#!/usr/local/cpython-3.5/bin/python3

'''Randomize the lines of input, but preserve a degree of locality'''

from __future__ import print_function

import os
import sys
import random

sys.path.insert(0, '/usr/local/lib')

import readline0


def usage(retval):
    '''Output a usage message'''
    if retval == 0:
        write = sys.stdout.write
    else:
        write = sys.stderr.write

    write('Usage: {} -n 10 --help\n'.format(sys.argv[0]))
    write('-n 10                says to use a randomizing window of 10.  It is possible for values to move further than this\n')
    write('                     but it\'s vanishingly unlikely\n')
    write('--newline-in         Read lines separated by newlines instead of nulls\n')
    write('--newline-out        Write lines separated by newlines instead of nulls\n')
    write('--no-newline-warning Do not warn about a single null-terminated line containing newlines\n')

    sys.exit(retval)


def main():
    '''Main function'''
    number = 10
    newline_in = False
    newline_out = False
    newline_warning = True
    while sys.argv[1:]:
        if sys.argv[1] == '-n':
            number = int(sys.argv[2])
            del sys.argv[1]
        elif sys.argv[1] == '--newline-in':
            newline_in = True
        elif sys.argv[1] == '--newline-out':
            newline_out = True
        elif sys.argv[1] == '--no-newline-warning':
            newline_warning = False
        elif sys.argv[1] in ('-h', '--help'):
            usage(0)
        else:
            sys.stderr.write('{}: Unrecognized option: {}\n'.format(sys.argv[0], sys.argv[1]))
            usage(1)
        del sys.argv[1]

    process(number, newline_warning, newline_in, newline_out)


def process(number, newline_warning, newline_in, newline_out):
    '''Process the input'''
    list_ = []
    if newline_in:
        separator = b'\n'
    else:
        separator = b'\0'

    for line in readline0.readline0(0, separator=separator):
        list_.append(line)

    
    if newline_warning:
        if len(list_) == 1:
            count = list_[0].count(b'\n')
            if count >= 1:
                string = '{}: Warning: 1 line with {} newlines found:\n'.format(sys.argv[0], count) + \
                    'Maybe use -newline-in or --no-newline-warning?\n'
                sys.stderr.write(string)

    # We don't really care about odd numbers being floor'd
    number_over_2 = number // 2

    len_list_minus_1 = len(list_) - 1

    for lineno, line in enumerate(list_):
        left = max(0, lineno - number_over_2)
        right = min(lineno + number_over_2, len_list_minus_1)
        # print('left is {}, right is {}'.format(left, right))
        random_int = random.randint(left, right)
        list_[lineno], list_[random_int] = list_[random_int], list_[lineno]

    if newline_out:
        separator = b'\n'
    else:
        separator = b'\0'

    for line in list_:
        os.write(1, line + separator)

main()