#!/usr/bin/python3
# -*- coding: utf-8 -*-

# Transposition Cipher Decryption
# https://www.nostarch.com/crackingcodes (BSD Licensed)

import math


def main() -> None:
    myMessage = "Cenoonommstmme oo snnio. s s c"
    myKey = 8
    plaintext = decryptMessage(myKey, myMessage)
    # Print with a | ("pipe" character) after it in case
    # there are spaces at the end of the decrypted message.
    print(plaintext + "|")


def decryptMessage(key: int, message: str) -> str:
    # The transposition decrypt function will simulate the "columns" and
    # "rows" of the grid that the plaintext is written on by using a list
    # of strings. First, we need to calculate a few values.
    # The number of "columns" in our transposition grid:
    numOfColumns = int(math.ceil(len(message) / float(key)))
    # The number of "rows" in our grid will need:
    numOfRows = key
    # The number of "shaded boxes" in the last "column" of the grid:
    numOfShadedBoxes = (numOfColumns * numOfRows) - len(message)
    # Each string in plaintext represents a column in the grid.
    plaintext = [""] * numOfColumns
    # The column and row variables point to where in the grid the next
    # character in the encrypted message will go.
    column = 0
    row = 0
    for symbol in message:
        plaintext[column] += symbol
        column += 1  # Point to next column.
        # If there are no more columns OR we're at a shaded box, go back to
        # the first column and the next row:
        if (column == numOfColumns) or (
            column == numOfColumns - 1 and row >= numOfRows - numOfShadedBoxes
        ):
            column = 0
            row += 1
    return "".join(plaintext)


# If transpositionDecrypt.py is run (instead of imported as a module) call
# the main() function.
if __name__ == "__main__":
    main()