import string
import collections

global_offset = ord('A')
global_length = ord('Z')-ord('A')+1

def clean(infilename, outfilename):
    """
    Takes a textfile and creates a new copy without punctuations and
    newlines.  All letters are translated to capital letters. The
    translation will loose digits as well. 
    """
    with open(infilename, encoding="latin-1") as infile, open(outfilename, "w", encoding="utf8") as outfile:
        for line in infile:
            newline = []
            for letter in line.strip():
                if line.startswith("Illustration:"):
                    continue
                if letter in string.ascii_letters:
                    newline.append(letter.upper())
            print("".join(newline), file = outfile, end="")
    print("done")
    return

def cipher(infilename, outfilename, password):
    """
    A function that encrypts infilename with the Vigenere cipher
    using secret key password and writes the result to outfilename.
    Outfilename contains a single long line.
    """
    count = 0
    print(len(password))
    with open(infilename, encoding="latin-1") as infile, open(outfilename, "w", encoding="utf8") as outfile:
        buffer = infile.read()
        outputbuffer = []
        for letter in buffer:
            index = count%len(password)
            newletter = change(letter, password[index])
            outputbuffer.append(newletter)
            count+=1
        print("".join(outputbuffer), file=outfile)
    return count

def decipher(infilename, outfilename, password):
    """
    Assumes that infilename has been encrypted with the Vigenere cipher
    that 
    """
    count = 0
    with open(infilename, encoding="latin-1") as infile, open(outfilename, "w", encoding="utf8") as outfile:
        buffer = infile.read()
        outputbuffer = []
        for letter in buffer:
            index = count%len(password)
            newletter = unchange(letter, password[index])
            outputbuffer.append(newletter)
            count+=1
        print("".join(outputbuffer), file=outfile)
    return count


def change(letter, pwd):
    """
    changes a capital letter by adding the capital letter pwd in the
    Caesar cipher
    """
    return chr( (ord(letter)+ord(pwd)-2*global_offset)%global_length+global_offset)

def unchange(letter, pwd):
    """
    undoes the change from the function change
    """
    return chr( (ord(letter)-ord(pwd)+global_length)%global_length + global_offset)
    
def displacement(infilename):
    pass
    
def find(infilename, displacement):
    pass

def caesar(string, pwd):
    """
    Encrypts the string using Caesar's cipher with letter pwd and
    returns the encrypted string.
    """
    result = []
    for letter in string:
        result.append(change(letter, pwd))
    return "".join(result)