from os import remove
import time


def next_int(file):
    str = ''
    ch = file.read(1)
    if ch == '-':
        str += '-'
        ch = file.read(1)
    while ch.isdigit():
        str += ch
        ch = file.read(1)
    if str == '':
        return False
    else:
        return int(str)


def int_count(file):
    position = file.tell()
    file.seek(0)
    count = 0
    i = next_int(file)
    while i:
        count += 1
        i = next_int(file)
    file.seek(position)
    return count


def merge(file_out_path, file_a_path, file_b_path, ascending_order):
    file_out = open(file_out_path, "r+")
    file_a = open(file_a_path, "r+")
    file_b = open(file_b_path, "r+")

    int_a = next_int(file_a)
    int_b = next_int(file_b)

    while int_a and int_b:
        if (ascending_order and int_a < int_b) or (not ascending_order and int_a >= int_b):
            file_out.write(str(int_a) + " ")
            int_a = next_int(file_a)
        else:
            file_out.write(str(int_b) + " ")
            int_b = next_int(file_b)
    while int_a:
        file_out.write(str(int_a) + " ")
        int_a = next_int(file_a)
    while int_b:
        file_out.write(str(int_b) + " ")
        int_b = next_int(file_b)

    file_out.close()
    file_a.close()
    file_b.close()


def mergesort(file_name, remove_temp_files=False, ascending_order=True):
    file = open(file_name, "r+")
    length = int_count(file)
    if length >= 2:
        file_a_name = file_name + "_a"
        file_b_name = file_name + "_b"

        file_a = open(file_a_name, "w+")
        file_b = open(file_b_name, "w+")

        for i in range(0, length // 2):
            file_a.write(str(next_int(file)) + " ")
        for i in range(0, length - (length // 2)):
            file_b.write(str(next_int(file)) + " ")

        file_a.close()
        file_b.close()

        mergesort(file_a_name, remove_temp_files, ascending_order)
        mergesort(file_b_name, remove_temp_files, ascending_order)
        merge(file_name, file_a_name, file_b_name, ascending_order)
        if remove_temp_files:
            remove(file_a_name)
            remove(file_b_name)


if __name__ == '__main__':
    print('Привет! Эта программа служит для сортировки чисел простым слиянием, хранящимся в файле.\n'
          'Чтобы выйти, введите q на любом этапе\n')

    buffer = ''
    file_name = ''
    ascending_order = False
    remove_temp_files = False
    while True:
        buffer = input('Введите имя файла:\n')
        if buffer.lower() == 'q':
            break
        file = ''
        try:
            file = open(buffer, 'r')
        except FileNotFoundError:
            print('Такого файла не существует! Попробуйте снова.\n\n')
            continue
        file.close()
        file_name = buffer

        buffer = input('Удалить временные файлы? (Y/n):\n')
        if buffer.lower() == 'q':
            break
        remove_temp_files = buffer.lower() == 'y'

        buffer = input('В порядке возрастания? (Y/n):\n')
        if buffer.lower() == 'q':
            break
        ascending_order = buffer.lower() == 'y'

        start_time = time.time_ns()
        mergesort(file_name, remove_temp_files, ascending_order)
        end_time = time.time_ns()
        print('Сортировка завершена!\nЗатраченное ввремя - ' + str(
            (end_time - start_time) / 1000000) + 'мс.\n\n')

    print('Спасибо!')