# Oliver Schuller


def encrypt(msg, n):
    encryptedText = ""

    # Make a "for loop" that will convert string to ascii, shifts character n positions and then convert back to
    # normal characters
    for letter in range(len(msg)):
        if ord(msg[letter]) < 97 or ord(msg[letter]) > 122:  # Leaves characters outside the alphabet unchanged
            encryptedText += chr(ord(msg[letter]))

        elif ord(msg[letter]) - n < 97:  # If the ascii number is less than 97, add 26 so it stays within the alphabet
            encryptedText += chr(ord(msg[letter]) - n + 26)

        else:
            encryptedText += chr(ord(msg[letter]) - n)  # Shifts character n positions

    return encryptedText


def decrypt(msg, n):
    clear_msg = ""

    # Make a "for loop" that will convert string to ascii, shifts character n positions and then convert back to
    # normal characters
    for letter in range(len(msg)):
        if ord(msg[letter]) < 97 or ord(msg[letter]) > 122: # Leaves characters outside the alphabet unchanged
            clear_msg += chr(ord(msg[letter]))

        elif ord(msg[letter]) + n > 122:
            clear_msg += chr(ord(msg[letter]) + n - 26)  # If the ascii number is greater than 122, subtract 26 so it
            # stays within the alphabet

        else:
            clear_msg += chr(ord(msg[letter]) + n)  # Shifts character n positions

    return clear_msg


def lfa(msg):
    count = {}
    for i in msg:
        if ord(i) < 97 or ord(i) > 122:  # Skip characters outside the alphabet
            continue
        elif i in count:  # If the letter already is in count, increment 1
            count[i] += 1
        else:  # Otherwise add the letter as a key and 1 as value
            count[i] = 1
    for letter, occurrence in count.items():  # Print how many times each letter occurs
        print('Character {} occurs {} times'.format(letter, occurrence))


print("Choose your option: \n 1. Encrypt message \n 2. Decrypt message \n 3. Read and write to file \n "
      "4. Letter frequency analysis \n")
choice = input("Write the number for your option: ")

if choice == "1":
    message = input("Enter your text here: ")
    message = message.lower()
    key = int(input("Enter your key here (1-25): "))
    print(encrypt(message, key))

elif choice == "2":
    message = input("Enter your text here: ")
    message = message.lower()
    key = int(input("Enter your key here (1-25): "))
    print(decrypt(message, key))

elif choice == "3":
    f1 = open("clearText.txt", "r")
    lines = f1.readlines()
    message = ""
    for line in lines:
        message += line
        message = message.replace("\n", " ")
    key = int(input("Enter your key here (1-25): "))

    f2 = open("encryptedText.txt", "a")
    lines = f2.write(encrypt(message, key))

elif choice == "4":
    text = input("Write your text here: ")
    text = text.lower()
    lfa(text)