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""" https://en.wikipedia.org/wiki/Rail_fence_cipher """

def encrypt(input_string: str, key: int) -> str:

"""

Shuffles the character of a string by placing each of them

in a grid (the height is dependent on the key) in a zigzag

formation and reading it left to right.

>>> encrypt("Hello World", 4)

'HWe olordll'

>>> encrypt("This is a message", 0)

Traceback (most recent call last):

...

ValueError: Height of grid can't be 0 or negative

>>> encrypt(b"This is a byte string", 5)

Traceback (most recent call last):

...

TypeError: sequence item 0: expected str instance, int found

"""

temp_grid: list[list[str]] = [[] for _ in range(key)]

lowest = key - 1

if key <= 0:

raise ValueError("Height of grid can't be 0 or negative")

if key == 1 or len(input_string) <= key:

return input_string

for position, character in enumerate(input_string):

num = position % (lowest * 2) # puts it in bounds

num = min(num, lowest * 2 - num) # creates zigzag pattern

temp_grid[num].append(character)

grid = ["".join(row) for row in temp_grid]

output_string = "".join(grid)

return output_string

def decrypt(input_string: str, key: int) -> str:

"""

Generates a template based on the key and fills it in with

the characters of the input string and then reading it in

a zigzag formation.

>>> decrypt("HWe olordll", 4)

'Hello World'

>>> decrypt("This is a message", -10)

Traceback (most recent call last):

...

ValueError: Height of grid can't be 0 or negative

>>> decrypt("My key is very big", 100)

'My key is very big'

"""

grid = []

lowest = key - 1

if key <= 0:

raise ValueError("Height of grid can't be 0 or negative")

if key == 1:

return input_string

temp_grid: list[list[str]] = [[] for _ in range(key)] # generates template

for position in range(len(input_string)):

num = position % (lowest * 2) # puts it in bounds

num = min(num, lowest * 2 - num) # creates zigzag pattern

temp_grid[num].append("*")

counter = 0

for row in temp_grid: # fills in the characters

splice = input_string[counter : counter + len(row)]

grid.append([character for character in splice])

counter += len(row)

output_string = "" # reads as zigzag

for position in range(len(input_string)):

num = position % (lowest * 2) # puts it in bounds

num = min(num, lowest * 2 - num) # creates zigzag pattern

output_string += grid[num][0]

grid[num].pop(0)

return output_string

def bruteforce(input_string: str) -> dict[int, str]:

"""Uses decrypt function by guessing every key

>>> bruteforce("HWe olordll")[4]

'Hello World'

"""

results = {}

for key_guess in range(1, len(input_string)): # tries every key

results[key_guess] = decrypt(input_string, key_guess)

return results

if __name__ == "__main__":

import doctest

doctest.testmod()

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