import sys

englishLetterFreq = [8.17, 1.49, 2.78, 4.25, 12.7, 2.23, 2.02, 6.09, 6.97, 0.15, 0.77, 4.03, 2.41, 6.75, 7.51, 1.93, 0.1, 5.99, 6.33, 9.06, 2.76, 0.98, 2.36, 0.15, 1.97, 0.07]
NUM_LETTERS_IN_ALPHABET = 26
ASCII_DEC_START = 65
ASCII_DEC_END = 90

# rotate array to the right
def rotate(l, n):
    return l[n:] + l[:n]

# get the distribution percentage of the letters in the file
def getDistribution(dist, total_len):
    # get percentage of occurrence for every letter
    for i in range(NUM_LETTERS_IN_ALPHABET):
        dist[i] = dist[i]/float(total_len)

    return dist

# calculate the total frequency sum by multiplying corresponding English letter frequency with distribution percentage of letters in file
def getTotalFreq(dist):
    total_frequency = 0
    for i in range(NUM_LETTERS_IN_ALPHABET):
        total_frequency += englishLetterFreq[i] * dist[i]
    return total_frequency

# create an array with 26 spots each representing the letters in the alphabet
# count the number of letters occurring at a specific key location and add to distribution array
# return the distribution count
def frequency(content, key_length, key_pos):
    dist = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
    letter_count = 0
    for i in range(len(content)):
        if content[i].isalpha():
            letter_count += 1
            if letter_count % key_length == key_pos:
                curr_letter = content[i]
                dist[ord(curr_letter) - ASCII_DEC_START] += 1

    return getDistribution(dist, letter_count)

def decodeVigereneKey(key_length):
    # take 2 argument as file name
    with open(str(sys.argv[1])) as f:
        content = f.readlines()

    # strip white spaces and lowercase all letters
    # content = re.sub(r'([^\s\w]|_)+', "", original_content)
    content = ''.join([x.strip() for x in content]).upper()
    # rotate the content by specified key amount to find each letter
    key = []
    for j in range(key_length):
        max_freq = 0
        shifts = 0
        dist = frequency(content, key_length, j)
        # shift 26 times to find the max frequency of the 26 shifts and the number(letter) it corresponds to
        for i in range(NUM_LETTERS_IN_ALPHABET):
            curr_frequency = getTotalFreq(rotate(dist, i))
            # print str(i) + ' ' + str(curr_frequency)
            if max_freq < curr_frequency:
                max_freq = curr_frequency
                shifts = i

        # add to key array
        key.append(chr(shifts + ASCII_DEC_START - 1))
    key = rotate(key, 1)
    return key

def decodeVigerene(key):
    # take 2 argument as file name
    with open(str(sys.argv[1])) as f:
        content = f.readlines()

    # strip white spaces and lowercase all letters
    # content = re.sub(r'([^\s\w]|_)+', "", original_content)
    content = ''.join([x.strip() for x in content]).upper()
    decoded_content = ''
    key_pos = 0
    for i in range(len(content)):
        if content[i].isalpha():
            # letter will loop back from end of alphabet
            if ord(content[i]) - ord(key[key_pos % len(key)]) < 0:
                decoded_content += chr(ASCII_DEC_END + ord(content[i]) - ord(key[key_pos % len(key)]))
            # letter subtracted
            else:
                decoded_content += chr(ASCII_DEC_START - 1 + ord(content[i]) - ord(key[key_pos % len(key)]))
            key_pos += 1
        else:
            decoded_content += content[i]

    return decoded_content


# repeat to determine length of key
print decodeVigereneKey(13)
print decodeVigerene(decodeVigereneKey(13))