fix: calculate useful days of asset's life correctly for existing asset (#47066)

* fix: calculate useful days of asset's life correctly for existing asset

* fix: test

* fix: test case correction

erpnext/assets/doctype/asset/asset.py

@@ -635,38 +635,44 @@ class Asset(AccountsController):
 		return add_days(self.available_for_use_date, -1)
 
 	# if it returns True, depreciation_amount will not be equal for the first and last rows
-	def check_is_pro_rata(self, row, wdv_or_dd_non_yearly=False):
+	def check_is_pro_rata(asset_doc, row, wdv_or_dd_non_yearly=False):
 		has_pro_rata = False
 
 		# if not existing asset, from_date = available_for_use_date
 		# otherwise, if number_of_depreciations_booked = 2, available_for_use_date = 01/01/2020 and frequency_of_depreciation = 12
 		# from_date = 01/01/2022
-		from_date = self.get_modified_available_for_use_date(row, wdv_or_dd_non_yearly)
-		days = date_diff(row.depreciation_start_date, from_date) + 1
-
-		if wdv_or_dd_non_yearly:
-			total_days = get_total_days(row.depreciation_start_date, 12)
+		if row.depreciation_method in ("Straight Line", "Manual"):
+			prev_depreciation_start_date = get_last_day(
+				add_months(
+					row.depreciation_start_date,
+					(row.frequency_of_depreciation * -1) * asset_doc.number_of_depreciations_booked,
+				)
+			)
+			from_date = asset_doc.available_for_use_date
+			days = date_diff(prev_depreciation_start_date, from_date) + 1
+			total_days = get_total_days(prev_depreciation_start_date, row.frequency_of_depreciation)
 		else:
-			# if frequency_of_depreciation is 12 months, total_days = 365
+			from_date = _get_modified_available_for_use_date(asset_doc, row, wdv_or_dd_non_yearly=False)
+			days = date_diff(row.depreciation_start_date, from_date) + 1
 			total_days = get_total_days(row.depreciation_start_date, row.frequency_of_depreciation)
 
+		if days <= 0:
+			frappe.throw(
+				_(
+					"""Error: This asset already has {0} depreciation periods booked.
+					The `depreciation start` date must be at least {1} periods after the `available for use` date.
+					Please correct the dates accordingly."""
+				).format(
+					asset_doc.number_of_depreciations_booked,
+					asset_doc.number_of_depreciations_booked,
+				)
+			)
+
 		if days < total_days:
 			has_pro_rata = True
 
 		return has_pro_rata
 
-	def get_modified_available_for_use_date(self, row, wdv_or_dd_non_yearly=False):
-		if wdv_or_dd_non_yearly:
-			return add_months(
-				self.available_for_use_date,
-				(self.number_of_depreciations_booked * 12),
-			)
-		else:
-			return add_months(
-				self.available_for_use_date,
-				(self.number_of_depreciations_booked * row.frequency_of_depreciation),
-			)
-
 	def validate_asset_finance_books(self, row):
 		if flt(row.expected_value_after_useful_life) >= flt(self.gross_purchase_amount):
 			frappe.throw(
@@ -1290,6 +1296,28 @@ def get_item_details(item_code, asset_category, gross_purchase_amount):
 	return books
 
 
+def _get_modified_available_for_use_date(asset_doc, row, wdv_or_dd_non_yearly=False):
+	"""
+	if Asset has opening booked depreciations = 9,
+	available for use date = 17-07-2023,
+	depreciation start date = 30-04-2024
+	then from date should be 01-04-2024
+	"""
+	if asset_doc.number_of_depreciations_booked > 0:
+		from_date = add_months(
+			asset_doc.available_for_use_date,
+			(asset_doc.number_of_depreciations_booked * row.frequency_of_depreciation) - 1,
+		)
+		if is_last_day_of_the_month(row.depreciation_start_date):
+			return add_days(get_last_day(from_date), 1)
+
+		# get from date when depreciation start date is not last day of the month
+		months_difference = month_diff(row.depreciation_start_date, from_date) - 1
+		return add_days(add_months(row.depreciation_start_date, -1 * months_difference), 1)
+	else:
+		return asset_doc.available_for_use_date
+
+
 def get_asset_account(account_name, asset=None, asset_category=None, company=None):
 	account = None
 	if asset:

erpnext/assets/doctype/asset/test_asset.py

@@ -1451,7 +1451,7 @@ class TestDepreciationBasics(AssetSetup):
 		affects `value_after_depreciation`
 		"""
 
-		asset = create_asset(calculate_depreciation=1)
+		asset = create_asset(calculate_depreciation=1, depreciation_start_date="2021-12-31")
 		asset.opening_accumulated_depreciation = 2000
 		asset.number_of_depreciations_booked = 1