# Vigenere Cipher Program
#

#import everything
import os, os.path, string

#Pretty Title
print "*************************************"
print "*       Vigenere Coder / Decoder    *"
print "*************************************"
print

# Get input directory, see if it exists, and change into it
def get_dir():
    directory = raw_input("Path to text file directory: ")
    if not os.path.isdir(directory):
        print "Invalid directory"
        directory = get_dir()
    return directory
directory = get_dir()
os.chdir(directory)

#Get filename, test for file
def get_file():
    input_file = raw_input("Name of text file: ")
    if not os.path.isfile(input_file):
        print "Invalid  file name."
        input_file = get_file()
    return input_file
in_file = get_file()

# Open and read input text
source = open(in_file, "r")
source_txt = source.read()
source.close()

#put in standard case to make encode easier
item = string.lower(source_txt)

#Encode or decode?
cypher = raw_input("[E]ncode or [D]ecode: ")
cypher = string.upper(cypher)

#prepare outfile
out_name = raw_input("Name of Output File: ")
outfile = open(out_name, "a")
out_text = []

#Request Code / Decode Key
key = raw_input("Cypher Key: ")
key = string.lower(key)


#make len(keyword) equal len(item)
padded_key = key
while len(padded_key) < len(source_txt):
    padded_key = padded_key + key


#convert padded_key to ascii number
num_key = []
for p in padded_key:
    num_p = ord(p)
    num_key.append(num_p)


#convert source_txt to ascii number
num_source = []
for i in source_txt:
    num_i = ord(i)
    num_source.append(num_i)


#add num values together
num_cypher = []
index = 0
for num in num_source:
    if cypher == "E":
        new_num = num_source[index] + num_key[index]
    elif cypher == "D":
        new_num = num_source[index] - num_key[index]
    else:
        pass
    #Adjust for numbers too big
    if new_num > 255:
        new_num = (new_num - 255)
    elif new_num < 0:
        new_num = (new_num + 255)
    else:
        pass
    num_cypher.append(new_num)
    index = index + 1
        
#convert ascii num to letters
cypher_chr = ""
for nc in num_cypher:
    cypher_chr = cypher_chr + chr(nc)

#Write new text to out file
outfile.write(cypher_chr)
outfile.close()

#Tell them we are all done now
if cypher == "E":
    print "Text encrypted."
elif cypher =="D":
    print "Text decoded."
else:
    print "I don't know what happened.  Probably nothing."