from __future__ import print_function

import os
import random
import unittest


DEBUG = os.environ.get('DEBUG') == '1'


def debug(msg):
    if DEBUG:
        print(msg)


def insertion_sort(arr):
    debug('BEGIN')
    for j in range(1, len(arr)):
        key = arr[j]
        i = j - 1
        debug('FOR:\tj={}, key={}, i={}'.format(j, key, i))

        while i > -1 and arr[i] > key:
            arr[i + 1] = arr[i]
            debug('WHILE:\tset: arr[{}] = {}'.format(i + 1, arr[i]))
            i = i - 1

        arr[i + 1] = key
        debug('FOR:\tset: arr[{}] = {}'.format(i + 1, key))

    debug('END')
    return arr


class TestStuff(unittest.TestCase):

    def test_insertion_sort_small(self):
        self.assertEqual(
            [1, 2, 3, 4, 5, 6],
            insertion_sort([5, 2, 4, 6, 1, 3])
        )

    def test_insertion_sort_large(self):
        inlist = range(1000)
        listcopy = inlist[:]
        random.shuffle(inlist)
        random.shuffle(inlist)
        self.assertEqual(listcopy, insertion_sort(inlist))

    def test_insertion_sort_large_reversed(self):
        inlist = range(1000)
        listcopy = inlist[:]
        self.assertEqual(listcopy, insertion_sort(list(reversed(inlist))))


if __name__ == '__main__':
    unittest.main()