# OddEvenEncryptionBOTH.py
#
# Description: Write a program that encrypts and decrypts messages
#              using a transposition algorithm called "odd&even".
#
# Anne Lavergne
# Date: Feb. 5 2024

# Ask the user for a message to encrypt/decrypt
plainMsg = input("Please, enter a message to encrypt/decrypt: ")

# ***Encryption***

# Create two empty strings
strOfOddChars = ""
strOfEvenChars = ""

# Start with position (i.e., index) 0
index = 0

# Consider each character in the user's plain message
for char in plainMsg:
    
    # If index of character is odd
    if index % 2 == 1:

        # Put this character in strOfOddChars
        strOfOddChars = strOfOddChars + char # strOfOddChars =+ char
        
    else:
        # Otherwise put it in strOfEvenChars
        strOfEvenChars = strOfEvenChars + char # strOfEvenChars =+ char
    
    # Go to the next position (i.e., index) in user's plain message
    index = index + 1 # index += 1

# When finish, create the cipher
cipherMsg = strOfOddChars + strOfEvenChars

# Print the cipherMsg, i.e., the encrypted user message
print(f'''\nThe original plain message you entered was "{plainMsg}".
Once encrypted, your message looked like this "{cipherMsg}".''')


# ***Decryption***
# Find the middle of cipherMsg
middleOfCipher = len(cipherMsg) // 2

# Store the first half of cipherMsg into a string
oddChars = cipherMsg[:middleOfCipher]

# Store the last half of cipherMsg into a string
evenChars = cipherMsg[middleOfCipher:]

# Set backToPlainMsg to an empty string
backToPlainMsg = ""

# Then merge these two strings to recreate plainMsg
# Consider each index from 0 to index at the middle of cipherMsg
for index in range(middleOfCipher): # 0,1,2,3,4,5

    # Concatenate the character at this index in evenChars with backToPlainMsg
    backToPlainMsg += evenChars[index]
    
    # Concatenate the character at this index in oddChars with backToPlainMsg         
    backToPlainMsg += oddChars[index]
    
# if one half is longer than the other ...
if len(evenChars) > len(oddChars):
    # concatenate this last character to backToPlainMsg
    backToPlainMsg += evenChars[-1]   
    
# Print the backToPlainMsg, i.e., the decrypted message
print(f'''\nThe original plain message you entered was "{plainMsg}".
Once encrypted, your message looked like this "{cipherMsg}".
Once this encrypted message was decrypted, we got "{backToPlainMsg}"''')
if plainMsg == backToPlainMsg:
    print(f'And it is exactly what you originally entered! Yay!')
else:
    print(f'And it is not quite what you originally entered! Oops!')