#!/usr/bin/env python3
# Filename: circuit_caesar.py
# Author: Jeoi Reqi
# Circuit Python implementation of a Caesar cipher

SYM = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
MAX_KEY_SIZE = len(SYM)

def gMode():
    while True:
        print('Type "e" to encrypt or "d" to decrypt:')
        mode = input().lower()
        if mode in ['e', 'd']:
            return mode
        else:
            print('ERROR: Invalid mode')

def gMessage():
    print('Type a message:')
    return input()

def gKey():
    while True:
        print('Shift strength (1-%s):' % (MAX_KEY_SIZE))
        key = int(input())
        if 1 <= key <= MAX_KEY_SIZE:
            return key
        else:
            print('ERROR: Invalid key')

def gTranslated(mode, message, key):
    if mode == 'd':
        key = -key
    translated = ''
    for symbol in message:
        if symbol.isalpha():
            symbolIndex = SYM.find(symbol)
            if symbolIndex == -1:
                # Symbol not within MAX_KEY_SIZE parameters.
                translated += symbol
            else:
                # Encryption or Decryption Magic!
                symbolIndex += key
                if symbolIndex >= len(SYM):
                    symbolIndex -= len(SYM)
                elif symbolIndex < 0:
                    symbolIndex += len(SYM)
                translated += SYM[symbolIndex]
        else:
            # Non-letter character, just append to translated message.
            translated += symbol
    return translated

# Metadata
__file_name__ = 'circuit_caesar.py'
__author__ = 'Jeoi Reqi'
__copyright__ = 'Copyright 2018, Jeoi Reqi'
__credits__ = 'Jeoi Reqi'
__dct_url__ = 'http://purl.org/dc/terms/'
__license__ = 'Creative Commons'
__rel_url__ = 'http://creativecommons.org/licenses/by-nc/4.0/'
__version__ = 'CC-by-nc/4.0/'
__maintainer__ = 'Jeoi Reqi'
__email__ = 'jeoireqi@gmail.com'

print('\n::%s is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License::\n\n'
      'File Name: %s\nAuthor: %s\nCopyright: %s\nCredits: %s\nDCT URL: %s\nLicense: %s\nRelease URL: %s\n'
      'Version: %s\nMaintainer: %s\nEmail: %s\n'
      % (__file_name__, __file_name__, __author__, __copyright__,
         __credits__, __dct_url__, __license__, __rel_url__, __version__,
         __maintainer__, __email__))

mode = gMode()
message = gMessage()
key = gKey()

print('\nTranslated:', gTranslated(mode, message, key), '\n')