feat: apply customer withholding automatically on new receipts

Tick Apply Tax Withholding Amount on unsaved customer receipts whose
references include a Sales Invoice carrying withholding: in the
get_payment_entry override (Create > Payment), in the
allocate_amount_to_references doc method (Get Outstanding Invoices /
Paid Amount changes, so the tax row updates live) and on first save.
Saved entries keep the user's choice; unticking now removes the row.
Client script recomputes the row when the checkbox or category changes.

default_thai_company/hooks.py

@@ -196,11 +196,11 @@ doc_events = {
 
 # Overriding Methods
 # ------------------------------
-#
-# override_whitelisted_methods = {
-# 	"frappe.desk.doctype.event.event.get_events": "default_thai_company.event.get_events"
-# }
-#
+
+override_whitelisted_methods = {
+	"erpnext.accounts.doctype.payment_entry.payment_entry.get_payment_entry": "default_thai_company.tax_withholding.get_payment_entry",
+}
+
 # each overriding function accepts a `data` argument;
 # generated from the base implementation of the doctype dashboard,
 # along with any modifications made in other Frappe apps

default_thai_company/public/js/payment_entry.js

@@ -1,10 +1,29 @@
 frappe.ui.form.on("Payment Entry", {
 	apply_tax_withholding_amount(frm) {
-		if (frm.doc.party_type !== "Customer" || !frm.doc.apply_tax_withholding_amount) return;
+		if (frm.doc.party_type !== "Customer" || frm.doc.payment_type !== "Receive") return;
+		if (!frm.doc.apply_tax_withholding_amount) {
+			frm.events.recompute_customer_withholding(frm);
+			return;
+		}
 		// ERPNext's handler looks the category up on Supplier and clears it for a
 		// Customer; wait for that request to settle, then set the Customer's value.
 		frappe.db.get_value("Customer", frm.doc.party, "tax_withholding_category").then(({ message }) => {
-			frappe.after_ajax(() => frm.set_value("tax_withholding_category", message.tax_withholding_category));
+			frappe.after_ajax(() => {
+				frm.set_value("tax_withholding_category", message.tax_withholding_category);
+				frm.events.recompute_customer_withholding(frm);
+			});
 		});
 	},
+
+	tax_withholding_category(frm) {
+		if (frm.doc.party_type === "Customer" && frm.doc.payment_type === "Receive") {
+			frm.events.recompute_customer_withholding(frm);
+		}
+	},
+
+	recompute_customer_withholding(frm) {
+		// allocate_amount_to_references is overridden server-side to refresh the withholding row
+		if (!frm.doc.references || !frm.doc.references.length) return;
+		frm.events.allocate_party_amount_against_ref_docs(frm, frm.doc.paid_amount, false);
+	},
 });

default_thai_company/tax_withholding.py

@@ -1,6 +1,7 @@
 import erpnext
 import frappe
 from erpnext.accounts.doctype.payment_entry.payment_entry import PaymentEntry
+from erpnext.accounts.doctype.payment_entry.payment_entry import get_payment_entry as _get_payment_entry
 from erpnext.accounts.doctype.sales_invoice.sales_invoice import SalesInvoice
 from erpnext.accounts.doctype.tax_withholding_category.tax_withholding_category import (
 	get_tax_withholding_details,
@@ -171,6 +172,46 @@ class ThaiPaymentEntry(PaymentEntry):
 					entry.post_net_value = True
 		return gl_entries
 
+	@frappe.whitelist()
+	def allocate_amount_to_references(self, *args, **kwargs):
+		"""Called by the form after Get Outstanding Invoices and on Paid Amount
+		changes; keep the withholding row in step with the allocation."""
+		super().allocate_amount_to_references(*args, **kwargs)
+		if self.party_type == "Customer" and self.payment_type == "Receive" and self.source_exchange_rate:
+			auto_apply_customer_withholding(self)
+			set_customer_withholding(self)
+
+
+@frappe.whitelist()
+def get_payment_entry(*args, **kwargs):
+	"""Create > Payment from a Sales Invoice: arrive with withholding applied."""
+	pe = _get_payment_entry(*args, **kwargs)
+	if auto_apply_customer_withholding(pe) and pe.source_exchange_rate:
+		set_customer_withholding(pe)
+	return pe
+
+
+def auto_apply_customer_withholding(doc):
+	"""Tick Apply Tax Withholding Amount on a new customer receipt whose
+	references include a Sales Invoice that carries withholding. Only for
+	unsaved entries: after the first save the checkbox is the user's."""
+	if (
+		doc.party_type != "Customer"
+		or doc.payment_type != "Receive"
+		or doc.apply_tax_withholding_amount
+		or not doc.is_new()
+	):
+		return False
+
+	invoices = [r.reference_name for r in doc.references if r.reference_doctype == "Sales Invoice"]
+	if not invoices or not frappe.db.exists(
+		"Sales Invoice", {"name": ("in", invoices), "withholding_tax_amount": (">", 0)}
+	):
+		return False
+
+	doc.apply_tax_withholding_amount = 1
+	return True
+
 
 def set_customer_withholding(doc, method=None):
 	"""Payment Entry.validate: tax withheld by the customer on a Receive entry
@@ -184,21 +225,32 @@ def set_customer_withholding(doc, method=None):
 	the controller's validate, then re-runs the tax computation so the row's
 	base amounts and totals are final within this save.
 	"""
-	if doc.party_type != "Customer" or doc.payment_type != "Receive" or not doc.apply_tax_withholding_amount:
+	if doc.party_type != "Customer" or doc.payment_type != "Receive":
 		return
 
-	if not doc.tax_withholding_category:
-		doc.tax_withholding_category = frappe.db.get_value("Customer", doc.party, "tax_withholding_category")
+	if method == "validate":
+		auto_apply_customer_withholding(doc)
 
 	account = frappe.db.get_value(
 		"Account",
 		{"company": doc.company, "account_name": ASSET_ACCOUNT, "root_type": "Asset", "is_group": 0},
 	)
+	row = next((d for d in doc.taxes if d.account_head == account), None) if account else None
+
+	if not doc.apply_tax_withholding_amount:
+		if row:
+			doc.remove(row)
+			doc.apply_taxes()
+			doc.set_amounts_after_tax()
+		return
+
 	if not account:
 		frappe.throw(_("Account {0} not found for Company {1}").format(ASSET_ACCOUNT, doc.company))
 
+	if not doc.tax_withholding_category:
+		doc.tax_withholding_category = frappe.db.get_value("Customer", doc.party, "tax_withholding_category")
+
 	amount, description = get_customer_withholding(doc)
-	row = next((d for d in doc.taxes if d.account_head == account), None)
 
 	if not amount:
 		if row:

default_thai_company/tests/test_tax_withholding.py

@@ -6,7 +6,12 @@ from frappe.modules.utils import sync_customizations_for_doctype
 from frappe.tests.utils import FrappeTestCase
 from frappe.utils import nowdate
 
-from default_thai_company.tax_withholding import ASSET_ACCOUNT, LIABILITY_ACCOUNT, thai_companies
+from default_thai_company.tax_withholding import (
+	ASSET_ACCOUNT,
+	LIABILITY_ACCOUNT,
+	get_payment_entry,
+	thai_companies,
+)
 
 COMPANY = "_Test WHT Company"
 ABBR = "_TWC"
@@ -229,12 +234,42 @@ class TestTaxWithholding(FrappeTestCase):
 
 	def test_below_single_threshold_has_no_deduction(self):
 		si = self.make_invoice(rate=800)  # net 800 < 1,000 threshold
-		pe = self.make_receipt(si, allocated=856)
+		pe = self.make_receipt(si, allocated=856, apply=0)
+		self.assertEqual(pe.apply_tax_withholding_amount, 0)  # invoice carries no withholding
 		self.assertEqual(pe.taxes, [])
 		self.assertEqual(pe.received_amount_after_tax, 856.0)
 
-	def test_unchecked_receipt_is_untouched(self):
+	def test_create_payment_from_invoice_applies_withholding(self):
+		si = self.make_invoice()
+		pe = get_payment_entry("Sales Invoice", si.name, bank_account=f"Cash - {ABBR}")
+		self.assertEqual(pe.apply_tax_withholding_amount, 1)
+		self.assertEqual(pe.tax_withholding_category, "WHT 3% - Service")
+		self.assertEqual(self.withheld(pe), [(self.receivable, "Deduct", 300.0)])
+		self.assertEqual((pe.paid_amount, pe.received_amount_after_tax), (10700.0, 10400.0))
+		pe.insert()
+		self.assertEqual(self.withheld(pe), [(self.receivable, "Deduct", 300.0)])
+
+	def test_new_receipt_referencing_withheld_invoice_applies_on_save(self):
 		si = self.make_invoice()
 		pe = self.make_receipt(si, allocated=10700, apply=0)
+		self.assertEqual(pe.apply_tax_withholding_amount, 1)
+		self.assertEqual(self.withheld(pe), [(self.receivable, "Deduct", 300.0)])
+
+	def test_unticking_after_save_removes_withholding(self):
+		si = self.make_invoice()
+		pe = self.make_receipt(si, allocated=10700)
+		pe.apply_tax_withholding_amount = 0
+		pe.save()
+		self.assertEqual(pe.apply_tax_withholding_amount, 0)  # saved docs keep the user's choice
 		self.assertEqual(pe.taxes, [])
 		self.assertEqual(pe.received_amount_after_tax, 10700.0)
+
+	def test_reallocation_on_form_recomputes_withholding(self):
+		si = self.make_invoice()
+		pe = get_payment_entry("Sales Invoice", si.name, bank_account=f"Cash - {ABBR}")
+		pe.paid_amount = pe.received_amount = 5350
+		pe.allocate_amount_to_references(
+			paid_amount=5350, paid_amount_change=True, allocate_payment_amount=True
+		)
+		self.assertEqual(pe.references[0].allocated_amount, 5350.0)
+		self.assertEqual(self.withheld(pe), [(self.receivable, "Deduct", 150.0)])