fix: use stock value diff for calculation
diff --git a/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py b/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
index d4ddd59..7599da4 100644
--- a/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
+++ b/erpnext/stock/report/cogs_by_item_group/cogs_by_item_group.py
@@ -9,7 +9,6 @@
 
 
 def execute(filters=None):
-	print(filters)
 	validate_filters(filters)
 	columns = get_columns()
 	data = get_data(filters)
@@ -17,9 +16,6 @@
 
 
 def validate_filters(filters):
-	if not filters.get("from_date") and not filters.get("to_date"):
-		frappe.throw(_("{0} and {1} are mandatory").format(frappe.bold(_("From Date")), frappe.bold(_("To Date"))))
-
 	if filters.from_date > filters.to_date:
 		frappe.throw(_("From Date must be before To Date"))
 
@@ -42,110 +38,100 @@
 
 
 def get_data(filters):
-	entries = get_filtered_entries(filters)
-	item_groups_list = frappe.get_all("Item Group", fields=("name", "is_group", "lft", "rgt"))
-	item_groups_dict = get_item_groups_dict(item_groups_list)
-	levels_dict = get_levels_dict(item_groups_dict)
+	filtered_entries = get_filtered_entries(filters)
+	svd_list = get_stock_value_difference_list(filtered_entries)
+	leveled_dict = get_leveled_dict()
 
-	update_levels_dict(levels_dict)
-	assign_self_values(levels_dict, entries)
-	assign_agg_values(levels_dict)
+	assign_self_values(leveled_dict, svd_list)
+	assign_agg_values(leveled_dict)
 	
 	data = []
-	for _, i in levels_dict.items():
+	for _, i in leveled_dict.items():
 		if i['agg_value'] == 0:
 			continue
 		data.append(get_row(i['name'], i['agg_value'], i['is_group'], i['level']))
 		if i['self_value'] < i['agg_value'] and i['self_value'] > 0:
 			data.append(get_row(i['name'], i['self_value'], 0, i['level'] + 1))
+	# append_blank()
 	return data
 
 
 def get_filtered_entries(filters):
 	gl_entries = get_gl_entries(filters, [])
-	entries = [frappe.get_doc(gle.voucher_type, gle.voucher_no)for gle in gl_entries]
 	filtered_entries = []
-	for entry in entries:
-		posting_date = entry.get("posting_date")
-		from_date = filters.get("from_date")
+	for entry in gl_entries:
+		posting_date = entry.get('posting_date')
+		from_date = filters.get('from_date')
 		if date_diff(from_date, posting_date) > 0:
 			continue
 		filtered_entries.append(entry)
 	return filtered_entries
 
 
-def append_blank(data):
-	if len(data) == 0:
-		data.append(get_row("", 0, 0, 0))
+def get_stock_value_difference_list(filtered_entries):
+	voucher_nos = [fe.get('voucher_no') for fe in filtered_entries]
+	svd_list = frappe.get_list('Stock Ledger Entry',
+				 fields=['item_code','stock_value_difference'], 
+				 filters=[('voucher_no', 'in', voucher_nos)])
+	assign_item_groups_to_svd_list(svd_list)
+	return svd_list
 
 
-def get_item_groups_dict(item_groups_list):
-	return { (i['lft'],i['rgt']):{'name':i['name'], 'is_group':i['is_group']}
-		for i in item_groups_list }
-
-
-def get_levels_dict(item_groups_dict):
-	lr_list = sorted(item_groups_dict, key=lambda x : x[0])
-	levels = OrderedDict()
+def get_leveled_dict():
+	item_groups_dict = get_item_groups_dict()
+	lr_list = sorted(item_groups_dict, key=lambda x : int(x[0]))
+	leveled_dict = OrderedDict()
 	current_level = 0
 	nesting_r = []
-	for l,r in lr_list:
+	for l, r in lr_list:
 		while current_level > 0 and nesting_r[-1] < l:
 			nesting_r.pop()
 			current_level -= 1
 
-		levels[(l,r)] = {
+		leveled_dict[(l,r)] = {
 			'level' : current_level,
 			'name' : item_groups_dict[(l,r)]['name'],
 			'is_group' : item_groups_dict[(l,r)]['is_group']
 		}
 
-		if r - l > 1:
+		if int(r) - int(l) > 1:
 			current_level += 1
 			nesting_r.append(r)
-	return levels
 
-			
-def update_levels_dict(levels_dict):
-	for k in levels_dict: levels_dict[k].update({'self_value':0, 'agg_value':0})
+	update_leveled_dict(leveled_dict)
+	return leveled_dict
 
 
-def assign_self_values(levels_dict, entries):
-	names_dict = {v['name']:k for k, v in levels_dict.items()}
-	for entry in entries:
-		items = entry.get("items")
-		items = [] if items is None else items
-		for item in items:
-			qty = item.get("qty")
-			incoming_rate = item.get("incoming_rate")
-			item_group = item.get("item_group")
-			key = names_dict[item_group]
-			levels_dict[key]['self_value'] += (incoming_rate * qty)
+def assign_self_values(leveled_dict, svd_list):
+	key_dict = {v['name']:k for k, v in leveled_dict.items()}
+	for item in svd_list:
+		key = key_dict[item.get("item_group")]
+		leveled_dict[key]['self_value'] += -item.get("stock_value_difference")
 
 
-def assign_agg_values(levels_dict):
-	keys = list(levels_dict.keys())[::-1]
-	prev_level = levels_dict[keys[-1]]['level']
+def assign_agg_values(leveled_dict):
+	keys = list(leveled_dict.keys())[::-1]
+	prev_level = leveled_dict[keys[-1]]['level']
 	accu = [0]
 	for k in keys[:-1]:
-		curr_level = levels_dict[k]['level']
+		curr_level = leveled_dict[k]['level']
 		if curr_level == prev_level:
-			accu[-1] += levels_dict[k]['self_value']
-			levels_dict[k]['agg_value'] = levels_dict[k]['self_value']
+			accu[-1] += leveled_dict[k]['self_value']
+			leveled_dict[k]['agg_value'] = leveled_dict[k]['self_value']
 
 		elif curr_level > prev_level:
-			accu.append(levels_dict[k]['self_value'])
-			levels_dict[k]['agg_value'] = accu[-1]
+			accu.append(leveled_dict[k]['self_value'])
+			leveled_dict[k]['agg_value'] = accu[-1]
 
 		elif curr_level < prev_level:
-			accu[-1] += levels_dict[k]['self_value']
-			levels_dict[k]['agg_value'] = accu[-1]
+			accu[-1] += leveled_dict[k]['self_value']
+			leveled_dict[k]['agg_value'] = accu[-1]
 
 		prev_level = curr_level
 
 	# root node
 	rk = keys[-1]
-	levels_dict[rk]['agg_value'] = sum(accu) + levels_dict[rk]['self_value']
+	leveled_dict[rk]['agg_value'] = sum(accu) + leveled_dict[rk]['self_value']
 
 
 def get_row(name:str, value:float, is_bold:int, indent:int):
@@ -153,3 +139,32 @@
 	if is_bold:
 		item_group = frappe.bold(item_group)
 	return frappe._dict(item_group=item_group, cogs_debit=value, indent=indent)
+			
+
+def assign_item_groups_to_svd_list(svd_list):
+	ig_map = get_item_groups_map(svd_list)
+	for item in svd_list:
+		item.item_group = ig_map[item.get("item_code")]
+
+def get_item_groups_map(svd_list):
+	# for items in svd_list: [{'item_code':'item_group'}]
+	item_codes = set([i['item_code'] for i in svd_list])
+	ig_list = frappe.get_list('Item',
+				 fields=['item_code','item_group'], 
+				 filters=[('item_code', 'in', item_codes)])
+	return {i['item_code']:i['item_group'] for i in ig_list}
+
+
+def append_blank(data):
+	if len(data) == 0:
+		data.append(get_row("", 0, 0, 0))
+
+
+def get_item_groups_dict():
+	item_groups_list = frappe.get_all("Item Group", fields=("name", "is_group", "lft", "rgt"))
+	return { (i['lft'],i['rgt']):{'name':i['name'], 'is_group':i['is_group']}
+		for i in item_groups_list }
+
+
+def update_leveled_dict(leveled_dict):
+	for k in leveled_dict: leveled_dict[k].update({'self_value':0, 'agg_value':0})