#!/usr/bin/env python
# coding: utf-8

# # Strategy Pattern
# 1. It belongs to Behavioral Pattern
# 1. Also Known As **Policy Pattern**
# 1. Used to control operations of some objects
# 
# > **Summary**
# > - It takes a family of Algos
# > - Encapsulates each one
# > - And make them interchangeable with each other
# > - Algos may vary independently
# > - No more if-elif
# > - Each Algo can be unit tested as well as system tested

# # Shipping Module
# 1. Supports FedEx, Postal, UPS
# 1. Must be extendable

# In[1]:


from abc import ABCMeta, abstractmethod


# ### Interface

# In[2]:


class IPaymentStrategy(metaclass = ABCMeta):
    @abstractmethod
    def calculate(self, order):
        pass


# ### Payment Methods

# In[3]:


class FedExStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.1 * order


# In[4]:


class PostalStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.05 * order


# In[5]:


class UPSStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.12 * order


# ### Unified Payment Calculator

# In[6]:


class ShippingCost():
    def __init__(self, payment_strategy):
        self._payment_strategy = payment_strategy
        
    def shipping_cost(self, order):
        return self._payment_strategy.calculate(order)


# # Driver Program

# In[7]:


payment_strategy = FedExStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))


# In[8]:


payment_strategy = PostalStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))


# In[9]:


payment_strategy = UPSStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))