feat: Income tax slab (#21399)

* Feat: Multiple tax as per new taxation rule

* patch:for multiple tax slab, fix: payroll and exemption validation

* Test: Fixture

* feat: income tax slab with other charges and tax exempted deduction components

* fix: added missing init file

* fix: Patch fixed

* fix: Patch fixed

* fix: test fixes

* fix: validate duplicate exemption declaration

* fix: payment entry test case

Co-authored-by: Anurag Mishra <mishranaman123@gmail.com>

erpnext/hr/utils.py

@@ -9,6 +9,8 @@ from frappe.model.document import Document
 from frappe.desk.form import assign_to
 from erpnext.hr.doctype.employee.employee import get_holiday_list_for_employee
 
+class DuplicateDeclarationError(frappe.ValidationError): pass
+
 class EmployeeBoardingController(Document):
 	'''
 		Create the project and the task for the boarding process
@@ -226,6 +228,17 @@ def get_employee_leave_policy(employee):
 	else:
 		frappe.throw(_("Please set leave policy for employee {0} in Employee / Grade record").format(employee))
 
+def validate_duplicate_exemption_for_payroll_period(doctype, docname, payroll_period, employee):
+	existing_record = frappe.db.exists(doctype, {
+		"payroll_period": payroll_period,
+		"employee": employee,
+		'docstatus': ['<', 2],
+		'name': ['!=', docname]
+	})
+	if existing_record:
+		frappe.throw(_("{0} already exists for employee {1} and period {2}")
+			.format(doctype, employee, payroll_period), DuplicateDeclarationError)
+
 def validate_tax_declaration(declarations):
 	subcategories = []
 	for d in declarations: