from django.db import models
from django.core.exceptions import ValidationError


class Category(models.Model):
    name = models.CharField(max_length=255, verbose_name='Название')
    slug = models.SlugField(unique=True, verbose_name='URL')

    class Meta:
        verbose_name = 'Категория'
        verbose_name_plural = 'Категории'

    def __str__(self):
        return self.name


class Subcategory(models.Model):
    category = models.ForeignKey(
        Category,
        on_delete=models.CASCADE,
        related_name='subcategories',
        verbose_name='Категория',
    )
    name = models.CharField(max_length=255, verbose_name='Название')
    slug = models.SlugField(verbose_name='URL')

    class Meta:
        ordering = ('category__name', 'name')
        constraints = [
            models.UniqueConstraint(
                fields=('category', 'slug'),
                name='unique_subcategory_slug_per_category',
            )
        ]
        verbose_name = 'Подкатегория'
        verbose_name_plural = 'Подкатегории'

    def __str__(self):
        return self.name


class Item(models.Model):
    name = models.CharField(max_length=255, verbose_name='Название')
    slug = models.SlugField(unique=True, verbose_name='URL')
    category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='items', verbose_name='Категория')
    subcategory = models.ForeignKey(
        Subcategory,
        on_delete=models.SET_NULL,
        related_name='items',
        null=True,
        blank=True,
        verbose_name='Подкатегория',
    )
    description = models.TextField(blank=True, verbose_name='Описание')
    price = models.DecimalField(max_digits=10, decimal_places=2, verbose_name='Цена')
    is_available = models.BooleanField(default=True, verbose_name='В наличии')
    created_at = models.DateTimeField(auto_now_add=True, verbose_name='Дата создания')
    updated_at = models.DateTimeField(auto_now=True, verbose_name='Дата обновления')

    class Meta:
        verbose_name = 'Товар'
        verbose_name_plural = 'Товары'

    def __str__(self):
        return self.name

    def clean(self):
        super().clean()

        if self.subcategory_id and self.category_id and self.subcategory.category_id != self.category_id:
            raise ValidationError({
                'subcategory': 'Подкатегория должна относиться к выбранной категории.'
            })

    @property
    def primary_image(self):
        return next(iter(self.images.all()), None)


class ItemImage(models.Model):
    item = models.ForeignKey(Item, on_delete=models.CASCADE, related_name='images', verbose_name='Товар')
    image = models.ImageField(upload_to='items/', verbose_name='Изображение')
    alt = models.CharField(max_length=255, blank=True, verbose_name='Alt-текст')
    sort_order = models.PositiveIntegerField(default=0, verbose_name='Порядок')
    is_primary = models.BooleanField(default=False, verbose_name='Главное изображение')

    class Meta:
        ordering = ('-is_primary', 'sort_order', 'id')
        verbose_name = 'Изображение товара'
        verbose_name_plural = 'Изображения товара'

    def __str__(self):
        return self.alt or f'Изображение товара {self.item.name}'