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   "cell_type": "markdown",
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   "source": [
    "# Strategy Pattern\n",
    "1. It belongs to Behavioral Pattern\n",
    "1. Also Known As **Policy Pattern**\n",
    "1. Used to control operations of some objects\n",
    "\n",
    "> **Summary**\n",
    "> - It takes a family of Algos\n",
    "> - Encapsulates each one\n",
    "> - And make them interchangeable with each other\n",
    "> - Algos may vary independently\n",
    "> - No more if-elif\n",
    "> - Each Algo can be unit tested as well as system tested"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Shipping Module\n",
    "1. Supports FedEx, Postal, UPS\n",
    "1. Must be extendable"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "from abc import ABCMeta, abstractmethod"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Interface"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class IPaymentStrategy(metaclass = ABCMeta):\n",
    "    @abstractmethod\n",
    "    def calculate(self, order):\n",
    "        pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Payment Methods"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class FedExStrategy(IPaymentStrategy):\n",
    "    def calculate(self, order):\n",
    "        return order + 0.1 * order"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class PostalStrategy(IPaymentStrategy):\n",
    "    def calculate(self, order):\n",
    "        return order + 0.05 * order"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class UPSStrategy(IPaymentStrategy):\n",
    "    def calculate(self, order):\n",
    "        return order + 0.12 * order"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Unified Payment Calculator"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class ShippingCost():\n",
    "    def __init__(self, payment_strategy):\n",
    "        self._payment_strategy = payment_strategy\n",
    "        \n",
    "    def shipping_cost(self, order):\n",
    "        return self._payment_strategy.calculate(order)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Driver Program"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "33.0\n"
     ]
    }
   ],
   "source": [
    "payment_strategy = FedExStrategy()\n",
    "cost_calc = ShippingCost(payment_strategy)\n",
    "\n",
    "print(cost_calc.shipping_cost(30))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "31.5\n"
     ]
    }
   ],
   "source": [
    "payment_strategy = PostalStrategy()\n",
    "cost_calc = ShippingCost(payment_strategy)\n",
    "\n",
    "print(cost_calc.shipping_cost(30))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "33.6\n"
     ]
    }
   ],
   "source": [
    "payment_strategy = UPSStrategy()\n",
    "cost_calc = ShippingCost(payment_strategy)\n",
    "\n",
    "print(cost_calc.shipping_cost(30))"
   ]
  }
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