refactor: Use status_updater as a class property

[marination]

Issue

• The current design entirely relies on __init__ to resolve/set the status_updater attribute
• Any changes to this attribute are later manually done elsewhere before evaluating the status_updater (on submit/cancel)
• This works fine via desk because each save/submit/cancel action creates a new instance of the class and so status_updater is (re)initialized with the doc's newer values
• This does not work fine/is not intuitive via scripts/tests. I discovered this while writing a test

Example:

Consider the status_updater in delivery_note.py where:

1 def __init__(self):
2	# Watered down for obvious reasons
3	...
4	self.status_updater = [1, 2]
5	if cint(self.is_return):
6		self.status_updater.extend([3,4])

On instantiation of class DeliveryNote if it does not have the document values, line 5 does not evaluate to True ever.

# Creates an instance of a Delivery Note -> runs `__init__` -> `self.status_updater` is computed and set
# `self.is_return` is falsy. So even though we intend to create a return document the status updater has an incorrect state
1	delivery_note_return = frappe.new_doc("Delivery Note")
# `self.status_updater` is already initialized so this has no automatic impact
2	delivery_note_return.is_return = 1
3	...
# Does not back update some fields because [3,4] are missing
4	delivery_note.submit()

---

_Our solution here is to modify this attribute explicitly, which now has to be done in tests as well._

Solution

• Switch this attribute to a property that dynamically determines status_updater based on the document's current state
• Behaviours are now predictable and status_updater's value definition is in one place

A pattern like:

def __init__(self):
	...
	self.status_updater = [1]

def on_submit(self):
	if self.some_value:
		self.status_updater = []
	self.status_updater.append(2)

	self.update_prevdoc_status()  # Applies the status updater

def on_cancel(self):
	if self.some_value:
		self.status_updater = []
	self.status_updater.append(2)

	self.update_prevdoc_status()  # Applies the status updater

Is rewritten like this:

def __init__(self):
	...

@property
def status_updater(self):
	updater = [2]
	if not self.some_value:
		updater.append(1)
	return updater

def on_submit(self):
	self.update_prevdoc_status()  # Applies the status updater

def on_cancel(self):
	self.update_prevdoc_status()  # Applies the status updater

Todo:

• Add a setter for the property as other apps might use self.status_updater = ...

[marination]

Buggy behaviour in tests is highlighted even more with breaking tests 😄
Eg:

• In many tests, return documents (like a return delivery note), did not update the linked previous delivery note
• Now that it does (it behaves exactly like it does in desk!), we have timestamp errors because the first DN doc instance needs to be reloaded before cancellation (return DN modified it)