gistfile1.py

from dataclasses import dataclass
from typing import List

T_co = TypeVar('T_co', Employee, Engineer, Manager, covariant=True)
T_contra = TypeVar('T_contra', Employee, Engineer, Manager, contravariant=True)


@dataclass
class Employee:
    salary: int
    years_in_company: int

@dataclass
class Engineer(Employee):
    pass

@dataclass
class Manager(Employee):
    has_achieved_kpis: bool


class EmployeeBonusCalculationStrategy(Generic[T_contra]):

    def calculate_bonus(self, employee: Manager) -> float:
        raise NotImplementedError()


class ManagersBonusCalculationStrategy(EmployeeBonusCalculationStrategy[Manager]):

    def calculate_bonus(self, employee: Manager) -> float:
        bonus = employee.salary * 1.05

        if employee.years_in_company > 5:
            bonus += employee.salary * 1.10

        if employee.has_achieved_kpis:
            bonus += employee.salary * 1.20

        return bonus

class EngineerBonusCalculationStrategy(EmployeeBonusCalculationStrategy[Engineer]):

    def calculate_bonus(self, employee: Engineer) -> float:
        bonus = employee.salary * 1.10

        if employee.years_in_company > 5:
            bonus += employee.salary * 1.10

        return bonus


class SalaryCalculator:

    bonus_calculation_strategy = {
        'Engineer': EngineerBonusCalculationStrategy(),
        'Manager': ManagersBonusCalculationStrategy(),
    }

    def calculate_salary(self, employee: Generic[T_con]) -> float:
        return employee.salary + self.get_employee_bonus(employee)

    def get_employee_bonus(self, employee: Generic[T_con]) -> float:
        return self.bonus_calculation_strategy[employee.__class__.__name__].calculate_bonus(employee)


def calculate_department_salary(employees: List[Generic[T_con]]) -> float:
    salary_calculator = SalaryCalculator()
    return sum([salary_calculator.calculate_salary(employee) for employee in employees])


worker1 = Engineer(100, 7)
worker2 = Engineer(120, 4)
worker3 = Engineer(200, 6)

worker4 = Manager(100, 4, False)
worker5 = Manager(120, 6, True)
worker6 = Manager(100, 3, True)
worker7 = Manager(110, 9, True)

department = []
department.append(worker1)
department.append(worker2)
department.append(worker3)
department.append(worker4)
department.append(worker5)
department.append(worker6)
department.append(worker7)

total_salary = calculate_department_salary(department)
print(total_salary)

assert(total_salary == 2742)