fix: Consider Website Item Groups in Item group page product listing

- Passed an argument to query engine to know when query is for item group page
- If for item group page, get data with regards to website item group table
- This query should be fast since there's one filter and that shortens the table beforehand
- This data is merged with the results from the Item master (results only considering item attributes and field filters)
- The combined data is then sorted as per weightage

Co-authored-by: Gavin D'souza <gavin18d@gmail.com>
diff --git a/erpnext/setup/doctype/item_group/item_group.py b/erpnext/setup/doctype/item_group/item_group.py
index bff806d..6687143 100644
--- a/erpnext/setup/doctype/item_group/item_group.py
+++ b/erpnext/setup/doctype/item_group/item_group.py
@@ -91,7 +91,7 @@
 		field_filters['item_group'] = self.name
 
 		engine = ProductQuery()
-		context.items = engine.query(attribute_filters, field_filters, search, start)
+		context.items = engine.query(attribute_filters, field_filters, search, start, item_group=self.name)
 
 		filter_engine = ProductFiltersBuilder(self.name)
 
diff --git a/erpnext/shopping_cart/product_query.py b/erpnext/shopping_cart/product_query.py
index 36d446e..bb31220 100644
--- a/erpnext/shopping_cart/product_query.py
+++ b/erpnext/shopping_cart/product_query.py
@@ -22,13 +22,14 @@
 		self.settings = frappe.get_doc("Products Settings")
 		self.cart_settings = frappe.get_doc("Shopping Cart Settings")
 		self.page_length = self.settings.products_per_page or 20
-		self.fields = ['name', 'item_name', 'item_code', 'website_image', 'variant_of', 'has_variants', 'item_group', 'image', 'web_long_description', 'description', 'route']
+		self.fields = ['name', 'item_name', 'item_code', 'website_image', 'variant_of', 'has_variants',
+			'item_group', 'image', 'web_long_description', 'description', 'route', 'weightage']
 		self.filters = []
 		self.or_filters = [['show_in_website', '=', 1]]
 		if not self.settings.get('hide_variants'):
 			self.or_filters.append(['show_variant_in_website', '=', 1])
 
-	def query(self, attributes=None, fields=None, search_term=None, start=0):
+	def query(self, attributes=None, fields=None, search_term=None, start=0, item_group=None):
 		"""Summary
 
 		Args:
@@ -44,6 +45,15 @@
 		if search_term: self.build_search_filters(search_term)
 
 		result = []
+		website_item_groups = []
+
+		# if from item group page consider website item group table
+		if item_group:
+			website_item_groups = frappe.db.get_all(
+				"Item",
+				fields=self.fields + ["`tabWebsite Item Group`.parent as wig_parent"],
+				filters=[["Website Item Group", "item_group", "=", item_group]]
+			)
 
 		if attributes:
 			all_items = []
@@ -65,18 +75,33 @@
 				)
 
 				items_dict = {item.name: item for item in items}
-				# TODO: Replace Variants by their parent templates
 
 				all_items.append(set(items_dict.keys()))
 
 			result = [items_dict.get(item) for item in list(set.intersection(*all_items))]
 		else:
-			result = frappe.get_all("Item", fields=self.fields, filters=self.filters, or_filters=self.or_filters, start=start, limit=self.page_length)
+			result = frappe.get_all(
+				"Item",
+				fields=self.fields,
+				filters=self.filters,
+				or_filters=self.or_filters,
+				start=start,
+				limit=self.page_length
+			)
+
+		# Combine results having context of website item groups into item results
+		if item_group and website_item_groups:
+			items_list = {row.name for row in result}
+			for row in website_item_groups:
+				if row.wig_parent not in items_list:
+					result.append(row)
+
+		result = sorted(result, key=lambda x: x.get("weightage"), reverse=True)
 
 		for item in result:
 			product_info = get_product_info_for_website(item.item_code, skip_quotation_creation=True).get('product_info')
 			if product_info:
-				item.formatted_price = product_info['price'].get('formatted_price') if product_info['price'] else None
+				item.formatted_price = product_info.get('price', {}).get('formatted_price')
 
 		return result