from django.db import models


class Customer(models.Model):
    name = models.CharField(max_length=150)
    email = models.EmailField(unique=True)
    phone = models.CharField(max_length=20, blank=True)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name


class Product(models.Model):
    name = models.CharField(max_length=200)
    sku = models.CharField(max_length=50, unique=True)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    stock = models.PositiveIntegerField(default=0)

    class Meta:
        ordering = ['name']


class Order(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    status = models.CharField(max_length=20, default='pending')
    total = models.DecimalField(max_digits=10, decimal_places=2)
    created_at = models.DateTimeField(auto_now_add=True)

    def calculate_total(self):
        items = self.orderitem_set.all()
        return sum(item.subtotal() for item in items)


class OrderItem(models.Model):
    order = models.ForeignKey(Order, on_delete=models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField(default=1)

    def subtotal(self):
        return self.product.price * self.quantity


def get_monthly_revenue(orders, month):
    filtered = orders.filter(created_at__month=month)
    return filtered.aggregate(total=models.Sum('total'))


def low_stock_alert(products, threshold=10):
    return products.filter(stock__lt=threshold)


class Dashboard:
    def __init__(self, user):
        self.user = user
        self.widgets = []

    def add_widget(self, widget):
        self.widgets.append(widget)
        return self