feat: LIFOValuation class for handling LIFO

erpnext/stock/tests/test_valuation.py

@@ -3,14 +3,14 @@ import unittest
 from hypothesis import given
 from hypothesis import strategies as st
 
-from erpnext.stock.valuation import FIFOValuation, _round_off_if_near_zero
+from erpnext.stock.valuation import FIFOValuation, LIFOValuation, _round_off_if_near_zero
 
 qty_gen = st.floats(min_value=-1e6, max_value=1e6)
 value_gen = st.floats(min_value=1, max_value=1e6)
 stock_queue_generator = st.lists(st.tuples(qty_gen, value_gen), min_size=10)
 
 
-class TestFifoValuation(unittest.TestCase):
+class TestFIFOValuation(unittest.TestCase):
 
 	def setUp(self):
 		self.queue = FIFOValuation([])
@@ -164,3 +164,123 @@ class TestFifoValuation(unittest.TestCase):
 				total_value -= sum(q * r for q, r in consumed)
 			self.assertTotalQty(total_qty)
 			self.assertTotalValue(total_value)
+
+
+class TestLIFOValuation(unittest.TestCase):
+
+	def setUp(self):
+		self.stack = LIFOValuation([])
+
+	def tearDown(self):
+		qty, value = self.stack.get_total_stock_and_value()
+		self.assertTotalQty(qty)
+		self.assertTotalValue(value)
+
+	def assertTotalQty(self, qty):
+		self.assertAlmostEqual(sum(q for q, _ in self.stack), qty, msg=f"stack: {self.stack}", places=4)
+
+	def assertTotalValue(self, value):
+		self.assertAlmostEqual(sum(q * r for q, r in self.stack), value, msg=f"stack: {self.stack}", places=2)
+
+	def test_simple_addition(self):
+		self.stack.add_stock(1, 10)
+		self.assertTotalQty(1)
+
+	def test_merge_new_stock(self):
+		self.stack.add_stock(1, 10)
+		self.stack.add_stock(1, 10)
+		self.assertEqual(self.stack, [[2, 10]])
+
+	def test_simple_removal(self):
+		self.stack.add_stock(1, 10)
+		self.stack.remove_stock(1)
+		self.assertTotalQty(0)
+
+	def test_adding_negative_stock_keeps_rate(self):
+		self.stack = LIFOValuation([[-5.0, 100]])
+		self.stack.add_stock(1, 10)
+		self.assertEqual(self.stack, [[-4, 100]])
+
+	def test_adding_negative_stock_updates_rate(self):
+		self.stack = LIFOValuation([[-5.0, 100]])
+		self.stack.add_stock(6, 10)
+		self.assertEqual(self.stack, [[1, 10]])
+
+	def test_rounding_off(self):
+		self.stack.add_stock(1.0, 1.0)
+		self.stack.remove_stock(1.0 - 1e-9)
+		self.assertTotalQty(0)
+
+	def test_lifo_consumption(self):
+		self.stack.add_stock(10, 10)
+		self.stack.add_stock(10, 20)
+		consumed = self.stack.remove_stock(15)
+		self.assertEqual(consumed, [[10, 20], [5, 10]])
+		self.assertTotalQty(5)
+
+	def test_lifo_consumption_going_negative(self):
+		self.stack.add_stock(10, 10)
+		self.stack.add_stock(10, 20)
+		consumed = self.stack.remove_stock(25)
+		self.assertEqual(consumed, [[10, 20], [10, 10], [5, 10]])
+		self.assertTotalQty(-5)
+
+	def test_lifo_consumption_multiple(self):
+		self.stack.add_stock(1, 1)
+		self.stack.add_stock(2, 2)
+		consumed = self.stack.remove_stock(1)
+		self.assertEqual(consumed, [[1, 2]])
+
+		self.stack.add_stock(3, 3)
+		consumed = self.stack.remove_stock(4)
+		self.assertEqual(consumed, [[3, 3], [1, 2]])
+
+		self.stack.add_stock(4, 4)
+		consumed = self.stack.remove_stock(5)
+		self.assertEqual(consumed, [[4, 4], [1, 1]])
+
+		self.stack.add_stock(5, 5)
+		consumed = self.stack.remove_stock(5)
+		self.assertEqual(consumed, [[5, 5]])
+
+
+	@given(stock_queue_generator)
+	def test_lifo_qty_hypothesis(self, stock_stack):
+		self.stack = LIFOValuation([])
+		total_qty = 0
+
+		for qty, rate in stock_stack:
+			if qty == 0:
+				continue
+			if qty > 0:
+				self.stack.add_stock(qty, rate)
+				total_qty += qty
+			else:
+				qty = abs(qty)
+				consumed = self.stack.remove_stock(qty)
+				self.assertAlmostEqual(qty, sum(q for q, _ in consumed), msg=f"incorrect consumption {consumed}")
+				total_qty -= qty
+			self.assertTotalQty(total_qty)
+
+	@given(stock_queue_generator)
+	def test_lifo_qty_value_nonneg_hypothesis(self, stock_stack):
+		self.stack = LIFOValuation([])
+		total_qty = 0.0
+		total_value = 0.0
+
+		for qty, rate in stock_stack:
+			# don't allow negative stock
+			if qty == 0 or total_qty + qty < 0 or abs(qty) < 0.1:
+				continue
+			if qty > 0:
+				self.stack.add_stock(qty, rate)
+				total_qty += qty
+				total_value += qty * rate
+			else:
+				qty = abs(qty)
+				consumed = self.stack.remove_stock(qty)
+				self.assertAlmostEqual(qty, sum(q for q, _ in consumed), msg=f"incorrect consumption {consumed}")
+				total_qty -= qty
+				total_value -= sum(q * r for q, r in consumed)
+			self.assertTotalQty(total_qty)
+			self.assertTotalValue(total_value)

erpnext/stock/valuation.py

@@ -3,7 +3,7 @@ from typing import Callable, List, NewType, Optional, Tuple
 
 from frappe.utils import flt
 
-StockBin = NewType("FifoBin", List[float])
+StockBin = NewType("StockBin", List[float])  # [[qty, rate], ...]
 
 # Indexes of values inside FIFO bin 2-tuple
 QTY = 0
@@ -164,11 +164,12 @@ class LIFOValuation(BinWiseValuation):
 	Stack is implemented using "bins" of [qty, rate].
 
 	ref: https://en.wikipedia.org/wiki/FIFO_and_LIFO_accounting
+	Implementation detail: appends and pops both at end of list.
 	"""
 
 	# specifying the attributes to save resources
 	# ref: https://docs.python.org/3/reference/datamodel.html#slots
-	__slots__ = ["queue",]
+	__slots__ = ["stack",]
 
 	def __init__(self, state: Optional[List[StockBin]]):
 		self.stack: List[StockBin] = state if state is not None else []
@@ -183,8 +184,26 @@ class LIFOValuation(BinWiseValuation):
 
 			args:
 				qty: new quantity to add
-				rate: incoming rate of new quantity"""
-		pass
+				rate: incoming rate of new quantity.
+
+			Behaviour of this is same as FIFO valuation.
+		"""
+		if not len(self.stack):
+			self.stack.append([0, 0])
+
+		# last row has the same rate, merge new bin.
+		if self.stack[-1][RATE] == rate:
+			self.stack[-1][QTY] += qty
+		else:
+			# Item has a positive balance qty, add new entry
+			if self.stack[-1][QTY] > 0:
+				self.stack.append([qty, rate])
+			else:  # negative balance qty
+				qty = self.stack[-1][QTY] + qty
+				if qty > 0:  # new balance qty is positive
+					self.stack[-1] = [qty, rate]
+				else:  # new balance qty is still negative, maintain same rate
+					self.stack[-1][QTY] = qty
 
 
 	def remove_stock(
@@ -194,10 +213,41 @@ class LIFOValuation(BinWiseValuation):
 
 		args:
 			qty: quantity to remove
-			rate: outgoing rate
+			rate: outgoing rate - ignored. Kept for backwards compatibility.
 			rate_generator: function to be called if stack is not found and rate is required.
 		"""
-		pass
+		if not rate_generator:
+			rate_generator = lambda : 0.0  # noqa
+
+		consumed_bins = []
+		while qty:
+			if not len(self.stack):
+				# rely on rate generator.
+				self.stack.append([0, rate_generator()])
+
+			# start at the end.
+			index = -1
+
+			stock_bin = self.stack[index]
+			if qty >= stock_bin[QTY]:
+				# consume current bin
+				qty = _round_off_if_near_zero(qty - stock_bin[QTY])
+				to_consume = self.stack.pop(index)
+				consumed_bins.append(list(to_consume))
+
+				if not self.stack and qty:
+					# stock finished, qty still remains to be withdrawn
+					# negative stock, keep in as a negative bin
+					self.stack.append([-qty, outgoing_rate or stock_bin[RATE]])
+					consumed_bins.append([qty, outgoing_rate or stock_bin[RATE]])
+					break
+			else:
+				# qty found in current bin consume it and exit
+				stock_bin[QTY] = _round_off_if_near_zero(stock_bin[QTY] - qty)
+				consumed_bins.append([qty, stock_bin[RATE]])
+				qty = 0
+
+		return consumed_bins
 
 
 def _round_off_if_near_zero(number: float, precision: int = 7) -> float: