from django.db import models
from products.models import Product


class Stock(models.Model):
    """
    Остатки по каждому товару.
    """
    product = models.OneToOneField(Product, on_delete=models.CASCADE, 
                                  related_name='stock', verbose_name="Товар")
    quantity_available = models.DecimalField(max_digits=10, decimal_places=3, default=0,
                                            verbose_name="Доступное количество")
    quantity_reserved = models.DecimalField(max_digits=10, decimal_places=3, default=0,
                                           verbose_name="Зарезервированное количество")
    updated_at = models.DateTimeField(auto_now=True, verbose_name="Дата обновления")

    class Meta:
        verbose_name = "Остаток на складе"
        verbose_name_plural = "Остатки на складе"
        indexes = [
            models.Index(fields=['product']),
        ]

    def __str__(self):
        return f"{self.product.name} - {self.quantity_available}"

    @property
    def quantity_free(self):
        """Свободное количество (доступное минус зарезервированное)"""
        return self.quantity_available - self.quantity_reserved


class StockMovement(models.Model):
    """
    Журнал всех складских операций (приход, списание, коррекция).
    """
    REASON_CHOICES = [
        ('purchase', 'Закупка'),
        ('sale', 'Продажа'),
        ('write_off', 'Списание'),
        ('adjustment', 'Корректировка'),
    ]

    product = models.ForeignKey(Product, on_delete=models.CASCADE, 
                               related_name='movements', verbose_name="Товар")
    change = models.DecimalField(max_digits=10, decimal_places=3, verbose_name="Изменение")
    reason = models.CharField(max_length=20, choices=REASON_CHOICES, verbose_name="Причина")
    order = models.ForeignKey('orders.Order', on_delete=models.SET_NULL, null=True, blank=True,
                             related_name='stock_movements', verbose_name="Заказ")
    created_at = models.DateTimeField(auto_now_add=True, verbose_name="Дата создания")

    class Meta:
        verbose_name = "Движение товара"
        verbose_name_plural = "Движения товаров"
        indexes = [
            models.Index(fields=['product']),
            models.Index(fields=['created_at']),
        ]

    def __str__(self):
        return f"{self.product.name}: {self.change} ({self.reason})"