feat(products): add support for product sales units

Add new models UnitOfMeasure and ProductSalesUnit to enable selling products in different units (e.g., bunches, kg). Update Product model with base_unit field and methods for unit conversions and availability. Extend Sale, Reservation, and OrderItem models with sales_unit fields and snapshots. Modify SaleProcessor to handle quantity conversions. Include admin interfaces for managing units. Add corresponding database migrations.

myproject/products/admin.py

@@ -12,6 +12,7 @@ from .models import ProductCategory, ProductTag, Product, ProductKit, KitItem
 from .models import ProductPhoto, ProductKitPhoto, ProductCategoryPhoto
 from .models import ProductVariantGroup, KitItemPriority, SKUCounter, CostPriceHistory
 from .models import ConfigurableProduct, ConfigurableProductOption, ConfigurableProductAttribute
+from .models import UnitOfMeasure, ProductSalesUnit
 from .admin_displays import (
     format_quality_badge,
     format_quality_display,
@@ -395,7 +396,7 @@ class ProductAdmin(TenantAdminOnlyMixin, admin.ModelAdmin):
     search_fields = ('name', 'sku', 'description', 'search_keywords')
     filter_horizontal = ('categories', 'tags', 'variant_groups')
     readonly_fields = ('photo_preview_large', 'archived_at', 'archived_by', 'cost_price', 'cost_price_details_display')
-    autocomplete_fields = []
+    autocomplete_fields = ['base_unit']
     actions = [
         restore_items,
         delete_selected,
@@ -407,7 +408,7 @@ class ProductAdmin(TenantAdminOnlyMixin, admin.ModelAdmin):
 
     fieldsets = (
         ('Основная информация', {
-            'fields': ('name', 'sku', 'variant_suffix', 'description', 'short_description', 'categories', 'unit', 'price', 'sale_price')
+            'fields': ('name', 'sku', 'variant_suffix', 'description', 'short_description', 'categories', 'base_unit', 'unit', 'price', 'sale_price')
         }),
         ('Себестоимость', {
             'fields': ('cost_price_details_display',),
@@ -832,7 +833,7 @@ class ProductKitAdminWithItems(ProductKitAdmin):
 
 # Update admin classes to include photo inlines
 class ProductAdminWithPhotos(ProductAdmin):
-    inlines = [ProductPhotoInline]
+    inlines = [ProductPhotoInline, ProductSalesUnitInline]
 
 class ProductKitAdminWithItemsAndPhotos(nested_admin.NestedModelAdmin, ProductKitAdmin):
     inlines = [KitItemInline, ProductKitPhotoInline]
@@ -943,6 +944,88 @@ class CostPriceHistoryAdmin(TenantAdminOnlyMixin, admin.ModelAdmin):
         return False
 
 
+# === Админка для единиц измерения ===
+
+@admin.register(UnitOfMeasure)
+class UnitOfMeasureAdmin(TenantAdminOnlyMixin, admin.ModelAdmin):
+    """Админка для справочника единиц измерения"""
+    list_display = ('code', 'name', 'short_name', 'position', 'is_active')
+    list_filter = ('is_active',)
+    search_fields = ('code', 'name', 'short_name')
+    list_editable = ('position', 'is_active')
+    ordering = ('position', 'code')
+
+    fieldsets = (
+        ('Основная информация', {
+            'fields': ('code', 'name', 'short_name')
+        }),
+        ('Настройки', {
+            'fields': ('position', 'is_active')
+        }),
+    )
+
+
+class ProductSalesUnitInline(admin.TabularInline):
+    """Инлайн для единиц продажи товара"""
+    model = ProductSalesUnit
+    extra = 0
+    fields = (
+        'unit', 'name', 'conversion_factor', 'price', 'sale_price',
+        'min_quantity', 'quantity_step', 'is_default', 'is_active'
+    )
+    autocomplete_fields = ['unit']
+    verbose_name = "Единица продажи"
+    verbose_name_plural = "Единицы продажи"
+
+
+@admin.register(ProductSalesUnit)
+class ProductSalesUnitAdmin(TenantAdminOnlyMixin, admin.ModelAdmin):
+    """Админка для единиц продажи товаров"""
+    list_display = (
+        'product', 'name', 'unit', 'conversion_factor',
+        'get_price_display', 'min_quantity', 'is_default', 'is_active'
+    )
+    list_filter = ('is_active', 'is_default', 'unit')
+    search_fields = ('product__name', 'product__sku', 'name')
+    autocomplete_fields = ['product', 'unit']
+    list_editable = ('is_default', 'is_active')
+    ordering = ('product', 'position')
+
+    fieldsets = (
+        ('Товар и единица', {
+            'fields': ('product', 'unit', 'name')
+        }),
+        ('Конверсия', {
+            'fields': ('conversion_factor',),
+            'description': 'Сколько единиц продажи получается из 1 базовой единицы товара. '
+                          'Например: 1 банч = 15 веток → conversion_factor = 15'
+        }),
+        ('Ценообразование', {
+            'fields': ('price', 'sale_price'),
+            'description': 'Цена за единицу продажи. sale_price - цена со скидкой (опционально).'
+        }),
+        ('Ограничения', {
+            'fields': ('min_quantity', 'quantity_step'),
+            'description': 'min_quantity - минимальное количество для заказа. '
+                          'quantity_step - шаг изменения количества.'
+        }),
+        ('Настройки', {
+            'fields': ('position', 'is_default', 'is_active')
+        }),
+    )
+
+    def get_price_display(self, obj):
+        """Отображение цены с учетом скидки"""
+        if obj.sale_price:
+            return format_html(
+                '<span style="text-decoration: line-through; color: #999;">{}</span> '
+                '<span style="color: #dc3545; font-weight: bold;">{}</span>',
+                obj.price, obj.sale_price
+            )
+        return obj.price
+    get_price_display.short_description = 'Цена'
+
+
 admin.site.register(ProductCategory, ProductCategoryAdminWithPhotos)
 admin.site.register(ProductTag, ProductTagAdmin)
 admin.site.register(Product, ProductAdminWithPhotos)