feat: Assign shift for period or create ongoing assignment
diff --git a/erpnext/hr/doctype/shift_assignment/shift_assignment.json b/erpnext/hr/doctype/shift_assignment/shift_assignment.json
index 72cbba8..ce2a10f 100644
--- a/erpnext/hr/doctype/shift_assignment/shift_assignment.json
+++ b/erpnext/hr/doctype/shift_assignment/shift_assignment.json
@@ -10,9 +10,11 @@
   "employee",
   "employee_name",
   "shift_type",
+  "status",
   "column_break_3",
   "company",
-  "date",
+  "start_date",
+  "end_date",
   "shift_request",
   "department",
   "amended_from"
@@ -60,12 +62,6 @@
    "reqd": 1
   },
   {
-   "fieldname": "date",
-   "fieldtype": "Date",
-   "in_list_view": 1,
-   "label": "Date"
-  },
-  {
    "fieldname": "shift_request",
    "fieldtype": "Link",
    "label": "Shift Request",
@@ -80,11 +76,36 @@
    "options": "Shift Assignment",
    "print_hide": 1,
    "read_only": 1
+  },
+  {
+   "fieldname": "start_date",
+   "fieldtype": "Date",
+   "in_list_view": 1,
+   "label": "Start Date",
+   "reqd": 1
+  },
+  {
+   "allow_on_submit": 1,
+   "fieldname": "end_date",
+   "fieldtype": "Date",
+   "label": "End Date",
+   "show_days": 1,
+   "show_seconds": 1
+  },
+  {
+   "allow_on_submit": 1,
+   "default": "Active",
+   "fieldname": "status",
+   "fieldtype": "Select",
+   "label": "Status",
+   "options": "Active\nInactive",
+   "show_days": 1,
+   "show_seconds": 1
   }
  ],
  "is_submittable": 1,
  "links": [],
- "modified": "2019-12-12 15:49:06.956901",
+ "modified": "2020-06-15 14:27:54.310773",
  "modified_by": "Administrator",
  "module": "HR",
  "name": "Shift Assignment",
diff --git a/erpnext/hr/doctype/shift_assignment/shift_assignment.py b/erpnext/hr/doctype/shift_assignment/shift_assignment.py
index 40c78cd..e2bb980 100644
--- a/erpnext/hr/doctype/shift_assignment/shift_assignment.py
+++ b/erpnext/hr/doctype/shift_assignment/shift_assignment.py
@@ -11,38 +11,64 @@
 from erpnext.hr.doctype.holiday_list.holiday_list import is_holiday
 from datetime import timedelta, datetime
 
-class OverlapError(frappe.ValidationError): pass
-
 class ShiftAssignment(Document):
 	def validate(self):
 		self.validate_overlapping_dates()
 
+		if self.end_date and self.end_date <= self.start_date:
+			frappe.throw(_("End Date should not be less than Start Date"))
+
 	def validate_overlapping_dates(self):
-			if not self.name:
-				self.name = "New Shift Assignment"
+		if not self.name:
+			self.name = "New Shift Assignment"
 
-			d = frappe.db.sql("""
-				select
-					name, shift_type, date
-				from `tabShift Assignment`
-				where employee = %(employee)s and docstatus < 2
-				and date = %(date)s
-				and name != %(name)s""", {
-					"employee": self.employee,
-					"shift_type": self.shift_type,
-					"date": self.date,
-					"name": self.name
-				}, as_dict = 1)
+		condition = """and (
+				end_date is null
+				or
+					%(start_date)s between start_date and end_date
+		"""
 
-			for date_overlap in d:
-				if date_overlap['name']:
-					self.throw_overlap_error(date_overlap)
+		if self.end_date:
+			condition  += """ or
+					%(end_date)s between start_date and end_date
+					or
+					start_date between %(start_date)s and %(end_date)s
+				) """
+		else:
+			condition += """ ) """
 
-	def throw_overlap_error(self, d):
-		msg = _("Employee {0} has already applied for {1} on {2} : ").format(self.employee,
-			d['shift_type'], formatdate(d['date'])) \
-			+ """ <b><a href="#Form/Shift Assignment/{0}">{0}</a></b>""".format(d["name"])
-		frappe.throw(msg, OverlapError)
+		assigned_shifts = frappe.db.sql("""
+			select name, shift_type, start_date ,end_date, docstatus, status
+			from `tabShift Assignment`
+			where
+				employee=%(employee)s and docstatus < 2
+				and name != %(name)s
+				and status = "Active"
+				{0}
+		""".format(condition), {
+			"employee": self.employee,
+			"shift_type": self.shift_type,
+			"start_date": self.start_date,
+			"end_date": self.end_date,
+			"name": self.name
+		}, as_dict = 1)
+
+		for shift in assigned_shifts:
+			if shift.name:
+				self.throw_overlap_error(shift)
+
+	def throw_overlap_error(self, shift_details):
+		shift_details = frappe._dict(shift_details)
+		if shift_details.docstatus == 0:
+			msg = _("Employee {0} has already applied for {1}: {2}").format(self.employee, self.shift_type, shift_details.name)
+		if shift_details.docstatus == 1 and shift_details.status == "Active":
+			msg = _("Employee {0} already have Active Shift {1}: {2}").format(self.employee, self.shift_type, shift_details.name)
+		if shift_details.start_date:
+			msg += _(" from {0}").format(getdate(self.start_date).strftime("%d-%m-%Y"))
+			if shift_details.end_date:
+				msg += _(" to {0}").format(getdate(self.end_date).strftime("%d-%m-%Y"))
+		if msg:
+			frappe.throw(msg)
 
 @frappe.whitelist()
 def get_events(start, end, filters=None):
@@ -62,19 +88,22 @@
 	return events
 
 def add_assignments(events, start, end, conditions=None):
-	query = """select name, date, employee_name, 
+	query = """select name, start_date, end_date, employee_name,
 		employee, docstatus
 		from `tabShift Assignment` where
-		date <= %(date)s
-		and docstatus < 2"""
+		start_date >= %(start_date)s
+		and docstatus < 2""".format()
 	if conditions:
 		query += conditions
 
-	for d in frappe.db.sql(query, {"date":start, "date":end}, as_dict=True):
+	for d in frappe.db.sql(query, {"start_date":start}, as_dict=True):
+		from pprint import pprint
+		pprint(d)
 		e = {
 			"name": d.name,
 			"doctype": "Shift Assignment",
-			"date": d.date,
+			"start_date": d.start_date,
+			"end_date": d.end_date if d.end_date else nowdate(),
 			"title": cstr(d.employee_name) + \
 				cstr(d.shift_type),
 			"docstatus": d.docstatus
@@ -92,7 +121,14 @@
 	:param next_shift_direction: One of: None, 'forward', 'reverse'. Direction to look for next shift if shift not found on given date.
 	"""
 	default_shift = frappe.db.get_value('Employee', employee, 'default_shift')
-	shift_type_name = frappe.db.get_value('Shift Assignment', {'employee':employee, 'date': for_date, 'docstatus': '1'}, 'shift_type')
+	shift_assignment_details = frappe.db.get_value('Shift Assignment', {'employee':employee, 'start_date':('<=', for_date), 'docstatus': '1', 'status': "Active"}, ['shift_type', 'end_date'])
+
+	shift_type_name = shift_assignment_details[0]
+
+	# if end_date present means that shift is over after end_date else it is a ongoing shift.
+	if shift_assignment_details[1] and for_date >= shift_assignment_details[1] :
+		shift_type_name = None
+
 	if not shift_type_name and consider_default_shift:
 		shift_type_name = default_shift
 	if shift_type_name:
@@ -117,12 +153,13 @@
 			direction = '<' if next_shift_direction == 'reverse' else '>'
 			sort_order = 'desc' if next_shift_direction == 'reverse' else 'asc'
 			dates = frappe.db.get_all('Shift Assignment',
-				'date',
-				{'employee':employee, 'date':(direction, for_date), 'docstatus': '1'},
+				'start_date',
+				{'employee':employee, 'start_date':(direction, for_date), 'docstatus': '1', "status": "Active"},
 				as_list=True,
 				limit=MAX_DAYS, order_by="date "+sort_order)
+
 			for date in dates:
-				shift_details = get_employee_shift(employee, date[0], consider_default_shift, None)
+				shift_details = get_employee_shift(employee, date.start_date, consider_default_shift, None)
 				if shift_details:
 					shift_type_name = shift_details.shift_type.name
 					for_date = date[0]
@@ -134,7 +171,7 @@
 def get_employee_shift_timings(employee, for_timestamp=now_datetime(), consider_default_shift=False):
 	"""Returns previous shift, current/upcoming shift, next_shift for the given timestamp and employee
 	"""
-	# write and verify a test case for midnight shift. 
+	# write and verify a test case for midnight shift.
 	prev_shift = curr_shift = next_shift = None
 	curr_shift = get_employee_shift(employee, for_timestamp.date(), consider_default_shift, 'forward')
 	if curr_shift: