feat: support taxable value overrides for custom resolvers

india_compliance/gst_india/constants/custom_fields.py

@@ -1556,6 +1556,41 @@
     "Supplier Quotation": {**reverse_charge_field, "insert_after": "has_unit_price_items"},
 }
 
+# no fallback: a blank value means 0
+SALES_ITEM_DOCTYPES = (
+    "Quotation Item",
+    "Sales Order Item",
+    "Delivery Note Item",
+    "Sales Invoice Item",
+    "POS Invoice Item",
+)
+
+RSP_FIELDS = {
+    SALES_ITEM_DOCTYPES: {
+        "fieldname": "gst_retail_sale_price",
+        "label": "Retail Sale Price (MRP)",
+        "fieldtype": "Currency",
+        "options": "Company:company:default_currency",
+        "insert_after": "price_list_rate",
+        "hidden": 1,
+        "print_hide": 1,
+        "translatable": 0,
+    }
+}
+
+MARGIN_FIELDS = {
+    SALES_ITEM_DOCTYPES: {
+        "fieldname": "gst_purchase_price",
+        "label": "Purchase Price",
+        "fieldtype": "Currency",
+        "options": "Company:company:default_currency",
+        "insert_after": "gst_retail_sale_price",
+        "hidden": 1,
+        "print_hide": 1,
+        "translatable": 0,
+    }
+}
+
 E_INVOICE_FIELDS = {
     "Sales Invoice": [
         {

india_compliance/gst_india/doctype/gst_settings/gst_settings.json

@@ -9,6 +9,8 @@
   "hsn_wise_tax_breakup",
   "enable_reverse_charge_in_sales",
   "enable_overseas_transactions",
+  "enable_taxes_on_mrp",
+  "enable_margin_scheme",
   "enable_sales_through_ecommerce_operators",
   "round_off_gst_values",
   "require_supplier_invoice_no",
@@ -258,6 +260,20 @@
    "fieldtype": "Check",
    "label": "Enable Reverse Charge in Sales Transactions"
   },
+  {
+   "default": "0",
+   "description": "Adds the 'On MRP' charge type for RSP-based valuation (e.g. tobacco, Rule 31D). Enter the Retail Sale Price (MRP) in company currency per item row.",
+   "fieldname": "enable_taxes_on_mrp",
+   "fieldtype": "Check",
+   "label": "Enable Taxes on MRP"
+  },
+  {
+   "default": "0",
+   "description": "Adds the 'On Margin' charge type for the margin scheme (Rule 32(5)). Enter the Purchase Price in company currency per item row.",
+   "fieldname": "enable_margin_scheme",
+   "fieldtype": "Check",
+   "label": "Enable Margin Scheme"
+  },
   {
    "default": "0",
    "depends_on": "eval: doc.enable_e_waybill",

india_compliance/gst_india/doctype/gst_settings/gst_settings.py

@@ -15,6 +15,8 @@
 from india_compliance.gst_india.constants.custom_fields import (
     E_INVOICE_FIELDS,
     E_WAYBILL_FIELDS,
+    MARGIN_FIELDS,
+    RSP_FIELDS,
     SALES_REVERSE_CHARGE_FIELDS,
 )
 from india_compliance.gst_india.doctype.gst_return_log.gst_return_log import (
@@ -217,6 +219,19 @@ def update_custom_fields(self):
         if self.has_value_changed("enable_reverse_charge_in_sales"):
             toggle_custom_fields(SALES_REVERSE_CHARGE_FIELDS, self.enable_reverse_charge_in_sales)
 
+        if self.has_value_changed("enable_taxes_on_mrp"):
+            toggle_custom_fields(RSP_FIELDS, self.enable_taxes_on_mrp)
+
+        if self.has_value_changed("enable_margin_scheme"):
+            toggle_custom_fields(MARGIN_FIELDS, self.enable_margin_scheme)
+
+        if self.has_value_changed("enable_taxes_on_mrp") or self.has_value_changed("enable_margin_scheme"):
+            from india_compliance.gst_india.setup.property_setters import (
+                toggle_charge_type_options,
+            )
+
+            toggle_charge_type_options(self)
+
         if self.has_value_changed("enable_e_waybill_from_asset_movement") and (
             self.enable_e_waybill_from_asset_movement
         ):

india_compliance/gst_india/overrides/taxable_value.py

@@ -0,0 +1,76 @@
+import frappe
+from frappe.utils import flt
+
+from india_compliance.gst_india.constants import TAX_TYPES
+
+
+def get_item_taxable_value(doc, item, default):
+    # reset: the same item is resolved again on every save
+    item._dont_update_taxable_value = False
+    item._deemed_taxable_value = None
+
+    resolvers = frappe.get_hooks("erpnext_taxable_base_resolvers") or {}
+    if not resolvers:
+        return default
+
+    for tax in doc.get("taxes") or []:
+        if tax.get("gst_tax_type") not in TAX_TYPES:
+            continue
+
+        path = resolvers.get(tax.charge_type)
+        if not path:
+            continue
+
+        method = path[-1] if isinstance(path, list | tuple) else path
+        base = flt(frappe.get_attr(method)(frappe._dict(doc=doc), item, tax))
+
+        # a resolver may tax a deemed base but report the net value (MRP)
+        if getattr(item, "_dont_update_taxable_value", None):
+            return default
+
+        return base * flt(doc.get("conversion_rate") or 1)
+
+    return default
+
+
+def _item_rate(item, tax):
+    item_tax_rate = frappe.parse_json(item.get("item_tax_rate")) or {}
+
+    if tax.get("account_head") in item_tax_rate:
+        return flt(item_tax_rate[tax.account_head])
+
+    return flt(tax.get("rate"))
+
+
+def _inclusive_rate(doc, item, tax):
+    # CGST and SGST rows share one base, so their rates add up
+    rates = [_item_rate(item, t) for t in doc.get("taxes") or [] if t.charge_type == tax.charge_type]
+    return sum(rates) or _item_rate(item, tax)
+
+
+# Rule 31D: tax from the MRP, report the net sale value
+def on_mrp(calc, item, tax):
+    conversion_rate = flt(calc.doc.get("conversion_rate")) or 1
+    rate = _inclusive_rate(calc.doc, item, tax)
+    rsp = flt(item.get("gst_retail_sale_price")) * flt(item.qty) / conversion_rate
+    deemed = rsp * 100 / (100 + rate) if rate else rsp
+
+    item._dont_update_taxable_value = True
+    item._deemed_taxable_value = deemed * conversion_rate
+
+    return deemed
+
+
+# Rule 32(5): only the margin is taxed; Rule 35 takes GST out when the price includes it
+def on_margin(calc, item, tax):
+    conversion_rate = flt(calc.doc.get("conversion_rate")) or 1
+    cost = flt(item.get("gst_purchase_price")) * flt(item.qty) / conversion_rate
+    margin = flt(item.amount) - cost
+    if abs(flt(item.amount)) < abs(cost):
+        margin = 0
+
+    if not tax.get("included_in_print_rate"):
+        return margin
+
+    rate = _inclusive_rate(calc.doc, item, tax)
+    return margin * 100 / (100 + rate) if rate else margin