from django.utils.timezone import now from customers.models import Customer from inventory.models import Product, Batch import logging logger = logging.getLogger(__name__) class Sale(models.Model): PAYMENT_METHOD_CHOICES = [ ('cash', 'Cash'), ('mpesa', 'M-Pesa'), ('credit', 'Credit'), ('cheque', 'Cheque'), ] # Schema separation provides tenant isolation - no tenant field needed # Core Fields customer = models.ForeignKey(Customer, null=True, blank=True, on_delete=models.SET_NULL) total_amount = models.DecimalField(max_digits=10, decimal_places=2, default=0) payment_method = models.CharField(max_length=10, choices=PAYMENT_METHOD_CHOICES) sale_date = models.DateTimeField(default=now, db_index=True) is_complete = models.BooleanField(default=False) user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) # Cash/M-Pesa Fields cash_given = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True) change_due = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True) mpesa_reference = models.CharField(max_length=255, null=True, blank=True) # Credit Fields credit_amount = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True) credit_paid_date = models.DateField(null=True, blank=True) # Cheque Fields cheque_number = models.CharField(max_length=50, null=True, blank=True) cheque_date = models.DateField(null=True, blank=True) cheque_cleared = models.BooleanField(default=False) class Meta: ordering = ['-sale_date'] def __str__(self): return f"Sale #{self.id} - {self.total_amount} ({self.payment_method})" def clean(self): """Validation for payment-specific fields""" if self.payment_method == 'cash' and not self.cash_given: raise ValidationError("Cash amount given is required for cash payments.") if self.payment_method == 'mpesa' and not self.mpesa_reference: raise ValidationError("M-Pesa reference is required.") if self.payment_method == 'credit': if self.credit_amount is None: # Only raise error if None (not 0) raise ValidationError("Credit amount must be specified (use 0 for no deposit).") if self.payment_method == 'cheque': if not self.cheque_number: raise ValidationError("Cheque number is required.") if not self.cheque_date: raise ValidationError("Cheque date is required.") # Check for duplicate cheque number for the same customer if self.customer and self.cheque_number: existing_cheque = Sale.objects.filter( customer=self.customer, cheque_number=self.cheque_number, payment_method='cheque' ).exclude(id=self.id if self.id else None) if existing_cheque.exists(): raise ValidationError(f"Cheque number {self.cheque_number} already exists for this customer.") # Warning for past dates (instead of blocking) if self.cheque_date and self.cheque_date < timezone.now().date(): logger.warning( f"Past-dated cheque recorded: #{self.cheque_number} " f"(Date: {self.cheque_date}, Amount: {self.total_amount})" ) def save(self, *args, **kwargs): """Handle payment completion logic""" self.full_clean() # Enforce validation # Auto-calculate change for cash payments if self.payment_method == 'cash' and self.cash_given: self.change_due = self.cash_given - self.total_amount self.is_complete = self.change_due >= 0 # Mark other payment methods as complete elif self.payment_method in ['mpesa', 'cheque']: self.is_complete = True super().save(*args, **kwargs) @property def outstanding_credit(self): """Calculate remaining credit for partial payments""" if self.payment_method == 'credit': return max(self.total_amount - (self.credit_amount or 0), Decimal(0)) return Decimal(0) class SaleItem(models.Model): # Schema separation provides tenant isolation - no tenant field needed sale = models.ForeignKey(Sale, related_name='items', on_delete=models.CASCADE) product = models.ForeignKey(Product, on_delete=models.PROTECT) batch = models.ForeignKey(Batch, on_delete=models.PROTECT, null=True, blank=True) quantity = models.PositiveIntegerField() selling_price = models.DecimalField(max_digits=10, decimal_places=2) subtotal = models.DecimalField(max_digits=10, decimal_places=2, editable=False) def clean(self): """Validate stock availability""" if self.batch and self.quantity > self.batch.quantity: raise ValidationError(f"Only {self.batch.quantity} units available in batch {self.batch.batch_code}") elif not self.batch and self.quantity > self.product.stock_quantity: raise ValidationError(f"Only {self.product.stock_quantity} units available") def save(self, *args, **kwargs): """Auto-calculate prices and update stock""" # Set price from batch or product only if not already set if not self.selling_price: self.selling_price = self.batch.selling_price if self.batch else self.product.selling_price self.subtotal = self.selling_price * self.quantity super().save(*args, **kwargs) class SalePayment(models.Model): """Track multiple payment methods for a single sale""" PAYMENT_METHOD_CHOICES = [ ('cash', 'Cash'), ('mpesa', 'M-Pesa'), ('credit', 'Credit'), ('cheque', 'Cheque'), ] # Schema separation provides tenant isolation - no tenant field needed sale = models.ForeignKey(Sale, related_name='payments', on_delete=models.CASCADE) payment_method = models.CharField(max_length=10, choices=PAYMENT_METHOD_CHOICES) amount = models.DecimalField(max_digits=10, decimal_places=2) # Payment method specific fields mpesa_reference = models.CharField(max_length=255, null=True, blank=True) cheque_number = models.CharField(max_length=50, null=True, blank=True) cheque_date = models.DateField(null=True, blank=True) created_at = models.DateTimeField(default=now) class Meta: ordering = ['-created_at'] def __str__(self): return f"Sale #{self.sale.id} - {self.get_payment_method_display()} - KSh {self.amount}"