Initial Domain Model with Tests

Author: jeantardelli

model.py

@@ -3,6 +3,19 @@
 from datetime import date
 from typing import Optional, List, Set
 
+class OutOfStock(Exception):
+ pass
+
+def allocate(line: OrderLine, batches: List[Batch]) -> str:
+ try:
+ batch = next(b for b in sorted(batches) if b.can_allocate(line))
+ batch.allocate(line)
+
+ return batch.reference
+
+ except StopIteration:
+ raise OutOfStock(f"Out of stock for sku {line.sku}")
+
 @dataclass(frozen=True)
 class OrderLine:
  orderid: str
@@ -14,10 +27,42 @@ def __init__(self, ref: str, sku: str, qty: int, eta: Optional[date]):
  self.reference = ref
  self.sku = sku
  self.eta = eta
- self.available_quantity = qty
+ self._purchased_quantity = qty
+ self._allocations = set() # type: Set[OrderLine]
+
+ def __repr__(self):
+ return f"<Batch {self.reference}>"
+
+ def __eq__(self, other):
+ if not isinstance(other, Batch):
+ return False
+ return other.reference == self.reference
+
+ def __hash__(self):
+ return hash(self.reference)
+
+ def __gt__(self, other):
+ if self.eta is None:
+ return False
+ if other.eta is None:
+ return True
+ return self.eta > other.eta
 
  def allocate(self, line: OrderLine):
- self.available_quantity -= line.qty
+ if self.can_allocate(line):
+ self._allocations.add(line)
+
+ def deallocate(self, line: OrderLine):
+ if line in self._allocations:
+ self._allocations.remove(line)
+
+ @property
+ def allocated_quantity(self) -> int:
+ return sum(line.qty for line in self._allocations)
+
+ @property
+ def available_quantity(self) -> int:
+ return self._purchased_quantity - self.allocated_quantity
 
  def can_allocate(self, line: OrderLine) -> bool:
  return self.sku == line.sku and self.available_quantity >= line.qty

test_allocate.py

@@ -0,0 +1,50 @@
+import pytest
+
+from datetime import date, timedelta
+from model import allocate, OrderLine, Batch, OutOfStock
+
+today = date.today()
+tomorrow = today + timedelta(days=1)
+later = today + timedelta(days=10)
+
+def test_prefers_current_stock_batches_to_shipments():
+ in_stock_batch = Batch("in-stock-batch", "RETRO-CLOCK", 100, eta=None)
+ shipment_batch = Batch("shipment-batch", "RETRO-CLOCK", 100, eta=tomorrow)
+ line = OrderLine("oref", "RETRO-CLOCK", 10)
+
+ allocate(line, [in_stock_batch, shipment_batch])
+
+ assert in_stock_batch.available_quantity == 90
+ assert shipment_batch.available_quantity == 100
+
+def test_prefers_earlier_batches():
+ earliest = Batch("speedy-batch", "MINIMALIST-SPOON", 100, eta=today)
+ medium = Batch("normal-batch", "MINIMALIST-SPOON", 100, eta=tomorrow)
+ latest = Batch("slow-batch", "MINIMALIST-SPOON", 100, eta=later)
+ line = OrderLine("order1", "MINIMALIST-SPOON", 10)
+
+ allocate(line, [medium, earliest, latest])
+
+ assert earliest.available_quantity == 90
+ assert medium.available_quantity == 100
+ assert latest.available_quantity == 100
+
+def test_returns_allocated_batch_ref():
+ in_stock_batch = Batch("in-stock-batch-ref", "HIGHBROW-POSTER", 100, eta=None)
+ shipment_batch = Batch("shipment-batch-ref", "HIGHBROW-POSTER", 100, eta=tomorrow)
+ line = OrderLine("oref", "HIGHBROW-POSTER", 10)
+
+ allocation = allocate(line, [in_stock_batch, shipment_batch])
+
+ assert allocation == in_stock_batch.reference
+
+def test_raises_out_of_stock_exception_if_cannot_allocate():
+ batch = Batch("batch1", "SMALL-FORK", 10, eta=today)
+ line = OrderLine("order1", "SMALL-FORK", 10)
+
+ allocate(line, [batch])
+
+ with pytest.raises(OutOfStock, match="SMALL-FORK"):
+ other_line = OrderLine("order2", "SMALL-FORK", 1)
+
+ allocate(other_line, [batch])

test_batches.py

@@ -23,3 +23,14 @@ def test_cannot_allocate_if_skus_do_not_match():
  batch = Batch("batch-001", "UNCOMFORTABLE-CHAIR", 100, eta=None)
  different_sku_line = OrderLine("order-123", "EXPENSIVE-TOASTER", 10)
  assert batch.can_allocate(different_sku_line) is False
+
+def test_can_only_deallocate_allocated_lines():
+ batch, unallocated_line = make_batch_and_line("DECORATIVE-TRINKET", 20, 2)
+ batch.deallocate(unallocated_line)
+ assert batch.available_quantity == 20
+
+def test_allocation_is_idempotent():
+ batch, line = make_batch_and_line("ANGULAR-DESK", 20, 2)
+ batch.allocate(line)
+ batch.allocate(line)
+ assert batch.available_quantity == 18