from django.db import models


class Supplier(models.Model):
    code = models.CharField(max_length=50, unique=True)
    name = models.CharField(max_length=200)
    contact_person = models.CharField(max_length=100, blank=True)
    email = models.EmailField(blank=True)
    phone = models.CharField(max_length=20, blank=True)
    address = models.TextField(blank=True)
    tax_id = models.CharField(max_length=50, blank=True)
    payment_terms = models.CharField(max_length=100, blank=True)
    is_active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    def __str__(self):
        return self.name


class PurchaseOrder(models.Model):
    STATUS_CHOICES = [
        ('ordered', 'Ordered'),
        ('completed', 'Completed'),
        ('cancelled', 'Cancelled'),
    ]

    po_number = models.CharField(max_length=50, unique=True, blank=True)
    supplier = models.ForeignKey(Supplier, on_delete=models.CASCADE)
    order_date = models.DateField()
    expected_delivery_date = models.DateField(null=True, blank=True)
    status = models.CharField(max_length=20, choices=STATUS_CHOICES, default='ordered')
    subtotal = models.DecimalField(max_digits=12, decimal_places=2, default=0)
    tax_amount = models.DecimalField(max_digits=12, decimal_places=2, default=0)
    total_amount = models.DecimalField(max_digits=12, decimal_places=2, default=0)
    notes = models.TextField(blank=True)
    created_by = models.ForeignKey('accounts.User', on_delete=models.SET_NULL, null=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    def save(self, *args, **kwargs):
        if not self.po_number:
            self.po_number = self.generate_po_number()
        super().save(*args, **kwargs)

    def generate_po_number(self):
        """Generate a unique purchase order number"""
        last_po = PurchaseOrder.objects.order_by('-id').first()

        if last_po and last_po.po_number and last_po.po_number.startswith('PO'):
            try:
                last_number = int(last_po.po_number[2:])  # Remove 'PO' prefix
                new_number = last_number + 1
            except ValueError:
                new_number = 1
        else:
            new_number = 1

        return f'PO{new_number:04d}'

    def __str__(self):
        return self.po_number


class PurchaseOrderItem(models.Model):
    po = models.ForeignKey(PurchaseOrder, on_delete=models.CASCADE, related_name='items')
    product = models.ForeignKey('inventory.Product', on_delete=models.CASCADE)
    quantity = models.DecimalField(max_digits=10, decimal_places=2)
    unit_price = models.DecimalField(max_digits=10, decimal_places=2)
    total_price = models.DecimalField(max_digits=12, decimal_places=2)
    received_quantity = models.DecimalField(max_digits=10, decimal_places=2, default=0)
    
    def save(self, *args, **kwargs):
        self.total_price = self.quantity * self.unit_price
        super().save(*args, **kwargs)


class GoodsReceipt(models.Model):
    gr_number = models.CharField(max_length=50, unique=True)
    po = models.ForeignKey(PurchaseOrder, on_delete=models.CASCADE)
    receipt_date = models.DateField()
    received_by = models.ForeignKey('accounts.User', on_delete=models.SET_NULL, null=True)
    notes = models.TextField(blank=True)
    created_at = models.DateTimeField(auto_now_add=True)
    
    def __str__(self):
        return self.gr_number


class GoodsReceiptItem(models.Model):
    receipt = models.ForeignKey(GoodsReceipt, on_delete=models.CASCADE, related_name='items')
    po_item = models.ForeignKey(PurchaseOrderItem, on_delete=models.CASCADE)
    received_quantity = models.DecimalField(max_digits=10, decimal_places=2)
    notes = models.TextField(blank=True)