adds validation:

- ensure trial period dates are in order

erpnext/accounts/doctype/subscriptions/subscriptions.py

@@ -42,3 +42,33 @@ class Subscriptions(Document):
 			self.status = 'Active'
 			# todo: then generate new invoice
 
+	def is_past_grace_period(self):
+		current_invoice = self.get_current_invoice()
+		if self.current_invoice_is_past_due(current_invoice):
+			grace_period = cint(SUBSCRIPTION_SETTINGS.grace_period)
+
+			return nowdate() > add_days(current_invoice.due_date, grace_period)
+
+	def current_invoice_is_past_due(self, current_invoice=None):
+		if not current_invoice:
+			current_invoice = self.get_current_invoice()
+
+		if not current_invoice:
+			return False
+		else:
+			return nowdate() > current_invoice.due_date
+
+	def is_new_subscription(self):
+		return len(self.invoices) == 0
+
+	def validate(self):
+		self.validate_trial_period()
+
+	def validate_trial_period(self):
+		if self.trial_period_start and self.trial_period_end:
+			if getdate(self.trial_period_end) > getdate(self.trial_period_start):
+				frappe.throw(_('Trial Period End Date Cannot be before Trial Period Start Date'))
+
+		elif self.trial_period_start or self.trial_period_end:
+			frappe.throw(_('Both Trial Period Start Date and Trial Period End Date must be set'))
+