import random
import bisect

class RandomGen(object):

    def __init__(self, random_nums, probabilities):
        assert len(random_nums), 'Random number list is empty.'
        assert len(random_nums) == len(probabilities), 'Random numbers and probabilities do not match.'
        assert abs(1. - sum(probabilities)) < 0.0000001, 'Probabilities do not sum to 1.'
            
        # Values that may be returned by next_num()
        self._random_nums = random_nums
        # Probability of the occurence of random_nums.
        # Actually we create range table here, such that all random numbers
        # ranging from (tbl[i-1],tbl[i]] map to random_number[i] 
        self._range_table = probabilities
        for i in range(1,len(self._range_table)):
            self._range_table[i] += self._range_table[i-1]
         # All random numbers which are not in any range will map 
         # to last _random_num. Therefore there is no point to have
         # last _random_num probability range in the table.
        self._range_table.pop()


    def next_num(self):
        """
        Returns one of the randomNums. When this method is called
        multiple times over a long period, it should return the
        numbers roughly with the initialized probabilities.
        """
        r = random.random()
        return self._random_nums[bisect.bisect_left(self._range_table, r)]


def test_init(random_nums, probabilities):
    try:
        rg = RandomGen(random_nums, probabilities)
    except AssertionError as e:
        return
    assert False, "Had to be assert, but no assert could be detected."


def test(input, rep_count = 1000):
    generate_stat = { _1 : 0 for _1,_ in input.items() }
    rg = RandomGen([key for key in input.keys()], [val for val in input.values()])
    for i in range(rep_count):
        generate_stat[rg.next_num()] += 1
    
    for rnum, rnum_stat in generate_stat.items():
        stat_prob = rnum_stat/rep_count
        orig_prob = input[rnum]
        print('{}: orig: {}  actual: {}'.format(rnum, orig_prob, stat_prob))
    print('')


if __name__ == '__main__':
    test_init([], []) # Empty list of numbers not allowed
    test_init([1, 2], [1. ]) # Probabilities don't match
    test_init([1, 2], [ 0.1, 0.1]) # Probabilities don't sum to 1.
    test({0 : 0.5,
          1 : 0.25,
          2 : 0.25 })
    test({-1 : 0.01,
           0 : 0.3,
           1 : 0.58,
           2 : 0.1,
           3 : 0.01 }, 100)
    test({-1 : 0.01,
           0 : 0.3,
           1 : 0.58,
           2 : 0.1,
           3 : 0.01 }, 100000)