import random
from collections import namedtuple

Transaction = namedtuple('Transaction', ('state', 'action', 'reward', 'next_state'))


class Memory(object):
    def __init__(self, capacity):
        self.capacity = capacity
        self.memory = []
        self.index = 0

    def push(self, state, action, reward, next_state):
        if len(self.memory) < self.capacity:
            self.memory.append(None)
        self.memory[self.index] = (state, action, reward, next_state)
        self.index = (self.index + 1) % self.capacity

    def sample(self, batch_size):
        assert len(self.memory) >= self.capacity
        return random.sample(self.memory, batch_size)

    def __len__(self):
        return len(self.memory)