arc_patterns_python_ch01_secondModel.py

from dataclasses import dataclass
from typing import Optional
from datetime import date


@dataclass(frozen=True)
class OrderLine:
    orderid: str
    sku: str
    qty: int


class Batch:
    def __init__(
            self,
            ref: str,
            sku: str,
            qty: int,
            eta: Optional[date]
    ):
        self.reference = ref
        self.sku = sku
        self.eta = eta        
        self._purchased_quantity = qty
        self._allocations = set()       # type: Set[OrderLine]

    def allocate(self, line: OrderLine):
        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