'''
    DS2000
    Spring 2023
    Sample code from class - decryption!
    
    Lookup table
        header ==>    a b c d
                    a a b c d
                    b b c d a
                    c c d a b
                    d d a b c
        
        Look up key in the first column
        Find word in the corresponding list
        Get decrypted letter from the header

    Given:  key bdad
            word babd
            Result = abba
'''

HEADER = ["a", "b", "c", "d"]
LOOKUP = {"a" : ["a", "b", "c", "d"],
          "b" : ["b", "c", "d", "a"],
          "c" : ["c", "d", "a", "b"],
          "d" : ["d", "a", "b", "c"]}

def decrypt(key, word, header, lookup):
    ''' Function: decrypt
        Parameters: key (string), word (string),
                    header (list of strings),
                    lookup (dictioanry of string: list)
        Returns: a string
        Does: uses vigenere cipher to look up each kye's
              list, find the position of the word in the list
              and retrieve that position from the header
    '''
    decrypted = ""
    for i in range(len(key)):
        # get the current letter in the key,
        # find the list that goes with it
        key_letter = key[i]
        lst = lookup[key_letter]
        
        # get the current letter in the word
        # find its position in the list
        word_letter = word[i]
        pos = lst.index(word_letter)
        
        # retrieve the letter from header at the same pos
        decrypted_letter = header[pos]
        decrypted += decrypted_letter
    
    return decrypted
        
    
def main():
    # sanity check version, a one-letter word
    key = "a"
    word = "b"
    expected = "b"
    actual = decrypt(key, word, HEADER, LOOKUP)
    print("I decrypted and expected.....", expected,
          "\nand got.......", actual)

    # sanity check version, a one-letter word
    key = "b"
    word = "d"
    expected = "c"
    actual = decrypt(key, word, HEADER, LOOKUP)
    print("\nI decrypted and expected.....", expected,
          "\nand got.......", actual)
    
    # actual decryption
    key = "bdad"
    word = "babd"
    expected = "abba"
    actual = decrypt(key, word, HEADER, LOOKUP)
    print("\nI decrypted and expected.....", expected,
          "\nand got.......", actual)
    
main()