feat: taxable-base resolver hook for custom charge types (#56175)

(cherry picked from commit 986cea2331)

erpnext/controllers/taxes_and_totals.py

@@ -314,33 +314,32 @@ class calculate_taxes_and_totals:
 		for item in self.doc.items:
 			item._unrounded_net_amount = None
 			item_tax_map = self._load_item_tax_rate(item.item_tax_rate)
-			cumulated_tax_fraction = 0
+			total_tax_slope = 0
-			total_inclusive_tax_amount_per_qty = 0
+			total_tax_intercept = 0
 			for i, tax in enumerate(self.doc.get("taxes")):
 				(
 					tax.tax_fraction_for_current_item,
-					inclusive_tax_amount_per_qty,
+					tax_intercept_per_qty,
-				) = self.get_current_tax_fraction(tax, item_tax_map)
+				) = self.get_current_tax_fraction(tax, item_tax_map, item)
+				tax.inclusive_amount_per_qty = tax_intercept_per_qty
 
 				if i == 0:
 					tax.grand_total_fraction_for_current_item = 1 + tax.tax_fraction_for_current_item
+					tax.grand_total_amount_per_qty = tax_intercept_per_qty
 				else:
+					prev = self.doc.get("taxes")[i - 1]
 					tax.grand_total_fraction_for_current_item = (
-						self.doc.get("taxes")[i - 1].grand_total_fraction_for_current_item
+						prev.grand_total_fraction_for_current_item + tax.tax_fraction_for_current_item
-						+ tax.tax_fraction_for_current_item
 					)
+					tax.grand_total_amount_per_qty = prev.grand_total_amount_per_qty + tax_intercept_per_qty
 
-				cumulated_tax_fraction += tax.tax_fraction_for_current_item
+				total_tax_slope += tax.tax_fraction_for_current_item
-				total_inclusive_tax_amount_per_qty += inclusive_tax_amount_per_qty * flt(item.qty)
+				total_tax_intercept += tax_intercept_per_qty * flt(item.qty)
 
-			if (
+			if not self.discount_amount_applied and item.qty and (total_tax_slope or total_tax_intercept):
-				not self.discount_amount_applied
+				amount = flt(item.amount) - total_tax_intercept
-				and item.qty
-				and (cumulated_tax_fraction or total_inclusive_tax_amount_per_qty)
-			):
-				amount = flt(item.amount) - total_inclusive_tax_amount_per_qty
 
-				item._unrounded_net_amount = amount / (1 + cumulated_tax_fraction)
+				item._unrounded_net_amount = amount / (1 + total_tax_slope)
 				item.net_amount = flt(item._unrounded_net_amount, item.precision("net_amount"))
 				item.net_rate = flt(item.net_amount / item.qty, item.precision("net_rate"))
 				item.discount_percentage = flt(
@@ -352,41 +351,48 @@ class calculate_taxes_and_totals:
 	def _load_item_tax_rate(self, item_tax_rate):
 		return json.loads(item_tax_rate) if item_tax_rate else {}
 
-	def get_current_tax_fraction(self, tax, item_tax_map):
+	def get_current_tax_fraction(self, tax, item_tax_map, item):
 		"""
-		Get tax fraction for calculating tax exclusive amount
+		tax = slope * net + intercept.
-		from tax inclusive amount
+		Returns (slope, intercept_per_qty)
 		"""
-		current_tax_fraction = 0
+		tax_slope = 0
-		inclusive_tax_amount_per_qty = 0
+		tax_intercept = 0
 
 		if cint(tax.included_in_print_rate):
 			tax_rate = self._get_tax_rate(tax, item_tax_map)
 
 			if tax_rate == NOT_APPLICABLE_TAX:
-				return current_tax_fraction, inclusive_tax_amount_per_qty
+				return tax_slope, tax_intercept
 
 			if tax.charge_type == "On Net Total":
-				current_tax_fraction = tax_rate / 100.0
+				tax_slope = tax_rate / 100.0
 
 			elif tax.charge_type == "On Previous Row Amount":
-				current_tax_fraction = (tax_rate / 100.0) * self.doc.get("taxes")[
+				row = self.doc.get("taxes")[cint(tax.row_id) - 1]
-					cint(tax.row_id) - 1
+				tax_slope = (tax_rate / 100.0) * row.tax_fraction_for_current_item
-				].tax_fraction_for_current_item
+				tax_intercept = (tax_rate / 100.0) * flt(getattr(row, "inclusive_amount_per_qty", 0))
 
 			elif tax.charge_type == "On Previous Row Total":
-				current_tax_fraction = (tax_rate / 100.0) * self.doc.get("taxes")[
+				row = self.doc.get("taxes")[cint(tax.row_id) - 1]
-					cint(tax.row_id) - 1
+				tax_slope = (tax_rate / 100.0) * row.grand_total_fraction_for_current_item
-				].grand_total_fraction_for_current_item
+				tax_intercept = (tax_rate / 100.0) * flt(getattr(row, "grand_total_amount_per_qty", 0))
 
 			elif tax.charge_type == "On Item Quantity":
-				inclusive_tax_amount_per_qty = flt(tax_rate)
+				tax_intercept = flt(tax_rate)
+
+			else:
+				# Custom charge_type: the rate applies to a resolved (fixed) base,
+				# e.g. a tax on MRP included in the printed price.
+				qty = flt(item.qty) or 1
+				base = self.get_item_taxable_base(item, tax)
+				tax_intercept = (tax_rate / 100.0) * base / qty
 
 		if getattr(tax, "add_deduct_tax", None) and tax.add_deduct_tax == "Deduct":
-			current_tax_fraction *= -1.0
+			tax_slope *= -1.0
-			inclusive_tax_amount_per_qty *= -1.0
+			tax_intercept *= -1.0
 
-		return current_tax_fraction, inclusive_tax_amount_per_qty
+		return tax_slope, tax_intercept
 
 	def _get_tax_rate(self, tax, item_tax_map):
 		if tax.account_head in item_tax_map:
@@ -612,7 +618,6 @@ class calculate_taxes_and_totals:
 		elif tax.charge_type == "On Net Total":
 			if tax.account_head in item_tax_map:
 				current_net_amount = item.net_amount
-
 			# Use unrounded net for inclusive taxes to avoid double rounding
 			if (
 				cint(tax.included_in_print_rate)
@@ -631,12 +636,46 @@ class calculate_taxes_and_totals:
 		elif tax.charge_type == "On Item Quantity":
 			# don't sum current net amount due to the field being a currency field
 			current_tax_amount = tax_rate * item.qty
+		else:
+			# Custom charge_type: rate applies to the resolver-provided base.
+			base = self.get_item_taxable_base(item, tax)
+			current_net_amount = base
+			current_tax_amount = (tax_rate / 100.0) * base
 
 		if not tax.get("dont_recompute_tax"):
 			self.set_item_wise_tax(item, tax, tax_rate, current_tax_amount, current_net_amount)
 
 		return current_net_amount, current_tax_amount
 
+	def get_item_taxable_base(self, item, tax):
+		"""Per-item base a custom charge_type's rate is applied to.
+
+		Override the base (gross, MRP, net of other taxes, …) via the
+		`erpnext_taxable_base_resolvers` hook
+
+		Register a resolver in `hooks.py`, keyed by charge_type:
+
+		        erpnext_taxable_base_resolvers = {"On Gross Amount": "my_app.taxes.gross_base"}
+
+		It receives (calc, item, tax) — calc is this instance, calc.doc the parent —
+		and returns the base (flt-coerced by the caller):
+
+		        def gross_base(calc, item, tax):
+		                return item.custom_field_mrp * item.qty
+
+		A resolver may stamp transient attributes on `item`; it can be called more than once
+		per item, so such stamping must be idempotent.
+		"""
+		resolvers = frappe.get_hooks("erpnext_taxable_base_resolvers") or {}
+		path = resolvers.get(tax.charge_type)
+
+		if path:
+			method = path[-1] if isinstance(path, list | tuple) else path
+			return flt(frappe.get_attr(method)(self, item, tax))
+
+		# fallback
+		return flt(item.net_amount)
+
 	def set_item_wise_tax(self, item, tax, tax_rate, current_tax_amount, current_net_amount):
 		# store tax breakup for each item
 		multiplier = -1 if tax.get("add_deduct_tax") == "Deduct" else 1

erpnext/controllers/tests/test_taxes_and_totals.py

@@ -1,12 +1,24 @@
+from unittest import mock
 from unittest.mock import patch
 
 import frappe
+from frappe.utils import flt
 
 from erpnext.controllers.taxes_and_totals import calculate_taxes_and_totals
 from erpnext.selling.doctype.sales_order.test_sales_order import make_sales_order
 from erpnext.tests.utils import ERPNextTestSuite
 
 
+def resolve_on_gross(calc, item, tax):
+	# base = gross printed line amount
+	return flt(item.amount)
+
+
+def resolve_on_mrp(calc, item, tax):
+	# base = MRP, not net
+	return flt(item.price_list_rate) * flt(item.qty)
+
+
 class TestTaxesAndTotals(ERPNextTestSuite):
 	def test_regional_round_off_accounts(self):
 		"""
@@ -30,6 +42,93 @@ class TestTaxesAndTotals(ERPNextTestSuite):
 
 		self.assertIn(test_account, frappe.flags.round_off_applicable_accounts)
 
+	def test_exclusive_custom_charge_on_resolved_base(self):
+		"""Added (exclusive) custom charge_type whose base is resolved by the
+		`erpnext_taxable_base_resolvers` hook. IPI 10% on the gross product value 1000
+		-> tax 100, net 1000, grand 1100."""
+		so = make_sales_order(do_not_save=True)
+		so.items = []
+		so.append(
+			"items",
+			{
+				"item_code": "_Test Item",
+				"qty": 1,
+				"rate": 1000,
+				"price_list_rate": 1000,
+				"warehouse": "_Test Warehouse - _TC",
+			},
+		)
+		so.set("taxes", [])
+		so.append(
+			"taxes",
+			{
+				"charge_type": "On Gross Value",
+				"account_head": "_Test Account Excise Duty - _TC",
+				"description": "IPI 10% on gross product value",
+				"rate": 10,
+				"cost_center": "_Test Cost Center - _TC",
+			},
+		)
+
+		real_get_hooks = frappe.get_hooks
+
+		def fake_get_hooks(hook=None, *args, **kwargs):
+			if hook == "erpnext_taxable_base_resolvers":
+				return {
+					"On Gross Value": ["erpnext.controllers.tests.test_taxes_and_totals.resolve_on_gross"]
+				}
+			return real_get_hooks(hook, *args, **kwargs)
+
+		with mock.patch("frappe.get_hooks", side_effect=fake_get_hooks):
+			calculate_taxes_and_totals(so)
+
+		self.assertEqual(so.net_total, 1000.0)
+		self.assertEqual(so.taxes[0].tax_amount, 100.0)
+		self.assertEqual(so.grand_total, 1100.0)
+
+	def test_inclusive_custom_charge_on_resolved_base(self):
+		"""Inclusive custom charge on a resolved base backs out non-compounding
+		(tax = rate x resolved base) — a resolved base is fixed, so it never
+		compounds. MRP 1200, printed 1000, rate 10%: tax 120, net 880."""
+		so = make_sales_order(do_not_save=True)
+		so.items = []
+		so.append(
+			"items",
+			{
+				"item_code": "_Test Item",
+				"qty": 1,
+				"rate": 1000,
+				"price_list_rate": 1200,
+				"warehouse": "_Test Warehouse - _TC",
+			},
+		)
+		so.set("taxes", [])
+		so.append(
+			"taxes",
+			{
+				"charge_type": "On MRP",
+				"account_head": "_Test Account VAT - _TC",
+				"description": "Tax 10% on MRP, inclusive",
+				"rate": 10,
+				"included_in_print_rate": 1,
+				"cost_center": "_Test Cost Center - _TC",
+			},
+		)
+
+		real_get_hooks = frappe.get_hooks
+
+		def fake_get_hooks(hook=None, *args, **kwargs):
+			if hook == "erpnext_taxable_base_resolvers":
+				return {"On MRP": ["erpnext.controllers.tests.test_taxes_and_totals.resolve_on_mrp"]}
+			return real_get_hooks(hook, *args, **kwargs)
+
+		with mock.patch("frappe.get_hooks", side_effect=fake_get_hooks):
+			calculate_taxes_and_totals(so)
+
+		self.assertEqual(so.taxes[0].tax_amount, 120.0)
+		self.assertEqual(so.net_total, 880.0)
+		self.assertEqual(so.grand_total, 1000.0)
+
 	def test_disabling_rounded_total_resets_base_fields(self):
 		"""Disabling rounded total should also clear base rounded values."""
 		so = make_sales_order(do_not_save=True)

erpnext/public/js/controllers/taxes_and_totals.js

@@ -3,6 +3,11 @@
 
 const NOT_APPLICABLE_TAX = "N/A";
 
+// Per-charge_type base resolvers, mirror of the `erpnext_taxable_base_resolvers`
+// server hook. A localization registers `fn(calc, item, tax)` returning the per-item
+// base, so the client preview matches the server for custom charge types.
+erpnext.taxable_base_resolvers = erpnext.taxable_base_resolvers || {};
+
 erpnext.taxes_and_totals = class TaxesAndTotals extends erpnext.payments {
 	setup() {
 		this.fetch_round_off_accounts();
@@ -278,32 +283,32 @@ erpnext.taxes_and_totals = class TaxesAndTotals extends erpnext.payments {
 		$.each(this.frm.doc.items || [], function (n, item) {
 			item._unrounded_net_amount = null;
 			var item_tax_map = me._load_item_tax_rate(item.item_tax_rate);
-			var cumulated_tax_fraction = 0.0;
+			var total_tax_slope = 0.0;
-			var total_inclusive_tax_amount_per_qty = 0;
+			var total_tax_intercept = 0;
 			$.each(me.frm.doc["taxes"] || [], function (i, tax) {
-				var current_tax_fraction = me.get_current_tax_fraction(tax, item_tax_map);
+				var tax_contribution = me.get_current_tax_fraction(tax, item_tax_map, item);
-				tax.tax_fraction_for_current_item = current_tax_fraction[0];
+				tax.tax_fraction_for_current_item = tax_contribution[0];
-				var inclusive_tax_amount_per_qty = current_tax_fraction[1];
+				var tax_intercept_per_qty = tax_contribution[1];
+				tax.inclusive_amount_per_qty = tax_intercept_per_qty;
 
 				if (i == 0) {
 					tax.grand_total_fraction_for_current_item = 1 + tax.tax_fraction_for_current_item;
+					tax.grand_total_amount_per_qty = tax_intercept_per_qty;
 				} else {
+					var prev = me.frm.doc["taxes"][i - 1];
 					tax.grand_total_fraction_for_current_item =
-						me.frm.doc["taxes"][i - 1].grand_total_fraction_for_current_item +
+						prev.grand_total_fraction_for_current_item + tax.tax_fraction_for_current_item;
-						tax.tax_fraction_for_current_item;
+					tax.grand_total_amount_per_qty =
+						flt(prev.grand_total_amount_per_qty) + tax_intercept_per_qty;
 				}
 
-				cumulated_tax_fraction += tax.tax_fraction_for_current_item;
+				total_tax_slope += tax.tax_fraction_for_current_item;
-				total_inclusive_tax_amount_per_qty += inclusive_tax_amount_per_qty * flt(item.qty);
+				total_tax_intercept += tax_intercept_per_qty * flt(item.qty);
 			});
 
-			if (
+			if (!me.discount_amount_applied && item.qty && (total_tax_intercept || total_tax_slope)) {
-				!me.discount_amount_applied &&
+				var amount = flt(item.amount) - total_tax_intercept;
-				item.qty &&
+				item._unrounded_net_amount = amount / (1 + total_tax_slope);
-				(total_inclusive_tax_amount_per_qty || cumulated_tax_fraction)
-			) {
-				var amount = flt(item.amount) - total_inclusive_tax_amount_per_qty;
-				item._unrounded_net_amount = amount / (1 + cumulated_tax_fraction);
 				item.net_amount = flt(item._unrounded_net_amount, precision("net_amount", item));
 				item.net_rate = item.qty ? flt(item.net_amount / item.qty, precision("net_rate", item)) : 0;
 
@@ -312,39 +317,53 @@ erpnext.taxes_and_totals = class TaxesAndTotals extends erpnext.payments {
 		});
 	}
 
-	get_current_tax_fraction(tax, item_tax_map) {
+	get_current_tax_fraction(tax, item_tax_map, item) {
-		// Get tax fraction for calculating tax exclusive amount
+		// tax = slope * net + intercept.
-		// from tax inclusive amount
+		// Returns [slope, intercept_per_qty]
-		var current_tax_fraction = 0.0;
+		var tax_slope = 0.0;
-		var inclusive_tax_amount_per_qty = 0;
+		var tax_intercept = 0;
 
 		if (cint(tax.included_in_print_rate)) {
 			var tax_rate = this._get_tax_rate(tax, item_tax_map);
 
 			if (tax_rate === NOT_APPLICABLE_TAX) {
-				return [current_tax_fraction, inclusive_tax_amount_per_qty];
+				return [tax_slope, tax_intercept];
 			}
 
 			if (tax.charge_type == "On Net Total") {
-				current_tax_fraction = tax_rate / 100.0;
+				tax_slope = tax_rate / 100.0;
 			} else if (tax.charge_type == "On Previous Row Amount") {
-				current_tax_fraction =
+				const row = this.frm.doc["taxes"][cint(tax.row_id) - 1];
-					(tax_rate / 100.0) *
+				tax_slope = (tax_rate / 100.0) * row.tax_fraction_for_current_item;
-					this.frm.doc["taxes"][cint(tax.row_id) - 1].tax_fraction_for_current_item;
+				tax_intercept = (tax_rate / 100.0) * flt(row.inclusive_amount_per_qty);
 			} else if (tax.charge_type == "On Previous Row Total") {
-				current_tax_fraction =
+				const row = this.frm.doc["taxes"][cint(tax.row_id) - 1];
-					(tax_rate / 100.0) *
+				tax_slope = (tax_rate / 100.0) * row.grand_total_fraction_for_current_item;
-					this.frm.doc["taxes"][cint(tax.row_id) - 1].grand_total_fraction_for_current_item;
+				tax_intercept = (tax_rate / 100.0) * flt(row.grand_total_amount_per_qty);
 			} else if (tax.charge_type == "On Item Quantity") {
-				inclusive_tax_amount_per_qty = flt(tax_rate);
+				tax_intercept = flt(tax_rate);
+			} else {
+				// Custom charge_type: the rate applies to a resolved (fixed) base,
+				// e.g. a tax on MRP included in the printed price.
+				const qty = flt(item.qty) || 1;
+				const base = this.get_item_taxable_base(item, tax);
+				tax_intercept = ((tax_rate / 100.0) * base) / qty;
 			}
 		}
 
 		if (tax.add_deduct_tax && tax.add_deduct_tax == "Deduct") {
-			current_tax_fraction *= -1;
+			tax_slope *= -1;
-			inclusive_tax_amount_per_qty *= -1;
+			tax_intercept *= -1;
 		}
-		return [current_tax_fraction, inclusive_tax_amount_per_qty];
+		return [tax_slope, tax_intercept];
+	}
+
+	get_item_taxable_base(item, tax) {
+		// Mirror of the server get_item_taxable_base: a custom charge_type's resolver
+		// overrides the base value; otherwise the net amount.
+		const resolver = erpnext.taxable_base_resolvers[tax.charge_type];
+		if (resolver) return flt(resolver(this, item, tax));
+		return flt(item.net_amount);
 	}
 
 	_get_tax_rate(tax, item_tax_map) {
@@ -606,6 +625,11 @@ erpnext.taxes_and_totals = class TaxesAndTotals extends erpnext.payments {
 		} else if (tax.charge_type == "On Item Quantity") {
 			// don't sum current net amount due to the field being a currency field
 			current_tax_amount = tax_rate * item.qty;
+		} else {
+			// Custom charge_type: rate applies to the resolver-provided base.
+			var resolved_base = this.get_item_taxable_base(item, tax);
+			current_net_amount = resolved_base;
+			current_tax_amount = (tax_rate / 100.0) * resolved_base;
 		}
 
 		return [current_net_amount, current_tax_amount];